Elaboration of Novel Biocomposite Hydrogel Polymers made of Alginate and Sepiolite and endowed with Enhanced Properties

Elaboration of Novel Biocomposite Hydrogel Polymers made of Alginate and Sepiolite and endowed with Enhanced Properties | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Elaboration of Novel Biocomposite Hydrogel Polymers made of Alginate and Sepiolite and endowed with Enhanced Properties Meriem BAZIZ, Mostefa KAMECHE, Nassira BENHARRATS, Liran HU, Samy REMITA This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5455380/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Jul, 2025 Read the published version in Polymer Bulletin → Version 1 posted 9 You are reading this latest preprint version Abstract Nowadays growing attention is given to the design and development of novel interpenetrating polymer networks (IPN) from the combination of hydrogel polymers loaded with natural clay. In this work, we used the eco-friendly IPN strategy to develop novel hydrogel biocomposite beads, made of alginate (ALG), with improved clay dispersion, higher pH sensitivity, better stretchability and swellability, together with enhanced regenerability properties and biodegradability resistance. Fibrous clay, namely sodium sepiolite (NaS), was loaded into alginate simple biocomposite network (SBN) beads, via manual co-grinding mixture/encapsulation method, at different sepiolite loads. Alginate double biocomposite network (DBN) beads were also prepared at different sepiolite loads, via the diffusion of acrylamide monomer (AAM) inside alginate single biocomposite network (SBN) beads, followed by in situ free radical polymerization of AAM into poly-acrylamide (pAAM), using ammonium persulfate (APS) as polymerization initiator and N,N-methylenebisacrylamide (Bis) as covalent crosslinker agent. The as-elaborated SBN and DBN beads were then characterized by digital camera recording, XRD analysis, ATR-FTIR characterization and SEM observation. FTIR results showed that NaS and pAAM were successfully incorporated into DBN beads, whilst XRD analysis revealed the enhancement of fibrous clay dispersion, even at relatively high sepiolite loads. Besides, SEM microscopy confirmed the porous spongious nature of DBN beads. The properties of the as-elaborated SBN and DBN beads were also evaluated by test touching, swelling rate measurements, adsorption/desorption experiments and biodegradability evaluation. DBN beads properties were always found enhanced in comparison with those of SBN beads: very good stretchability, good swelling behavior and stability in water whatever the pH, either in acidic or alkaline solution, enhanced adsorption/desorption properties towards methylene blue (MB) dye, very good regenerability and delayed biodegradability. In summary, this work showed an interesting and safe IPN/biocomposite approach to develop high-performance alginate biocomposite polymers as a promising system towards their use in eco-friendly processes. Biocomposite Polymers Alginate Xerogel Beads Sepiolite Swellability Biodegradability Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Highlights - Novel, low-cost and eco-friendly double biocomposite network (DBN) beads were designed by a soft and efficient interpenetrating polymer network approach - DBN beads were prepared by dispersion of sepiolite clay and polymerization of AAM monomers within an alginate network - DBN beads were found characterized by good stretchability, good swelling behavior, excellent stability in water and increased biodegradability resistance - DBN beads were characterized by enhanced adsorption properties and reusability Introduction Currently, hydrogel beads derived from polysaccharides such as chitosan, carrageenan and alginate have gained popularity for their use as bio-adsorbents in eliminating several organic pollutants [ 1 – 4 ]. Among these biosorbents, sodium alginate (NaA) matrix is regarded as a natural anionic biopolymer, which can be extracted from brown seaweed. It contains different amounts of β-D-mannuronic (M-chains) and α-L-guluronic (G-chains) acid fragments linked in non-regular blocks [ 5 – 8 ]. As a promising application, in water treatment, this bioadsorbant could be an alternative to conventional adsorbents for pollutants removal. In addition, it has several advantages: i) presence of a large number of functional groups, ii) nontoxicity and biodegradability and iii) easy hydrogel beads formation by addition of Ca 2+ [ 8 – 13 ]. However, utilization of such beads for bio-adsorption applications is limited by some drawbacks such as low adsorption capacity, macro-porous structure, high biodegradability and instability in aqueous solutions [ 14 – 19 ]. Previous research reviews that incorporation of clay particles in ALG bio-nanocomposites, without increasing the cost of production, can adjust the properties and considerably improve the performances of alginate hydrogels, such as bead shape, mechanical and thermal stabilities, gel strength, swelling capacity, adsorption rate [ 16 , 18 , 20 – 28 ]. While most of the as-elaborated clay composites contain montmorillonite [ 29 – 32 ], the alternative use of sepiolite leads to a fibrous clay biocomposite that exhibits very promising properties [ 33 – 36 ]. However, at room temperature, ALG beads drying, reinforced by clay, results in a shinked gel with a significant loss of form and surface area due to the action of the capillary forces on the walls of the pores [ 37 , 38 ]. Consequently, alginate biocomposite xerogel beads become rigid with a non-porous structure [ 39 – 44 ]. Even in the wet form, the beads disintegrate rapidly resulting in fast liberation of the trapped contaminants [ 18 ]. Owing to the outstanding properties of interpenetrating polymer networks (IPN), an IPN strategy combined with biocomposite hierarchical structure, appears as an interesting eco-friendly way to limit several drawbacks of the previously described ALG hydrogel beads. In this context, we propose in this paper a new way for synthesizing alginate biocomposite xerogel beads, as effective biosorbents, by blending sodium alginate biocomposite with another hydrogel. The aim is to prepare beads with enhanced clay dispersion, stretchability, stability, biodegradability, swelling capacities and improved adsorption/desorption properties towards methylene blue (MB) used as a model of organic toxic dye. Experimental procedures Materials Sodium Alginate (NaA, C 6 H 7 O 6 Na), from Aldrich, was used as received. Sepiolite clay mineral (S), from Aldrich, was 95% purity. Its mineralogical composition was 53.63% in SiO 2 , 24.56% in MgO, 2.19% in Al 2 O 3 , 1.27% in Fe 2 O 3 and 0.82% in Mn 2 O 3 (in wt. %), showing silica and magnesium oxide as major constituents. N,N-methylenebisacrylamide (Bis, 99% purity), ultra-pure Acrylamide (AAM) and Ammonium persulfate (APS, 98% purity), from Sigma–Aldrich, were all used without prior purification. The crosslinker used was hydrated calcium chloride (CaCl 2 , 2H 2 O) from Aldrich. The organic dye used in this work, namely methylene blue (MB), was from Soitex (Textile Company, Algeria). Preparation of sodium sepiolite (NaS) 10 g of sepiolite clay (S) was dispersed in 1 L of NaCl aqueous solution (1 mol·L − 1 ) at room temperature and left for 24 h. Then, the dispersion product was separated by centrifugation at 3500 tr.min − 1 . The operation was repeated three times to reach saturation and to obtain the Na + ions saturated - clay, thanks to a quantitative cationic exchange of Ca 2+ and Mg 2+ by sodium ions. The as-prepared Na + -sepiolite was then washed several times with distilled water to totally remove chloride anions. Finally, the sepiolite material was dried, ground and sieved with a sieve of 100 µm, resulting in a solid product, noted NaS. Elaboration of alginate single biocomposite network (SBN) beads A series of SBN beads made of sodium alginate (NaA) and sodium sepiolite (NaS) were prepared by ionotropic gelation according to the drop method as described in previous work [ 45 ]. The manual co-grinding of NaA and NaS mixture was carried out, with different weight ratios of NaS in the range 0–10 wt. %. The as-prepared single biocomposite network beads were named ANaS x -SBN, where x refers to NaS weight ratio (Table 1 ) . Table 1 Formulation of single biocomposite network (ANaSx-SBN) beads Sample NaS:NaA weight ratio (x) (wt.%) ANaS 0 -SBN 0 ANaS 3 -SBN 3 ANaS 5 -SBN 5 ANaS 10 -SBN 10 While sepiolite is a non-swelling clay with weak dispersion in aqueous medium, NaA/NaS mixture was efficiently dispersed in distilled water at room temperature under high stirring for many hours. It was observed that the manual co-grinding treatment decreased the dissolution time of sodium alginate even at the highest NaS load, without any clay deposition for a long period. Thence, the obtained viscous and homogeneous solutions were further extruded in the form of droplets through a burette under magnetic stirring. The droplets were collected in a 50 mL CaCl 2 ·2H 2 O (0.1 M) aqueous solution. The resulting spherical smooth beads were cured in bath overnight. Afterwards, they were vigorously rinsed and suspended in deionized water and stored at room temperature until their use in adsorption experiments. It is important to note that co-grinding treatment of NaA and NaS was not only used to avoid NaS agglomeration and enhance NaA dissolution, but also to reduce the biodegradability of the elaborated alginate beads in aqueous medium by developing effective interactions between both organic and inorganic components. Finally, in order to obtain the biocomposite xerogel beads, the resulting hydrogels were dried in vacuum at 60°C until the beads attained a constant weight. Note that among all the obtained ANaS x -SBN samples, a single network biocomposite beads, ANaS 0 -SBN was prepared in the absence of sepiolite for comparison (Table 1 ). Elaboration of alginate double biocomposite network (DBN) beads A series of DBN beads were prepared using appropriate sequential dual ionotropic-covalent crosslinked gelation methodology. They were combined with free radical polymerization of AAM into pAAM by IPN method in an aqueous medium under atmospheric oxygen, according to the procedure described in a previous work [ 46 ]. The DBN samples were prepared with different NaS:NaA weight ratios (x) in the range 0–10 wt. %. The details of the designation of the various ANaSx-DBN beads are listed in Table 2 . Note that the amounts of Bis, APS, AAM and ANaS x -SBN which were used for DBN preparation were always the same. Table 2 Formulation of double biocomposite network (ANaSx-DBN) beads Sample NaS/NaA ratio (wt. %) ANaS x -SBN (g) AAM (g) AAM/Bis (molar ratio) Temperature (°C) Diffusion Polymerization ANaS 0 -DBN 0 1 1 0.01 25 40 ANaS 3 -DBN 3 1 1 0.01 25 40 ANaS 5 -DBN 5 1 1 0.01 25 40 ANaS 10 -DBN 10 1 1 0.01 25 40 Monomer solutions were firstly prepared by dissolving equal amounts of AAM and Bis (AAM/Bis molar ratio of 0.01) at room temperature under constant stirring. A same amount of ANaS x -SBN beads (but with different NaS:NaA weight ratios) was then added to the AAM/Bis solutions under stirring (for 1 hour) at room temperature, allowing both AAM and Bis to diffuse inside the SBN beads. Then, the obtained mixtures were heated at 40°C for 30 min, before the addition of APS (0.023 g) to avoid single network disintegration in solution and to initiate the polymerization reaction and the growth of pAAM chains within and on the surface of the beads. Afterwards, the obtained ANaS x -DBN beads were immersed in distilled water for 4 days to remove unreacted monomers and homopolymers from the materials. Finally, the obtained hydrogel beads were dried in the oven at 60 ºC overnight. Note that among the ANaS x -DBN samples, a double network of alginate biocomposite beads, ANaS 0 -DBN was prepared in the absence of sepiolite for comparison (Table 2 ). Figure 1 summarizes the synthesis procedure of ANaS x -SBN and ANaS x -DBN. ANaS x -SBN preparation process includes single biocomposite network beads using both CaCl 2 and NaS as ionic crosslinkers under mechanical co-grinding mixture /encapsulation method (Fig. 1 a), while double cross-linked network was obtained by free radical polymerization of AAM monomers by immersing ANaS x -SBN into an aqueous solution containing a mixture of AAM, Bis and APS (Fig. 1 b). Reaction temperature during the synthesis can affect structure and final properties of the beads making it important to control it. Especially, polymerization temperature allows the re-swelling of the beads as observed in laboratory experiments and as highlighted later by SEM microscopy. Physico-chemical characterization of SBN and DBN beads The Fourier transform infrared (FTIR) spectra of ANaS x -SBN and ANaS x -DBN were recorded with a double-beam Perkin- Elmer 1600 FTIR spectrometer in the wavenumber range 4000 − 400 cm − 1 by performing the analysis in attenuated total reflection (ATR) mode. The XRD analysis of SBN and DBN beads was carried out by using P-Analytical (model-X’ pert PRO PW-3040/60) with Mo Kα radiation and scan speed of 1.2 ° min − 1 over the angle range of 1–50 ° . Surface morphology of ANaS x -SBN and ANaS x -DBN beads, used as bio-adsorbents, was examined by scanning electron microscopy (SEM) (Leica Cambridge S 360) at an accelerated voltage of 15 kV. Study of water absorption equilibrium and swelling rates Swelling capacities of ANaS x -SBN and ANaS x -DBN beads were evaluated and compared in distilled water as a function of time. Swelling kinetics was studied by immersing 0.1 g of xerogel beads in 100 mL of distilled water at 25°C. Subsequently, the beads were filtered and weighted at different times using an electronic balance. The swelling percentages (swelling rate) Ps (%) were calculated according to Eq. 1 : where W t (g) is the weight of the swollen beads at a given time (t) and W 0 (g) is the weight of the dried beads at t = 0. Ps values of ANaS x -SBN and ANaS x -DBN beads were examined for the different NaS ratios and at different pH values (2; 4; 7 and 12). Batch sorption experiments Experiments of dye adsorption/desorption were carried out by the batch adsorption method in an Erlenmeyer flask. The adsorption measurements were registered for both ANaS 5 -SBN and ANaS 5 -DBN beads at the same MB (used as organic dye) initial concentration. The concentration of MB was measured by UV-Visible absorption spectroscopy thanks to a Shimadzu UV-1800 model at 664 nm. The adsorption percentages, Ads (%), were determined by using Eq. 2 : where C 0 and C f are respectively the initial and the final MB concentrations (in mg L − 1 ). Sorption/desorption cycle experiments 50 mg of either ANaS 5 -SBN or ANaS 5 -DBN swollen beads were first added at ambient temperature (25°C) to 10 mL of a neutral aqueous solution containing 25 mg L -1 of MB. The mixture was then stirred for 3 hours to favor the sorption of MB. Finally, the filtered products were immersed in 100 mL ethanolic solution (C 2 H 5 OH, 0.01 mol L -1 ) for 3 hours to desorb the MB. Sorption/desorption cycles were repeated five times. The desorption percentages, Desor (%), were calculated thanks to Eq. 3 : \(\:Desor\left(\%\right)=\frac{{C}_{des}}{({C}_{0}-{C}_{f})}\) x100 (Eq. 3) where 𝐶 𝑑𝑒𝑠 is the desorbed concentration of MB in mg L -1 . Soil compost test and biodegradability evaluation Beads degradation was studied by weight loss during soil burial. A known weight of ANaS 5 -SBN and ANaS 5 -DBN (as well ANaS 0 -DBN) beads were placed under 4 cm of commercially available compost at ambient temperature. They were maintained at a fixed moisture content. The beads were dug out after few hours, 1, 3, 4, 7 and 8 days of degradation, then cleaned. The weight loss differences were calculated as a function of time by using Eq. 4 : where W 0 is the initial dry weight of beads and where W t is the dry weight of beads after cleaning at a time t. Results and Discussions Macroscopic morphology of SBN and DBN beads Digital images of ANaS x -SBN and ANaS x -DBN beads were recorded for the different NaS loads. Figure 2 illustrates the images of the beads both in their hydrogel state and in their xerogel state after air drying. As observed in Fig. 2 a, ANaS x -SBN beads, in their hydrogel state, are all characterized by a more or less spherical shape and by a smooth surface whatever the NaS load. In contrast, Fig. 2 b reveals that ANaS x -DBN beads, in their hydrogel state, are less spherical than ANaS x -SBN ones. Additionally, the waves appearing on the surface of the DBN beads in their hydrogel state (Fig. 2 b), indicate that the IPN method greatly influences the surface structure of alginate biocomposites beads. Such a rough structure which characterizes ANaS x -DBN beads should nevertheless be beneficial for adsorption properties, allowing stronger interactions with pollutants as mentioned in previous work [ 47 ]. When comparing Fig. 2 a and Fig. 2 b, the bead diameters are noticeably different between ANaS x -DBN and ANaS x -SBN in their hydrogel state. For instance, the mean diameter of ANaS 5 -DBN beads (5 mm) is larger than that of ANaS 5 -SBN beads which only amounts to approximatively 3 mm. Nevertheless, the mean diameter progressively increases with NaS ratio for both kinds of beads (either SBN or DBN ones) in their hydrogel state. The change from hydrogel to xerogel state significantly modifies the appearance of the beads as observed in Fig. 2 a and Fig. 2 b. Their color turns from slightly transparent to opaque yellow for ANaS x -SBN and to translucid for ANaS x -DBN. Note that the color of ANaS x -DBN beads could be attributed to the presence of pAAM. The air-drying of ANaS x -SBN and ANaS x -DBN induces a decrease in size of all the beads due to water removal. The air-drying of ANaS x -SBN beads lead to the loss of their shape since they look like as flat disks in their xerogel state (Fig. 2 a). Differently, ANaS x -DBN beads, even if they are found retracted, mainly keep their shape unchanged after drying (Fig. 2 b). This behavior, can be explained by the increase of the crosslinking density of the double network within ANaS x -DBN beads, suggesting that pAAM polymers act as a structural support to control the shrinkage and subsequently to maintain the shape of the beads in their xerogel state. Furthermore, a stretching touching test was carried out to confirm the formation of ANaS x -SBN and ANaS x -DBN hydrogel beads with stretchable properties. Among all the beads, ANaS x -DBN ones were found extremely stretchable. For instance, Fig. 2 c illustrates the touching test applied to an ANaS 5 -DBN bead, which appears strong and elastic (steps 1, 2 and 3) and which preserves its initial shape and size under the hand after finger removing (step 4). The as-observed strength and stretchability of ANaS x -DBN beads can be explained by the formation of an interpenetrating double network composite structure. These characteristics could be particularly advantageous for the reuse of such beads in adsorption-desorption cycles and for the enhancement of their stability, delaying their biodegradability. Chemical composition of SBN and DBN beads To validate the chemical composition of ANaS x -SBN and ANaS x -DBN elaborated beads and to highlight the polymerization of AAM acrylamide monomers within ANaS x -DBN ones, ATR-FTIR characterization was conducted (Fig. 3 ). The spectra of ANaS 5 -SBN and ANaS 5 -DBN together with that of sodium alginate (ANaS 0 -SBN, in the absence of sepiolite) are shown in Fig. 3 a and are in agreement with previous work [ 48 ]. All ATR-FTIR spectra highlight a broad peak at 3600–3000 cm –1 together with peaks at around 1588 cm − 1 and 1425 cm − 1 , which can be identified as the stretching vibrations of O-H, -COO (asymmetric) and -COO (symmetric) bonds respectively, and which indicate the presence of alginate within all the beads. Also, the peaks in the region 1155 − 900 cm − 1 are attributed to C-O stretching vibration of alginate. When comparing with ANaS x -SBN spectra, the characteristic peaks located at 2931 cm − 1 , 1648 cm − 1 and 1409 cm − 1 , are respectively attributed to CH 2 , C = O and CH groups within ANaS 5 -DBN beads. Importantly, the presence in the spectrum of ANaS 5 -DBN (Fig. 3 a) of an additional intense broad band at 3500 − 3200 cm − 1 (with a notable overlap with O-H band), which is absent in the spectra of ANaS x -SBN, can be attributed to the asymmetric vibration of N-H groups, highlighting the specific presence of AAM within DBN beads. Also, the new characteristic band appearing at around 2900 cm − 1 in case of ANaS 5 -DBN, which corresponds to the symmetric and asymmetric stretching vibrations of methylene groups (CH in CH 2 and CH 3 ), can also be attributed to acrylamide monomers present in DBN double network of ANaS 5 -DBN beads. The peak present at 1700 cm − 1 only in the spectrum of ANaS 5 -DBN is due to the stretching of the amide group in polyacrylamide (i.e. >C = O), indicating that AAM monomers were successfully polymerized within the DBN beads as it had already been pointed out in literature [ 48 ]. Moreover, the presence of pAAM polymers in ANaS 5 -DBN beads is further supported by new bands at 1645 cm − 1 and 1600 cm − 1 , associated with the C-N (amide bond) stretching vibrations, and another weaker band at 1454 cm − 1 , attributed to the stretching vibration of CH = CH 2 bond. ATR-FTIR spectra of ANaS x -DBN were also recorded for different NaS loads and are shown in Fig. 3 b together with the spectrum of sepiolite (NaS) and that of polyacrylamide polymers (pAAM). NaS spectrum highlights the presence of a band at 1212 cm − 1 , related to Si-O bonds, together with a strong band at 1016 cm − 1 related to the asymmetric stretching vibration of Si–OH groups which are present in sepiolite. In addition, the characteristic infrared bands of the -OH groups of sepiolite are observed at 3687 cm − 1 , 3562 cm − 1 and 3418 cm − 1 in agreement with literature [ 49 – 51 ]. pAAM spectrum shows the presence of an intense broad band between 3500 and 3000 cm − 1 which is the signature of the asymmetric vibration of N-H groups, while the peaks present at 1700 cm − 1 , 1645 cm − 1 and 1600 cm − 1 are due to the amide bonds within pAAM polymers. When comparing with NaS and pAAm spectra (Fig. 3 b), we note for ANaS 5 -DBN and ANaS 10 -DBN, the presence of an intense broad band from 3600 to 3300 cm − 1 which can be attributed to the overlapping of the N–H vibration band of pAAm with the O-H band of NaS. This proves the concomitant presence of both sepiolite and polyacrylamide within these beads. However, the band at 1212 cm − 1 , related to Si-O bonds, does not appear in ANaS 5 -DBN and ANaS 10 -DBN spectra. Moreover, the strong band at 1016 cm − 1 corresponding to the asymmetric stretching vibration of Si–OH groups, shifts to a lower wavenumber. Besides, the characteristic bands of the -OH groups of sepiolite at 3687 cm − 1 , 3562 cm − 1 and 3418 cm − 1 are not observed in the spectra of ANaS 5 -DBN and ANaS 10 -DBN. The same observation has already been reported by Whang et al and Zhi et al [ 49 – 51 ], where the disappearance of the signature of -OH groups in vermiculite and attapulgite clays was observed in case of hydroxyethyl cellulose-g-poly(acrylic acid)/vermiculite nanocomposites and in case of poly(Acrylic Acid-Co-2-Acrylamido-2-Methyl-1-Propane Sulfonic Acid)/Attapulgite composite, respectively. We can also note that the Si–O–Si-stretching vibration band of sepiolite, initially present at 1212 cm − 1 in NaS, progressively shifts to higher wavenumbers in ANaS 5 -DBN and ANaS 10 -DBN. In addition, upon increasing NaS load, the symmetric stretching band of -COO- of alginate (ANaS o -SBN), initially present at 1414 cm − 1 (Fig. 3 a), progressively shifts to 1411 cm − 1 , 1410 cm − 1 and 1408 cm − 1 in ANaS 0 -DBN, ANaS 5 -DBN and ANaS 10 -DBN respectively. These observations indicate that pAMM chains interact with biopolymer chains within all ANaS x -DBN beads. Sepiolite dispersion within SBN and DBN beads To confirm the polymerization of AAM monomers and to evaluate the effect of IPN strategy on enhancing sepiolite dispersion, XRD analysis was carried out. The XRD patterns of ANaS 5 -SBN, ANaS 5 -DBN and ANaS x -DBN with different NaS load ratios are shown in Fig. 4 . As observed for ANaS 5 -SBN (Fig. 4 a), most reflection peaks characteristic of NaS are absent, except for smaller reflection angles, at 2θ = 6.8° corresponding to the (110) planes, this peak being slightly shifted to a lower angle compared with pristine NaS. These results are in good agreement with those reported by Kara et al [ 52 ] and Bidkoski et al [ 53 ]. These observed effects are attributed to the needles of NaS which are generally delaminated to fiber sticks and which are dispersed inside the alginate beads, forming an intercalated nano-biocomposite structure [ 52 , 54 – 56 ]. In ANaS 5 -DBN diffractogram (Fig. 4 b), a new broad peak appears at 21.7°. This peak is also present in the diffractograms of all ANaS x -DBN beads whatever the NaS load (x) (Fig. 4 c). In literature, this additional peak was attributed to the presence of pAAM polymers [ 57 , 58 ]. This confirms, in agreement with our previous FTIR results, that AAM was successfully polymerized within the DBN beads. The acrylamide monomers thus interfere with the arrangement of alginate chains in ANaS x -DBN beads and polymerize to form ordered crystal regions. Evidently, the d 110 crystalline peak of NaS is totally absent in ANaS 0 -DBN diffractogram and remains weak at low NaS loads (x = 3 and 5). For the highest NaS percentage, in case of ANaS 10 -DBN, the d 110 crystalline peak of NaS is clearly observed, but remains sharp and diffused, indicating that NaS fibrous clay has maintained its high exfoliation degree in the alginate biocomposite double network. Meanwhile, the intensity of pAAM peak at 21.7° in ANaS 10 -DBN diffractogram is significantly reduced compared to ANaS 0 -DBN, ANaS 3 -DBN (Fig. 4 b) and ANaS 5 -DBN (Fig. 4 c), due to the interactions between pAAM and sepiolite needles, as observed by Zaharia et al [ 59 ]. Surface morphology of SBN and DBN beads Morphology evolution of SBN and DBN beads (with different NaS loads) was checked by SEM microscopy (Fig. 5) in order to observe the effect of IPN strategy on texture modification. The SEM images of the surface and cross-section of ANaS x -SBN and ANaS x -DBN beads in their hydrogel state were first recorded for different NaS loads (Fig. 5a). It can be observed that whatever NaS percentage (x value), both internal and external surfaces of ANaS x -DBN beads in their wet state, appear changed compared to their single network version, namely ANaS x -SBN beads. We can indeed compare for instance ANaS 3 -SBN images with those of ANaS 3 -DBN. This observation suggests once again that pAAM was successfully incorporated on the surface and within the bulk of the alginate biocomposite beads. If we compare now ANaS 5 -SBN and ANaS 5 -DBN beads in their wet states, it can clearly be observed a morphological difference between the two networks, which is reflected in the porosity level. As depicted in Fig. 5a , the ANaS 5 -SBN bead in its hydrogel state has a slightly porous structure. On the contrary, the corresponding ANaS 5 -DBN bead is characterized in the same state by a more homogeneous network and a highly porous spongy structure. The initial morphology of ANaS 5 -SBN beads is thus modified by pAAM polymer chains, which support the bead structure by linking the pores and by increasing their size, which results in the spongy shape of the ANaS 5 -DBN beads. Such structural homogeneity and porosity of the network should obviously improve the adsorption properties of the DBN beads in solution, as previously reported by Mittal et al [ 60 ], and should positively affect their swelling behavior. To further examine the effect of our IPN strategy on the texture of alginate biocomposite beads at the highest NaS load (x = 10), SEM images of ANaS 10 -SBN and ANaS 10 -DBN beads were recorded (Fig. 5a). In this case, some agglomerated NaS particles can be observed, although the external SEM image of ANaS 10 -DBN beads could depict that the number of aggregated NaS particles has been reduced compared to ANaS 10 -SBN. The uniformed dispersion of NaS can be attributed to co-grinding mixture as well as in situ polymerization of AAM monomers on the surface of sepiolite, in agreement with XRD results and as already described by Mahdavinia and Zaharia [ 59 , 61 ]. Besides, the internal cross-section morphology of ANaS 10 -DBN beads (Fig. 5a) exhibits a thin-film membrane onto the surface of the core as a coating that indicates the presence of pAAM not only in the internal but also on the external surface of the beads. It can be noted from Fig. 5a that the external surface roughness of ANaS 10 -DBN is lower than that of both ANaS 3 -DBN and ANaS 5 -DBN. This observation is in good agreement with our previous XRD results (Fig. 4 ) and with the further discussion about the decrease in the swelling of DBN beads. The increased cross-linking points within the beads create a more compact and smoother surface, which suggests that the incorporation of a proper amount of NaS fibrous clay is beneficial to improve the surface structure of the ANaS x -DBN and therefore allows to obtain beads with controlled swelling. However, an increased amount of NaS fibrous clay content may reduce the swelling properties of the elaborated beads as shown in the swelling results which will be discussed below. The SEM images of the surface and cross-section of ANaS x -SBN and ANaS x -DBN beads in their xerogel state were also recorded for the different NaS loads. For illustration, the images corresponding to ANaS 5 -DBN beads in their dry state are shown in Fig. 5b at two different magnifications. It can be noted that the surface of ANaS 5 -DBN beads presents significant cracks, and their cross-section exhibits a rough surface and abrupt sharp edges. The same observations were carried out on all the SBN and DBN beads prepared in this work. Such a rough structure may be beneficial for adsorption of pollutants, due to the increased surface area and the resulting stronger interactions. In order to examine the evolution of surface morphology during swelling, ANaS x -DBN beads, initially in their xerogel state, were re-swelled for two hours and then observed by SEM microscopy. Figure 5c shows for illustration the re-hydrated structure of ANaS 3 -DBN beads. When comparing these micrographs with the images of the same beads in their xerogel state, it can be noticed that the porosity of the beads is clearly visible after re-swelling in water. The same observation can be made for all prepared ANaS x -DBN beads, whatever the NaS load. The porosity of the beads is thus completely restored after re-hydration. Thanks to the used IPN strategy, DBN beads, in their xerogel state, are able to maintain their porosity and their high swelling properties, unlike their single structure version (ANaS x -SBN beads) which becomes non-porous. Swelling behavior of SBN and DBN beads Swelling capacities of ANaS x -SBN and ANaS x -DBN beads were evaluated in distilled water as a function of time. Figure 6 a compares the swelling percentages (swelling rates), and thus the water absorbencies as a function of time, of both ANaS 5 -SBN and ANaS 5 -DBN beads, which were prepared with the same NaS load. After immersing both xerogel beads in distilled water, the swelling kinetics of ANaS 5 -SBN and ANaS 5 -DBN exhibit similar behavior. A rapid increase in the swelling percentage at the beginning is followed by a slower increase of the swelling ratio until reaching a water absorption equilibrium. Interestingly, after 5 min of immersion, a swelling percentage of about 1300 g/g of adsorbed water is reached in case of ANaS 5 -DBN, while a much lower percentage (600 g/g in absorbed water) is reached at the same time in case of ANaS 5 -SBN. In both cases, it takes about 15 min of immersion to reach a quasi-swelling equilibrium. The swelling percentage values finally reach 1400 g/g and 650 g/g of adsorbed water after 110 min for ANaS 5 -DBN and ANaS 5 -SBN respectively. Whatever NaS load, swelling behavior of ANaS x -DBN always remains higher than that of ANaS x -SBN beads at a given NaS load (results not shown). The swelling capacities of ANaS x -SBN and ANaS x -DBN beads are evidently related to the presence of numerous hydrophilic functional groups, such as hydroxyl groups which were initially present into both sepiolite and alginate. The highest water uptake capacity of DBN beads is certainly due to their higher porous structure (which results from a superior cross-link density) as previously observed by SEM microscopy (Fig. 5), but not only. Indeed, ANaS x -DBN beads also contain additional hydrophilic groups, namely the amide groups present all along pAAM polymer chains [ 59 , 62 ]. Note that the swelling ability of DBN beads is also in correlation with their adsorption/desorption capacities as already described [ 63 ] and as it will be demonstrated later. Besides, swelling rates of ANaS x -DBN beads were evaluated in distilled water as a function of NaS load as illustrated in Fig. 6 b. Once again, after immersing xerogel beads in distilled water, a rapid increase in the swelling percentage is followed, after 15 min, by a slower increase of the swelling ratio until reaching a water absorption quasi-equilibrium. The swelling percentage values finally reach 1700, 1600, 1400 and 1300 g/g of adsorbed water after 120 min for NaS loads of 0, 3, 5 and 10% respectively. As observed, the swelling behavior of ANaS x -DBN beads continuously decreases when increasing NaS load. A similar decrease in swelling behavior has already been reported in literature in case of chitosan-g-poly(acrylic acid) composites upon incorporation of raw sepiolite [ 64 ]. The observed decrease in DBN swelling behavior, when NaS content increases, can be explained by the fact that sepiolite fibrous clay is a non-swelling reinforcing agent. This property leads to the limit swelling prorates of DBN beads but is promising for controlling their swelling properties by loading sepiolite into alginate beads. In order to assess the pH sensitivity of the elaborated beads, swelling rates of ANaS 5 -SBN and ANaS 5 -DBN were evaluated in water at different pHs as illustrated in Fig. 6 c and 6 d respectively. Whatever the pH of the aqueous medium, after immersing both kinds of xerogel beads, the swelling behavior exhibit the same time evolution as previously observed in Fig. 6 a and 6 b. Interestingly, whatever the pH, ANaS 5 -SBN exhibits once again a lower swelling rate than ANaS 5 -DBN. Noticeably, for both SBN and DBN beads, the swelling percentage increases with the pH value of the medium. Indeed, at water absorption equilibrium after 110 min, the swelling percentage of ANaS 5 -SBN beads amounts to 300 g/g of adsorbed water between pH 2 and pH 4 and reaches about 600 g/g of adsorbed water at pHs higher than 7. In the same way, after 110 min, the swelling percentage of ANaS 5 -DBN beads amounts to 950 g/g of adsorbed water at pH 2, 1100 g/g at pH 4, 1400 g/g at pH 7 and finally 2000 g/g of adsorbed water at pH 12. This can be explained by the presence of acid-base functionalities within the beads, the protonation rate of which depends on the pH. In very acidic medium, at pH 2, carboxylic groups (-COOH) of sodium alginate and silanol groups (-Si-OH) of sepiolite are mainly protonated, while at pH 12, these functionalities mainly deprotonate and transform into their anionic form (-COO − and -Si-O − ). When the pH increases, even though water molecules can maintain their hydrophilic interactions with these groups, the hydrogen bond interactions between the acid-base functionalities of alginate and sepiolite strongly decrease within the beads and the anion-anion repulsive electrostatic forces between the deprotonated groups become predominant, which probably favors the porosity of the beads. As a consequence, beads are characterized by a relatively lower water uptake behavior in acidic medium, while the swelling ability of the beads drastically increases in alkaline medium (Fig. 6 c and 6 d ) . In order to check whether ANaS 5 -SBN and ANaS 5 -DBN beads maintain their structure and shape after swelling in water at different pHs, digital images of the beads in their hydrogel state were recorded (Fig. 6 e ) . One can observe on the figure that the shape and size of the beads are kept unchanged whatever the pH. However, we can importantly note that ANaS 5 -SBN beads are mainly ruptured and disintegrated at pH 12. This explains why swelling percentage of SBN beads at this pH is not higher than that obtained at pH 7 (Fig. 6 c ) , contrarily to what is observed in the case of ANaS 5 -DBN beads (Fig. 6 d ) . While the presence of pAAM polymers strengthen the interpenetrating double network composite structure of DBN beads, its absence within ANaS 5 -SBN could explain the disintegration of these simple network structures under the constraint of electrostatic repulsive forces between the deprotonated groups on the one hand and water osmotic pressure on the other hand. As demonstrated, ANaS 5 -DBN beads remain stable whatever the pH thanks to their strong IPN network structure. Also, they preserve their swelling ability and maintain their shape without shrinking thanks to the highly cross-linked flexible chain network of pAAM which strengthens their architecture. This behavior will be used for the adsorption of MB dye as it will be seen next. Use of SBN and DBN beads in adsorption/desorption cycles Experiments of dye adsorption/desorption were carried out by the batch adsorption method. Either ANaS 5 -SBN beads or ANaS 5 -DBN ones were added at ambient temperature to a neutral aqueous solution containing the organic toxic Methylene Blue (MB) dye at a concentration of 25 mg L -1 in a first adsorption step. Then filtered products were immersed in ethanolic solution, as green eluent, to desorb the MB. Such an adsorption/desorption cycle was repeated five times (cycles C1 to C5) for either SBN or DBN beads to evaluate the adsorption/desorption rates/percentages of both kinds of beads together with their potential reuse in water decontamination (Fig. 7 ). The results are depicted in Fig. 7 a for the five successive adsorption steps and in Fig. 7 b for the successive desorption steps. As highlighted in Fig. 7 a, the adsorption percentage of MB by ANaS 5 -SBN beads, as deduced from UV-visible absorption spectroscopy measurements, amounts to 63% in the first cycle. However, this adsorption rate by ANaS 5 -SBN beads decreases to 53% in the second cycle and to 32% in the third one. It drastically drops after the third cycle, reaching 0%. When considering the digital images of SBN beads in their hydrogel state after MB adsorption (Fig. 7 c), one can observe the intense blue color of the beads which traduces the quantitative adsorption of the dye. Nevertheless, one can note the decrease in the size of SBN beads in the third cycle. After this cycle, ANaS 5 -SBN beads are mainly ruptured and disintegrated, which explains the complete release of MB contaminants in the medium and the observed drastic decrease in adsorption rate of SBN beads. Differently, the adsorption percentage of MB by ANaS 5 -DBN beads, which amounts to 57% in the first cycle, remains almost unchanged after five cycles (about 50%) (Fig. 7 a). This proves that contrarily to SBN beads, DBN ones keep their adsorption behavior constant even after five adsorption/desorption cycles. When considering the digital images of DBN beads in their hydrogel state after MB adsorption (Fig. 7 c), one can once again observe the intense blue color of the beads which traduces the quantitative adsorption of the dye, but this time all along the five successive cycles. Besides, contrarily to SBN beads, DBN ones keep their shape and size unchanged even after five cycles, which should explain the constant adsorption behavior of DBN beads. During the fifth cycle, after MB dye adsorption and after air-drying, ANaS 5 -DBN beads, this time in their xerogel state, appear dark blue as observed in the digital image of Fig. 7 d, demonstrating that their porous structure nature was preserved even after the successive adsorption/desorption cycles and even after drying. The porous structure of these beads was confirmed by SEM microscopy as shown in Fig. 7 e. The rough surface of ANaS 5 -DBN beads, decorated by a few pores, is indeed observed after drying. These pores probably correspond to the channels which enable the diffusion of water and MB dye molecules within the network of DBN beads. It can thus be confirmed that the IPN strategy, combined with the biocomposite structure of the beads, which was developed in this work, prevents the common observed collapse of the pores during air-drying of alginate beads. Evidently, the very good adsorption rate of ANaS 5 -DBN beads results from their porosity and their important swelling behavior (Fig. 6 ). Also, structural and functional stability of DBN beads during the repeated adsorption/desorption cycles comes from their stretchability (Fig. 2 ) on one hand and from the strength and the resistance of their structure on the other hand. This enables the reproducible reuse of ANaS 5 -DBN beads without any loss of their shape or decrease in their adsorption behavior. When considering the successive desorption steps (Fig. 7 b), one can observe that desorption percentages of MB from ANaS 5 -SBN beads (51%, 50% and 30% respectively after the three first cycles) are slightly lower than the successive adsorption percentages (63%, 53% and 32%). This means that most of MB molecules have been released from SBN beads upon immersion in ethanol. More interestingly, in case of ANaS 5 -DBN beads, desorption percentages are very close to adsorption rate values (53% after first cycle and 50% after fifth one), highlighting the fact that even after 5 cycles, MB molecules are completely released from DBN beads, which implies a nearly perfect regeneration of ANaS 5 -DBN beads in their hydrogel state. Ethanol appears also here as a very efficient eluent for desorbing MB from DBN beads. Evaluation of SBN and DBN bead biodegradability The drawback of alginate beads in their hydrogel state is their fast biodegradation properties which limit their use in some applications. In order to evaluate the degradation rate of ANaS 5 -DBN beads, and to compare it with the degradation rates of other SBN and DBN beads, namely ANaS 5 -SBN and ANaS 0 -DBN, the beads were buried under 4 cm of compost at ambient temperature and fixed moisture content. Then, bead degradation rate was followed by their weight loss as a function of time (Fig. 8 ). In Fig. 8 a, one can observe that the biodegradability rate of ANaS 5 -SBN beads is higher than that of DBN beads. Indeed, single network ANaS 5 -SBN beads are totally degraded after one day, while double network ANaS 0 -DBN and ANaS 5 -DBN beads are completely degraded after 4 days and 8 days respectively. For better illustration, Fig. 8 b displays the digital images of SBN and DBN beads recorded just after their extraction from the compost, at different time intervals, and before any cleaning and weighing. The changes in bead characteristics (i.e. color, number and shape) during the compost burial can be easily distinguished. All the beads appear brown due to the adsorption of the compost at their surface and probably to its diffusion within the bulk of the beads. Interestingly, SBN beads quickly shrink, deform and break down into smaller size and cracks over hours, their number being also decreased rapidly. In case of ANaS 0 -DBN beads which were prepared in the absence of sepiolite, a slower evolution is observed. A slight breaking down into smaller sizes and the appearance of irregular shapes are nevertheless observed over 4 days. Differently, ANaS 5 -DBN beads, prepared in the presence of sepiolite, mainly maintain their spheroidal shape and keep their size and surface structure over about 8 days (Fig. 8 b). These observations prove that IPN strategy combined with biocomposite hierarchical structure endows DBN beads a good resistance towards biodegradation. It is well known that reinforcing biopolymers by clay or blending with other biopolymers can accelerate their biodegradation. This is what we observe in case of SBN beads in the presence of NaS load since ANaS 5 -SBN beads deteriorate in less than one day. Contrarily to SBN beads, DBN ones degrade more slowly even in the presence of NaS load. This result certainly comes from the presence of pAAM polymer chains within the network of DBN beads and is in good agreement with previous studies where it was clearly demonstrated that degradation rate of biocomposites decreases when the amount of hydrolytically degradable components increases. In our case, a relatively long time is thus needed to complete the hydrolysis of amide groups which are present in the polymer chains of pAAM, which explains the slow degradation of DBN beads. Nevertheless, how could it be possible to explain the fact that ANaS 5 -DBN beads are less degradable than ANaS 0 -DBN ones, which were prepared in the absence of sepiolite? The observed decrease in DBN biodegradability behavior when NaS content increases, could be explained by the fact that sepiolite fibrous clay is a non-swelling reinforcing agent (see Fig. 6 ) which strongly interacts with pAAM (as deduced from Fig. 4 ) delaying its hydrolysis. Conclusion In this work, we successfully designed new hydrogel biocomposite beads, made of two biopolymers, namely alginate and polyacrylamide, together with natural sepiolite clay. Two kinds of materials were prepared: i) simple biocomposite network (SBN) beads by the dispersion of different loads of sepiolite within the alginate network and ii) double biocomposite network (DBN) beads by the in situ polymerization of AAM monomers within SBN bead network. The as-prepared SBN and DBN materials were characterized by different physico-chemical methods, which revealed the good dispersion of sepiolite and the successful incorporation of pAAM within DBN beads. Polymer chains act as a structural support which maintains the shape, controls the shrinkage and increases the porosity of the double network DBN beads either in their xerogel or in their hydrogel state. Consequently, DBN beads were found characterized by improved properties: very good stretchability, good swelling behavior, excellent stability in acidic, neutral or alkaline aqueous media, good stability upon air drying and increased biodegradability resistance, which should enable the use of DBN beads as green materials in different applications, such as pollutant removal. Compared to SBN materials, DBN beads were shown to be characterized by enhanced adsorption rate towards methylene blue, used as a model toxic pollutant, and were found reproducibly reusable as very stable bioadsorbent materials. In summary, this work describes a novel, soft and green approach, based on IPN strategy, to design high-performance alginate biocomposite materials as promising systems towards their use in eco-friendly processes. In the future, the as-prepared DBN beads will be used for removal of different kinds of dyes and contaminants from water and will also be tested in some medical applications. Besides, preparation of double biocomposite network beads, by the way of an alternative radiation-based methodology, is in due course. Declarations Author Contribution M.B.: methodology, formal analysis, investigation, validation, writing first version of the manuscript. M.K. and N.B.: conceptualization, visualization, validation, supervision. L.H. : formal analysis, corrections to the manuscript. S.R.: validation, writing final version of the manuscript, review and editing, supervision. References Kumar MNR (2000) A review of chitin and chitosan applications. Reactive Funct Polym 46(1):1–27 Bajpai J, Shrivastava R, Bajpai A (2007) Binary biopolymeric beads of alginate and gelatin as potential adsorbent for removal of toxic Ni2 + ions: a dynamic and equilibrium study. J Appl Polym Sci 103(4):2581–2590 Chatterjee S, Lee MW, Woo SH (2010) Adsorption of congo red by chitosan hydrogel beads impregnated with carbon nanotubes. Bioresour Technol 101(6):1800–1806 Thakur S et al (2018) Recent progress in sodium alginate based sustainable hydrogels for environmental applications. J Clean Prod 198:143–159 Haug A, Larsen BR (1963) The solubility of alginate at low pH. Acta Chem Scand 17(6):1653–1662 Johnson FA, Craig DQ, Mercer AD (1997) Characterization of the block structure and molecular weight of sodium alginates. J Pharm Pharmacol 49(7):639–643 Velings NM, Mestdagh MM (1995) Physico-chemical properties of alginate gel beads. Polym Gels Networks 3(3):311–330 Grant GT et al (1973) Biological interactions between polysaccharides and divalent cations: the egg-box model. FEBS Lett 32(1):195–198 McNeely WH, Kang KS (1973) Xanthan and some other biosynthetic gums , in Industrial gums . Elsevier, pp 473–497 Lee KY, Mooney DJ (2012) Alginate: properties and biomedical applications. Prog Polym Sci 37(1):106–126 Zia KM et al (2015) Alginate based polyurethanes: A review of recent advances and perspective. Int J Biol Macromol 79:377–387 Martinsen A, Storrø I, Skjårk-Bræk G (1992) Alginate as immobilization material: III. Diffusional properties. Biotechnol Bioeng 39(2):186–194 Radoor S et al (2023) Recent advances in cellulose-and alginate-based hydrogels for water and wastewater treatment: A review. Carbohydr Polym, : p. 121339 Adzmi F et al (2012) Preparation, characterisation and viability of encapsulated Trichoderma harzianum UPM40 in alginate-montmorillonite clay. J Microencapsul 29:205–210 Hua S et al (2010) pH-sensitive sodium alginate/poly(vinyl alcohol) hydrogel beads prepared by combined Ca2 + crosslinking and freeze-thawing cycles for controlled release of diclofenac sodium. Int J Biol Macromol 46(5):517–523 Yadav M, Rhee KY (2012) Superabsorbent nanocomposite (alginate-g-PAMPS/MMT): Synthesis, characterization and swelling behavior. Carbohydr Polym 90(1):165–173 Martin M et al (2013) Effect of unmodified starch on viability of alginate-encapsulated Lactobacillus fermentum CECT5716. LWT-Food Sci Technol 53(2):480–486 Mahdavinia GR et al (2016) Magnetic hydrogel beads based on PVA/sodium alginate/laponite RD and studying their BSA adsorption. Carbohydr Polym 147:379–391 ALSamman MT, Sánchez J (2022) Chitosan-and alginate-based hydrogels for the adsorption of anionic and cationic dyes from water. Polymers 14(8):1498 Haraguchi K, Takehisa T, Fan S (2002) Effects of clay content on the properties of nanocomposite hydrogels composed of poly (N-isopropylacrylamide) and clay. Macromolecules 35(27):10162–10171 Xiang Y, Peng Z, Chen D (2006) A new polymer/clay nano-composite hydrogel with improved response rate and tensile mechanical properties. Eur Polymer J 42(9):2125–2132 Kaşgöz H, Durmuş A, Kaşgöz A (2008) Enhanced swelling and adsorption properties of AAm-AMPSNa/clay hydrogel nanocomposites for heavy metal ion removal. Polym Adv Technol 19(3):213–220 Ruiz-Hitzky E, Darder M, Aranda P (2008) An introduction to bio-nanohybrid materials. Bio-inorganic hybrid nanomaterials, : p. 1–40 Wang W, Wang A (2009) Preparation, characterization and properties of superabsorbent nanocomposites based on natural guar gum and modified rectorite. Carbohydr Polym 77(4):891–897 Unuabonah EI, Taubert A (2014) Clay–polymer nanocomposites (CPNs): Adsorbents of the future for water treatment. Appl Clay Sci 99:83–92 Darder M, Aranda P, Ruiz-Hitzky E (2007) Bionanocomposites: a new concept of ecological, bioinspired, and functional hybrid materials. Adv Mater 19(10):1309–1319 Mittal V (2011) Nanocomposites with biodegradable polymers: synthesis, properties, and future perspectives, vol 68. Oxford University Press Nigmatullin R, Bencsik M, Gao F (2014) Influence of polymerisation conditions on the properties of polymer/clay nanocomposite hydrogels. Soft Matter 10:2035–2046 Kausar A et al (2022) Cellulose, clay and sodium alginate composites for the removal of methylene blue dye: Experimental and DFT studies. Int J Biol Macromol 209:576–585 Essifi K et al (2023) Investigating the effect of clay content and type on the mechanical performance of calcium alginate-based hybrid bio-capsules. Int J Biol Macromol 242:125011 Alboofetileh M et al (2013) Effect of montmorillonite clay and biopolymer concentration on the physical and mechanical properties of alginate nanocomposite films. J Food Eng 117(1):26–33 Dean K, Yu L, Wu D (2007) Preparation and characterization of melt-extruded thermoplastic starch/clay nanocomposites. Compos Sci Technol, : p. 413–421 Ruiz AI, Ruiz-García C, Ruiz-Hitzky E (2023) From old to new inorganic materials for advanced applications: The paradigmatic example of the sepiolite clay mineral. Appl Clay Sci 235:106874 Chivrac F et al (2010) Starch nano-biocomposites based on needle-like sepiolite clays. Carbohydr Polym 80:145–153 Ruiz-Hitzky E et al (2011) Chap. 1 7 - Advanced Materials and New Applications of Sepiolite and Palygorskite , in Developments in Clay Science , E. Galàn and A. Singer, Editors. Elsevier. pp. 393–452 Fernandez C et al (2016) Reprint of Study of spatial distribution of sepiolite in sepiolite/polyamide6,6 nanocomposites. Applied clay science, 130 Quignard F, Renzo FD, Guibal E (2010) From Natural Polysaccharides to Materials for Catalysis, Adsorption, and Remediation. Carbohydrates in Sustainable Development I. Springer, Berlin Heidelberg: Berlin, Heidelberg, pp 165–197. A.P. Rauter, P. Vogel, and Y. Queneau, Editors Kusuktham B, Prasertgul J, Srinun P (2013) Morphology and Property of Calcium Silicate Encapsulated with Alginate Beads. Silicon 6:191–197 Papageorgiou SK et al (2006) Heavy metal sorption by calcium alginate beads from Laminaria digitata. J Hazard Mater 137(3):1765–1772 Budtova T (2019) Cellulose II aerogels: A review. Cellulose 26:81–121 Valentin R et al (2007) Accessibility of the functional groups of chitosan aerogel probed by FT-IR-monitored deuteration. Biomacromolecules 8(11):3646–3650 García-González CA, Alnaief M, Smirnova I (2011) Polysaccharide-based aerogels—Promising biodegradable carriers for drug delivery systems. Carbohydr Polym 86(4):1425–1438 Santagapita PR, Mazzobre MF, Buera MP (2011) Formulation and drying of alginate beads for controlled release and stabilization of invertase. Biomacromolecules 12(9):3147–3155 Belalia F, Djelali N (2016) Investigation of swelling/adsorption behavior of calcium alginate beads. Rev Roum Chim 61(10):747–754 Lee B-B, Ravindra P, Chan E-S (2013) Size and Shape of Calcium Alginate Beads Produced by Extrusion Dripping, vol 36. Chemical Engineering & Technology, pp 1627–1642. 10 Yang CH et al (2013) Strengthening Alginate/Polyacrylamide Hydrogels Using Various Multivalent Cations. ACS Appl Mater Interfaces 5(21):10418–10422 Venkatakrishnan A, Kuppa VK (2018) Polymer adsorption on rough surfaces. Curr Opin Chem Eng 19:170–177 Karadağ E, Kundakcı S (2015) Application of highly swollen novel biosorbent hydrogels in uptake of uranyl ions from aqueous solutions. Fibers Polym 16(10):2165–2176 Zhu L et al (2014) Synthesis of Sodium Alginate Graft Poly (Acrylic Acid-Co-2-Acrylamido-2-Methyl-1-Propane Sulfonic Acid)/Attapulgite Hydrogel Composite and the Study of its Adsorption. Polymer-Plastics Technology and Engineering, 53(1): pp. 74–79 Li A, Wang A, Chen J (2004) Studies on poly (acrylic acid)/attapulgite superabsorbent composite. I. Synthesis and characterization. J Appl Polym Sci 92(3):1596–1603 Zhang J, Wang Q, Wang A (2007) Synthesis and characterization of chitosan-g-poly(acrylic acid)/attapulgite superabsorbent composites. Carbohydr Polym 68(2):367–374 Kara A et al (2016) Physicochemical parameters of Hg(II) ions adsorption from aqueous solution by sepiolite/poly(vinylimidazole). J Environ Chem Eng 4(2):1642–1652 Cheraghi Bidsorkhi H et al (2014) Mechanical, thermal and flammability properties of Ethylene-vinyl acetate (EVA)/ sepiolite nanocomposites. Polym Test, 37 Wang J et al (2011) Effects of modified vermiculite on the synthesis and swelling behaviors of hydroxyethyl cellulose-g-poly(acrylic acid)/vermiculite superabsorbent nanocomposites. J Polym Res 18(3):401–408 Chen H et al (2007) Characterization and properties of sepiolite/polyurethane nanocomposites. Mater Sci Engineering: A 445:725–730 Liu M, Pu M, Ma H (2012) Preparation, structure and thermal properties of polylactide/sepiolite nanocomposites with and without organic modifiers. Compos Sci Technol 72:1508–1514 Ibraeva ZE et al (2015) Preparation and Characterization of Organic-Inorganic Composite Materials Based on Poly(acrylamide) Hydrogels and Clay Minerals. Macromolecular Symposia 351(1):97–111 Kumar A, Rao KM, Han SS (2018) Mechanically viscoelastic nanoreinforced hybrid hydrogels composed of polyacrylamide, sodium carboxymethylcellulose, graphene oxide, and cellulose nanocrystals. Carbohydr Polym 193:228–238 Zaharia A et al (2015) Preparation and characterization of polyacrylamide-modified kaolinite containing poly [acrylic acid-co-methylene bisacrylamide] nanocomposite hydrogels. Appl Clay Sci 103:46–54 Mittal H, Al Alili A, Alhassan SM (2022) Utilization of clay based super-porous hydrogel composites in atmospheric water harvesting. Appl Clay Sci 230:106712 Mahdavinia GR, Asgari A (2013) Synthesis of kappa-carrageenan-g-poly(acrylamide)/sepiolite nanocomposite hydrogels and adsorption of cationic dye. Polym Bull 70(8):2451–2470 Ekici S, Işıkver Y, Saraydın D (2006) Poly(Acrylamide-Sepiolite) Composite Hydrogels: Preparation, Swelling and Dye Adsorption Properties. Polym Bull 57(2):231–241 Li P et al (2009) Poly(Acrylamide/Laponite) Nanocomposite Hydrogels: Swelling and Cationic Dye Adsorption Properties. J Appl Polym Sci 111:1786–1798 Xie Y, Wang A, Liu G (2009) Superabsorbent Composite XXII: Effects of Modified Sepiolite on Water Absorbency and Swelling Behavior of Chitosan-g-Poly(acrylic acid)/Sepiolite Superabsorbent Composite. Polym Compos 31:89–96 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5455380","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":380382167,"identity":"2eef6ac0-4eba-4632-8131-17ae56d4951a","order_by":0,"name":"Meriem BAZIZ","email":"","orcid":"","institution":"Université des Sciences et de la Technologie d’Oran Mohamed Boudiaf, USTO","correspondingAuthor":false,"prefix":"","firstName":"Meriem","middleName":"","lastName":"BAZIZ","suffix":""},{"id":380382168,"identity":"30ed3b44-077a-41d3-9076-201020d35bf0","order_by":1,"name":"Mostefa KAMECHE","email":"","orcid":"","institution":"Université des 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REMITA","email":"data:image/png;base64,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","orcid":"","institution":"Institut de Chimie Physique, ICP, UMR 8000, CNRS, Université Paris-Saclay","correspondingAuthor":true,"prefix":"","firstName":"Samy","middleName":"","lastName":"REMITA","suffix":""}],"badges":[],"createdAt":"2024-11-14 16:23:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5455380/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5455380/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00289-025-05897-y","type":"published","date":"2025-07-02T15:58:53+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":71562455,"identity":"11395c18-24e0-4b4d-86ab-2c9400ef70e9","added_by":"auto","created_at":"2024-12-16 17:09:30","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":422717,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eIllustration of synthesis procedure of \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ea-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN and \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN together with the photography of the as-prepared ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads in aqueous solution.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure1Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/a9cab2e91c9d101c90a65a90.jpg"},{"id":71563309,"identity":"e6f33942-7f46-4c8b-ac1a-33d53d86003d","added_by":"auto","created_at":"2024-12-16 17:17:30","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1234514,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eDigital images of \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ea- \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN beads and \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb- \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN at different NaS loads\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003ein their hydrogel and xerogel states \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ec-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Stretching test touching of an ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN bead\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003ein its hydrogel state\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure2Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/92ea5ac99984c53b35d58187.jpg"},{"id":71562460,"identity":"a27932f5-0f58-4c3a-adef-cd88dd9d4404","added_by":"auto","created_at":"2024-12-16 17:09:30","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":579880,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eATR-FTIR spectra of \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ea-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN (alginate without sepiolite), ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN and ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN and\u003cbr\u003e\n\u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb- \u003c/strong\u003e\u003c/em\u003e\u003cem\u003ePAAM (in the absence of sepiolite and alginate, NaS (sepiolite without alginate) and\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads at different NaS loads\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure3Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/575f3093257fef48c11bc525.jpg"},{"id":71563308,"identity":"808ea9d0-c6b7-439a-89c2-0bd0037cd2f5","added_by":"auto","created_at":"2024-12-16 17:17:30","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":604501,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eXRD patterns of \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ea-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN; \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN and \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ec- \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads with different NaS loads\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure4Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/2ef11b4a84970f8186a5f05c.jpg"},{"id":71564620,"identity":"c3dffb46-977f-4c8a-b9fa-e6f44cf6c92e","added_by":"auto","created_at":"2024-12-16 17:25:30","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1806518,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003ea-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Internal/External\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003ecross section SEM images of SBN beads and DBN beads in their hydrogel state before swelling at different magnifications.\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e b- \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eExternal and internal cross section SEM images of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads in their xerogel state at two different magnifications and \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ec-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Internal cross section\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eSEM image of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN at xerogel state and after being swelled during\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003e2 hours at two different magnifications\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure5Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/ace62e1eee6a33e7c05fd63e.jpg"},{"id":71563313,"identity":"64eedad6-a93b-454c-9498-eaaaf8474bfe","added_by":"auto","created_at":"2024-12-16 17:17:30","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1126234,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSwelling kinetic curves of \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ea-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN and ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN in distilled water; \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb- \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eEffect of NaS load\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eon swelling rate of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads in distilled water\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e;\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ec-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Effect of the pH on swelling rate of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN beads\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e; d-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Effect of the pH on swelling rate of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads\u003c/em\u003e\u003cem\u003e\u003cstrong\u003e; e-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Digital images of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN and ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads after \u003c/em\u003e\u003cem\u003e\u003cstrong\u003es\u003c/strong\u003e\u003c/em\u003e\u003cem\u003ewelling at room temperature in water at three different pHs\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure6Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/9487a2f67655da4e06e5c89b.jpg"},{"id":71564619,"identity":"9e0b1673-68cb-4e67-a536-f8522f5f0420","added_by":"auto","created_at":"2024-12-16 17:25:30","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1569510,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003ea-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Adsorption percentages and \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Desorption percentages of MB by either ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN or ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads determined at each step of the five successive cycles; \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ec-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Digital images of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN and ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN in their hydrogel state after MB adsorption step for each cycle; \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ed-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e Digital image of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN in their xerogel state after MB adsorption at the fifth cycle; \u003c/em\u003e\u003cem\u003e\u003cstrong\u003ee-\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e \u0026nbsp;SEM Cross Section images at three different magnifications of\u0026nbsp;ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN beads in their xerogel state after MB dye adsorption at the fifth cycle\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure7Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/36ee33f46fae3abb82fee109.jpg"},{"id":71562463,"identity":"30b0c985-28d9-42af-ba30-6b79f163b69d","added_by":"auto","created_at":"2024-12-16 17:09:31","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1215131,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea-\u003c/strong\u003e \u003cem\u003eBiodegradability rate profile of ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-SBN, ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN and ANaS\u003c/em\u003e\u003csub\u003e\u003cem\u003e5\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e-DBN; \u003c/em\u003e\u003cem\u003e\u003cstrong\u003eb- \u003c/strong\u003e\u003c/em\u003e\u003cem\u003eDigital images of these beads in compost burial at different time intervals before cleaning\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Figure8Finalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/8e568cb0205f4b05c7047a4a.jpg"},{"id":86180645,"identity":"4b17e057-77b1-448d-927c-3bc3fa0b0b44","added_by":"auto","created_at":"2025-07-07 16:22:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9734044,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/e9c16cbe-cc93-4fbf-bc1c-51723bd0540b.pdf"},{"id":71563311,"identity":"ea2188cb-6c53-4251-939f-a8d98a16d014","added_by":"auto","created_at":"2024-12-16 17:17:30","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":711829,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGraphical abstract\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Graphicalabstractfinalversion.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5455380/v1/933e20045f61e9ab5dd36345.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Elaboration of Novel Biocomposite Hydrogel Polymers made of Alginate and Sepiolite and endowed with Enhanced Properties","fulltext":[{"header":"Highlights","content":"\u003cp\u003e- Novel, low-cost and eco-friendly double biocomposite network (DBN) beads were designed by a soft and efficient interpenetrating polymer network approach\u003c/p\u003e\n\u003cp\u003e- DBN beads were prepared by dispersion of sepiolite clay and polymerization of AAM monomers within an alginate network\u003c/p\u003e\n\u003cp\u003e- DBN beads were found characterized by good stretchability, good swelling behavior, excellent stability in water and increased biodegradability resistance\u003c/p\u003e\n\u003cp\u003e- DBN beads were characterized by enhanced adsorption properties and reusability\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eCurrently, hydrogel beads derived from polysaccharides such as chitosan, carrageenan and alginate have gained popularity for their use as bio-adsorbents in eliminating several organic pollutants [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Among these biosorbents, sodium alginate (NaA) matrix is regarded as a natural anionic biopolymer, which can be extracted from brown seaweed. It contains different amounts of β-D-mannuronic (M-chains) and α-L-guluronic (G-chains) acid fragments linked in non-regular blocks [\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. As a promising application, in water treatment, this bioadsorbant could be an alternative to conventional adsorbents for pollutants removal. In addition, it has several advantages: i) presence of a large number of functional groups, ii) nontoxicity and biodegradability and iii) easy hydrogel beads formation by addition of Ca\u003csup\u003e2+\u003c/sup\u003e [\u003cspan additionalcitationids=\"CR9 CR10 CR11 CR12\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. However, utilization of such beads for bio-adsorption applications is limited by some drawbacks such as low adsorption capacity, macro-porous structure, high biodegradability and instability in aqueous solutions [\u003cspan additionalcitationids=\"CR15 CR16 CR17 CR18\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePrevious research reviews that incorporation of clay particles in ALG bio-nanocomposites, without increasing the cost of production, can adjust the properties and considerably improve the performances of alginate hydrogels, such as bead shape, mechanical and thermal stabilities, gel strength, swelling capacity, adsorption rate [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan additionalcitationids=\"CR21 CR22 CR23 CR24 CR25 CR26 CR27\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. While most of the as-elaborated clay composites contain montmorillonite [\u003cspan additionalcitationids=\"CR30 CR31\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], the alternative use of sepiolite leads to a fibrous clay biocomposite that exhibits very promising properties [\u003cspan additionalcitationids=\"CR34 CR35\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. However, at room temperature, ALG beads drying, reinforced by clay, results in a shinked gel with a significant loss of form and surface area due to the action of the capillary forces on the walls of the pores [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Consequently, alginate biocomposite xerogel beads become rigid with a non-porous structure [\u003cspan additionalcitationids=\"CR40 CR41 CR42 CR43\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Even in the wet form, the beads disintegrate rapidly resulting in fast liberation of the trapped contaminants [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOwing to the outstanding properties of interpenetrating polymer networks (IPN), an IPN strategy combined with biocomposite hierarchical structure, appears as an interesting eco-friendly way to limit several drawbacks of the previously described ALG hydrogel beads. In this context, we propose in this paper a new way for synthesizing alginate biocomposite xerogel beads, as effective biosorbents, by blending sodium alginate biocomposite with another hydrogel. The aim is to prepare beads with enhanced clay dispersion, stretchability, stability, biodegradability, swelling capacities and improved adsorption/desorption properties towards methylene blue (MB) used as a model of organic toxic dye.\u003c/p\u003e"},{"header":"Experimental procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eMaterials\u003c/h2\u003e\n \u003cp\u003eSodium Alginate (NaA, C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eO\u003csub\u003e6\u003c/sub\u003eNa), from Aldrich, was used as received. Sepiolite clay mineral (S), from Aldrich, was 95% purity. Its mineralogical composition was 53.63% in SiO\u003csub\u003e2\u003c/sub\u003e, 24.56% in MgO, 2.19% in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, 1.27% in Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and 0.82% in Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (in wt. %), showing silica and magnesium oxide as major constituents. N,N-methylenebisacrylamide (Bis, 99% purity), ultra-pure Acrylamide (AAM) and Ammonium persulfate (APS, 98% purity), from Sigma\u0026ndash;Aldrich, were all used without prior purification. The crosslinker used was hydrated calcium chloride (CaCl\u003csub\u003e2\u003c/sub\u003e, 2H\u003csub\u003e2\u003c/sub\u003eO) from Aldrich. The organic dye used in this work, namely methylene blue (MB), was from Soitex (Textile Company, Algeria).\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003ePreparation of sodium sepiolite (NaS)\u003c/h3\u003e\n\u003cp\u003e10 g of sepiolite clay (S) was dispersed in 1 L of NaCl aqueous solution (1 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) at room temperature and left for 24 h. Then, the dispersion product was separated by centrifugation at 3500 tr.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The operation was repeated three times to reach saturation and to obtain the Na\u003csup\u003e+\u003c/sup\u003e ions saturated - clay, thanks to a quantitative cationic exchange of Ca\u003csup\u003e2+\u003c/sup\u003e and Mg\u003csup\u003e2+\u003c/sup\u003e by sodium ions. The as-prepared Na\u003csup\u003e+\u003c/sup\u003e-sepiolite was then washed several times with distilled water to totally remove chloride anions. Finally, the sepiolite material was dried, ground and sieved with a sieve of 100 \u0026micro;m, resulting in a solid product, noted NaS.\u003c/p\u003e\n\u003ch3\u003eElaboration of alginate single biocomposite network (SBN) beads\u003c/h3\u003e\n\u003cp\u003eA series of SBN beads made of sodium alginate (NaA) and sodium sepiolite (NaS) were prepared by ionotropic gelation according to the drop method as described in previous work [\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e]. The manual co-grinding of NaA and NaS mixture was carried out, with different weight ratios of NaS in the range 0\u0026ndash;10 wt. %. The as-prepared single biocomposite network beads were named ANaS\u003csub\u003ex\u003c/sub\u003e-SBN, where x refers to NaS weight ratio (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e.\u0026nbsp;\u003c/p\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003e\u003cem\u003eFormulation of single biocomposite network (ANaSx-SBN) beads\u003c/em\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNaS:NaA weight ratio (x)\u003c/p\u003e\n \u003cp\u003e(wt.%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e0\u003c/sub\u003e-SBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e3\u003c/sub\u003e-SBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e5\u003c/sub\u003e-SBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e10\u003c/sub\u003e-SBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eWhile sepiolite is a non-swelling clay with weak dispersion in aqueous medium, NaA/NaS mixture was efficiently dispersed in distilled water at room temperature under high stirring for many hours. It was observed that the manual co-grinding treatment decreased the dissolution time of sodium alginate even at the highest NaS load, without any clay deposition for a long period. Thence, the obtained viscous and homogeneous solutions were further extruded in the form of droplets through a burette under magnetic stirring. The droplets were collected in a 50 mL CaCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO (0.1 M) aqueous solution. The resulting spherical smooth beads were cured in bath overnight. Afterwards, they were vigorously rinsed and suspended in deionized water and stored at room temperature until their use in adsorption experiments. It is important to note that co-grinding treatment of NaA and NaS was not only used to avoid NaS agglomeration and enhance NaA dissolution, but also to reduce the biodegradability of the elaborated alginate beads in aqueous medium by developing effective interactions between both organic and inorganic components. Finally, in order to obtain the biocomposite xerogel beads, the resulting hydrogels were dried in vacuum at 60\u0026deg;C until the beads attained a constant weight. Note that among all the obtained ANaS\u003csub\u003ex\u003c/sub\u003e-SBN samples, a single network biocomposite beads, ANaS\u003csub\u003e0\u003c/sub\u003e-SBN was prepared in the absence of sepiolite for comparison (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eElaboration of alginate double biocomposite network (DBN) beads\u003c/h3\u003e\n\u003cp\u003eA series of DBN beads were prepared using appropriate sequential dual ionotropic-covalent crosslinked gelation methodology. They were combined with free radical polymerization of AAM into pAAM by IPN method in an aqueous medium under atmospheric oxygen, according to the procedure described in a previous work [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. The DBN samples were prepared with different NaS:NaA weight ratios (x) in the range 0\u0026ndash;10 wt. %. The details of the designation of the various ANaSx-DBN beads are listed in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Note that the amounts of Bis, APS, AAM and ANaS\u003csub\u003ex\u003c/sub\u003e-SBN which were used for DBN preparation were always the same.\u0026nbsp;\u003c/p\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003e\u003cem\u003eFormulation of double biocomposite network (ANaSx-DBN) beads\u003c/em\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eNaS/NaA ratio\u003c/p\u003e\n \u003cp\u003e(wt. %)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eANaS\u003csub\u003ex\u003c/sub\u003e-SBN\u003c/p\u003e\n \u003cp\u003e(g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAAM\u003c/p\u003e\n \u003cp\u003e(g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAAM/Bis\u003c/p\u003e\n \u003cp\u003e(molar ratio)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eTemperature\u003c/p\u003e\n \u003cp\u003e(\u0026deg;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDiffusion\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePolymerization\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e0\u003c/sub\u003e-DBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e3\u003c/sub\u003e-DBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e5\u003c/sub\u003e-DBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eANaS\u003csub\u003e10\u003c/sub\u003e-DBN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eMonomer solutions were firstly prepared by dissolving equal amounts of AAM and Bis (AAM/Bis molar ratio of 0.01) at room temperature under constant stirring. A same amount of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN beads (but with different NaS:NaA weight ratios) was then added to the AAM/Bis solutions under stirring (for 1 hour) at room temperature, allowing both AAM and Bis to diffuse inside the SBN beads. Then, the obtained mixtures were heated at 40\u0026deg;C for 30 min, before the addition of APS (0.023 g) to avoid single network disintegration in solution and to initiate the polymerization reaction and the growth of pAAM chains within and on the surface of the beads. Afterwards, the obtained ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads were immersed in distilled water for 4 days to remove unreacted monomers and homopolymers from the materials. Finally, the obtained hydrogel beads were dried in the oven at 60 \u0026ordm;C overnight. Note that among the ANaS\u003csub\u003ex\u003c/sub\u003e-DBN samples, a double network of alginate biocomposite beads, ANaS\u003csub\u003e0\u003c/sub\u003e-DBN was prepared in the absence of sepiolite for comparison (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes the synthesis procedure of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN. ANaS\u003csub\u003ex\u003c/sub\u003e-SBN preparation process includes single biocomposite network beads using both CaCl\u003csub\u003e2\u003c/sub\u003e and NaS as ionic crosslinkers under mechanical co-grinding mixture /encapsulation method (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea), while double cross-linked network was obtained by free radical polymerization of AAM monomers by immersing ANaS\u003csub\u003ex\u003c/sub\u003e-SBN into an aqueous solution containing a mixture of AAM, Bis and APS (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb). Reaction temperature during the synthesis can affect structure and final properties of the beads making it important to control it. Especially, polymerization temperature allows the re-swelling of the beads as observed in laboratory experiments and as highlighted later by SEM microscopy.\u003c/p\u003e\n\u003ch3\u003ePhysico-chemical characterization of SBN and DBN beads\u003c/h3\u003e\n\u003cp\u003eThe Fourier transform infrared (FTIR) spectra of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN were recorded with a double-beam Perkin- Elmer 1600 FTIR spectrometer in the wavenumber range 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm \u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e by performing the analysis in attenuated total reflection (ATR) mode. The XRD analysis of SBN and DBN beads was carried out by using P-Analytical (model-X\u0026rsquo; pert PRO PW-3040/60) with Mo K\u0026alpha; radiation and scan speed of 1.2\u003csup\u003e\u0026deg;\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e over the angle range of 1\u0026ndash;50\u003csup\u003e\u0026deg;\u003c/sup\u003e. Surface morphology of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads, used as bio-adsorbents, was examined by scanning electron microscopy (SEM) (Leica Cambridge S 360) at an accelerated voltage of 15 kV.\u003c/p\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003eStudy of water absorption equilibrium and swelling rates\u003c/h2\u003e\n \u003cp\u003eSwelling capacities of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads were evaluated and compared in distilled water as a function of time. Swelling kinetics was studied by immersing 0.1 g of xerogel beads in 100 mL of distilled water at 25\u0026deg;C. Subsequently, the beads were filtered and weighted at different times using an electronic balance. The swelling percentages (swelling rate) Ps (%) were calculated according to \u003cstrong\u003eEq.\u0026nbsp;1\u003c/strong\u003e:\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/58894_9946feeafa4c1df7/58894_custom_files/img173436680630.png\" width=\"447\" height=\"39\"\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003ewhere W\u003csub\u003et\u003c/sub\u003e (g) is the weight of the swollen beads at a given time (t) and W\u003csub\u003e0\u003c/sub\u003e (g) is the weight of the dried beads at t\u0026thinsp;=\u0026thinsp;0.\u003c/p\u003e\n \u003cp\u003ePs values of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads were examined for the different NaS ratios and at different pH values (2; 4; 7 and 12).\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eBatch sorption experiments\u003c/h3\u003e\n\u003cp\u003eExperiments of dye adsorption/desorption were carried out by the batch adsorption method in an Erlenmeyer flask. The adsorption measurements were registered for both ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads at the same MB (used as organic dye) initial concentration. The concentration of MB was measured by UV-Visible absorption spectroscopy thanks to a Shimadzu UV-1800 model at 664 nm. The adsorption percentages, Ads (%), were determined by using \u003cstrong\u003eEq.\u0026nbsp;2\u003c/strong\u003e:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"405\" height=\"33\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003eC\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e and C\u003csub\u003ef\u003c/sub\u003e are respectively the initial and the final MB concentrations (in mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e\n\u003ch3\u003eSorption/desorption cycle experiments\u003c/h3\u003e\n\u003cp\u003e50 mg of either ANaS\u003csub\u003e5\u003c/sub\u003e-SBN or ANaS\u003csub\u003e5\u003c/sub\u003e-DBN swollen beads were first added at ambient temperature (25\u0026deg;C) to 10 mL of a neutral aqueous solution containing 25 mg L\u003csup\u003e-1\u003c/sup\u003e of MB. The mixture was then stirred for 3 hours to favor the sorption of MB. Finally, the filtered products were immersed in 100 mL ethanolic solution (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH, 0.01 mol L\u003csup\u003e-1\u003c/sup\u003e) for 3 hours to desorb the MB. Sorption/desorption cycles were repeated five times. The desorption percentages, Desor (%), were calculated thanks to \u003cstrong\u003eEq.\u0026nbsp;3\u003c/strong\u003e:\u003c/p\u003e\n\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\:Desor\\left(\\%\\right)=\\frac{{C}_{des}}{({C}_{0}-{C}_{f})}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003ex100 \u003cstrong\u003e(Eq.\u0026nbsp;3)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ewhere 𝐶\u003csub\u003e𝑑𝑒𝑠\u003c/sub\u003e is the desorbed concentration of MB in mg L\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003eSoil compost test and biodegradability evaluation\u003c/h2\u003e\n \u003cp\u003eBeads degradation was studied by weight loss during soil burial. A known weight of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN (as well ANaS\u003csub\u003e0\u003c/sub\u003e-DBN) beads were placed under 4 cm of commercially available compost at ambient temperature. They were maintained at a fixed moisture content. The beads were dug out after few hours, 1, 3, 4, 7 and 8 days of degradation, then cleaned. The weight loss differences were calculated as a function of time by using \u003cstrong\u003eEq.\u0026nbsp;4\u003c/strong\u003e:\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/58894_9946feeafa4c1df7/58894_custom_files/img1734366806.png\" width=\"402\" height=\"37\"\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003ewhere W\u003csub\u003e0\u003c/sub\u003e is the initial dry weight of beads and where W\u003csub\u003et\u003c/sub\u003e is the dry weight of beads after cleaning at a time t.\u003c/p\u003e\n\u003c/div\u003e\n"},{"header":"Results and Discussions","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003ch2\u003eMacroscopic morphology of SBN and DBN beads\u003c/h2\u003e\n \u003cp\u003eDigital images of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads were recorded for the different NaS loads. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the images of the beads both in their hydrogel state and in their xerogel state after air drying. As observed in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea, ANaS\u003csub\u003ex\u003c/sub\u003e-SBN beads, in their hydrogel state, are all characterized by a more or less spherical shape and by a smooth surface whatever the NaS load. In contrast, Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb reveals that ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads, in their hydrogel state, are less spherical than ANaS\u003csub\u003ex\u003c/sub\u003e-SBN ones. Additionally, the waves appearing on the surface of the DBN beads in their hydrogel state (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb), indicate that the IPN method greatly influences the surface structure of alginate biocomposites beads. Such a rough structure which characterizes ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads should nevertheless be beneficial for adsorption properties, allowing stronger interactions with pollutants as mentioned in previous work [\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e]. When comparing Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb, the bead diameters are noticeably different between ANaS\u003csub\u003ex\u003c/sub\u003e-DBN and ANaS\u003csub\u003ex\u003c/sub\u003e-SBN in their hydrogel state. For instance, the mean diameter of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads (5 mm) is larger than that of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads which only amounts to approximatively 3 mm. Nevertheless, the mean diameter progressively increases with NaS ratio for both kinds of beads (either SBN or DBN ones) in their hydrogel state.\u003c/p\u003e\n \u003cp\u003eThe change from hydrogel to xerogel state significantly modifies the appearance of the beads as observed in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb. Their color turns from slightly transparent to opaque yellow for ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and to translucid for ANaS\u003csub\u003ex\u003c/sub\u003e-DBN. Note that the color of ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads could be attributed to the presence of pAAM. The air-drying of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN induces a decrease in size of all the beads due to water removal. The air-drying of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN beads lead to the loss of their shape since they look like as flat disks in their xerogel state (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). Differently, ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads, even if they are found retracted, mainly keep their shape unchanged after drying (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb). This behavior, can be explained by the increase of the crosslinking density of the double network within ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads, suggesting that pAAM polymers act as a structural support to control the shrinkage and subsequently to maintain the shape of the beads in their xerogel state.\u003c/p\u003e\n \u003cp\u003eFurthermore, a stretching touching test was carried out to confirm the formation of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN hydrogel beads with stretchable properties. Among all the beads, ANaS\u003csub\u003ex\u003c/sub\u003e-DBN ones were found extremely stretchable. For instance, Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec illustrates the touching test applied to an ANaS\u003csub\u003e5\u003c/sub\u003e-DBN bead, which appears strong and elastic (steps 1, 2 and 3) and which preserves its initial shape and size under the hand after finger removing (step 4). The as-observed strength and stretchability of ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads can be explained by the formation of an interpenetrating double network composite structure. These characteristics could be particularly advantageous for the reuse of such beads in adsorption-desorption cycles and for the enhancement of their stability, delaying their biodegradability.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003eChemical composition of SBN and DBN beads\u003c/h2\u003e\n \u003cp\u003eTo validate the chemical composition of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN elaborated beads and to highlight the polymerization of AAM acrylamide monomers within ANaS\u003csub\u003ex\u003c/sub\u003e-DBN ones, ATR-FTIR characterization was conducted (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The spectra of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN together with that of sodium alginate (ANaS\u003csub\u003e0\u003c/sub\u003e-SBN, in the absence of sepiolite) are shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea and are in agreement with previous work [\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e]. All ATR-FTIR spectra highlight a broad peak at 3600\u0026ndash;3000 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e together with peaks at around 1588 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1425 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which can be identified as the stretching vibrations of O-H, -COO (asymmetric) and -COO (symmetric) bonds respectively, and which indicate the presence of alginate within all the beads. Also, the peaks in the region 1155\u0026thinsp;\u0026minus;\u0026thinsp;900 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to C-O stretching vibration of alginate. When comparing with ANaS\u003csub\u003ex\u003c/sub\u003e-SBN spectra, the characteristic peaks located at 2931 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1648 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1409 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, are respectively attributed to CH\u003csub\u003e2\u003c/sub\u003e, C\u0026thinsp;=\u0026thinsp;O and CH groups within ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads.\u003c/p\u003e\n \u003cp\u003eImportantly, the presence in the spectrum of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea) of an additional intense broad band at 3500\u0026thinsp;\u0026minus;\u0026thinsp;3200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (with a notable overlap with O-H band), which is absent in the spectra of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN, can be attributed to the asymmetric vibration of N-H groups, highlighting the specific presence of AAM within DBN beads. Also, the new characteristic band appearing at around 2900 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in case of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN, which corresponds to the symmetric and asymmetric stretching vibrations of methylene groups (CH in CH\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e3\u003c/sub\u003e), can also be attributed to acrylamide monomers present in DBN double network of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads. The peak present at 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e only in the spectrum of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN is due to the stretching of the amide group in polyacrylamide (i.e. \u0026gt;C\u0026thinsp;=\u0026thinsp;O), indicating that AAM monomers were successfully polymerized within the DBN beads as it had already been pointed out in literature [\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e]. Moreover, the presence of pAAM polymers in ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads is further supported by new bands at 1645 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, associated with the C-N (amide bond) stretching vibrations, and another weaker band at 1454 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, attributed to the stretching vibration of CH\u0026thinsp;=\u0026thinsp;CH\u003csub\u003e2\u003c/sub\u003e bond.\u003c/p\u003e\n \u003cp\u003eATR-FTIR spectra of ANaS\u003csub\u003ex\u003c/sub\u003e-DBN were also recorded for different NaS loads and are shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb together with the spectrum of sepiolite (NaS) and that of polyacrylamide polymers (pAAM). NaS spectrum highlights the presence of a band at 1212 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, related to Si-O bonds, together with a strong band at 1016 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e related to the asymmetric stretching vibration of Si\u0026ndash;OH groups which are present in sepiolite. In addition, the characteristic infrared bands of the -OH groups of sepiolite are observed at 3687 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 3562 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3418 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in agreement with literature [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e]. pAAM spectrum shows the presence of an intense broad band between 3500 and 3000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which is the signature of the asymmetric vibration of N-H groups, while the peaks present at 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1645 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are due to the amide bonds within pAAM polymers.\u003c/p\u003e\n \u003cp\u003eWhen comparing with NaS and pAAm spectra (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb), we note for ANaS\u003csub\u003e5\u003c/sub\u003e-DBN and ANaS\u003csub\u003e10\u003c/sub\u003e-DBN, the presence of an intense broad band from 3600 to 3300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e which can be attributed to the overlapping of the N\u0026ndash;H vibration band of pAAm with the O-H band of NaS. This proves the concomitant presence of both sepiolite and polyacrylamide within these beads. However, the band at 1212 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, related to Si-O bonds, does not appear in ANaS\u003csub\u003e5\u003c/sub\u003e-DBN and ANaS\u003csub\u003e10\u003c/sub\u003e-DBN spectra. Moreover, the strong band at 1016 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to the asymmetric stretching vibration of Si\u0026ndash;OH groups, shifts to a lower wavenumber. Besides, the characteristic bands of the -OH groups of sepiolite at 3687 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 3562 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3418 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are not observed in the spectra of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN and ANaS\u003csub\u003e10\u003c/sub\u003e-DBN. The same observation has already been reported by Whang et al and Zhi et al [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e], where the disappearance of the signature of -OH groups in vermiculite and attapulgite clays was observed in case of hydroxyethyl cellulose-g-poly(acrylic acid)/vermiculite nanocomposites and in case of poly(Acrylic Acid-Co-2-Acrylamido-2-Methyl-1-Propane Sulfonic Acid)/Attapulgite composite, respectively. We can also note that the Si\u0026ndash;O\u0026ndash;Si-stretching vibration band of sepiolite, initially present at 1212 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in NaS, progressively shifts to higher wavenumbers in ANaS\u003csub\u003e5\u003c/sub\u003e-DBN and ANaS\u003csub\u003e10\u003c/sub\u003e-DBN. In addition, upon increasing NaS load, the symmetric stretching band of -COO- of alginate (ANaS\u003csub\u003eo\u003c/sub\u003e-SBN), initially present at 1414 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea), progressively shifts to 1411 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1410 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1408 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in ANaS\u003csub\u003e0\u003c/sub\u003e-DBN, ANaS\u003csub\u003e5\u003c/sub\u003e-DBN and ANaS\u003csub\u003e10\u003c/sub\u003e-DBN respectively. These observations indicate that pAMM chains interact with biopolymer chains within all ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003eSepiolite dispersion within SBN and DBN beads\u003c/h2\u003e\n \u003cp\u003eTo confirm the polymerization of AAM monomers and to evaluate the effect of IPN strategy on enhancing sepiolite dispersion, XRD analysis was carried out. The XRD patterns of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN, ANaS\u003csub\u003e5\u003c/sub\u003e-DBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN with different NaS load ratios are shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. As observed for ANaS\u003csub\u003e5\u003c/sub\u003e-SBN (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea), most reflection peaks characteristic of NaS are absent, except for smaller reflection angles, at 2\u0026theta;\u0026thinsp;=\u0026thinsp;6.8\u0026deg; corresponding to the (110) planes, this peak being slightly shifted to a lower angle compared with pristine NaS. These results are in good agreement with those reported by Kara et al [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e] and Bidkoski et al [\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e]. These observed effects are attributed to the needles of NaS which are generally delaminated to fiber sticks and which are dispersed inside the alginate beads, forming an intercalated nano-biocomposite structure [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eIn ANaS\u003csub\u003e5\u003c/sub\u003e-DBN diffractogram (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb), a new broad peak appears at 21.7\u0026deg;. This peak is also present in the diffractograms of all ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads whatever the NaS load (x) (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec). In literature, this additional peak was attributed to the presence of pAAM polymers [\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e58\u003c/span\u003e]. This confirms, in agreement with our previous FTIR results, that AAM was successfully polymerized within the DBN beads. The acrylamide monomers thus interfere with the arrangement of alginate chains in ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads and polymerize to form ordered crystal regions. Evidently, the d\u003csub\u003e110\u003c/sub\u003e crystalline peak of NaS is totally absent in ANaS\u003csub\u003e0\u003c/sub\u003e-DBN diffractogram and remains weak at low NaS loads (x\u0026thinsp;=\u0026thinsp;3 and 5). For the highest NaS percentage, in case of ANaS\u003csub\u003e10\u003c/sub\u003e-DBN, the d\u003csub\u003e110\u003c/sub\u003e crystalline peak of NaS is clearly observed, but remains sharp and diffused, indicating that NaS fibrous clay has maintained its high exfoliation degree in the alginate biocomposite double network. Meanwhile, the intensity of pAAM peak at 21.7\u0026deg; in ANaS\u003csub\u003e10\u003c/sub\u003e-DBN diffractogram is significantly reduced compared to ANaS\u003csub\u003e0\u003c/sub\u003e-DBN, ANaS\u003csub\u003e3\u003c/sub\u003e-DBN (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb) and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec), due to the interactions between pAAM and sepiolite needles, as observed by Zaharia et al [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003eSurface morphology of SBN and DBN beads\u003c/h2\u003e\n \u003cp\u003eMorphology evolution of SBN and DBN beads (with different NaS loads) was checked by SEM microscopy (Fig.\u0026nbsp;5) in order to observe the effect of IPN strategy on texture modification. The SEM images of the surface and cross-section of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads in their hydrogel state were first recorded for different NaS loads (Fig.\u0026nbsp;5a). It can be observed that whatever NaS percentage (x value), both internal and external surfaces of ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads in their wet state, appear changed compared to their single network version, namely ANaS\u003csub\u003ex\u003c/sub\u003e-SBN beads. We can indeed compare for instance ANaS\u003csub\u003e3\u003c/sub\u003e-SBN images with those of ANaS\u003csub\u003e3\u003c/sub\u003e-DBN. This observation suggests once again that pAAM was successfully incorporated on the surface and within the bulk of the alginate biocomposite beads.\u003c/p\u003e\n \u003cp\u003eIf we compare now ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads in their wet states, it can clearly be observed a morphological difference between the two networks, which is reflected in the porosity level. As depicted in \u003cstrong\u003eFig.\u0026nbsp;5a\u003c/strong\u003e, the ANaS\u003csub\u003e5\u003c/sub\u003e-SBN bead in its hydrogel state has a slightly porous structure. On the contrary, the corresponding ANaS\u003csub\u003e5\u003c/sub\u003e-DBN bead is characterized in the same state by a more homogeneous network and a highly porous spongy structure. The initial morphology of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads is thus modified by pAAM polymer chains, which support the bead structure by linking the pores and by increasing their size, which results in the spongy shape of the ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads. Such structural homogeneity and porosity of the network should obviously improve the adsorption properties of the DBN beads in solution, as previously reported by Mittal et al [\u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e], and should positively affect their swelling behavior.\u003c/p\u003e\n \u003cp\u003eTo further examine the effect of our IPN strategy on the texture of alginate biocomposite beads at the highest NaS load (x\u0026thinsp;=\u0026thinsp;10), SEM images of ANaS\u003csub\u003e10\u003c/sub\u003e-SBN and ANaS\u003csub\u003e10\u003c/sub\u003e-DBN beads were recorded (Fig.\u0026nbsp;5a). In this case, some agglomerated NaS particles can be observed, although the external SEM image of ANaS\u003csub\u003e10\u003c/sub\u003e-DBN beads could depict that the number of aggregated NaS particles has been reduced compared to ANaS\u003csub\u003e10\u003c/sub\u003e-SBN. The uniformed dispersion of NaS can be attributed to co-grinding mixture as well as \u003cem\u003ein situ\u003c/em\u003e polymerization of AAM monomers on the surface of sepiolite, in agreement with XRD results and as already described by Mahdavinia and Zaharia [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e]. Besides, the internal cross-section morphology of ANaS\u003csub\u003e10\u003c/sub\u003e-DBN beads (Fig.\u0026nbsp;5a) exhibits a thin-film membrane onto the surface of the core as a coating that indicates the presence of pAAM not only in the internal but also on the external surface of the beads.\u003c/p\u003e\n \u003cp\u003eIt can be noted from \u003cstrong\u003eFig.\u0026nbsp;5a\u003c/strong\u003e that the external surface roughness of ANaS\u003csub\u003e10\u003c/sub\u003e-DBN is lower than that of both ANaS\u003csub\u003e3\u003c/sub\u003e-DBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN. This observation is in good agreement with our previous XRD results (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) and with the further discussion about the decrease in the swelling of DBN beads. The increased cross-linking points within the beads create a more compact and smoother surface, which suggests that the incorporation of a proper amount of NaS fibrous clay is beneficial to improve the surface structure of the ANaS\u003csub\u003ex\u003c/sub\u003e-DBN and therefore allows to obtain beads with controlled swelling. However, an increased amount of NaS fibrous clay content may reduce the swelling properties of the elaborated beads as shown in the swelling results which will be discussed below.\u003c/p\u003e\n \u003cp\u003eThe SEM images of the surface and cross-section of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads in their xerogel state were also recorded for the different NaS loads. For illustration, the images corresponding to ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads in their dry state are shown in \u003cstrong\u003eFig.\u0026nbsp;5b\u003c/strong\u003e at two different magnifications. It can be noted that the surface of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads presents significant cracks, and their cross-section exhibits a rough surface and abrupt sharp edges. The same observations were carried out on all the SBN and DBN beads prepared in this work. Such a rough structure may be beneficial for adsorption of pollutants, due to the increased surface area and the resulting stronger interactions.\u003c/p\u003e\n \u003cp\u003eIn order to examine the evolution of surface morphology during swelling, ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads, initially in their xerogel state, were re-swelled for two hours and then observed by SEM microscopy. Figure\u0026nbsp;5c shows for illustration the re-hydrated structure of ANaS\u003csub\u003e3\u003c/sub\u003e-DBN beads. When comparing these micrographs with the images of the same beads in their xerogel state, it can be noticed that the porosity of the beads is clearly visible after re-swelling in water. The same observation can be made for all prepared ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads, whatever the NaS load. The porosity of the beads is thus completely restored after re-hydration. Thanks to the used IPN strategy, DBN beads, in their xerogel state, are able to maintain their porosity and their high swelling properties, unlike their single structure version (ANaS\u003csub\u003ex\u003c/sub\u003e-SBN beads) which becomes non-porous.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003eSwelling behavior of SBN and DBN beads\u003c/h2\u003e\n \u003cp\u003eSwelling capacities of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads were evaluated in distilled water as a function of time. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea compares the swelling percentages (swelling rates), and thus the water absorbencies as a function of time, of both ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads, which were prepared with the same NaS load. After immersing both xerogel beads in distilled water, the swelling kinetics of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN exhibit similar behavior. A rapid increase in the swelling percentage at the beginning is followed by a slower increase of the swelling ratio until reaching a water absorption equilibrium. Interestingly, after 5 min of immersion, a swelling percentage of about 1300 g/g of adsorbed water is reached in case of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN, while a much lower percentage (600 g/g in absorbed water) is reached at the same time in case of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN. In both cases, it takes about 15 min of immersion to reach a quasi-swelling equilibrium. The swelling percentage values finally reach 1400 g/g and 650 g/g of adsorbed water after 110 min for ANaS\u003csub\u003e5\u003c/sub\u003e-DBN and ANaS\u003csub\u003e5\u003c/sub\u003e-SBN respectively. Whatever NaS load, swelling behavior of ANaS\u003csub\u003ex\u003c/sub\u003e-DBN always remains higher than that of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN beads at a given NaS load (results not shown). The swelling capacities of ANaS\u003csub\u003ex\u003c/sub\u003e-SBN and ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads are evidently related to the presence of numerous hydrophilic functional groups, such as hydroxyl groups which were initially present into both sepiolite and alginate. The highest water uptake capacity of DBN beads is certainly due to their higher porous structure (which results from a superior cross-link density) as previously observed by SEM microscopy (Fig.\u0026nbsp;5), but not only. Indeed, ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads also contain additional hydrophilic groups, namely the amide groups present all along pAAM polymer chains [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e62\u003c/span\u003e]. Note that the swelling ability of DBN beads is also in correlation with their adsorption/desorption capacities as already described [\u003cspan class=\"CitationRef\"\u003e63\u003c/span\u003e] and as it will be demonstrated later.\u003c/p\u003e\n \u003cp\u003eBesides, swelling rates of ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads were evaluated in distilled water as a function of NaS load as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb. Once again, after immersing xerogel beads in distilled water, a rapid increase in the swelling percentage is followed, after 15 min, by a slower increase of the swelling ratio until reaching a water absorption quasi-equilibrium. The swelling percentage values finally reach 1700, 1600, 1400 and 1300 g/g of adsorbed water after 120 min for NaS loads of 0, 3, 5 and 10% respectively. As observed, the swelling behavior of ANaS\u003csub\u003ex\u003c/sub\u003e-DBN beads continuously decreases when increasing NaS load. A similar decrease in swelling behavior has already been reported in literature in case of chitosan-g-poly(acrylic acid) composites upon incorporation of raw sepiolite [\u003cspan class=\"CitationRef\"\u003e64\u003c/span\u003e]. The observed decrease in DBN swelling behavior, when NaS content increases, can be explained by the fact that sepiolite fibrous clay is a non-swelling reinforcing agent. This property leads to the limit swelling prorates of DBN beads but is promising for controlling their swelling properties by loading sepiolite into alginate beads.\u003c/p\u003e\n \u003cp\u003eIn order to assess the pH sensitivity of the elaborated beads, swelling rates of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN were evaluated in water at different pHs as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ec and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ed respectively. Whatever the pH of the aqueous medium, after immersing both kinds of xerogel beads, the swelling behavior exhibit the same time evolution as previously observed in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb. Interestingly, whatever the pH, ANaS\u003csub\u003e5\u003c/sub\u003e-SBN exhibits once again a lower swelling rate than ANaS\u003csub\u003e5\u003c/sub\u003e-DBN. Noticeably, for both SBN and DBN beads, the swelling percentage increases with the pH value of the medium. Indeed, at water absorption equilibrium after 110 min, the swelling percentage of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads amounts to 300 g/g of adsorbed water between pH 2 and pH 4 and reaches about 600 g/g of adsorbed water at pHs higher than 7. In the same way, after 110 min, the swelling percentage of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads amounts to 950 g/g of adsorbed water at pH 2, 1100 g/g at pH 4, 1400 g/g at pH 7 and finally 2000 g/g of adsorbed water at pH 12. This can be explained by the presence of acid-base functionalities within the beads, the protonation rate of which depends on the pH. In very acidic medium, at pH 2, carboxylic groups (-COOH) of sodium alginate and silanol groups (-Si-OH) of sepiolite are mainly protonated, while at pH 12, these functionalities mainly deprotonate and transform into their anionic form (-COO\u003csup\u003e\u0026minus;\u003c/sup\u003e and -Si-O\u003csup\u003e\u0026minus;\u003c/sup\u003e). When the pH increases, even though water molecules can maintain their hydrophilic interactions with these groups, the hydrogen bond interactions between the acid-base functionalities of alginate and sepiolite strongly decrease within the beads and the anion-anion repulsive electrostatic forces between the deprotonated groups become predominant, which probably favors the porosity of the beads. As a consequence, beads are characterized by a relatively lower water uptake behavior in acidic medium, while the swelling ability of the beads drastically increases in alkaline medium (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ec and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ed\u003cstrong\u003e)\u003c/strong\u003e.\u003c/p\u003e\n \u003cp\u003eIn order to check whether ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads maintain their structure and shape after swelling in water at different pHs, digital images of the beads in their hydrogel state were recorded (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ee\u003cstrong\u003e)\u003c/strong\u003e. One can observe on the figure that the shape and size of the beads are kept unchanged whatever the pH. However, we can importantly note that ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads are mainly ruptured and disintegrated at pH 12. This explains why swelling percentage of SBN beads at this pH is not higher than that obtained at pH 7 (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ec\u003cstrong\u003e)\u003c/strong\u003e, contrarily to what is observed in the case of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ed\u003cstrong\u003e)\u003c/strong\u003e. While the presence of pAAM polymers strengthen the interpenetrating double network composite structure of DBN beads, its absence within ANaS\u003csub\u003e5\u003c/sub\u003e-SBN could explain the disintegration of these simple network structures under the constraint of electrostatic repulsive forces between the deprotonated groups on the one hand and water osmotic pressure on the other hand.\u003c/p\u003e\n \u003cp\u003eAs demonstrated, ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads remain stable whatever the pH thanks to their strong IPN network structure. Also, they preserve their swelling ability and maintain their shape without shrinking thanks to the highly cross-linked flexible chain network of pAAM which strengthens their architecture. This behavior will be used for the adsorption of MB dye as it will be seen next.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003eUse of SBN and DBN beads in adsorption/desorption cycles\u003c/h2\u003e\n \u003cp\u003eExperiments of dye adsorption/desorption were carried out by the batch adsorption method. Either ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads or ANaS\u003csub\u003e5\u003c/sub\u003e-DBN ones were added at ambient temperature to a neutral aqueous solution containing the organic toxic Methylene Blue (MB) dye at a concentration of 25 mg L\u003csup\u003e-1\u003c/sup\u003e in a first adsorption step. Then filtered products were immersed in ethanolic solution, as green eluent, to desorb the MB. Such an adsorption/desorption cycle was repeated five times (cycles C1 to C5) for either SBN or DBN beads to evaluate the adsorption/desorption rates/percentages of both kinds of beads together with their potential reuse in water decontamination (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe results are depicted in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea for the five successive adsorption steps and in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb for the successive desorption steps. As highlighted in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea, the adsorption percentage of MB by ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads, as deduced from UV-visible absorption spectroscopy measurements, amounts to 63% in the first cycle. However, this adsorption rate by ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads decreases to 53% in the second cycle and to 32% in the third one. It drastically drops after the third cycle, reaching 0%. When considering the digital images of SBN beads in their hydrogel state after MB adsorption (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec), one can observe the intense blue color of the beads which traduces the quantitative adsorption of the dye. Nevertheless, one can note the decrease in the size of SBN beads in the third cycle. After this cycle, ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads are mainly ruptured and disintegrated, which explains the complete release of MB contaminants in the medium and the observed drastic decrease in adsorption rate of SBN beads.\u003c/p\u003e\n \u003cp\u003eDifferently, the adsorption percentage of MB by ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads, which amounts to 57% in the first cycle, remains almost unchanged after five cycles (about 50%) (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea). This proves that contrarily to SBN beads, DBN ones keep their adsorption behavior constant even after five adsorption/desorption cycles. When considering the digital images of DBN beads in their hydrogel state after MB adsorption (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec), one can once again observe the intense blue color of the beads which traduces the quantitative adsorption of the dye, but this time all along the five successive cycles. Besides, contrarily to SBN beads, DBN ones keep their shape and size unchanged even after five cycles, which should explain the constant adsorption behavior of DBN beads.\u003c/p\u003e\n \u003cp\u003eDuring the fifth cycle, after MB dye adsorption and after air-drying, ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads, this time in their xerogel state, appear dark blue as observed in the digital image of Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ed, demonstrating that their porous structure nature was preserved even after the successive adsorption/desorption cycles and even after drying. The porous structure of these beads was confirmed by SEM microscopy as shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ee. The rough surface of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads, decorated by a few pores, is indeed observed after drying. These pores probably correspond to the channels which enable the diffusion of water and MB dye molecules within the network of DBN beads. It can thus be confirmed that the IPN strategy, combined with the biocomposite structure of the beads, which was developed in this work, prevents the common observed collapse of the pores during air-drying of alginate beads.\u003c/p\u003e\n \u003cp\u003eEvidently, the very good adsorption rate of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads results from their porosity and their important swelling behavior (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). Also, structural and functional stability of DBN beads during the repeated adsorption/desorption cycles comes from their stretchability (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) on one hand and from the strength and the resistance of their structure on the other hand. This enables the reproducible reuse of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads without any loss of their shape or decrease in their adsorption behavior.\u003c/p\u003e\n \u003cp\u003eWhen considering the successive desorption steps (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb), one can observe that desorption percentages of MB from ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads (51%, 50% and 30% respectively after the three first cycles) are slightly lower than the successive adsorption percentages (63%, 53% and 32%). This means that most of MB molecules have been released from SBN beads upon immersion in ethanol. More interestingly, in case of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads, desorption percentages are very close to adsorption rate values (53% after first cycle and 50% after fifth one), highlighting the fact that even after 5 cycles, MB molecules are completely released from DBN beads, which implies a nearly perfect regeneration of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads in their hydrogel state. Ethanol appears also here as a very efficient eluent for desorbing MB from DBN beads.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n \u003ch2\u003eEvaluation of SBN and DBN bead biodegradability\u003c/h2\u003e\n \u003cp\u003eThe drawback of alginate beads in their hydrogel state is their fast biodegradation properties which limit their use in some applications. In order to evaluate the degradation rate of ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads, and to compare it with the degradation rates of other SBN and DBN beads, namely ANaS\u003csub\u003e5\u003c/sub\u003e-SBN and ANaS\u003csub\u003e0\u003c/sub\u003e-DBN, the beads were buried under 4 cm of compost at ambient temperature and fixed moisture content. Then, bead degradation rate was followed by their weight loss as a function of time (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e). In Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea, one can observe that the biodegradability rate of ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads is higher than that of DBN beads. Indeed, single network ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads are totally degraded after one day, while double network ANaS\u003csub\u003e0\u003c/sub\u003e-DBN and ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads are completely degraded after 4 days and 8 days respectively.\u003c/p\u003e\n \u003cp\u003eFor better illustration, Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eb displays the digital images of SBN and DBN beads recorded just after their extraction from the compost, at different time intervals, and before any cleaning and weighing. The changes in bead characteristics (i.e. color, number and shape) during the compost burial can be easily distinguished. All the beads appear brown due to the adsorption of the compost at their surface and probably to its diffusion within the bulk of the beads. Interestingly, SBN beads quickly shrink, deform and break down into smaller size and cracks over hours, their number being also decreased rapidly. In case of ANaS\u003csub\u003e0\u003c/sub\u003e-DBN beads which were prepared in the absence of sepiolite, a slower evolution is observed. A slight breaking down into smaller sizes and the appearance of irregular shapes are nevertheless observed over 4 days. Differently, ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads, prepared in the presence of sepiolite, mainly maintain their spheroidal shape and keep their size and surface structure over about 8 days (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eb). These observations prove that IPN strategy combined with biocomposite hierarchical structure endows DBN beads a good resistance towards biodegradation.\u003c/p\u003e\n \u003cp\u003eIt is well known that reinforcing biopolymers by clay or blending with other biopolymers can accelerate their biodegradation. This is what we observe in case of SBN beads in the presence of NaS load since ANaS\u003csub\u003e5\u003c/sub\u003e-SBN beads deteriorate in less than one day. Contrarily to SBN beads, DBN ones degrade more slowly even in the presence of NaS load. This result certainly comes from the presence of pAAM polymer chains within the network of DBN beads and is in good agreement with previous studies where it was clearly demonstrated that degradation rate of biocomposites decreases when the amount of hydrolytically degradable components increases. In our case, a relatively long time is thus needed to complete the hydrolysis of amide groups which are present in the polymer chains of pAAM, which explains the slow degradation of DBN beads. Nevertheless, how could it be possible to explain the fact that ANaS\u003csub\u003e5\u003c/sub\u003e-DBN beads are less degradable than ANaS\u003csub\u003e0\u003c/sub\u003e-DBN ones, which were prepared in the absence of sepiolite? The observed decrease in DBN biodegradability behavior when NaS content increases, could be explained by the fact that sepiolite fibrous clay is a non-swelling reinforcing agent (see Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) which strongly interacts with pAAM (as deduced from Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) delaying its hydrolysis.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work, we successfully designed new hydrogel biocomposite beads, made of two biopolymers, namely alginate and polyacrylamide, together with natural sepiolite clay. Two kinds of materials were prepared: i) simple biocomposite network (SBN) beads by the dispersion of different loads of sepiolite within the alginate network and ii) double biocomposite network (DBN) beads by the \u003cem\u003ein situ\u003c/em\u003e polymerization of AAM monomers within SBN bead network.\u003c/p\u003e \u003cp\u003eThe as-prepared SBN and DBN materials were characterized by different physico-chemical methods, which revealed the good dispersion of sepiolite and the successful incorporation of pAAM within DBN beads. Polymer chains act as a structural support which maintains the shape, controls the shrinkage and increases the porosity of the double network DBN beads either in their xerogel or in their hydrogel state. Consequently, DBN beads were found characterized by improved properties: very good stretchability, good swelling behavior, excellent stability in acidic, neutral or alkaline aqueous media, good stability upon air drying and increased biodegradability resistance, which should enable the use of DBN beads as green materials in different applications, such as pollutant removal. Compared to SBN materials, DBN beads were shown to be characterized by enhanced adsorption rate towards methylene blue, used as a model toxic pollutant, and were found reproducibly reusable as very stable bioadsorbent materials.\u003c/p\u003e \u003cp\u003eIn summary, this work describes a novel, soft and green approach, based on IPN strategy, to design high-performance alginate biocomposite materials as promising systems towards their use in eco-friendly processes. In the future, the as-prepared DBN beads will be used for removal of different kinds of dyes and contaminants from water and will also be tested in some medical applications. Besides, preparation of double biocomposite network beads, by the way of an alternative radiation-based methodology, is in due course.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.B.: methodology, formal analysis, investigation, validation, writing first version of the manuscript. M.K. and N.B.: conceptualization, visualization, validation, supervision. L.H. : formal analysis, corrections to the manuscript. S.R.: validation, writing final version of the manuscript, review and editing, supervision.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKumar MNR (2000) A review of chitin and chitosan applications. Reactive Funct Polym 46(1):1\u0026ndash;27\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBajpai J, Shrivastava R, Bajpai A (2007) Binary biopolymeric beads of alginate and gelatin as potential adsorbent for removal of toxic Ni2\u0026thinsp;+\u0026thinsp;ions: a dynamic and equilibrium study. J Appl Polym Sci 103(4):2581\u0026ndash;2590\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChatterjee S, Lee MW, Woo SH (2010) Adsorption of congo red by chitosan hydrogel beads impregnated with carbon nanotubes. Bioresour Technol 101(6):1800\u0026ndash;1806\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eThakur S et al (2018) Recent progress in sodium alginate based sustainable hydrogels for environmental applications. J Clean Prod 198:143\u0026ndash;159\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaug A, Larsen BR (1963) The solubility of alginate at low pH. Acta Chem Scand 17(6):1653\u0026ndash;1662\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJohnson FA, Craig DQ, Mercer AD (1997) Characterization of the block structure and molecular weight of sodium alginates. J Pharm Pharmacol 49(7):639\u0026ndash;643\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVelings NM, Mestdagh MM (1995) Physico-chemical properties of alginate gel beads. Polym Gels Networks 3(3):311\u0026ndash;330\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGrant GT et al (1973) Biological interactions between polysaccharides and divalent cations: the egg-box model. FEBS Lett 32(1):195\u0026ndash;198\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcNeely WH, Kang KS (1973) \u003cem\u003eXanthan and some other biosynthetic gums\u003c/em\u003e, in \u003cem\u003eIndustrial gums\u003c/em\u003e. Elsevier, pp 473\u0026ndash;497\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee KY, Mooney DJ (2012) Alginate: properties and biomedical applications. Prog Polym Sci 37(1):106\u0026ndash;126\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZia KM et al (2015) Alginate based polyurethanes: A review of recent advances and perspective. Int J Biol Macromol 79:377\u0026ndash;387\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartinsen A, Storr\u0026oslash; I, Skj\u0026aring;rk-Br\u0026aelig;k G (1992) Alginate as immobilization material: III. Diffusional properties. Biotechnol Bioeng 39(2):186\u0026ndash;194\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRadoor S et al (2023) Recent advances in cellulose-and alginate-based hydrogels for water and wastewater treatment: A review. Carbohydr Polym, : p. 121339\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAdzmi F et al (2012) Preparation, characterisation and viability of encapsulated Trichoderma harzianum UPM40 in alginate-montmorillonite clay. J Microencapsul 29:205\u0026ndash;210\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHua S et al (2010) pH-sensitive sodium alginate/poly(vinyl alcohol) hydrogel beads prepared by combined Ca2\u0026thinsp;+\u0026thinsp;crosslinking and freeze-thawing cycles for controlled release of diclofenac sodium. Int J Biol Macromol 46(5):517\u0026ndash;523\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYadav M, Rhee KY (2012) Superabsorbent nanocomposite (alginate-g-PAMPS/MMT): Synthesis, characterization and swelling behavior. Carbohydr Polym 90(1):165\u0026ndash;173\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin M et al (2013) Effect of unmodified starch on viability of alginate-encapsulated Lactobacillus fermentum CECT5716. LWT-Food Sci Technol 53(2):480\u0026ndash;486\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMahdavinia GR et al (2016) Magnetic hydrogel beads based on PVA/sodium alginate/laponite RD and studying their BSA adsorption. Carbohydr Polym 147:379\u0026ndash;391\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eALSamman MT, S\u0026aacute;nchez J (2022) Chitosan-and alginate-based hydrogels for the adsorption of anionic and cationic dyes from water. Polymers 14(8):1498\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaraguchi K, Takehisa T, Fan S (2002) Effects of clay content on the properties of nanocomposite hydrogels composed of poly (N-isopropylacrylamide) and clay. Macromolecules 35(27):10162\u0026ndash;10171\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXiang Y, Peng Z, Chen D (2006) A new polymer/clay nano-composite hydrogel with improved response rate and tensile mechanical properties. Eur Polymer J 42(9):2125\u0026ndash;2132\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKaşg\u0026ouml;z H, Durmuş A, Kaşg\u0026ouml;z A (2008) Enhanced swelling and adsorption properties of AAm-AMPSNa/clay hydrogel nanocomposites for heavy metal ion removal. Polym Adv Technol 19(3):213\u0026ndash;220\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRuiz-Hitzky E, Darder M, Aranda P (2008) An introduction to bio-nanohybrid materials. Bio-inorganic hybrid nanomaterials, : p. 1\u0026ndash;40\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang W, Wang A (2009) Preparation, characterization and properties of superabsorbent nanocomposites based on natural guar gum and modified rectorite. Carbohydr Polym 77(4):891\u0026ndash;897\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUnuabonah EI, Taubert A (2014) Clay\u0026ndash;polymer nanocomposites (CPNs): Adsorbents of the future for water treatment. Appl Clay Sci 99:83\u0026ndash;92\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDarder M, Aranda P, Ruiz-Hitzky E (2007) Bionanocomposites: a new concept of ecological, bioinspired, and functional hybrid materials. Adv Mater 19(10):1309\u0026ndash;1319\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMittal V (2011) Nanocomposites with biodegradable polymers: synthesis, properties, and future perspectives, vol 68. Oxford University Press\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNigmatullin R, Bencsik M, Gao F (2014) Influence of polymerisation conditions on the properties of polymer/clay nanocomposite hydrogels. Soft Matter 10:2035\u0026ndash;2046\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKausar A et al (2022) Cellulose, clay and sodium alginate composites for the removal of methylene blue dye: Experimental and DFT studies. Int J Biol Macromol 209:576\u0026ndash;585\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEssifi K et al (2023) Investigating the effect of clay content and type on the mechanical performance of calcium alginate-based hybrid bio-capsules. Int J Biol Macromol 242:125011\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlboofetileh M et al (2013) Effect of montmorillonite clay and biopolymer concentration on the physical and mechanical properties of alginate nanocomposite films. J Food Eng 117(1):26\u0026ndash;33\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDean K, Yu L, Wu D (2007) Preparation and characterization of melt-extruded thermoplastic starch/clay nanocomposites. Compos Sci Technol, : p. 413\u0026ndash;421\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRuiz AI, Ruiz-Garc\u0026iacute;a C, Ruiz-Hitzky E (2023) From old to new inorganic materials for advanced applications: The paradigmatic example of the sepiolite clay mineral. Appl Clay Sci 235:106874\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChivrac F et al (2010) Starch nano-biocomposites based on needle-like sepiolite clays. Carbohydr Polym 80:145\u0026ndash;153\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRuiz-Hitzky E et al (2011) Chap. 1\u003cem\u003e7 - Advanced Materials and New Applications of Sepiolite and Palygorskite\u003c/em\u003e, in \u003cem\u003eDevelopments in Clay Science\u003c/em\u003e, E. Gal\u0026agrave;n and A. Singer, Editors. Elsevier. pp. 393\u0026ndash;452\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFernandez C et al (2016) Reprint of Study of spatial distribution of sepiolite in sepiolite/polyamide6,6 nanocomposites. Applied clay science, 130\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQuignard F, Renzo FD, Guibal E (2010) From Natural Polysaccharides to Materials for Catalysis, Adsorption, and Remediation. Carbohydrates in Sustainable Development I. Springer, Berlin Heidelberg: Berlin, Heidelberg, pp 165\u0026ndash;197. A.P. Rauter, P. Vogel, and Y. Queneau, Editors\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKusuktham B, Prasertgul J, Srinun P (2013) Morphology and Property of Calcium Silicate Encapsulated with Alginate Beads. Silicon 6:191\u0026ndash;197\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePapageorgiou SK et al (2006) Heavy metal sorption by calcium alginate beads from Laminaria digitata. J Hazard Mater 137(3):1765\u0026ndash;1772\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBudtova T (2019) Cellulose II aerogels: A review. Cellulose 26:81\u0026ndash;121\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eValentin R et al (2007) Accessibility of the functional groups of chitosan aerogel probed by FT-IR-monitored deuteration. Biomacromolecules 8(11):3646\u0026ndash;3650\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGarc\u0026iacute;a-Gonz\u0026aacute;lez CA, Alnaief M, Smirnova I (2011) Polysaccharide-based aerogels\u0026mdash;Promising biodegradable carriers for drug delivery systems. Carbohydr Polym 86(4):1425\u0026ndash;1438\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSantagapita PR, Mazzobre MF, Buera MP (2011) Formulation and drying of alginate beads for controlled release and stabilization of invertase. Biomacromolecules 12(9):3147\u0026ndash;3155\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBelalia F, Djelali N (2016) Investigation of swelling/adsorption behavior of calcium alginate beads. Rev Roum Chim 61(10):747\u0026ndash;754\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee B-B, Ravindra P, Chan E-S (2013) Size and Shape of Calcium Alginate Beads Produced by Extrusion Dripping, vol 36. Chemical Engineering \u0026amp; Technology, pp 1627\u0026ndash;1642. 10\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang CH et al (2013) Strengthening Alginate/Polyacrylamide Hydrogels Using Various Multivalent Cations. ACS Appl Mater Interfaces 5(21):10418\u0026ndash;10422\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVenkatakrishnan A, Kuppa VK (2018) Polymer adsorption on rough surfaces. Curr Opin Chem Eng 19:170\u0026ndash;177\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKaradağ E, Kundakcı S (2015) Application of highly swollen novel biosorbent hydrogels in uptake of uranyl ions from aqueous solutions. Fibers Polym 16(10):2165\u0026ndash;2176\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu L et al (2014) \u003cem\u003eSynthesis of Sodium Alginate Graft Poly (Acrylic Acid-Co-2-Acrylamido-2-Methyl-1-Propane Sulfonic Acid)/Attapulgite Hydrogel Composite and the Study of its Adsorption.\u003c/em\u003e Polymer-Plastics Technology and Engineering, 53(1): pp. 74\u0026ndash;79\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi A, Wang A, Chen J (2004) Studies on poly (acrylic acid)/attapulgite superabsorbent composite. I. Synthesis and characterization. J Appl Polym Sci 92(3):1596\u0026ndash;1603\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang J, Wang Q, Wang A (2007) Synthesis and characterization of chitosan-g-poly(acrylic acid)/attapulgite superabsorbent composites. Carbohydr Polym 68(2):367\u0026ndash;374\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKara A et al (2016) Physicochemical parameters of Hg(II) ions adsorption from aqueous solution by sepiolite/poly(vinylimidazole). J Environ Chem Eng 4(2):1642\u0026ndash;1652\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheraghi Bidsorkhi H et al (2014) Mechanical, thermal and flammability properties of Ethylene-vinyl acetate (EVA)/ sepiolite nanocomposites. Polym Test, 37\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang J et al (2011) Effects of modified vermiculite on the synthesis and swelling behaviors of hydroxyethyl cellulose-g-poly(acrylic acid)/vermiculite superabsorbent nanocomposites. J Polym Res 18(3):401\u0026ndash;408\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen H et al (2007) Characterization and properties of sepiolite/polyurethane nanocomposites. Mater Sci Engineering: A 445:725\u0026ndash;730\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu M, Pu M, Ma H (2012) Preparation, structure and thermal properties of polylactide/sepiolite nanocomposites with and without organic modifiers. Compos Sci Technol 72:1508\u0026ndash;1514\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIbraeva ZE et al (2015) Preparation and Characterization of Organic-Inorganic Composite Materials Based on Poly(acrylamide) Hydrogels and Clay Minerals. Macromolecular Symposia 351(1):97\u0026ndash;111\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar A, Rao KM, Han SS (2018) Mechanically viscoelastic nanoreinforced hybrid hydrogels composed of polyacrylamide, sodium carboxymethylcellulose, graphene oxide, and cellulose nanocrystals. Carbohydr Polym 193:228\u0026ndash;238\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZaharia A et al (2015) Preparation and characterization of polyacrylamide-modified kaolinite containing poly [acrylic acid-co-methylene bisacrylamide] nanocomposite hydrogels. Appl Clay Sci 103:46\u0026ndash;54\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMittal H, Al Alili A, Alhassan SM (2022) Utilization of clay based super-porous hydrogel composites in atmospheric water harvesting. Appl Clay Sci 230:106712\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMahdavinia GR, Asgari A (2013) Synthesis of kappa-carrageenan-g-poly(acrylamide)/sepiolite nanocomposite hydrogels and adsorption of cationic dye. Polym Bull 70(8):2451\u0026ndash;2470\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEkici S, Işıkver Y, Saraydın D (2006) Poly(Acrylamide-Sepiolite) Composite Hydrogels: Preparation, Swelling and Dye Adsorption Properties. Polym Bull 57(2):231\u0026ndash;241\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi P et al (2009) Poly(Acrylamide/Laponite) Nanocomposite Hydrogels: Swelling and Cationic Dye Adsorption Properties. J Appl Polym Sci 111:1786\u0026ndash;1798\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXie Y, Wang A, Liu G (2009) Superabsorbent Composite XXII: Effects of Modified Sepiolite on Water Absorbency and Swelling Behavior of Chitosan-g-Poly(acrylic acid)/Sepiolite Superabsorbent Composite. Polym Compos 31:89\u0026ndash;96\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"polymer-bulletin","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobu","sideBox":"Learn more about [Polymer Bulletin](http://link.springer.com/journal/289)","snPcode":"289","submissionUrl":"https://submission.nature.com/new-submission/289/3","title":"Polymer Bulletin","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Biocomposite Polymers, Alginate Xerogel Beads, Sepiolite, Swellability, Biodegradability","lastPublishedDoi":"10.21203/rs.3.rs-5455380/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5455380/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eNowadays growing attention is given to the design and development of novel interpenetrating polymer networks (IPN) from the combination of hydrogel polymers loaded with natural clay. In this work, we used the eco-friendly IPN strategy to develop novel hydrogel biocomposite beads, made of alginate (ALG), with improved clay dispersion, higher pH sensitivity, better stretchability and swellability, together with enhanced regenerability properties and biodegradability resistance. Fibrous clay, namely sodium sepiolite (NaS), was loaded into alginate simple biocomposite network (SBN) beads, via manual co-grinding mixture/encapsulation method, at different sepiolite loads. Alginate double biocomposite network (DBN) beads were also prepared at different sepiolite loads, via the diffusion of acrylamide monomer (AAM) inside alginate single biocomposite network (SBN) beads, followed by \u003cem\u003ein situ\u003c/em\u003e free radical polymerization of AAM into poly-acrylamide (pAAM), using ammonium persulfate (APS) as polymerization initiator and N,N-methylenebisacrylamide (Bis) as covalent crosslinker agent. The as-elaborated SBN and DBN beads were then characterized by digital camera recording, XRD analysis, ATR-FTIR characterization and SEM observation. FTIR results showed that NaS and pAAM were successfully incorporated into DBN beads, whilst XRD analysis revealed the enhancement of fibrous clay dispersion, even at relatively high sepiolite loads. Besides, SEM microscopy confirmed the porous spongious nature of DBN beads. The properties of the as-elaborated SBN and DBN beads were also evaluated by test touching, swelling rate measurements, adsorption/desorption experiments and biodegradability evaluation. DBN beads properties were always found enhanced in comparison with those of SBN beads: very good stretchability, good swelling behavior and stability in water whatever the pH, either in acidic or alkaline solution, enhanced adsorption/desorption properties towards methylene blue (MB) dye, very good regenerability and delayed biodegradability. In summary, this work showed an interesting and safe IPN/biocomposite approach to develop high-performance alginate biocomposite polymers as a promising system towards their use in eco-friendly processes.\u003c/p\u003e","manuscriptTitle":"Elaboration of Novel Biocomposite Hydrogel Polymers made of Alginate and Sepiolite and endowed with Enhanced Properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-16 17:09:25","doi":"10.21203/rs.3.rs-5455380/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-03-29T02:20:05+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-25T07:32:34+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-22T22:58:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"272334054787812002207038332237963542130","date":"2025-03-16T05:23:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"321081544369211258289801006482628139099","date":"2025-03-09T10:48:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-02-24T08:19:11+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-11-20T09:10:32+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-11-16T01:40:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Polymer Bulletin","date":"2024-11-14T16:16:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"polymer-bulletin","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"pobu","sideBox":"Learn more about [Polymer Bulletin](http://link.springer.com/journal/289)","snPcode":"289","submissionUrl":"https://submission.nature.com/new-submission/289/3","title":"Polymer Bulletin","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4b131fe2-896c-405b-9637-5be35c0d5325","owner":[],"postedDate":"December 16th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-07T16:18:30+00:00","versionOfRecord":{"articleIdentity":"rs-5455380","link":"https://doi.org/10.1007/s00289-025-05897-y","journal":{"identity":"polymer-bulletin","isVorOnly":false,"title":"Polymer Bulletin"},"publishedOn":"2025-07-02 15:58:53","publishedOnDateReadable":"July 2nd, 2025"},"versionCreatedAt":"2024-12-16 17:09:25","video":"","vorDoi":"10.1007/s00289-025-05897-y","vorDoiUrl":"https://doi.org/10.1007/s00289-025-05897-y","workflowStages":[]},"version":"v1","identity":"rs-5455380","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5455380","identity":"rs-5455380","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}