Fabrication of a novel eco-friendly hybrid biocomosite based on carboxymethyl chitosan /polypropylene glycol /activated carbon for the highly efficient removal of Cr (III) from the aquatic medium: Adsorption, kinetic and antimicrobial evaluations

Fabrication of a novel eco-friendly hybrid biocomosite based on carboxymethyl chitosan /polypropylene glycol /activated carbon for the highly efficient removal of Cr (III) from the aquatic medium: Adsorption, kinetic and antimicrobial evaluations | 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 Fabrication of a novel eco-friendly hybrid biocomosite based on carboxymethyl chitosan /polypropylene glycol /activated carbon for the highly efficient removal of Cr (III) from the aquatic medium: Adsorption, kinetic and antimicrobial evaluations Eslam A. Mohamed, Amal A. Altalhi, Nabel. A. Negm This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1558232/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 6 You are reading this latest preprint version Abstract Different nonionic biocomposite frameworks were prepared by supporting carboxymethylated chitosan polypropylene glycol on active carbon and characterized using sufficient characterization techniques. The prepared biocomposites comprised different modified chitosan to active carbon ratios. The biocomposites were achieved during remediation of chromium (III) ions from an aqueous medium. The influences of pH, chromium (III) ions concentration, time, and weight used in the remediation process were extensively studied to point out the optimized process conditions. The assigned optimum conditions of chromium (III) ions remediation were: 25 o C, using 0.6 g sorbents, and 100 ppm of ions concentration for 300 minutes at semi-neutral to neutral pH range of 6–7 to attain removal efficiency of 98.7%. The process was followed Freundlich adsorption isotherm and pseudo-second-order kinetics. The accumulation of ions onto biocomposites was regulated according to the intraparticle diffusion model, and the rate-determining step was the diffusion step. Increasing the active carbon-modified chitosan ratio in the biocomposites from 1:4 to 4:1, enhanced the remediation effectiveness of carboxymethylated chitosan in terms of equilibrium adsorption capacities increase from 67.93 mg/g to 70.25 mg/g. An opposing attitude was achieved by increasing the incorporated active carbon in the biocomposites during their antimicrobial efficacies assessments. The study presents a low-cost, eco-friendly, highly effective eliminator for highly contaminated aqueous media with Cr 3+ ions. Furthermore, the prepared adsorbents exhibited high elimination efficiency in the presence of a high abundance of Cr 3+ in the medium. Carboxymethylated chitosan active carbon chromium (III) remediation antimicrobial activity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 1. Introduction The extensive utilization of heavy metals in industrial activities leads to a gradual rising in their ionic abundance in the activities drain water, which causes diverse ecological and health defects. Consequently, economic feasibility, sustainability, and effective remediation of various varieties of lethal contaminations have priority during ecological studies and research[ 1 – 3 ]. Chitin, chitosan, and agricultural wastes [ 4 ] are important substrates for remediation processes, which are ecofriendly and have the ability towards bio-deterioration [ 5 ]. During the removal of different pollutants from wastewater, including dyes, organics, metal ions, and drugs, chitosan represented marvel removal efficiency for all these pollutants[ 6 , 7 ]. Chitosan is the second abundance biopolymer in nature that comes from the de-acetylation of chitin, the first abundant biopolymer in nature[ 8 ]. Chitosan lacks toxicity, is highly biocompatible, and has fast bio-deterioration; consequently, it attracted the attention of researchers for producing economically and efficiently modified adsorbents[ 9 , 10 ]. Due to its superior characteristics, chitosan was modified to produce hydrogels with high swelling tendency, microcapsules, and microspheres, with enhanced mechanical and diffusion characteristics[ 11 ]. The motivating centers for chitosan adsorption tendencies are the amino (-NH 2 ), and hydroxyl (-OH) groups. These groups are not enough for presenting high adsorption tendencies for pure chitosan biopolymer, but chitosan always requires chemical modifications in its skeleton to present the required and expected efficiency[ 12 , 13 ]. Several chemical modifications can be performed for pure chitosan to increase its susceptibility during adsorption. The modification processes include the introduction of glutaraldehyde[ 14 , 15 ], glyoxal[ 16 ], N,N-[bis(2-hydroxyl-3-formyl-5-methylbenzyl-dimethyl)]ethylene diamine[ 17 ], and ethylene glycol diglycidylether[ 18 ], in addition to carboxymethylation of chitosan to obtain caboxymthyl chitosan[ 19 ]. These derivatives contain hydroxyl (-OH), carboxyl (-COOH), amino (-NH 2 ) groups, which are good candidates for high adsorption efficiency.Active carbon is a natural product that can be produced from several processes including pyrolysis of biomass[ 20 ], charring of agricultural wastes, and chemical modification of organic wastes [ 21 ]. Active carbon can be used in wastewater treatment due to the presence of several active functional groups with high abundance which are mainly hydroxyl and carboxyl groups, in addition to some ester and carbonyl groups[ 22 ]. Wheat straw [ 23 ], waste biomass [ 24 ], seeds shells [ 25 ], and other agricultural products can be used as feedstock for the production of active carbon.Cr metal ions are presented in water sources in + 3, +5, and + 6 oxidation states, and the last is the most lethal form of them, due to its particular damages on DNA[ 26 ]. Among several applications: catalysts, glass production, and leather tanning used Cr 3+ salts are extensivelyused.Nevertheless, Cr 3+ effectively impacts some biological and metabolic processes, at which glucose level is increased in the cells. Hence, it was a necessity to establisha save protocol for the elimination of Cr 3+ [ 27 ]. Among chemical oxidation [ 28 ], flocculation/coagulation [ 29 ], and biological remediation[ 30 ]; the adsorption method is regarded as a talented process for metal ions removal from contaminated water. This is due to its advantages including cost-effectively, easinessduring the application, the diversity of contaminants and pollutants which can be removed, high capacity during adsorption, and minimum produced sludge[ 31 ].In this study, carboxymethylated chitosan polypropylene glycol-active carbon biocomposite was prepared using different active carbon ratios and characterized. The biocomposites were achieved in the removal of chromium (III) ions from an aqueous medium. The influences of pH, chromium (III) ions concentration, time, and weight used in the remediation process were extensively studied. The adsorption isotherm and kinetic models of the process was studied 2. Experimental Section 2.1 Materials Chitosan (CHI, 20–100 mPa/s)waspurchased from Shaanxi Pioneer Biotech Co., Ltd. Chloroacetic acid, triethylamine, sodium hydroxide, 2-propyl alcohol, methyl alcohol, and sodium bicarbonate were procured from Sinopharma Chem. Co., CHINA. Propylene oxide and activated carbon were purchased from Henan Tianfu Chemical Co., Ltd, 2.2 Preparation of carboxymethyl chitosan Carboxymethyl chitosan was prepared according to the reported methodology [ 32 ]. In a typical method, CHI (7.5 gram), and sodium hydroxide (10.13 gram) were suspended in a suitable amount of 2-propyl alcohol (225 mL), and the medium moved at room temperature for2 h. Alcoholic solution of chloroacetic acid (7.5 g) in 50 mL of 2-propyl alcohol was added portion-wise during 1 h, and the temperature then was raised to 60 o C for 3 h; followed by filtration and recrystallization of the product from 75% aqueous methyl alcohol, and dried overnight to obtain the carboxymethylated chitosan (CMCN), ( Scheme 1 ) . 2.3 The reaction of CMCN and propylene oxide Dried CMCN (5 g) was swelled in 5% ethanolic solution of acetic acid for 3 h under stirring, and then the reaction medium was desiccated at 65 o C for one day. The produced chitosonium acetate product (5 g), propylene oxide (0.3 mol, 17.4 g), and triethylamine (1 mL) were charged into a 250 mL closed glass reactor and tightly closed, and agitated at 45 o C for 10 h. The reactor was cooled to room temperature and evacuated (0.5 atm) at 40 o C for 1 h to eliminate triethylamine and excess propylene oxide and weighted 32 . The product then was neutralized by washing with sodium bicarbonate solution (0.1 M/20 mL), and then the product was dried at 80 o C under vacuum for 4 h, ( Scheme 1 ) . 2.4 Formation of CMCN-PG/activated carbon biocomposite CMCN/PG and activated carbon were swelled individually in deionized water for 4 h, at 40 o C. Then, the two suspensions were mixed in different weight percent ratios (1:4, 1:1, 4:1 CMCN/PG: AC) and agitated at 50 o C for 4 h, followed by ultrasonic treating for 2 min (50% strength, CP505, Cole-Parmer, USA) to obtain the dispersed CMCN-PG/AC[ 33 ]. The dispersed product was settled down and decanted several times from distilled water, followed by drying under vacuum at 80 o C for 24 h to obtain three biocomposites, designated as CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC ( Scheme 1 ) corresponded to the weight ratio of CMCN-PG to activated carbon. 2.5 Adsorption experiment Adsorption experiments were progressed for the adsorption of Cr 3+ metal ions onto the prepared biocomposites to determine the various parameters which influence the adsorption efficiencies of the biocomposites. The determined parameters were: influence of process time, initial metal ion concentration, amount of processed biocomposite, and pH of the medium. The amount of biocomposite : different weights of the prepared biocomposites (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 g) were dispersed individually mechanically in 100 mL of Cr 3+ solution (100 ppm) for 120 min. Process time :0.6 gram of biocomposite disseminated in 100 mL of Cr 3+ solution (100 ppm) for different durations (60, 120, 180, 240, 300, and 360 min). Metal ion concentration :0.6 gram of biocomposites disseminated in 100 mL of Cr 3+ solution (50, 100, 150, 200, and 250 ppm) for 120 minutes. pH : 0.6 gram of each biocomposite disseminated in 100 mL of Cr 3+ solution (100 ppm) at different pH values (4–9) for 120 min. Each run was progressed in a 200 mL vessel with a stirring rate of 150 rpm under the thermostated condition at 25 o C. After each run, the medium was filtered, and the filtrate was collected and stored, while the residual biocomposites were dried and kept for further analysis. The concentration of the residual Cr 3+ ions was determined using atomic absorption spectroscopy (Agilent-220 FS Atomic Spectrophotometer, United States). The removal percentage of the metal ions was calculated using Eq. 1 : $$\mathbf{R}\mathbf{e}\mathbf{m}\mathbf{o}\mathbf{v}\mathbf{a}\mathbf{l} \mathbf{\%}=\frac{{\mathbf{C}}_{\mathbf{o}}-{\mathbf{C}}_{\mathbf{e}}}{{\mathbf{C}}_{\mathbf{e}}}\times 100$$ 1 C o , C e : initial and equilibrium concentrations of Cr 3+ ions, respectively. 2.6 Adsorption isotherm Adsorption equilibrium study was carried out using 0.5 g of biocomposite in 100 mL Cr 3+ solution at different concentrations of 50–250 ppm, pH of 7, and mixing speed of 150 rpm for 300 min. Isotherm models of Langmuir[ 34 ], and Freundlich [ 35 ] were applied to the experimental data using Eqs. 2 – 3 , respectively. q e and q m (mg.g − 1 ): concentration of Cr 3+ metal ions at equilibrium, the maximum adsorption capacity of biocomposites; K L is the Langmuir constant (L.mg − 1 ); K F , n: Freundlich constant, adsorption intensity, respectively. 2.7 Kinetic study The adsorption kinetics was determined by considering the influence of the immersion time on the adsorption process. The investigationalstatistics were scrutinized considering pseudo-first-order, pseudo-second-order, and interparticle diffusion rendering Eqns. 4–6 , respectively[ 36 , 37 ]. R 2 was judged during inspecting the suitability of the correct model designates the kinetic performances of the adsorption progression. k 1 , k 2 , t, k int (min − 1 , g.mg − 1 .min − 1 , min, mg.g − 1 .min 1/2 ): rate constants of pseudo-first and -second order models, contact time, and interparticle diffusion rate constant, respectively. 2.8 Anti-microbial activity The modified chitosan-activated carbon biocomposites were screened for their anti-microbial action using well-diffusion methodology[ 38 ], using S. aureus, S. mutants, E. coli , P. aeruginosa , and K.pneumonia, C. Albicans , and A. Nigar , as tested micro-organisms, while ampicillin and gentamicin operated as standards for the used bacterial genera, and dimethyl sulfoxide as a diluent. CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were achieved at a dosage of 15 mg/mL. 3. Results And Discussion 3.1 Adsorbents characterization 3.1.a FTIR spectroscopy(Nicolet 6700, Thermoelectron, USA) FTIR spectra of both two raw materials (chitosan, and activated carbon) were provided to determine the essential absorption bands of each one and were shown as follows: FTIR of chitosan bared the subsequent bands (Fig. 1) : broad absorption band centered at 3425 cm − 1 represented for OH and NH 2 stretching band[ 39 ] − [ 40 ]; stretching bands within 2870–2920 cm − 1 resembled C-H bonds[ 41 ]; the skeletal vibrations of C-O-C stretching band at 1026 and 1072 cm − 1 ; –CH 2 – bending appeared at 1420 cm − 1 ; asymmetric stretching of the C-O-C bridge gotten around 1153 cm − 1 ; 1540, 1318 cm − 1 C = O amide; 1650 cm − 1 –C = O bending of –NH; 815 cm − 1 C-O-C glycoside bridge[ 42 ].activated carbon analysis using FTIR spectroscopy showed five types of absorption bands as follows (Fig. 1) : 3500 cm − 1 , (2920 cm − 1 , 2870 cm − 1 ), 1690 cm − 1 , 1035 cm − 1 , and 875 cm − 1 corresponding to O-H stretching, symmetric and asymmetric stretching of aliphatic C-H, C = O of aldehyde groups, C-O-C of ether vibration, and C = C (alkenes), respectively [ 43 , 44 ]. The reaction between chitosan and propylene oxide in the presence of chloroacetic acid revealed the formation of carboxymethyl chitosan polypropylene glycol polymer (CMCN-PG) . The formation of CMCN-PG was confirmed by the presence of similar absorption bands of chitosan with the relative increase in the intensities of the three bands at 1100 cm − 1 corresponded to ether groups of the formed propylene glycol as the result of the grafting of propylene glycol units in the main structure of chitosan, and 2920 cm − 1 , and 2870 cm − 1 assigned for symmetric and asymmetric stretching bands of aliphatic C-H of polypropylene glycol units which increased by increasing the propylene glycol units[ 45 ]. Initially, the formation of carboxymethyl chitosan was confirmed by the presence of an intense absorption near 1734 cm − 1 corresponding to the formed ester groups, which proved the methylation of chitosan CMCN (Fig. 1) [ 46 ]. The formation of the targeted carboxymethyl chitosan polypropylene glycol-activated carbon biocomposites (CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4) happened via interaction between the formed carboxymethyl chitosan-polypropylene glycol and the activated carbon and their chemical structures were confirmed via FTIR analysis. FTIR spectra of CMCN-PG-AC biocomposite (representative for the prepared biocomposites) (Fig. 1) showed a combination of the absorption bands of carboxymethyl chitosan polypropylene glycol and activated carbon. The essential absorption band of the aldehyde groups characterized the activated carbon was appeared at 1690 cm − 1 , while the absorption band characterized the carboxymethyl chitosan polypropylene glycol appeared at 1735 cm − 1 [ 19 ]. The two composites of CMCN-PG4-AC and CMCN-PG-AC4 showed similar absorption bands with different intensities, confirming the formation of their expected chemical skeleton. The presented FTIR spectra confirmed the formation of CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4 biocomposites as shown in Scheme 1 . 3.1.bSEM image(JEM-7500F, China) SEM images of the chitosan and the prepared biocomposites were printed in Fig. 2 . It is clear that chitosan has different particle forms ranging between 50 and 200 µm, also it can be seen the asymmetrical particles in the form of sheets, in addition to a smooth un-voided surface[ 47 ]. The formed biocomposites showed the presence of activated carbon aggregates on the surface of chitosan flakes[ 48 ]. As can be observed in Fig. 2 , the gradual increase in the distribution of activated carbon in chitosan film from 1:4 to 1:1, and 4:1 (CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4) increases the crystal-like structures of the activated carbon[ 49 ]. 3.1.c XRD spectra(Empyrean, Netherlands) XRD patterns of chitosan, activated carbon, CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were obtained at 2θ of 5 to 80°. XRD patterns of chitosan showed two characteristic signals at 10 o and 20 o , which is following the XRD fingerprint reported in several reports[ 50 , 51 ]. Activated carbon showed a high amorphous structure as represented[ 52 ] in Fig. 3 . The prepared biocomposites showed the characteristic fingerprint patterns of chitosan at 10 o , and 20 o , but the crystallinity in terms of the intensities of the characteristic peaks was decreased gradually by increasing the amount of activated carbon in the biocomposites. That can be attributed to the amorphous structure of activated carbon, which affects the crystallinity of the chitosan crystalline structure[ 53 ]. Generally, the performances of adsorption by different sorbents depend on adsorptive active sites accessibility. The highly crystalline adsorbents have low adsorption efficiencies due to the low accessibility of their adsorptive active sites[ 54 ]. Herein, the crystallinity of the prepared biocomposites is decreased and consequently, it will be expected the adsorption efficiencies will increase. That is due to the high accessibility of the different adsorptive sites of chitosan and activated carbon. 3.2 Optimization of adsorption parameters Figure 4 represents the adsorption efficiencies of Cr 3+ metal ions from the aqueous medium onto different amounts of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites. As a general observation, the removal efficiency of Cr 3+ from the aqueous solution is gradually increased by the gradual increase in the number of used adsorbents. That increase in the adsorptive performance can be ascribed to the increase in the effective adsorptive sites on the adsorbents by increasing their amounts in the medium. The maximum adsorption efficiency can be obtained in the presence of 0.6 g/L of the three adsorbents as reported in several reports[ 55 , 56 ]. Figure 5 showed the influence of the immersion time during 6 hours on the adsorption of Cr 3+ ions from the aqueous medium on CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites (0.6 g/L). As obtained from the analysis results, the adsorption efficiency profile was rapidly increased at the initial time of the process (1–2 h), and then the increment was decreased steadily after longer periods. The rapid increase in the adsorption efficiency can be ascribed for the different Cr 3+ ions concentration gradient between the bulk and the aqueous solution and the high concentration of unoccupied adsorptive centers on the biocomposites surfaces. The steady decrease in the adsorption efficiencies of the biosorbents after longer periods can be ascribed to the partial occupation of the adsorptive sites and the decrease in Cr 3+ ions concentration gradient between the solution bulk and the metal ions on the adsorbent's surface. The maximum adsorption efficiency of the three biocomposite adsorbents was pointed at 5 h [ 57 ].Increasing the contact time increases the hydration of the biocomposites by water molecules, which increases the surface area of the biocomposites. The increase in the surface area makes the adsorption sites more available or accessible for interaction by Cr 3+ metal ions. Comparison between the reported equilibrium times of modified chitosan [ 58 ], and the studied biocomposites showed that the prepared biocomposites have fewer equilibrium times. That can be attributed to the presence of propylene glycol units within the biocomposites framework, which eases their hydration throughout hydrogen bonding formation by the aqueous medium. The effect of the initial concentration of Cr 3+ metal ions on adsorption efficiencies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites was explored at the initial concentration of Cr 3+ metal ions from 50–250 ppm. Adsorbent dosage, pH, temperature, and contact time were secured as 7, 25 ◦C, 0.6 g for 5 h, Fig. 6 . The gradual increase in the concentration of Cr 3+ metal ions in the medium has a gradual decreasing effect on the adsorption efficiencies, which can be attributed to the ratio between the adsorptive sites and the free metal ions in the medium. At lower Cr 3+ ions concentration, the adsorption is occurred effectively (> 99%) due to the absence of competition between the free and bounded Cr 3+ ions (in the medium, or on the adsorbents). While, at high Cr 3+ ions concentration in the medium, the complete removal is decreased (less than 99%) due to the presence of competition between the adsorbed and free metal ions [ 59 ], and also due to the decrease in the unbounded adsorptive sites on the surface of the biocomposite adsorbents. The increase in Cr 3+ ion concentration than 250 ppm exhibited low adsorption efficiency for the different adsorbents, hence the optimal initial metal ion concentration was determined at 100 ppm. The influence of pH of the medium on Cr 3+ ions adsorption using CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites at the range of 4–10 were represented in Fig. 7 , in terms of adsorption efficiency. Figure 7 represented three concluding points at the studied pH range 4–10. In an acidic medium (pH = 4–5), the adsorption efficiencies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were low, which can be ascribed for the protonation of the adsorption active sites. The protonation process occurred for CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites by H + ions in an acidic medium decrease the available deprotonated sites which can adsorb Cr 3+ from the medium. In neutral medium at pH = 6–7, the adsorption efficiency of Cr 3+ using CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites was increased considerably to reach its maximum value at pH = 6 ( Fig. 7 ) . In an alkaline medium (pH = 8–10), a considerable decrease in the adsorption efficiencies of the three biocomposite adsorbents upon increasing the alkalinity to 10. That behavior can be attributed to the charge of Cr 3+ ionsin the medium, which mainly depends on the pH of the medium as represented, Eq. 7–11 [ 60 ]: Cr ↔Cr 3+ (7) Cr 3+ + H 2 O ↔Cr(OH) 2+ + H + (8) Cr(OH) 2+ + H 2 O ↔ Cr(OH) 2 1+ + H + (9) Cr(OH) 2 1+ + H 2 O ↔ Cr(OH) 3 (aq.) + H + (10) Cr(OH) 3 (aq.) + H 2 O ↔ Cr(OH) 4 1− + H + (11) As represented from the above equations (Eqs. 7–11) , the ionic form of Cr 3+ ions is changed gradually by increasing the pH of the medium. Increasing the pH converted the Crions into the bi-positively charged hydroxyl ions (Cr(OH) 2+ ), further increase in the pH changed the formed ions in Eq. 8 into chromium mono-cation (Cr(OH) 2 1+ ). At higher alkalinity, the chromium ions will precipitate as insoluble chromium hydroxide, which changed into negatively charged tetrahydroxy chromium complex with a negative charge (Cr(OH) 4 − ). The adsorption active sites presented on the prepared CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites are the hydroxyl and amino groups which have partially negative charges due to the presence of the lone pairs of electrons on oxygen and nitrogen atoms of –OH, and –NH 2 groups. Consequently, decreasing the positive charges on the metal ions will decrease their adsorption on the negatively charged adsorptive sites. As presented from Eqs. 7–11 , the positive charges on Cr 3+ ions are gradually decreased by the gradual increase in the pH. At high pH = 9, the high decrease in adsorption efficiencies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites can be accounted for by the formation of the negatively charged species (Cr(OH) 4 − ) in the medium. As represented from Figs. 4 – 7 , the adsorption efficiencies of the prepared adsorbents are dependent on the ratio of the activated carbon to the carboxymethyl chitosan polypropylene glycol presented in the nanocomposites. The gradual increase in the ratio of the activated carbon to modified chitosan from 1:4 to 4:1 is gradually increasing the obtained adsorption efficiencies. That can be ascribed for the diverse functional groups presented in the activated carbon, which acted as adsorption sites for Cr 3+ ions from the medium. Increasing the activated carbon ratio up to 4:1 obtained the maximum adsorption efficiency among the three prepared adsorbents. From the adsorption study results, the removal of Cr 3+ ions was optimally obtained from their aqueous medium using 0.6 g/L of CMCN-PG-AC4 after 6 hours at pH of 6–7, in the presence of 100 ppm of Cr 3+ to obtain the maximum adsorption efficiency at 98.1%. 3.3 Adsorption isotherms of the adsorption process Plotting the Langmuir adsorption isotherm equation variables, i.e., C e vs. C e /q e , and extracting the correlation coefficient of the data according to the equation of state showed that R 2 values were 0.7886, 0.9361, and 0.9488 ( Fig. 8 ) . These values were lower than the unity, which displays the disagreement of the data of the adsorption process by the Langmuir adsorption isotherm[ 61 ]. Consequently, the data of the adsorption process required another isotherm model which can hold the process variables, which is the Freundlich adsorption isotherm[ 62 ]. This model in contrast to the Langmuir adsorption isotherm considers the interaction between the adsorbed species on the adsorbent surface. The model suggests a profile between log C e and log q e , Fig. 9 . The model includes two parameters, K F , and n, which signify the number of ions at equilibrium attached to the adsorbents, while n indicates the strength of adsorption onto the adsorbents surface, Table 1 . Table 1 Freundlich isotherm parameters of Cr 3+ adsorption on CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites Biocomposite Equation K F n 1/n R 2 CMCN-PG4-AC y = 1.9536x + 0.509 1.66 0.51 1.960 0.9994 CMCN-PG-AC y = 1.2139x + 1.2179 3.38 0.82 1.219 0.9995 CMCN-PG-AC4 y = 0.9289x + 1.5509 4.72 1.08 0.926 0.9999 The equation of state of Freundlich adsorption isotherm, K F as a constant, is represented in Eq. 3 . The valuen indicated in Table 1 figures the strength of Cr 3+ ions adsorption onto the three biocomposites are increased by increasing the concentration of the activated carbon in the biocomposite. That proves the positive impact of activated carbon on the adsorption tendencies of the carboxymethyl chitosan polypropylene glycol biopolymer. This was confirmed by the increase in the K F values, which indicate the number of ions at equilibrium attached to the adsorbents, and reached the maximum for CMCN-PG-AC4 biocomposite. CMCN-PG4-AC biocomposite has the lowest activated carbon (4CMCN-PG:1AC molar ratio) showed the lowest ability to adsorb metal ions as the corresponding n value was the lowest (n = 0.51) and lowest adsorption capacity as indicated by K F value (1.66). While, CMCN-PG-AC4 biocomposite (1CMCN-PG:4AC molar ratio) exhibited the strongest adsorption to Cr 3+ metal ions on its surface regarding n = 1.08, and the highest adsorption capacity regarding K F value = 4.72.As concluded from the data in Table 1 , it can be informed that the adsorption of Cr 3+ metal ions onto CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites obeys Freundlich adsorption isotherm. That leads to describe the adsorption of Cr 3+ metal ions are occurs with interaction (repulsive) between the adsorbed metal ions on the biocomposites surface. The numeral amounts of 1/n lower than 1 reflect high adsorption intensity and surface heterogeneity[ 63 , 64 ]. The constant value of n in Cr 3+ ion adsorption by CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4 biocomposites was decreased by increasing the abundance of activated carbon in the formed biocomposite.This can be ascribed to the gradual increase in the heterogeneity, and consequently suggests the raising of the adsorption capacity of the adsorbents in the following order: CMCN-PG4-AC < CMCN-PG-AC < CMCN-PG-AC4. 3.4 Kinetic evaluation The kinetic evaluation was achieved using 100 ppm of Cr 3+ metal ions at pH 6, in the presence of 0.2 g of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites, at ambient temperature. The residual concentrations of Cr 3+ ions in the medium after the adsorption process for different interval times (120, 180, 240, 300, and 360 minutes) were determined in ppm. Concentrations were fitted using different kinetic models including pseudo-first-, second-order, and intra-particle diffusion kinetic models. Pseudo-first orders kinetic model the equation of state of the pseudo-first-order kinetic model comprises several factors, e.g., q e , q t , and k 1 which indicated the concentration of Cr 3+ at equilibrium, and after the time (t), and pseudo-first-order rate constant, in mg/g, mg/g, and (1/min) units, respectively. Figure 10 represented the graphical presentation of the adsorption data according to the pseudo-first-order kinetic equation of state ( Eq. 4 ).The adsorption data did not comply with the pseudo-first-order model due to the intersection of the profile line with the x-axis and deeper with more negative values. Analyzing the profile during the first stage of adsorption revealed that this model is applicable at the short time adsorption process. This was referred to as the highly unoccupied concentration of the adsorptive active sites at the biocomposites surfaces during the first stage of the adsorption process[ 65 ]. Pseudo-second order kinetic model this model commonly can fit adsorption data of metal ions in the solutions, using its equation of state ( Eq. 5 ), and the variables of the pseudo-first-order model, in addition to additional parameters describing the rate-determining step of the second-order process (k 2 , g.mg − 1 /min), and graphically illustrated in Fig. 11 , as follows[ 66 ] Evidently, in Table 2 , R 2 varied within 0.9998 to 1 (≈ 1) illustrating the appropriateness of the model for explaining the kinetics of the process. Further, calculating q e gave comparable values to the experimental values[ 67 ], ( Table 2 ) . Table 2 Kinetic data of Pseudo-second order model (* rate constant) Biocomposites R 2 q e (mg/g) Intercept k 2 * Theoretical Experimental CMCN-PG4-AC 0.9998 78.13 74.55 0.2952 5.6x10 − 4 CMCN-PG-AC 0.9999 78.13 74.34 0.2519 6.5x10 − 4 CMCN-PG-AC4 1 78.74 73.95 0.2028 7.9x10 − 4 As reported for the Pseudo-second order kinetic model [ 68 , 69 ] the validity of this model is covering the entire time range of the process, additionally, the adsorption of Cr 3+ ions occurred via electrostatic interaction between the positively charged metal ions and the electron lone-pairs located in the functional groups of the adsorbents (adsorptive sites). Intraparticle diffusion model : this model supposes that the adsorption on the porous adsorbents is achieved throughout several stages, which can be summarized in the following: migration of high strength region (solution bulk) to lower concentration gradient (adsorbents/medium interface), adsorbed species film formation, and finally the diffusion of adsorbed species into the different adsorbent pores to interact with the adsorptive sites. Additionally, the rate-determining step was suggested to be the intraparticle diffusion step, and k int , the rate constant can be determined according to Eq. 6 (k int = constant related to intraparticle diffusion stage, mg/g min 1/2 )[ 70 ]: Figure 12 represented the relationship between the square root of adsorption process time and the adsorbed amount of Cr 3+ ions at the time (t), which illustrates the intraparticle diffusion model equation. The profile shows three characteristic regions that corresponded to the adsorption stages of Cr 3+ ions on CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites. Several parameters were extracted for the two major regions of the profile (the first and the third regions) including correlation coefficients (R 2 ), rate constant of rate-determining step (K int ), and adsorption capacity at equilibrium (q e ), Table 3 . Table 3 Extracted parameters from intraparticle diffusion kinetic model Region Migration from high to low concentration gradient Diffusion region Biocomposites R 2 K int q e R 2 K int q e CMCN-PG4-AC 0.9999 0.9912 55.88 1 03176 67.90 CMCN-PG-AC 0.9962 0.9450 57.52 1 03176 68.30 CMCN-PG-AC4 0.9943 0.8790 59.45 1 02268 70.25 Analyzing the data in Table 3 represents the following: In the first region, R 2 alternatedbetween 0.9999 to 0.9943, and the equilibrium adsorption capacity is ranged between 55.88 and 59.45 mg/g. The obtained values of the first region were out of the experimental values, which cannot be considered the rate-determining step. The diffusion region showed a correlation coefficient equal to unity (R 2 = 1), and the equilibrium adsorption capacity (q e ) were ranged between 67.9 mg/g and 70.25 mg/g. These values are following the experimental values, indicating that the diffusion step is the rate-determining step. The obtained values of the equilibrium adsorption capacity can be ordered in the following sequence: 70.25 mg/g, 68.30 mg/g, and 67.90 mg/g, for CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposite. The upsurge values of q e by rising the activated carbon ratio in the different biocomposites confirms the occurrence of a synergistic performance between the modified chitosan and the activated carbon during the adsorption process of Cr 3+ ions from the medium. 3.5 Mechanism of CMCN-PG-AC4 biocomposites The adsorption mechanism is defined by several elements such as functional groups, electric charge, and the structures of the adsorbent and adsorbate. The functional groups of the adsorbent and the structuring of the adsorbate are two of the most critical factors that influence adsorption mechanism. In the CMCN-PG-AC4 biocomposites, the presence of -NH 2 and -OH groups in chitosan creates active locations for hydrogen bonds with Cr3 + ions. As previously discussion (effect of pH part), Cr(III) ions can exist in a variety of forms depending on the pH. Investigation the highly uptake of Cr(III) ions was obtained at pH = 6. In order to have a better knowledge of the adsorption mechanism, the FT-IR analysis of the CMCN-PG-AC4 biocomposites before and after adsorption process of Cr(III). As shown in Fig. 13 , after Cr(III) adsorption, two additional peaks at 782 and 950 cm-1 were observed, which can be attributed to the Cr-O asymmetric and stretching vibrations, respectively. The vanishing of Cr–O and Cr—O—Cr vibration peaks in the spectrum of CMCN-PG-AC4 biocomposites after Cr desorption process, suggest that the adsorption mechanism involving the electrostatic attraction between adsorbent and Cr(VI) anionic species (Zhang, Xia, et al., 2015; Zhao et al., 2010). 3.6 Regeneration and reusability of adsorbents According to previous studies, the regeneration and reusability of adsorbentare the perfect indicators for the evaluation of their performance for practical industrial applications, Recycling studies were conducted under ideal adsorption conditions, and the solvents for Cr (III) desorption were NaOH (0.1 M) solutions. As shown in Fig. 14 after five cycles, the adsorption efficient of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites remained at about 83%, 81%, and 80% respectively for Cr (III) metal ions, The slight decrease in adsorption capacity may be due to the formation of stable complexs, metal hydroxides between CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites and heavy metal ions. However, the adsorbent still showed great reusability, which is beneficial to its practical application in the field of heavy metal wastewater treatment. 3.7 Antimicrobial activity The antimicrobial activities of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were tested against Gram–ve bacteria ( E. coli, K. pneumonia ), Gram + ve bacteria ( S. aureus, S. mutans ), and Fungi ( C. Albicans, A. Nigar ), Table 4 .It was reported that chitosan biopolymer has acceptable antimicrobial activities against several types of microorganisms [ 71 ]. The efficacy of chitosan was found to increase by increasing the degree of deacetylation [ 72 ]. The reports pointed out that the origin of its antimicrobial activity comes from the presence of the amino groups along with chitosan segments[ 73 ]. Table 4 Antimicrobial efficacies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites Sample Microorganism Gram –ve bacteria Gram + ve bacteria Fungi E. coli K. pneumonia S. aureus S. mutans C. albicans A. Nigar CMCN-PG4-AC 16 ± 0.5 14 ± 0.5 22.3 ± 0.5 30 ± 0.5 12.3 ± 0.5 NA CMCN-PG-AC 12 ± 0.5 11 ± 0.5 20 ± 0.5 29 ± 0.5 11.6 ± 0.5 NA CMCN-PG-AC4 9 ± 0.5 6 ± 0.5 16 ± 0.5 26 ± 0.5 10.3 ± 0.5 NA Gentamicin 27 ± 0.6 25 ± 0.5 NA NA NA NA Ampicillin NA NA 22 ± 0.5 30 ± 0.5 NA NA Nystatin NA NA NA NA 21 ± 0.5 20 ± 0.5 Various descriptions were proposed of the antimicrobial function of chitosan biopolymer. Most of them suggested an interaction between the cellular membrane of bacteria and the chitosan, which leads to an upsurge in cellular permeability[ 74 ]. This consequently resulted in leakage of cellular components outside or inside the cells. This leakage causes growth disturbances as a result of reducing oxygen consumption required for the biosynthesis of essential components inside cells such as carbohydrates, protein, lipids, nucleotides, and genes[ 75 ]. Finally, the synthesis of RNA and DNA will be decayed and,directly decrease the bacterial cells[ 76 ].Assessment of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites during the antimicrobial tests showed the presence of a regular trend in the efficiency variation, which was depending on the ratio of active carbon in each biocomposite. It was found that the gradual increase in the ratio of active carbon in the biocomposites decreases gradually the antimicrobial activities, Table 4 . That was attributed to the variation of the chitosan ratio in each biocomposite, which has enhanced antimicrobial efficiency by increasing its concentration. This was following several published reports. Conclusions Chitosan was carboxymethylated and grafted by propylene oxide to obtain grafted carboxymethyl chitosan, then its biocomposites by activated carbon at different ratios of the latter were formed to achieve efficient adsorbents for Cr 3+ ions. The composition and texture of the prepared biocomposites were determined and the porosity was increased by increasing the activated carbon ratio. The adsorption experiments of Cr 3+ from aqueous solutions revealed the effective role of activated carbon in the adsorption process. The adsorption of Cr 3+ was increased by increasing the time, Cr 3+ initial concentration, adsorbents amounts, and the ratio of activated carbon. The adsorption process obeyed Freundlich adsorption isotherm according to the Pseudo-second order kinetic model. 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Int J Biol Macromol 186:724–734. https://doi.org/10.1016/j.ijbiomac.2021.07.086 Altalhi A, Hashem H, Negm N, Mohamed E, Azmy E (2021) Synthesis, characterization, computational study, and screening of novel 1-phenyl-4-(2-phenylacetyl)-thiosemicarbazide derivatives for their antioxidant and antimicrobial activities. J Mol Liq 333:115977. https://doi.org/10.1016/j.molliq.2021.115977 Raafat D, Von Bargen K, Haas A, Sahl HG (2008) Insights into the mode of action of chitosan as an antibacterial compound. Appl Environ Microbiol 74:3764–3773. https://doi.org/10.1128/AEM.00453-08 Scheme Scheme 1 is available in Supplementary Files section. Supplementary Files scheme.png Scheme 1: Schematic presentation of preparation of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Major Revisions Needed 24 May, 2022 Reviewers agreed at journal 17 May, 2022 Reviews received at journal 27 Apr, 2022 Reviewers invited by journal 26 Apr, 2022 Editor assigned by journal 18 Apr, 2022 First submitted to journal 14 Apr, 2022 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-1558232","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":101574108,"identity":"d79005e9-c17a-4902-b98f-fc6c5c8aa20c","order_by":0,"name":"Eslam A. Mohamed","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8UlEQVRIiWNgGAWjYFAC5gYIzd7Y+ICB4QAxWhihWngOHzYgUYuEW5oEUVr4+Q82frpRUxdtcIPHrJqn5o4cPwPzw0c38GiRnJHYLJ1zjC13w+0es9s8x54ZSzawGRvn4NFicIOxQTqHjSd3w50zQC1shxM3HOBhk8anxf78webfOf8kcjfcyDEr5vlHhBYDhsQ26dw2A6CWtDRm3jYitEjcSGyzzu1LyJ155vBhybl9h40lmwn4hb//8OHbOd/qcvuONzZ+ePPtsBw/e/PDx/i0wIHCAQYGJh4Qi5kY5SAg3wCM1R/Eqh4Fo2AUjIIRBQCQ6VXUVsgdcQAAAABJRU5ErkJggg==","orcid":"","institution":"Egyptian Petroleum Research Institute","correspondingAuthor":true,"prefix":"","firstName":"Eslam","middleName":"A.","lastName":"Mohamed","suffix":""},{"id":101574109,"identity":"52352610-6b1e-42f3-84fc-225348d435e5","order_by":1,"name":"Amal A. Altalhi","email":"","orcid":"","institution":"Taif University College of Science","correspondingAuthor":false,"prefix":"","firstName":"Amal","middleName":"A.","lastName":"Altalhi","suffix":""},{"id":101574110,"identity":"e118b024-44bd-4804-aaa3-10f273f3a2fd","order_by":2,"name":"Nabel. A. Negm","email":"","orcid":"","institution":"Egyptian Petroleum Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Nabel.","middleName":"A.","lastName":"Negm","suffix":""}],"badges":[],"createdAt":"2022-04-14 13:07:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1558232/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1558232/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":21342195,"identity":"c22b79b0-2fb9-42b5-acbe-842161fd8b5f","added_by":"auto","created_at":"2022-05-11 15:43:52","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":324143,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/f4ad25c50022d0c9b94608e2.png"},{"id":21341515,"identity":"46926226-171b-41c0-aa9a-fcfdda4b9298","added_by":"auto","created_at":"2022-05-11 15:33:52","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":143915,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/dfb3226be1424f5cb13bf82c.png"},{"id":21341513,"identity":"0a6aeb86-9dbe-451b-b200-1a1539382939","added_by":"auto","created_at":"2022-05-11 15:33:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":4493,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not provided with this version\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/0c21936797c359cf84f3a62f.png"},{"id":21341893,"identity":"08fcb742-6a23-4805-8733-0032e21c7902","added_by":"auto","created_at":"2022-05-11 15:38:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":27584,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites amounts on the adsorption efficiency of Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e metal ions.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/9b0adefa092c1ce9fa58209a.png"},{"id":21341523,"identity":"6429b7b0-4ed9-40d5-91ee-a85ef7ff8fdb","added_by":"auto","created_at":"2022-05-11 15:33:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":28593,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of immersion time of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites on the adsorption efficiency of Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e metal ions.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/96a05d56231e02c8f030487c.png"},{"id":21341886,"identity":"c570cb7e-b0df-48f7-ada0-05b94fa6e6f5","added_by":"auto","created_at":"2022-05-11 15:38:52","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":27109,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of initial Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e metal ion concentration on the adsorption efficiency of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/c226ac2768e3ce3392b0e7f6.png"},{"id":21341892,"identity":"0839696c-9c29-4ddb-9c0f-a50617859162","added_by":"auto","created_at":"2022-05-11 15:38:52","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":33402,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of pH of the medium on the adsorption of Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e metal ion using CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/4595389079adc97c534ebff5.png"},{"id":21341516,"identity":"4aba2f73-c4e7-411e-8ea0-ca555dcbcbcf","added_by":"auto","created_at":"2022-05-11 15:33:52","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":30312,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLangmuir adsorption isotherm presentation of the adsorption process of Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e onto CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/e3d373d29b9f05c9c06051f0.png"},{"id":21341526,"identity":"de394643-6e21-4aa1-86fc-a4d5c1c721c2","added_by":"auto","created_at":"2022-05-11 15:33:52","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":33477,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFreundlich adsorption isotherm presentation of the adsorption process of Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e onto CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/6cc3d2e5d33f65015a9d56d4.png"},{"id":21342196,"identity":"e5667a68-ac79-41f9-ab70-cbf60200db82","added_by":"auto","created_at":"2022-05-11 15:43:52","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":31901,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFitting data of Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e adsorption on CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites according to Pseudo-first order kinetic model.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/f41aaf4b8a92bd0896dcd6fe.png"},{"id":21341525,"identity":"baf764c9-97ad-4ad3-83fb-40cbc56d2f5f","added_by":"auto","created_at":"2022-05-11 15:33:52","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":25228,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePresentation of adsorption data using pseudo-second-order kinetic model.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/d494e92450caad9ef887605d.png"},{"id":21341888,"identity":"c80369ce-f015-4e20-ac16-c9521c58dc85","added_by":"auto","created_at":"2022-05-11 15:38:52","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":25750,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eInterpretation of experimental adsorption data using intraparticle diffusion model.\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/cf366e6475f77ef200f5f9dc.png"},{"id":21341527,"identity":"bd95859f-50b4-4b2e-9a86-e1c65afed99d","added_by":"auto","created_at":"2022-05-11 15:33:52","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":160365,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFTIR spectrum of CMCN-PG-AC4 biocomposite before and after adsorption process of Cr(III) ions .\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/6b5019f6f88574804185dd57.png"},{"id":21343613,"identity":"c3a4ab20-ecfe-470f-a9ef-90ca8fad37da","added_by":"auto","created_at":"2022-05-11 15:48:52","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":106438,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eReusability studies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites in the adsorption process of Cr\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e metal ion.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/ed31b7ed2bb7c6467c906fa7.png"},{"id":21343615,"identity":"fc0ed0bb-6305-4b41-b0e0-4c8841bf2ef2","added_by":"auto","created_at":"2022-05-11 15:48:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1428768,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/449cf363-f584-46a8-bcb8-bbbbfca221e5.pdf"},{"id":21343614,"identity":"eabfb389-9bbd-4eec-9253-1d81c78ff915","added_by":"auto","created_at":"2022-05-11 15:48:52","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":155549,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1: Schematic presentation of preparation of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites.\u003c/strong\u003e\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"scheme.png","url":"https://assets-eu.researchsquare.com/files/rs-1558232/v1/1087287da6f9cba82e1797b0.png"}],"financialInterests":"","formattedTitle":"Fabrication of a novel eco-friendly hybrid biocomosite based on carboxymethyl chitosan /polypropylene glycol /activated carbon for the highly efficient removal of Cr (III) from the aquatic medium: Adsorption, kinetic and antimicrobial evaluations","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe extensive utilization of heavy metals in industrial activities leads to a gradual rising in their ionic abundance in the activities drain water, which causes diverse ecological and health defects. Consequently, economic feasibility, sustainability, and effective remediation of various varieties of lethal contaminations have priority during ecological studies and research[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Chitin, chitosan, and agricultural wastes [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] are important substrates for remediation processes, which are ecofriendly and have the ability towards bio-deterioration [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. During the removal of different pollutants from wastewater, including dyes, organics, metal ions, and drugs, chitosan represented marvel removal efficiency for all these pollutants[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Chitosan is the second abundance biopolymer in nature that comes from the de-acetylation of chitin, the first abundant biopolymer in nature[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Chitosan lacks toxicity, is highly biocompatible, and has fast bio-deterioration; consequently, it attracted the attention of researchers for producing economically and efficiently modified adsorbents[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Due to its superior characteristics, chitosan was modified to produce hydrogels with high swelling tendency, microcapsules, and microspheres, with enhanced mechanical and diffusion characteristics[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The motivating centers for chitosan adsorption tendencies are the amino (-NH\u003csub\u003e2\u003c/sub\u003e), and hydroxyl (-OH) groups. These groups are not enough for presenting high adsorption tendencies for pure chitosan biopolymer, but chitosan always requires chemical modifications in its skeleton to present the required and expected efficiency[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Several chemical modifications can be performed for pure chitosan to increase its susceptibility during adsorption. The modification processes include the introduction of glutaraldehyde[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], glyoxal[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], N,N-[bis(2-hydroxyl-3-formyl-5-methylbenzyl-dimethyl)]ethylene diamine[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], and ethylene glycol diglycidylether[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], in addition to carboxymethylation of chitosan to obtain caboxymthyl chitosan[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. These derivatives contain hydroxyl (-OH), carboxyl (-COOH), amino (-NH\u003csub\u003e2\u003c/sub\u003e) groups, which are good candidates for high adsorption efficiency.Active carbon is a natural product that can be produced from several processes including pyrolysis of biomass[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], charring of agricultural wastes, and chemical modification of organic wastes [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Active carbon can be used in wastewater treatment due to the presence of several active functional groups with high abundance which are mainly hydroxyl and carboxyl groups, in addition to some ester and carbonyl groups[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Wheat straw [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], waste biomass [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], seeds shells [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], and other agricultural products can be used as feedstock for the production of active carbon.Cr metal ions are presented in water sources in +\u0026thinsp;3, +5, and +\u0026thinsp;6 oxidation states, and the last is the most lethal form of them, due to its particular damages on DNA[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Among several applications: catalysts, glass production, and leather tanning used Cr\u003csup\u003e3+\u003c/sup\u003esalts are extensivelyused.Nevertheless, Cr\u003csup\u003e3+\u003c/sup\u003eeffectively impacts some biological and metabolic processes, at which glucose level is increased in the cells. Hence, it was a necessity to establisha save protocol for the elimination of Cr\u003csup\u003e3+\u003c/sup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Among chemical oxidation [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], flocculation/coagulation [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], and biological remediation[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]; the adsorption method is regarded as a talented process for metal ions removal from contaminated water. This is due to its advantages including cost-effectively, easinessduring the application, the diversity of contaminants and pollutants which can be removed, high capacity during adsorption, and minimum produced sludge[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].In this study, carboxymethylated chitosan polypropylene glycol-active carbon biocomposite was prepared using different active carbon ratios and characterized. The biocomposites were achieved in the removal of chromium (III) ions from an aqueous medium. The influences of pH, chromium (III) ions concentration, time, and weight used in the remediation process were extensively studied. The adsorption isotherm and kinetic models of the process was studied\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv class=\"Section2\" id=\"Sec3\"\u003e\n \u003ch2\u003e2.1 Materials\u003c/h2\u003e\n \u003cp\u003eChitosan (CHI, 20\u0026ndash;100 mPa/s)waspurchased from Shaanxi Pioneer Biotech Co., Ltd. Chloroacetic acid, triethylamine, sodium hydroxide, 2-propyl alcohol, methyl alcohol, and sodium bicarbonate were procured from Sinopharma Chem. Co., CHINA. Propylene oxide and activated carbon were purchased from Henan Tianfu Chemical Co., Ltd,\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec4\"\u003e\n \u003ch2\u003e2.2 Preparation of carboxymethyl chitosan\u003c/h2\u003e\n \u003cp\u003eCarboxymethyl chitosan was prepared according to the reported methodology [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. In a typical method, CHI (7.5 gram), and sodium hydroxide (10.13 gram) were suspended in a suitable amount of 2-propyl alcohol (225 mL), and the medium moved at room temperature for2 h. Alcoholic solution of chloroacetic acid (7.5 g) in 50 mL of 2-propyl alcohol was added portion-wise during 1 h, and the temperature then was raised to 60 \u003csup\u003eo\u003c/sup\u003eC for 3 h; followed by filtration and recrystallization of the product from 75% aqueous methyl alcohol, and dried overnight to obtain the carboxymethylated chitosan (CMCN), \u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003e(\u003c/span\u003eScheme \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003e)\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec5\"\u003e\n \u003ch2\u003e2.3 The reaction of CMCN and propylene oxide\u003c/h2\u003e\n \u003cp\u003eDried CMCN (5 g) was swelled in 5% ethanolic solution of acetic acid for 3 h under stirring, and then the reaction medium was desiccated at 65\u003csup\u003eo\u003c/sup\u003eC for one day. The produced chitosonium acetate product (5 g), propylene oxide (0.3 mol, 17.4 g), and triethylamine (1 mL) were charged into a 250 mL closed glass reactor and tightly closed, and agitated at 45 \u003csup\u003eo\u003c/sup\u003eC for 10 h. The reactor was cooled to room temperature and evacuated (0.5 atm) at 40 \u003csup\u003eo\u003c/sup\u003eC for 1 h to eliminate triethylamine and excess propylene oxide and weighted\u003csup\u003e32\u003c/sup\u003e. The product then was neutralized by washing with sodium bicarbonate solution (0.1 M/20 mL), and then the product was dried at 80 \u003csup\u003eo\u003c/sup\u003eC under vacuum for 4 h, \u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003e(\u003c/span\u003eScheme \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003e)\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec6\"\u003e\n \u003ch2\u003e2.4 Formation of CMCN-PG/activated carbon biocomposite\u003c/h2\u003e\n \u003cp\u003eCMCN/PG and activated carbon were swelled individually in deionized water for 4 h, at 40 \u003csup\u003eo\u003c/sup\u003eC. Then, the two suspensions were mixed in different weight percent ratios (1:4, 1:1, 4:1 CMCN/PG: AC) and agitated at 50 \u003csup\u003eo\u003c/sup\u003eC for 4 h, followed by ultrasonic treating for 2 min (50% strength, CP505, Cole-Parmer, USA) to obtain the dispersed CMCN-PG/AC[\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. The dispersed product was settled down and decanted several times from distilled water, followed by drying under vacuum at 80 \u003csup\u003eo\u003c/sup\u003eC for 24 h to obtain three biocomposites, designated as CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC \u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003e(\u003c/span\u003eScheme \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003e)\u003c/span\u003e corresponded to the weight ratio of CMCN-PG to activated carbon.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec7\"\u003e\n \u003ch2\u003e2.5 Adsorption experiment\u003c/h2\u003e\n \u003cp\u003eAdsorption experiments were progressed for the adsorption of Cr\u003csup\u003e3+\u003c/sup\u003e metal ions onto the prepared biocomposites to determine the various parameters which influence the adsorption efficiencies of the biocomposites. The determined parameters were: influence of process time, initial metal ion concentration, amount of processed biocomposite, and pH of the medium.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eThe amount of biocomposite\u003c/em\u003e: different weights of the prepared biocomposites (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 g) were dispersed individually mechanically in 100 mL of Cr\u003csup\u003e3+\u003c/sup\u003e solution (100 ppm) for 120 min. \u003cem\u003eProcess time\u003c/em\u003e:0.6 gram of biocomposite disseminated in 100 mL of Cr\u003csup\u003e3+\u003c/sup\u003e solution (100 ppm) for different durations (60, 120, 180, 240, 300, and 360 min). \u003cem\u003eMetal ion concentration\u003c/em\u003e:0.6 gram of biocomposites disseminated in 100 mL of Cr\u003csup\u003e3+\u003c/sup\u003e solution (50, 100, 150, 200, and 250 ppm) for 120 minutes. \u003cem\u003epH\u003c/em\u003e: 0.6 gram of each biocomposite disseminated in 100 mL of Cr\u003csup\u003e3+\u003c/sup\u003e solution (100 ppm) at different pH values (4\u0026ndash;9) for 120 min. Each run was progressed in a 200 mL vessel with a stirring rate of 150 rpm under the thermostated condition at 25 \u003csup\u003eo\u003c/sup\u003eC. After each run, the medium was filtered, and the filtrate was collected and stored, while the residual biocomposites were dried and kept for further analysis. The concentration of the residual Cr\u003csup\u003e3+\u003c/sup\u003e ions was determined using atomic absorption spectroscopy (Agilent-220 FS Atomic Spectrophotometer, United States).\u003c/p\u003e\n \u003cp\u003eThe removal percentage of the metal ions was calculated using Eq. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e:\u003c/p\u003e\n \u003cdiv class=\"Equation\" id=\"Equ1\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$\\mathbf{R}\\mathbf{e}\\mathbf{m}\\mathbf{o}\\mathbf{v}\\mathbf{a}\\mathbf{l} \\mathbf{\\%}=\\frac{{\\mathbf{C}}_{\\mathbf{o}}-{\\mathbf{C}}_{\\mathbf{e}}}{{\\mathbf{C}}_{\\mathbf{e}}}\\times 100$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eC\u003csub\u003eo\u003c/sub\u003e, C\u003csub\u003ee\u003c/sub\u003e: initial and equilibrium concentrations of Cr\u003csup\u003e3+\u003c/sup\u003e ions, respectively.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003e2.6 Adsorption isotherm\u003c/h2\u003e\n \u003cp\u003eAdsorption equilibrium study was carried out using 0.5 g of biocomposite in 100 mL Cr\u003csup\u003e3+\u003c/sup\u003e solution at different concentrations of 50\u0026ndash;250 ppm, pH of 7, and mixing speed of 150 rpm for 300 min. Isotherm models of Langmuir[\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e], and Freundlich [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e] were applied to the experimental data using Eqs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, respectively.\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e and q\u003csub\u003em\u003c/sub\u003e (mg.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e): concentration of Cr\u003csup\u003e3+\u003c/sup\u003e metal ions at equilibrium, the maximum adsorption capacity of biocomposites; K\u003csub\u003eL\u003c/sub\u003e is the Langmuir constant (L.mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e); K\u003csub\u003eF\u003c/sub\u003e, n: Freundlich constant, adsorption intensity, respectively.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec9\"\u003e\n \u003ch2\u003e2.7 Kinetic study\u003c/h2\u003e\n \u003cp\u003eThe adsorption kinetics was determined by considering the influence of the immersion time on the adsorption process. The investigationalstatistics were scrutinized considering pseudo-first-order, pseudo-second-order, and interparticle diffusion rendering\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eEqns. 4\u0026ndash;6\u003c/span\u003e, respectively[\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. R\u003csup\u003e2\u003c/sup\u003e was judged during inspecting the suitability of the correct model designates the kinetic performances of the adsorption progression.\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n \u003cp\u003ek\u003csub\u003e1\u003c/sub\u003e, k\u003csub\u003e2\u003c/sub\u003e, t, k\u003csub\u003eint\u003c/sub\u003e (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, g.mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, min, mg.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.min\u003csup\u003e1/2\u003c/sup\u003e): rate constants of pseudo-first and -second order models, contact time, and interparticle diffusion rate constant, respectively.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec10\"\u003e\n \u003ch2\u003e2.8 Anti-microbial activity\u003c/h2\u003e\n \u003cp\u003eThe modified chitosan-activated carbon biocomposites were screened for their anti-microbial action using well-diffusion methodology[\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e], using \u003cem\u003eS. aureus, S. mutants, E. coli\u003c/em\u003e, \u003cem\u003eP. aeruginosa\u003c/em\u003e, and \u003cem\u003eK.pneumonia, C. Albicans\u003c/em\u003e, and \u003cem\u003eA. Nigar\u003c/em\u003e, as tested micro-organisms, while ampicillin and gentamicin operated as standards for the used bacterial genera, and dimethyl sulfoxide as a diluent. CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were achieved at a dosage of 15 mg/mL.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results And Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Adsorbents characterization\u003c/h2\u003e \u003cp\u003e \u003cb\u003e3.1.a FTIR spectroscopy(Nicolet 6700, Thermoelectron, USA)\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFTIR spectra of both two raw materials (chitosan, and activated carbon) were provided to determine the essential absorption bands of each one and were shown as follows: FTIR of chitosan bared the subsequent bands \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(Fig.\u0026nbsp;1)\u003c/span\u003e: broad absorption band centered at 3425 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e represented for OH and NH\u003csub\u003e2\u003c/sub\u003e stretching band[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003csup\u003e\u0026minus;\u003c/sup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]; stretching bands within 2870\u0026ndash;2920 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e resembled C-H bonds[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]; the skeletal vibrations of C-O-C stretching band at 1026 and 1072 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash; bending appeared at 1420 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; asymmetric stretching of the C-O-C bridge gotten around 1153 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; 1540, 1318 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e C\u0026thinsp;=\u0026thinsp;O amide; 1650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026ndash;C\u0026thinsp;=\u0026thinsp;O bending of \u0026ndash;NH; 815 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e C-O-C glycoside bridge[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e].activated carbon analysis using FTIR spectroscopy showed five types of absorption bands as follows \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(Fig.\u0026nbsp;1)\u003c/span\u003e: 3500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, (2920 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 2870 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), 1690 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1035 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 875 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to O-H stretching, symmetric and asymmetric stretching of aliphatic C-H, C\u0026thinsp;=\u0026thinsp;O of aldehyde groups, C-O-C of ether vibration, and C\u0026thinsp;=\u0026thinsp;C (alkenes), respectively [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. The reaction between chitosan and propylene oxide in the presence of chloroacetic acid revealed the formation of carboxymethyl chitosan polypropylene glycol polymer \u003cem\u003e(CMCN-PG)\u003c/em\u003e. The formation of \u003cem\u003eCMCN-PG\u003c/em\u003e was confirmed by the presence of similar absorption bands of chitosan with the relative increase in the intensities of the three bands at 1100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponded to ether groups of the formed propylene glycol as the result of the grafting of propylene glycol units in the main structure of chitosan, and 2920 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 2870 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e assigned for symmetric and asymmetric stretching bands of aliphatic C-H of polypropylene glycol units which increased by increasing the propylene glycol units[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. Initially, the formation of carboxymethyl chitosan was confirmed by the presence of an intense absorption near 1734 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to the formed ester groups, which proved the methylation of chitosan \u003cem\u003eCMCN\u003c/em\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(Fig.\u0026nbsp;1)\u003c/span\u003e[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The formation of the targeted carboxymethyl chitosan polypropylene glycol-activated carbon biocomposites (CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4) happened via interaction between the formed carboxymethyl chitosan-polypropylene glycol and the activated carbon and their chemical structures were confirmed via FTIR analysis. FTIR spectra of CMCN-PG-AC biocomposite (representative for the prepared biocomposites) \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(Fig.\u0026nbsp;1)\u003c/span\u003e showed a combination of the absorption bands of carboxymethyl chitosan polypropylene glycol and activated carbon. The essential absorption band of the aldehyde groups characterized the activated carbon was appeared at 1690 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while the absorption band characterized the carboxymethyl chitosan polypropylene glycol appeared at 1735 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The two composites of CMCN-PG4-AC and CMCN-PG-AC4 showed similar absorption bands with different intensities, confirming the formation of their expected chemical skeleton. The presented FTIR spectra confirmed the formation of CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4 biocomposites as shown in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003e3.1.bSEM image(JEM-7500F, China)\u003c/b\u003e \u003c/p\u003e \u003cp\u003eSEM images of the chitosan and the prepared biocomposites were printed in \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eFig.\u0026nbsp;2\u003c/span\u003e. It is clear that chitosan has different particle forms ranging between 50 and 200 \u0026micro;m, also it can be seen the asymmetrical particles in the form of sheets, in addition to a smooth un-voided surface[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. The formed biocomposites showed the presence of activated carbon aggregates on the surface of chitosan flakes[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. As can be observed in \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eFig.\u0026nbsp;2\u003c/span\u003e, the gradual increase in the distribution of activated carbon in chitosan film from 1:4 to 1:1, and 4:1 (CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4) increases the crystal-like structures of the activated carbon[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cb\u003e3.1.c XRD spectra(Empyrean, Netherlands)\u003c/b\u003e \u003c/p\u003e \u003cp\u003eXRD patterns of chitosan, activated carbon, CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were obtained at 2θ of 5 to 80\u0026deg;. XRD patterns of chitosan showed two characteristic signals at 10\u003csup\u003eo\u003c/sup\u003e and 20\u003csup\u003eo\u003c/sup\u003e, which is following the XRD fingerprint reported in several reports[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Activated carbon showed a high amorphous structure as represented[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] in \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eFig.\u0026nbsp;3\u003c/span\u003e. The prepared biocomposites showed the characteristic fingerprint patterns of chitosan at 10\u003csup\u003eo\u003c/sup\u003e, and 20\u003csup\u003eo\u003c/sup\u003e, but the crystallinity in terms of the intensities of the characteristic peaks was decreased gradually by increasing the amount of activated carbon in the biocomposites. That can be attributed to the amorphous structure of activated carbon, which affects the crystallinity of the chitosan crystalline structure[\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Generally, the performances of adsorption by different sorbents depend on adsorptive active sites accessibility. The highly crystalline adsorbents have low adsorption efficiencies due to the low accessibility of their adsorptive active sites[\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. Herein, the crystallinity of the prepared biocomposites is decreased and consequently, it will be expected the adsorption efficiencies will increase. That is due to the high accessibility of the different adsorptive sites of chitosan and activated carbon.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Optimization of adsorption parameters\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e4\u003c/span\u003e represents the adsorption efficiencies of Cr\u003csup\u003e3+\u003c/sup\u003e metal ions from the aqueous medium onto different amounts of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites. As a general observation, the removal efficiency of Cr\u003csup\u003e3+\u003c/sup\u003e from the aqueous solution is gradually increased by the gradual increase in the number of used adsorbents. That increase in the adsorptive performance can be ascribed to the increase in the effective adsorptive sites on the adsorbents by increasing their amounts in the medium. The maximum adsorption efficiency can be obtained in the presence of 0.6 g/L of the three adsorbents as reported in several reports[\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e5\u003c/span\u003e showed the influence of the immersion time during 6 hours on the adsorption of Cr\u003csup\u003e3+\u003c/sup\u003e ions from the aqueous medium on CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites (0.6 g/L). As obtained from the analysis results, the adsorption efficiency profile was rapidly increased at the initial time of the process (1\u0026ndash;2 h), and then the increment was decreased steadily after longer periods. The rapid increase in the adsorption efficiency can be ascribed for the different Cr\u003csup\u003e3+\u003c/sup\u003e ions concentration gradient between the bulk and the aqueous solution and the high concentration of unoccupied adsorptive centers on the biocomposites surfaces. The steady decrease in the adsorption efficiencies of the biosorbents after longer periods can be ascribed to the partial occupation of the adsorptive sites and the decrease in Cr\u003csup\u003e3+\u003c/sup\u003e ions concentration gradient between the solution bulk and the metal ions on the adsorbent's surface. The maximum adsorption efficiency of the three biocomposite adsorbents was pointed at 5 h [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e].Increasing the contact time increases the hydration of the biocomposites by water molecules, which increases the surface area of the biocomposites. The increase in the surface area makes the adsorption sites more available or accessible for interaction by Cr\u003csup\u003e3+\u003c/sup\u003emetal ions. Comparison between the reported equilibrium times of modified chitosan [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e], and the studied biocomposites showed that the prepared biocomposites have fewer equilibrium times. That can be attributed to the presence of propylene glycol units within the biocomposites framework, which eases their hydration throughout hydrogen bonding formation by the aqueous medium.\u003c/p\u003e \u003cp\u003eThe effect of the initial concentration of Cr\u003csup\u003e3+\u003c/sup\u003emetal ions on adsorption efficiencies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites was explored at the initial concentration of Cr\u003csup\u003e3+\u003c/sup\u003emetal ions from 50\u0026ndash;250 ppm. Adsorbent dosage, pH, temperature, and contact time were secured as 7, 25 ◦C, 0.6 g for 5 h, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The gradual increase in the concentration of Cr\u003csup\u003e3+\u003c/sup\u003e metal ions in the medium has a gradual decreasing effect on the adsorption efficiencies, which can be attributed to the ratio between the adsorptive sites and the free metal ions in the medium. At lower Cr\u003csup\u003e3+\u003c/sup\u003e ions concentration, the adsorption is occurred effectively (\u0026gt;\u0026thinsp;99%) due to the absence of competition between the free and bounded Cr\u003csup\u003e3+\u003c/sup\u003e ions (in the medium, or on the adsorbents). While, at high Cr\u003csup\u003e3+\u003c/sup\u003e ions concentration in the medium, the complete removal is decreased (less than 99%) due to the presence of competition between the adsorbed and free metal ions [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e], and also due to the decrease in the unbounded adsorptive sites on the surface of the biocomposite adsorbents. The increase in Cr\u003csup\u003e3+\u003c/sup\u003e ion concentration than 250 ppm exhibited low adsorption efficiency for the different adsorbents, hence the optimal initial metal ion concentration was determined at 100 ppm.\u003c/p\u003e \u003cp\u003eThe influence of pH of the medium on Cr\u003csup\u003e3+\u003c/sup\u003e ions adsorption using CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites at the range of 4\u0026ndash;10 were represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e7\u003c/span\u003e, in terms of adsorption efficiency. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e7\u003c/span\u003e represented three concluding points at the studied pH range 4\u0026ndash;10. In an acidic medium (pH\u0026thinsp;=\u0026thinsp;4\u0026ndash;5), the adsorption efficiencies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were low, which can be ascribed for the protonation of the adsorption active sites. The protonation process occurred for CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites by H\u003csup\u003e+\u003c/sup\u003e ions in an acidic medium decrease the available deprotonated sites which can adsorb Cr\u003csup\u003e3+\u003c/sup\u003e from the medium. In neutral medium at pH\u0026thinsp;=\u0026thinsp;6\u0026ndash;7, the adsorption efficiency of Cr\u003csup\u003e3+\u003c/sup\u003e using CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites was increased considerably to reach its maximum value at pH\u0026thinsp;=\u0026thinsp;6\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(\u003c/span\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e7\u003c/span\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e)\u003c/span\u003e. In an alkaline medium (pH\u0026thinsp;=\u0026thinsp;8\u0026ndash;10), a considerable decrease in the adsorption efficiencies of the three biocomposite adsorbents upon increasing the alkalinity to 10. That behavior can be attributed to the charge of Cr\u003csup\u003e3+\u003c/sup\u003eionsin the medium, which mainly depends on the pH of the medium as represented, \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eEq.\u0026nbsp;7\u0026ndash;11\u003c/span\u003e [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003e \u003cb\u003eCr \u0026harr;Cr\u003c/b\u003e \u003csup\u003e \u003cb\u003e3+\u003c/b\u003e \u003c/sup\u003e \u003cb\u003e(7)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eCr\u003c/b\u003e \u003csup\u003e \u003cb\u003e3+\u003c/b\u003e \u003c/sup\u003e \u003cb\u003e+ H\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO \u0026harr;Cr(OH)\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e \u003cb\u003e+ H\u003c/b\u003e\u003csup\u003e\u003cb\u003e+\u003c/b\u003e\u003c/sup\u003e \u003cb\u003e(8)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eCr(OH)\u003c/b\u003e \u003csup\u003e \u003cb\u003e2+\u003c/b\u003e \u003c/sup\u003e \u003cb\u003e+ H\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO \u0026harr; Cr(OH)\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003csup\u003e\u003cb\u003e1+\u003c/b\u003e\u003c/sup\u003e \u003cb\u003e+ H\u003c/b\u003e\u003csup\u003e\u003cb\u003e+\u003c/b\u003e\u003c/sup\u003e \u003cb\u003e(9)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eCr(OH)\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003csup\u003e \u003cb\u003e1+\u003c/b\u003e \u003c/sup\u003e \u003cb\u003e+ H\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO \u0026harr; Cr(OH)\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e(aq.)\u0026thinsp;+\u0026thinsp;H\u003c/b\u003e\u003csup\u003e\u003cb\u003e+\u003c/b\u003e\u003c/sup\u003e \u003cb\u003e(10)\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eCr(OH)\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e(aq.)\u0026thinsp;+\u0026thinsp;H\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eO \u0026harr; Cr(OH)\u003c/b\u003e \u003csub\u003e \u003cb\u003e4\u003c/b\u003e \u003c/sub\u003e \u003csup\u003e \u003cb\u003e1\u0026minus;\u003c/b\u003e \u003c/sup\u003e \u003cb\u003e+ H\u003c/b\u003e\u003csup\u003e\u003cb\u003e+\u003c/b\u003e\u003c/sup\u003e \u003cb\u003e(11)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eAs represented from the above equations \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(Eqs.\u0026nbsp;7\u0026ndash;11)\u003c/span\u003e, the ionic form of Cr\u003csup\u003e3+\u003c/sup\u003e ions is changed gradually by increasing the pH of the medium. Increasing the pH converted the Crions into the bi-positively charged hydroxyl ions (Cr(OH)\u003csup\u003e2+\u003c/sup\u003e), further increase in the pH changed the formed ions in \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eEq.\u0026nbsp;8\u003c/span\u003e into chromium mono-cation (Cr(OH)\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e1+\u003c/sup\u003e). At higher alkalinity, the chromium ions will precipitate as insoluble chromium hydroxide, which changed into negatively charged tetrahydroxy chromium complex with a negative charge (Cr(OH)\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e). The adsorption active sites presented on the prepared CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites are the hydroxyl and amino groups which have partially negative charges due to the presence of the lone pairs of electrons on oxygen and nitrogen atoms of \u0026ndash;OH, and \u0026ndash;NH\u003csub\u003e2\u003c/sub\u003e groups. Consequently, decreasing the positive charges on the metal ions will decrease their adsorption on the negatively charged adsorptive sites. As presented from \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eEqs.\u0026nbsp;7\u0026ndash;11\u003c/span\u003e, the positive charges on Cr\u003csup\u003e3+\u003c/sup\u003e ions are gradually decreased by the gradual increase in the pH. At high pH\u0026thinsp;=\u0026thinsp;9, the high decrease in adsorption efficiencies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites can be accounted for by the formation of the negatively charged species (Cr(OH)\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) in the medium.\u003c/p\u003e \u003cp\u003eAs represented from Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the adsorption efficiencies of the prepared adsorbents are dependent on the ratio of the activated carbon to the carboxymethyl chitosan polypropylene glycol presented in the nanocomposites. The gradual increase in the ratio of the activated carbon to modified chitosan from 1:4 to 4:1 is gradually increasing the obtained adsorption efficiencies. That can be ascribed for the diverse functional groups presented in the activated carbon, which acted as adsorption sites for Cr\u003csup\u003e3+\u003c/sup\u003e ions from the medium. Increasing the activated carbon ratio up to 4:1 obtained the maximum adsorption efficiency among the three prepared adsorbents. From the adsorption study results, the removal of Cr\u003csup\u003e3+\u003c/sup\u003e ions was optimally obtained from their aqueous medium using 0.6 g/L of CMCN-PG-AC4 after 6 hours at pH of 6\u0026ndash;7, in the presence of 100 ppm of Cr\u003csup\u003e3+\u003c/sup\u003e to obtain the maximum adsorption efficiency at 98.1%.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Adsorption isotherms of the adsorption process\u003c/h2\u003e \u003cp\u003ePlotting the Langmuir adsorption isotherm equation variables, i.e., C\u003csub\u003ee\u003c/sub\u003e vs. C\u003csub\u003ee\u003c/sub\u003e/q\u003csub\u003ee\u003c/sub\u003e, and extracting the correlation coefficient of the data according to the equation of state showed that R\u003csup\u003e2\u003c/sup\u003e values were 0.7886, 0.9361, and 0.9488 \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(\u003c/span\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e8\u003c/span\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e)\u003c/span\u003e. These values were lower than the unity, which displays the disagreement of the data of the adsorption process by the Langmuir adsorption isotherm[\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. Consequently, the data of the adsorption process required another isotherm model which can hold the process variables, which is the Freundlich adsorption isotherm[\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]. This model in contrast to the Langmuir adsorption isotherm considers the interaction between the adsorbed species on the adsorbent surface. The model suggests a profile between log C\u003csub\u003ee\u003c/sub\u003e and log q\u003csub\u003ee\u003c/sub\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The model includes two parameters, K\u003csub\u003eF\u003c/sub\u003e, and n, which signify the number of ions at equilibrium attached to the adsorbents, while n indicates the strength of adsorption onto the adsorbents surface, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFreundlich isotherm parameters of Cr\u003csup\u003e3+\u003c/sup\u003e adsorption on CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocomposite\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEquation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u003csub\u003eF\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1/n\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG4-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;1.9536x\u0026thinsp;+\u0026thinsp;0.509\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.960\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9994\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;1.2139x\u0026thinsp;+\u0026thinsp;1.2179\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9995\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;0.9289x\u0026thinsp;+\u0026thinsp;1.5509\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.926\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.9999\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe equation of state of Freundlich adsorption isotherm, K\u003csub\u003eF\u003c/sub\u003e as a constant, is represented in Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The valuen indicated in\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eTable 1\u003c/span\u003e figures the strength of Cr\u003csup\u003e3+\u003c/sup\u003e ions adsorption onto the three biocomposites are increased by increasing the concentration of the activated carbon in the biocomposite. That proves the positive impact of activated carbon on the adsorption tendencies of the carboxymethyl chitosan polypropylene glycol biopolymer. This was confirmed by the increase in the K\u003csub\u003eF\u003c/sub\u003e values, which indicate the number of ions at equilibrium attached to the adsorbents, and reached the maximum for CMCN-PG-AC4 biocomposite. CMCN-PG4-AC biocomposite has the lowest activated carbon (4CMCN-PG:1AC molar ratio) showed the lowest ability to adsorb metal ions as the corresponding n value was the lowest (n\u0026thinsp;=\u0026thinsp;0.51) and lowest adsorption capacity as indicated by K\u003csub\u003eF\u003c/sub\u003e value (1.66). While, CMCN-PG-AC4 biocomposite (1CMCN-PG:4AC molar ratio) exhibited the strongest adsorption to Cr\u003csup\u003e3+\u003c/sup\u003e metal ions on its surface regarding n\u0026thinsp;=\u0026thinsp;1.08, and the highest adsorption capacity regarding K\u003csub\u003eF\u003c/sub\u003e value\u0026thinsp;=\u0026thinsp;4.72.As concluded from the data in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, it can be informed that the adsorption of Cr\u003csup\u003e3+\u003c/sup\u003e metal ions onto CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites obeys Freundlich adsorption isotherm. That leads to describe the adsorption of Cr\u003csup\u003e3+\u003c/sup\u003e metal ions are occurs with interaction (repulsive) between the adsorbed metal ions on the biocomposites surface. The numeral amounts of 1/n lower than 1 reflect high adsorption intensity and surface heterogeneity[\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]. The constant value of n in Cr\u003csup\u003e3+\u003c/sup\u003e ion adsorption by CMCN-PG4-AC, CMCN-PG-AC, and CMCN-PG-AC4 biocomposites was decreased by increasing the abundance of activated carbon in the formed biocomposite.This can be ascribed to the gradual increase in the heterogeneity, and consequently suggests the raising of the adsorption capacity of the adsorbents in the following order: CMCN-PG4-AC\u0026thinsp;\u0026lt;\u0026thinsp;CMCN-PG-AC\u0026thinsp;\u0026lt;\u0026thinsp;CMCN-PG-AC4.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Kinetic evaluation\u003c/h2\u003e \u003cp\u003eThe kinetic evaluation was achieved using 100 ppm of Cr\u003csup\u003e3+\u003c/sup\u003e metal ions at pH 6, in the presence of 0.2 g of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites, at ambient temperature. The residual concentrations of Cr\u003csup\u003e3+\u003c/sup\u003e ions in the medium after the adsorption process for different interval times (120, 180, 240, 300, and 360 minutes) were determined in ppm. Concentrations were fitted using different kinetic models including pseudo-first-, second-order, and intra-particle diffusion kinetic models.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003ePseudo-first orders kinetic model\u003c/strong\u003e \u003cp\u003ethe equation of state of the pseudo-first-order kinetic model comprises several factors, e.g., q\u003csub\u003ee\u003c/sub\u003e, q\u003csub\u003et\u003c/sub\u003e, and k\u003csub\u003e1\u003c/sub\u003e which indicated the concentration of Cr\u003csup\u003e3+\u003c/sup\u003e at equilibrium, and after the time (t), and pseudo-first-order rate constant, in mg/g, mg/g, and (1/min) units, respectively.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e10\u003c/span\u003e represented the graphical presentation of the adsorption data according to the pseudo-first-order kinetic equation of state \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(\u003c/span\u003eEq.\u0026nbsp;\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).The adsorption data did not comply with the pseudo-first-order model due to the intersection of the profile line with the x-axis and deeper with more negative values. Analyzing the profile during the first stage of adsorption revealed that this model is applicable at the short time adsorption process. This was referred to as the highly unoccupied concentration of the adsorptive active sites at the biocomposites surfaces during the first stage of the adsorption process[\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cstrong\u003ePseudo-second order kinetic model\u003c/strong\u003e \u003cp\u003ethis model commonly can fit adsorption data of metal ions in the solutions, using its equation of state \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(\u003c/span\u003eEq.\u0026nbsp;\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), and the variables of the pseudo-first-order model, in addition to additional parameters describing the rate-determining step of the second-order process (k\u003csub\u003e2\u003c/sub\u003e, g.mg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/min), and graphically illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e11\u003c/span\u003e, as follows[\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]\u003c/p\u003e \u003c/p\u003e \u003cp\u003eEvidently, in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, R\u003csup\u003e2\u003c/sup\u003e varied within 0.9998 to 1 (\u0026asymp;\u0026thinsp;1) illustrating the appropriateness of the model for explaining the kinetics of the process. Further, calculating q\u003csub\u003ee\u003c/sub\u003e gave comparable values to the experimental values[\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e], \u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e(\u003c/span\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003e)\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eKinetic data of Pseudo-second order model (* rate constant)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eBiocomposites\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eq\u003csub\u003ee\u003c/sub\u003e (mg/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eIntercept\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ek\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eTheoretical\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003eExperimental\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG4-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9998\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e78.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e74.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.2952\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5.6x10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9999\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e78.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e74.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.2519\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.5x10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e78.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e73.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.2028\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.9x10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAs reported for the Pseudo-second order kinetic model [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e, \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e] the validity of this model is covering the entire time range of the process, additionally, the adsorption of Cr\u003csup\u003e3+\u003c/sup\u003e ions occurred via electrostatic interaction between the positively charged metal ions and the electron lone-pairs located in the functional groups of the adsorbents (adsorptive sites).\u003c/p\u003e \u003cp\u003e \u003cem\u003eIntraparticle diffusion model\u003c/em\u003e: this model supposes that the adsorption on the porous adsorbents is achieved throughout several stages, which can be summarized in the following: migration of high strength region (solution bulk) to lower concentration gradient (adsorbents/medium interface), adsorbed species film formation, and finally the diffusion of adsorbed species into the different adsorbent pores to interact with the adsorptive sites. Additionally, the rate-determining step was suggested to be the intraparticle diffusion step, and k\u003csub\u003eint\u003c/sub\u003e, the rate constant can be determined according to Eq.\u0026nbsp;\u003cspan refid=\"Equ6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(k\u003csub\u003eint\u003c/sub\u003e= constant related to intraparticle diffusion stage, mg/g min\u003csup\u003e1/2\u003c/sup\u003e)[\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e12\u003c/span\u003e represented the relationship between the square root of adsorption process time and the adsorbed amount of Cr\u003csup\u003e3+\u003c/sup\u003e ions at the time (t), which illustrates the intraparticle diffusion model equation. The profile shows three characteristic regions that corresponded to the adsorption stages of Cr\u003csup\u003e3+\u003c/sup\u003e ions on CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites. Several parameters were extracted for the two major regions of the profile (the first and the third regions) including correlation coefficients (R\u003csup\u003e2\u003c/sup\u003e), rate constant of rate-determining step (K\u003csub\u003eint\u003c/sub\u003e), and adsorption capacity at equilibrium (q\u003csub\u003ee\u003c/sub\u003e), Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExtracted parameters from intraparticle diffusion kinetic model\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRegion\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eMigration from high to\u003c/p\u003e \u003cp\u003elow concentration gradient\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eDiffusion region\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBiocomposites\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csup\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eK\u003c/b\u003e\u003csub\u003e\u003cb\u003eint\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003eq\u003c/b\u003e\u003csub\u003e\u003cb\u003ee\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csup\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003eK\u003c/b\u003e\u003csub\u003e\u003cb\u003eint\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003eq\u003c/b\u003e\u003csub\u003e\u003cb\u003ee\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG4-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9999\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.9912\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e55.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e03176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e67.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9962\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.9450\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e57.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e03176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e68.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.9943\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.8790\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e59.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e02268\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e70.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAnalyzing the data in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e represents the following: In the first region, R\u003csup\u003e2\u003c/sup\u003e alternatedbetween 0.9999 to 0.9943, and the equilibrium adsorption capacity is ranged between 55.88 and 59.45 mg/g. The obtained values of the first region were out of the experimental values, which cannot be considered the rate-determining step. The diffusion region showed a correlation coefficient equal to unity (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;1), and the equilibrium adsorption capacity (q\u003csub\u003ee\u003c/sub\u003e) were ranged between 67.9 mg/g and 70.25 mg/g. These values are following the experimental values, indicating that the diffusion step is the rate-determining step. The obtained values of the equilibrium adsorption capacity can be ordered in the following sequence: 70.25 mg/g, 68.30 mg/g, and 67.90 mg/g, for CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposite. The upsurge values of q\u003csub\u003ee\u003c/sub\u003e by rising the activated carbon ratio in the different biocomposites confirms the occurrence of a synergistic performance between the modified chitosan and the activated carbon during the adsorption process of Cr\u003csup\u003e3+\u003c/sup\u003e ions from the medium.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Mechanism of CMCN-PG-AC4 biocomposites\u003c/h2\u003e \u003cp\u003eThe adsorption mechanism is defined by several elements such as functional groups, electric charge, and the structures of the adsorbent and adsorbate. The functional groups of the adsorbent and the structuring of the adsorbate are two of the most critical factors that influence adsorption mechanism. In the CMCN-PG-AC4 biocomposites, the presence of -NH\u003csub\u003e2\u003c/sub\u003e and -OH groups in chitosan creates active locations for hydrogen bonds with Cr3\u0026thinsp;+\u0026thinsp;ions. As previously discussion (effect of pH part), Cr(III) ions can exist in a variety of forms depending on the pH. Investigation the highly uptake of Cr(III) ions was obtained at pH\u0026thinsp;=\u0026thinsp;6. In order to have a better knowledge of the adsorption mechanism, the FT-IR analysis of the CMCN-PG-AC4 biocomposites before and after adsorption process of Cr(III). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e13\u003c/span\u003e, after Cr(III) adsorption, two additional peaks at 782 and 950 cm-1 were observed, which can be attributed to the Cr-O asymmetric and stretching vibrations, respectively. The vanishing of Cr\u0026ndash;O and Cr\u0026mdash;O\u0026mdash;Cr vibration peaks in the spectrum of CMCN-PG-AC4 biocomposites after Cr desorption process, suggest that the adsorption mechanism involving the electrostatic attraction between adsorbent and Cr(VI) anionic species (Zhang, Xia, et al., 2015; Zhao et al., 2010).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Regeneration and reusability of adsorbents\u003c/h2\u003e \u003cp\u003eAccording to previous studies, the regeneration and reusability of adsorbentare the perfect indicators for the evaluation of their performance for practical industrial applications, Recycling studies were conducted under ideal adsorption conditions, and the solvents for Cr (III) desorption were NaOH (0.1 M) solutions. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e14\u003c/span\u003e after five cycles, the adsorption efficient of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites remained at about 83%, 81%, and 80% respectively for Cr (III) metal ions, The slight decrease in adsorption capacity may be due to the formation of stable complexs, metal hydroxides between CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites and heavy metal ions. However, the adsorbent still showed great reusability, which is beneficial to its practical application in the field of heavy metal wastewater treatment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.7 Antimicrobial activity\u003c/h2\u003e \u003cp\u003eThe antimicrobial activities of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites were tested against Gram\u0026ndash;ve bacteria (\u003cem\u003eE. coli, K. pneumonia\u003c/em\u003e), Gram\u0026thinsp;+\u0026thinsp;ve bacteria (\u003cem\u003eS. aureus, S. mutans\u003c/em\u003e), and Fungi (\u003cem\u003eC. Albicans, A. Nigar\u003c/em\u003e), Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.It was reported that chitosan biopolymer has acceptable antimicrobial activities against several types of microorganisms [\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e]. The efficacy of chitosan was found to increase by increasing the degree of deacetylation [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e]. The reports pointed out that the origin of its antimicrobial activity comes from the presence of the amino groups along with chitosan segments[\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAntimicrobial efficacies of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c7\" namest=\"c2\"\u003e \u003cp\u003eMicroorganism\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e\u003cb\u003eGram \u0026ndash;ve bacteria\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e\u003cb\u003eGram\u0026thinsp;+\u0026thinsp;ve bacteria\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e\u003cb\u003eFungi\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eE. coli\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eK. pneumonia\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eS. aureus\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eS. mutans\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eC. albicans\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cspan type=\"BoldItalic\" class=\"BoldItalic\" name=\"Emphasis\"\u003eA. Nigar\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG4-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e12.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e11.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCMCN-PG-AC4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGentamicin\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAmpicillin\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNystatin\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eVarious descriptions were proposed of the antimicrobial function of chitosan biopolymer. Most of them suggested an interaction between the cellular membrane of bacteria and the chitosan, which leads to an upsurge in cellular permeability[\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e]. This consequently resulted in leakage of cellular components outside or inside the cells. This leakage causes growth disturbances as a result of reducing oxygen consumption required for the biosynthesis of essential components inside cells such as carbohydrates, protein, lipids, nucleotides, and genes[\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e]. Finally, the synthesis of RNA and DNA will be decayed and,directly decrease the bacterial cells[\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e].Assessment of CMCN-PG-AC4, CMCN-PG-AC, and CMCN-PG4-AC biocomposites during the antimicrobial tests showed the presence of a regular trend in the efficiency variation, which was depending on the ratio of active carbon in each biocomposite. It was found that the gradual increase in the ratio of active carbon in the biocomposites decreases gradually the antimicrobial activities, Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. That was attributed to the variation of the chitosan ratio in each biocomposite, which has enhanced antimicrobial efficiency by increasing its concentration. This was following several published reports.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":" \u003cp\u003eChitosan was carboxymethylated and grafted by propylene oxide to obtain grafted carboxymethyl chitosan, then its biocomposites by activated carbon at different ratios of the latter were formed to achieve efficient adsorbents for Cr\u003csup\u003e3+\u003c/sup\u003e ions. The composition and texture of the prepared biocomposites were determined and the porosity was increased by increasing the activated carbon ratio. The adsorption experiments of Cr\u003csup\u003e3+\u003c/sup\u003e from aqueous solutions revealed the effective role of activated carbon in the adsorption process. The adsorption of Cr\u003csup\u003e3+\u003c/sup\u003e was increased by increasing the time, Cr\u003csup\u003e3+\u003c/sup\u003e initial concentration, adsorbents amounts, and the ratio of activated carbon. The adsorption process obeyed Freundlich adsorption isotherm according to the Pseudo-second order kinetic model. The adsorption was preceded through three steps and the rate-controlling process was the diffusion of Cr\u003csup\u003e3+\u003c/sup\u003e ions into the adsorbents. The optimal adsorption efficiency was found at 98.1% using 0.6 g of adsorbents after 6 hours in the presence of 100 ppm of Cr\u003csup\u003e3+\u003c/sup\u003e ions concentration in pH 6\u0026ndash;7.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgment\u003c/h2\u003e \u003cp\u003eI would like to thank Taif University Researcher supporting project number (TURP-2020/243), Taif University, Taif, Saudi Arabia.\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAzmy EAM, Hashem HE, Mohamed EA, Negm NA (2019) Synthesis, characterization, swelling and antimicrobial efficacies of chemically modified chitosan biopolymer. 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Appl Environ Microbiol 74:3764\u0026ndash;3773. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1128/AEM.00453-08\u003c/span\u003e\u003cspan address=\"10.1128/AEM.00453-08\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme","content":"\u003cp\u003eScheme 1 is available in Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Carboxymethylated chitosan, active carbon, chromium (III) remediation,antimicrobial activity","lastPublishedDoi":"10.21203/rs.3.rs-1558232/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1558232/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDifferent nonionic biocomposite frameworks were prepared by supporting carboxymethylated chitosan polypropylene glycol on active carbon and characterized using sufficient characterization techniques. The prepared biocomposites comprised different modified chitosan to active carbon ratios. The biocomposites were achieved during remediation of chromium (III) ions from an aqueous medium. The influences of pH, chromium (III) ions concentration, time, and weight used in the remediation process were extensively studied to point out the optimized process conditions. The assigned optimum conditions of chromium (III) ions remediation were: 25 \u003csup\u003eo\u003c/sup\u003eC, using 0.6 g sorbents, and 100 ppm of ions concentration for 300 minutes at semi-neutral to neutral pH range of 6\u0026ndash;7 to attain removal efficiency of 98.7%. The process was followed Freundlich adsorption isotherm and pseudo-second-order kinetics. The accumulation of ions onto biocomposites was regulated according to the intraparticle diffusion model, and the rate-determining step was the diffusion step. Increasing the active carbon-modified chitosan ratio in the biocomposites from 1:4 to 4:1, enhanced the remediation effectiveness of carboxymethylated chitosan in terms of equilibrium adsorption capacities increase from 67.93 mg/g to 70.25 mg/g. An opposing attitude was achieved by increasing the incorporated active carbon in the biocomposites during their antimicrobial efficacies assessments. The study presents a low-cost, eco-friendly, highly effective eliminator for highly contaminated aqueous media with Cr\u003csup\u003e3+\u003c/sup\u003e ions. Furthermore, the prepared adsorbents exhibited high elimination efficiency in the presence of a high abundance of Cr\u003csup\u003e3+\u003c/sup\u003e in the medium.\u003c/p\u003e","manuscriptTitle":"Fabrication of a novel eco-friendly hybrid biocomosite based on carboxymethyl chitosan /polypropylene glycol /activated carbon for the highly efficient removal of Cr (III) from the aquatic medium: Adsorption, kinetic and antimicrobial evaluations","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-05-11 15:33:50","doi":"10.21203/rs.3.rs-1558232/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revisions Needed","date":"2022-05-24T05:06:09+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2022-05-18T01:17:14+00:00","index":0,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2022-04-27T10:31:20+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-04-26T13:53:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-04-18T08:38:09+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymers and the Environment","date":"2022-04-14T09:06:21+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"97bdc7e5-e46a-443f-9ba4-e799d9c30617","owner":[],"postedDate":"May 11th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2022-10-14T14:34:53+00:00","versionOfRecord":[],"versionCreatedAt":"2022-05-11 15:33:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-1558232","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1558232","identity":"rs-1558232","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}