Organic and inorganic polymeric matrix of modified chitosan with algae and coal fly ash for cationic toxic dye removal: Multivariable optimization by Box-Behnken Design

Organic and inorganic polymeric matrix of modified chitosan with algae and coal fly ash for cationic toxic dye removal: Multivariable optimization by Box-Behnken Design | 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 Organic and inorganic polymeric matrix of modified chitosan with algae and coal fly ash for cationic toxic dye removal: Multivariable optimization by Box-Behnken Design RuiHong Wu, Elmira Kashi, Ali H. Jawad, Salis Awal Musa, Zeid A. ALOthman, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4508283/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Oct, 2024 Read the published version in Journal of Inorganic and Organometallic Polymers and Materials → Version 1 posted 18 You are reading this latest preprint version Abstract In this study, a composite adsorbent of chitosan/algae/coal fly ash (CS/Alg/FA) was synthesized to be an effective and renewable adsorbent for cationic methyl violet 2B dye (MV2B) removal from synthetic wastewater. The optimization of key adsorption variables (A: CS/Alg/FA dosage (0.02-0.1 g/100 mL), B: solution pH (4-10); C: contact time (20-180 min)) was carried out using the Box-Behnken design (BBD). The Langmuir isotherm model (coefficient of determination R² = 0.94) provided a good fit for the empirical data, and the pseudo-second-order model accurately described the kinetic data. The maximum adsorption capacity ( q max ) of CS/Alg/FA for MV2B was determined to be 63.4 mg/g at 25 ⁰C. The possible adsorption mechanism of MV2B can be assigned to electrostatic attractions along with n-π, and H-bonding interactions. Thus, this comprehensive study underscores the potential of CS/Alg/FA as a preferable adsorbent for the removal of cationic organic dyes from industrial wastewater. Algae Chitosan Coal fly ash Methyl violet 2B dye Box-Behnken Design Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction Synthetic dyes are increasingly employed across various industries, and the discharge of their effluents significantly contributes to water pollution [ 1 ]. These deleterious dyes pose severe threats to aquatic organisms and may exhibit teratogenic, mutagenic, or carcinogenic hazards to humans [ 2 – 5 ]. Consequently, the development of advanced technologies capable of effectively removing these pollutants has become imperative. Various treatment methods such as coagulation and flocculation [ 6 ], photocatalytic degradation [ 7 ], electro flocculation [ 8 ], adsorption [ 9 – 12 ], advanced oxidation processes [ 13 , 14 ], and anaerobic degradation [ 15 , 16 ] have been employed for the removal of organic pollutants from wastewater. Among these methods, adsorption stands out as the preferred method due to its cost-effectiveness and high efficiency [ 17 ]. The second most prevalent biopolymer following cellulose is chitosan (CS), a cationic biomaterial derived from the partial deacetylation of chitin [ 18 ]. CS is a distinguished biopolymer due to its non-toxicity, biodegradability, abundant sources, preferable adsorption capacity, and biocompatibility [ 19 ]. The adsorption efficacy of CS can be ascribed to the abundant hydroxyl (-OH) and amine (NH 2 ) functional groups on its polymeric backbone [ 20 – 25 ]. Nevertheless, CS faces challenges such as susceptibility to dissolution and swelling in acidic environments, a limited specific surface area, and inadequate mechanical stability, drawbacks that significantly constrain its practical utility in adsorption processes [ 26 ]. Given these limitations, enhancing the physicochemical properties of CS becomes imperative. The capability of chitosan (CS) hybrid composites to amalgamate the benefits of CS with biomaterials rich in functional groups, thereby enhancing surface area, porosity, chemical stability, mechanical stability, and reducing internal diffusion resistance, has garnered considerable attention [ 27 ]. In the fabrication of CS hybrid composites, materials with multifunctional moieties, including titanium dioxide nanoparticles [ 28 ], silica nanoparticles [ 26 ], clays [ 29 ], fly ash particles [ 30 ], algae [ 31 – 34 ], cellulose [ 35 ], and starch [ 36 ], have been employed to augment the adsorption and physicochemical properties of the composites. Notably, coal fly ash (FA), a by-product from coal combustion in thermal power plants, primarily comprises metal oxides such as silica, and alumina in addition to unburned carbon [ 37 ]. Due to its chemical composition, preferable surface area, and porosity, FA can engage with CS biopolymers, making it a valuable component for the removal of organic water pollutants [ 38 ]. Moreover, algae (Alg) are a diverse group of aquatic organisms that have the capability to conduct photosynthesis. However, the surface functional groups of Alg species indicate the existence of various acidic/oxygenated functional groups in its biological molecular structure such as hydroxyl (-OH), carboxyl (-COOH), sulphate (SO 4 − 2 ), phosphate (-PO 4 − 3 ), and amino (− NH 2 ) groups. These acidic functional groups of Alg exhibit high affinity towards capturing toxic cationic dye species [ 39 ]. Therefore, the main aim of this study is to synthesize a chitosan (CS) based composite adsorbent by incorporating CS with algae (Alg) and fly ash (FA) (CS/Alg/FA). The incorporation of Alg into polymeric backbone of CS will enrich the CS functionality with acidic functional groups, and as a result improve its affinity towards capturing cationic dye molecules. Moreover, incorporating FA into the polymeric backbone of CS will improve its chemical stability, surface properties, and functionality. Thus, the efficacy of CS/Alg/FA composite was assessed for the removal of cationic methyl violet 2B dye (MV2B) from aqueous environment. To achieve optimal removal of MV2B dye, the adsorption key parameters of MV2B dye were optimized using response surface methodology and Box-Behnken design (RSM-BBD). Furthermore, various characterization methods (FTIR, FE-SEM, XRD) as well as equilibrium adsorption data (adsorption isotherm model, adsorption kinetic data, and thermodynamic parameters) were utilized to derive the plausible pathways to the adsorption of MV2B dye by CS/Alg/FA. 2. Materials and methods 2.1 Materials The fly ash (FA) utilized in this study was obtained from a thermal power station located in Kapar, Klang, Selangor, Malaysia. Algae (Alg) was procured from Henan Yuzhong Bioengineering in China. Methyl violet 2B (MV 2B) was acquired from R&M Chemicals, possessing a molecular formula of C 24 H 28 ClN 3 with a molecular weight of 393.94 g/mol and a maximum absorption wavelength (λ max ) of 584 nm. The chitosan (CS) powder used, with a degree of deacetylation of 80, was sourced from Tianjin Damao Chemical Reagent Factory in China. High analytical grade chemical reagents, such as acetic acid, hydrochloric acid, and sodium hydroxide, were supplied by R&M Chemicals. 2.2 Synthesis of Chitosan/Algae/Fly ash The chitosan/algae/fly ash (CS/Alg/FA) biocompsite was formed by mixing 2 g CS powder, 1g algae powder, and 1 g fly ash powder in a glass beaker containing 80 mL of acetic acid solution (5% v/v) and stirred at room temperature for 24 h to form a viscous gel solution of CS/Alg/FA. Then, by injecting droplets of the CS/Alg/FA viscous solution into a beaker containing 1000 mL of sodium hydroxide solution (0.5 M) the viscous solution was transformed into beads form. To completely remove all traces of NaOH from the CS/Alg/FA beads, deionized water was used. Then the beads were left to oven-dry at 50°C overnight. The CS/Alg/FA sample was ultimately crushed to achieve a final consistent particle size (150 µm < particle size < 250) for future investigations. 2.3 Characterization The properties of CS/Alg/FA, including surface charge, surface area, surface morphology, elemental composition, surface crystalline and amorphous nature, and surface functional groups, were investigated using various techniques. These techniques include zero point of charge (pH pzc ) for surface charge analysis, a Micromeritics ASAP 2060 analyzer for surface area determination, scanning electron microscopy-energy dispersive X-ray (SEM-EDX, BRUKER, model: Apreo 2 S) for surface morphology and elemental composition analysis, X-ray diffractometer (XRD; X’Pert PRO, PANalytical) for examining crystalline and amorphous nature of the surface, and Fourier transform infrared spectroscopy (FTIR, Perkin-Elmer, Spectrum RX I) for studying surface functional groups. 2.4 Statistical optimization methodology Box-Behnken design (BBD) in response surface methodology RSM was used to optimize the adsorption process of MV2B by the CS/Alg/FA. Thus, three independent variables including solution pH, CS/Alg/FA dosage, and contact time were optimized by BBD. The design of the experiments and data processing was accomplished using Design-Expert 13.0 (Stat-Ease, USA). Values of inputs (factors) at various BBD levels are shown in Table 1 . The relationship between the inputs (adsorption parameters) and output (MV2B removal) to determine the optimal operational conditions is essentially represented by the following expression (Eq. 1). $$\mathbf{Y}={\varvec{\beta }}_{0}+\sum _{}^{}{\varvec{\beta }}_{\mathbf{i}}{\mathbf{X}}_{\mathbf{i}}+\sum _{}^{}{\varvec{\beta }}_{\mathbf{i}\mathbf{i}}{\mathbf{X}}_{\mathbf{i}}^{2}+\sum _{}^{}\sum _{}^{}{\varvec{\beta }}_{\mathbf{i}\mathbf{j}}{\mathbf{X}}_{\mathbf{i}}^{}{\mathbf{X}}_{\mathbf{j}} \left(1\right)$$ Where Y represents the predicted MV2B removal % (output), β 0 is the constant coefficient, X i and X j are inputs (factors), and β ij , β ii , and β i are the coefficients of interaction, quadratic, and linear terms, respectively. The BBD matrix and results for the removal of MV2B are detailed in Table 2. For the MV2B removal experiments, 100 mL of MV2B solutions with fixed concentration 50 mg/L were introduced into a 250 mL Erlenmeyer flask along with a fixed amount of CS/Alg/FA. Subsequently, the flasks containing MV2B solutions were stirred for a specified duration in a shaking water bath at 80 rpm. Following the completion of the adsorption process, CS/Alg/FA was separated from the mixture using a 0.45 µm syringe filter. The quantity of MV2B in the solution was determined using a UV-Vis analyzer at the wavelength of 584 nm. The percentage of MV2B removal was calculated using the following equation (Eq. 2). $$\text{R} \text{%}=\frac{\left({\text{C}}_{\text{o}}-{\text{C}}_{\text{e}}\right)}{{\text{C}}_{\text{o}}} \times 100 \left(2\right)$$ This equation calculates the percentage of MV2B removal, where C e represents the equilibrium concentration of MV2B in mg/L, and C 0 is its initial concentration. 2.5 Adsorption study of MV2B by CS/Alg/FA The optimal values for the adsorption variables were determined using the Box-Behnken design (BBD), and these values were subsequently employed in the isotherm, kinetic, thermodynamic, and batch adsorption study [ 39 ]. As indicated in Table 2, the optimal conditions leading to the maximum removal of MV 2B (78.4%) were a CS/Alg/FA dosage of 0.10 g/100 mL, a pH of 10, and a duration of 100 min. Following the methodology outlined in Section 2.4 , optimal input parameters (dosage: 0.10 g/100 mL, pH: 10) and initial concentrations (C o ) of MV 2B ranging from 20 to 250 mg/L were utilized for kinetic and isothermal studies in batch adsorption equilibrium experiments. Furthermore, the optimal input parameters (dosage: 0.10 g/100 mL, pH: 10) were employed for the removal of MV 2B (initial concentration = 100 mg/L) using the CS/Alg/FA adsorbent material at various temperature ranges (25°C, 35°C, 45°C, 55°C). The adsorption capacity (q e , mg/g) of the CS/Alg/FA adsorbent for MV2B dye was calculated according to the following Eq. (3). $${\text{q}}_{\text{e}}=\frac{\left({\text{C}}_{\text{o}}-{\text{C}}_{\text{e}}\right)\text{V}}{\text{W}} \left(3\right)$$ where W (g) represents the CS/Alg/FA's weight, and V (L) stands for the dye solution's volume. 3. Results and Discussion 3.1 Characterization of CS/Alg/FA The specific surface area results obtained through the Brunauer, Emmett, and Teller (BET) analysis are presented in Table 3 . Specifically, the specific surface area (BET) was measured to be 1.43 (m 2 /g), Langmuir surface area at 16.5 (m 2 /g), pore volume at 0.0023 (cm 3 /g), with an average pore size of 14.4 (nm) which indicates a mesoporous structure of CS/Alg/FA composites in accordance with the International Union of Pure and Applied Chemistry (IUPAC) classification [ 40 ]. Moreover, the N 2 adsorption-desorption isotherm of CS/Alg/FA (depicted in Fig. 1 ) aligns with the type IV isotherm, providing additional confirmation of the mesoporosity of CS/Alg/FA. Notably, the curve exhibits the H3 hysteresis loop associated with the presence of macropores in the pore network, further supporting the mesoporous pore size range (2–50 nm) of CS/Alg/FA [ 41 , 42 ]. This observation is reinforced by the inset in Fig. 1 . The average pore size of CS/Alg/FA being significantly larger than that of MV2B dye molecules implies that MV2B molecules can easily access the pores of CS/Alg/FA [ 41 , 43 ]. The crystalline/amorphous structure of the synthesized CS/Alg/FA composite was investigated by XRD analysis as depicted in Fig. 2 . The XRD spectra of CS/Alg/FA shows two broad and weak peaks corresponding to the characteristic peaks of chitosan (CS) and algae (Alg) at distinct 2θ values (10.7°, 20.7°) [ 31 , 34 ]. Additional peaks observed at 2θ = 27°, 38.4°, 44.7°, 64.8°, and 78° were attributed to fly ash (FA) particles [ 30 ], including alumina (Al 2 O 3 ) and quartz (SiO 2 ). The XRD bands of CS/Alg/FA encompass all the characteristic peaks of CS, Alg, and FA, confirming the successful integration of algae and fly ash with the chitosan matrix. The FTIR spectra of CS/Alg/FA biocomposites before and after MV2B dye adsorption are presented in Fig. 3 a and Fig. 3 b, respectively. In the FTIR spectrum of CS/Alg/FA (Fig. 3 a), the peaks at 545 cm − 1 indicated a weak phosphate group attributed to the vibration of the O-P-O bond, originating from Algae [ 40 ]. Additionally, characteristic peaks at 1070 cm − 1 and 790 cm − 1 represented asymmetric Si-O-Si bond and symmetric Si-O-Si bond stretching, respectively [ 44 ], corresponding to the SiO 2 band in the fly ash. The FTIR spectra of CS/Alg/FA biocomposites also exhibited the main peaks of CS polymers, with assignments at 1155 cm − 1 (skeletal vibration of C-O), 1400 cm − 1 (stretching vibration of C-N), 1560 cm − 1 (stretching vibration of C-C), 1650 cm − 1 (N-H bending vibration), and 2880 cm − 1 (symmetric and asymmetric C-H stretching vibrations of aliphatic groups) [ 45 ]. The FTIR spectra of CS/Alg/FA biocomposite after the adsorption of MV2B dye (Fig. 3 b) showed the same bands as observed in the spectra before adsorption (Fig. 3 a). Notably, the band at 3770 cm − 1 is enhanced after MV2B adsorption, possibly attributed to hydrogen bonding interactions formed between CS/Alg/FA and dye molecules [ 32 ]. Furthermore, the intensities of other relevant peaks corresponding to surface functional groups decreased, indicating that the enriched functional groups of CS/Alg/FA biocomposites were effectively engaged in the decolorization of MV2B dye. SEM images of FA, CS, Alg, CS/Alg/FA, and CS/Alg/FA after the adsorption process (Fig. 4 a-e) were employed to assess changes in the surface morphology of CS/Alg/FA following the adsorption of MV2B dye. Fly ash (FA) particles exhibited embedded spherical objects of various sizes (Fig. 4 a). The surface of Chitosan (CS) appeared relatively smooth (Fig. 4 b). Algae particles displayed an amorphous nature (Fig. 4 c). In contrast, the surface of physically composited CS/Alg/FA (Fig. 4 d) exhibited roughness, slits, cavities, and pores, favorable for the effective adsorption of dye molecules. Faintly visible small-sized FA particles, representing spherical objects embedded in the surface of CS/Alg/FA biocomposite, indicated the successful incorporation of FA particles into the molecular structure of CS/Alg/FA. EDX analysis demonstrated that CS/Alg/FA biocomposite primarily contained elements C, O, N, Si, Al, and Ca, confirming the successful doping of FA particles into the polymeric structure of CS. Following the adsorption of MV2B dye, the surface of CS/Alg/FA (Fig. 4 e) became smoother and denser, with reduced roughness and particles. This indicated that MV2B molecules were trapped by the surface functional groups of CS/Alg/FA, filling in uneven surface areas and pores, resulting in a smoother surface [ 46 ]. EDX analysis after MV2B adsorption on CS/Alg/FA revealed an increase in the elemental content of C, further confirming the effective adsorption of MV2B dye on the surface of CS/Alg/FA. 3.2 ANOVA validation ANOVA is a crucial analysis in assessing the applicability of the model, and the characteristics of ANOVA are presented in Table 4 . The significance of the correlation coefficient was indicated by the F-value and the p-value, with higher F-values and lower p-values suggesting a more significant correlation. In the ANOVA analysis (Table 4 ), the model exhibited an F-value of 165.47 and a corresponding p-value of < 0.0001, indicating the statistical significance of the model [ 47 ]. The coefficient of determination ( R ²) value, close to 1 at 0.9953, suggested a high correlation between actual and predicted values [ 48 ]. In general, model terms with p-values less than 0.05 (Prob > F < 0.0500) were considered significant for MV2B dye removal under the chosen conditions [ 49 ]. As per Table 4 , BBD model terms A, B, C, AB, AC, and B² were found to be significant for MV2B dye removal. Terms with p-values greater than 0.05 were excluded from the second-order polynomial model to achieve a better fit. Consequently, the second-order polynomial model equation describing the relationship between the test factors and MV2B dye removal (response) was expressed as follows (Eq. 4): $$\text{M}\text{V}2\text{B} \text{r}\text{e}\text{m}\text{o}\text{v}\text{a}\text{l} \left(\text{%}\right){=+63.96+17.90\text{A}+15.40\text{B}+11.08\text{C}-7.40\text{A}\text{B}-10.95\text{A}\text{C}+4.25\text{B}\text{C}+3.90{\text{A}}^{2}-13.50{\text{B}}^{2} -21.0{\text{C}}^{2} \left(4\right)}_{}$$ Model validation can be accomplished by examining the relationship between the model predicted MV2B dye removal values and the actual MV2B dye removal values, along with assessing the nature of the residual distribution [ 50 ]. In Fig. 5 a, a normal probability plot of the model residuals is presented. The residuals exhibit a nearly perfect normal distribution, with points appearing closely aligned to a straight line. This observation affirms the accuracy of assumptions and the independence of the residuals [ 51 ]. Figure 5 b illustrates the relationship between predicted and actual MV2B dye removal (%), revealing a proximity between predicted and actual values. This alignment confirms the statistical validity of the model [ 52 ]. 3.3 Interactive impact of factors on MV2B removal The pH pzc test (Fig. 6 g) confirms the net surface charge of the adsorbent over a pH range of 3–11. Specifically, CS/Alg/FA maintained its functionality and adsorption capacity across a spectrum of pH conditions. The pronounced influence of pH on MV2B adsorption was ascribed to the variation in the surface charge of CS/Alg/FA at different pH values. Illustrated in Fig. 6 g, the pH pzc value for CS/Alg/FA was determined to be 8.0. When the pH exceeds the pH pzc (8.0), the surface charge of CS/Alg/FA composites shifts to a negative state, thereby enhancing the adsorption of cationic MV2B dye. To further explore the interactive effects of dose and pH on MV2B dye removal, 3D response surface plots and 2D contour curves were employed, as depicted in Fig. 6 . Figure 6 (a, b) pertaining to the significant interaction of dose and pH (AB) at a retention time of 100 minutes revealed that MV2B dye removal (%) escalated from 4.8–78.4% as the solution pH increased from 4 to 10. This phenomenon can be attributed to the negative surface charge of CS/Alg/FA at high pH (10), which facilitates the adsorption of MV2B cations by CS/Alg/FA through electrostatic forces, as described in Eq. (5). $${ {\text{C}\text{S}/\text{A}\text{l}\text{g}/\text{F}\text{A}}_{ }^{-} + {\text{M}\text{V}2\text{B}}^{+} ⟷ {\text{C}\text{S}/\text{A}\text{l}\text{g}/\text{F}\text{A}}_{ }^{-}\dots {}^{+}\text{M}\text{V}2\text{B} \left(5\right)}^{}$$ As the dosage of CS/Alg/FA increased from 0.02g to 0.1g, there was a gradual improvement in the removal of MV2B dye in Fig. 6 (a, b). This enhancement could be attributed to the correlation between the CS/Alg/FA dosage and the availability of active adsorption sites, with a higher dosage resulting in an increased number of active sites. Figure 6 (c, d) illustrates 3D and 2D plots depicting the impact of adsorbent dosage (A) and time (C) on MV2B dye removal (%). The findings indicate a rise in dye removal (%) as the adsorption time extended from 20 to 180 min. This phenomenon could be explained by the prolonged time facilitating the accumulation of MV2B dye molecules within the pores of CS/Alg/FA. Furthermore, Fig. 6 (e, f) demonstrates that the simultaneous increase in pH (B) and adsorption time (C) led to a gradual augmentation in dye removal (%). This occurrence could be attributed to both electrostatic attractions, as described earlier, and the continuous accumulation of MV2B dye molecules within the pores of CS/Alg/FA. 3.4 Adsorption study Figure 7 illustrates the adsorption capacity ( q t , mg/g) as a function of time, considering various initial concentrations of MV2B (20, 40, 60, 80, 100, 150, and 200 mg/L), while maintaining optimal conditions (adsorbent dosage of 0.10 g/100 mL, temperature at 25°C, and solution pH at 10). As the initial MV2B dye concentration increased from 20 mg/L to 200 mg/L, the quantity of MV2B dye molecules adsorbed onto the surface of CS/Alg/FA composites rose from 14.5 mg/g to 61.4 mg/g. This observation can be attributed to the concentration gradient acting as a driving force, compelling MV2B molecules towards the active adsorption sites and thereby enhancing the adsorption of CS/Alg/FA [ 53 ]. 3.5 Adsorption kinetics The rate parameters of the adsorption process for various initial MV2B dye concentrations on CS/Alg/FA composite were analyzed using the nonlinear pseudo-primary (PFO) [ 54 ] and nonlinear pseudo-secondary (PSO) [ 55 ] kinetic models. The expressions of the nonlinear equations for the kinetic models PFO and PSO are summarized in Table 5. The kinetic model parameters and R ² values were documented in Table 6 . The adsorption of MV2B dye molecules by CS/Alg/FA aligns with the PSO model, as evidenced by the high values obtained for the coefficient of determination (R²). Additionally, the computed q e ( q e , cal ) values closely matched the experimental q e ( q e,exp ) values [ 26 ]. This observation suggests that the adsorption process is through chemisorption of MV2B dyes onto the surface of CS/Alg/FA composite which primarily involves electrostatic interactions between negatively charged CS/Alg/FA particles and MV2B cations, along with the influence of electron sharing by the active functional groups on the adsorbent's surface. 3.6 Adsorption isotherms The interaction between MV 2B and CS/Alg/FA adsorbent was evaluated using Freundlich, Langmuir, and Temkin isotherms [ 56 – 58 ]. The nonlinear equations and descriptions for each isotherm model are provided in Table 5. Parameters for the various isothermal models have been determined and summarized in Table 7 , while the graphical display of the nonlinear curves of the isothermal models for the equilibrium adsorption data is depicted in Fig. 8 . Figure 8 clearly illustrated that both the Langmuir and Temkin isotherm models exhibit a superior fit to the experimental data, as indicated by the high coefficient of determination of 0.94 for both, as presented in Table 7 . This finding suggests that the MV 2B molecules adsorbed on the CS/Alg/FA surface form a monolayer with a uniform distribution of active sites, facilitated by the presence of various functional groups on the CS/Alg/FA surface [ 59 ]. The 1/n exponential term in the Freundlich model displays a value of 0.20, indicating that the adsorption process was favorable, and the adsorbed dye did not readily desorb from the solid surface [ 60 ]. The Langmuir model estimates a monolayer adsorption capacity ( q max ) of 63.4 mg/g for MV 2B using the CS/Alg/FA. This capacity was comparable to or higher than values reported for other adsorbents investigated by various researchers (Table 8 ). Consequently, CS/Alg/FA could be considered a preferable adsorbent for toxic cationic dyes such as MV2B. 3.7 Thermodynamic study Thermodynamic analyses of adsorption were conducted under ideal conditions (0.10 g/100 mL CS/Alg/FA, pH 10) at four different temperatures (298.15 to 328.15 K) to assess the spontaneity and irregularities of MV 2B adsorption on CS/Alg/FA. The equations and descriptions for the adsorption thermodynamic parameters are detailed in Table 5. The analysis of Van’t Hoff plot ( lnK d versus 1/T) (Fig. 9 ) facilitated the determination of ΔS° and ΔH°, represented by the intercept and slope of the resultant trend lines, respectively, as summarized in Table 9 . Negative ΔG° values affirmed the favorable spontaneous adsorption of CS/Alg/FA on MV2B dye [ 31 ]. Moreover, the positive ΔH° value (42.6 kJ/mol) indicated the heat-absorbing nature of the adsorption process, enhancing the adsorption rate and capacity of CS/Alg/FA with the increase of temperature. This phenomenon was attributed to the accelerated diffusion of MV2B dye molecules into the structural interstitials of CS/Alg/FA facilitated by heat transfer to the system [ 27 ]. Additionally, the positive ΔS° value (0.15 kJ/mol K) suggested that the rise in ambient temperature augments the degree of freedom for MV2B to bind to the surface of CS/Alg/FA [ 26 ]. 3.8 MV2B adsorption mechanism The adsorption mechanism of MV2B dye on the surface of CS/Alg/FA involving various types of interactions is illustrated in Fig. 10 . The surface of CS/Alg/FA encompasses diverse functional groups (-OH, -COOH, Si-O-Si, and PO 4 3− ), which, in alkaline environments at pH > 8, could become negatively charged and form electrostatic interactions with positively charged MV2B dye molecules. Furthermore, the abundant amino (NH 2 ) and hydroxyl (OH) groups in the CS/Alg/FA adsorbent provide opportunities for hydrogen bonding between these groups and the nitrogen atoms of MV2B dye molecules [ 26 ]. Additionally, Yoshida hydrogen bonding (Fig. 10 ) can occur between -OH on the surface of CS/Alg/FA composites and the aromatic ring in the structure of MV2B dye [ 31 ]. Moreover, the adsorption of MV2B dye on the CS/Alg/FA surface involves n-π interactions (Fig. 10 ) which facilitated by the lone-pair electron delocalization of the N and O heteroatoms of the CS/Alg/FA adsorbent to the π orbitals of the dye's aromatic ring [ 43 ]. In summary, the adsorption mechanism of MV2B on CS/Alg/FA involved electrostatic interactions, hydrogen bonding, and n-π interactions (Fig. 10 ). These interactions collectively contributed to the effective enhancement of MV2B dye adsorption on the CS/Alg/FA surface. 4. Conclusion Chitosan/algae/fly ash (CS/Alg/FA) adsorbent was successfully fabricated through physical modification for efficient removal of MV 2B dye. Optimization of adsorption parameters using Box-Behnken design resulted in the identification of optimum conditions (dose: 0.10 g/100 mL; pH: 10) for subsequent adsorption equilibrium studies. Owing to the diverse functional groups on the CS/Alg/FA surface, MV2B formed a monolayer with a uniform distribution of active sites on the CS/Alg/FA surface, primarily undergoing a chemisorption mechanism. The Langmuir model estimated the maximum adsorption capacity of CS/Alg/FA at 63.4 mg/g. Thermodynamic analysis revealed a negative ΔG° value, confirming the spontaneous nature of MV dye adsorption on CS/Alg/FA. The substantial adsorption of MV2B on CS/Alg/FA primarily arises from electrostatic forces between the negatively charged CS/Alg/FA and MV2B cations, as well as n-π and H-bonding interactions. This study underscores the promise of CS/Alg/FA as a potent adsorbent for the removal of organic dyes from aqueous systems. Declarations Acknowledgments The authors are thankful to the Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia for the research facilities. The author (Ruihong Wu) would like to thank Hengshui University for its scientific research funding (2023ZRZ01). The author (Zeid A. ALOthman) is grateful to the Researchers Supporting Project No. (RSP2024R1), King Saud University, Riyadh, Saudi Arabia. -Ethical Approval Not applicable - Competing interests The authors declare that they have no competing interests. -Authors Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Ruihong Wu, Elmira Kashi, Ali H. Jawad, Salis Awal Musa, and Zeid A. ALOthman, Lee D. Wilson. The first draft of the manuscript was written by Ruihong Wu, Elmira Kashi, Ali H. Jawad and all authors commented on previous versions of the manuscript. 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for MV2B removal by CS/Alg/FA\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/57569408e8a217fb50b747cd.png"},{"id":58354804,"identity":"f43e6bb2-e129-4714-9e54-ada5c4d6806c","added_by":"auto","created_at":"2024-06-14 09:45:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":282836,"visible":true,"origin":"","legend":"\u003cp\u003e3D surface plots and 2D contour curves of the interactive impact of variable pairs on MV2B removal response by CS/Alg/FA (plus pH\u003csub\u003epzc\u003c/sub\u003e plot of CS/Alg/FA)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/8d4642ea0c44064dcf053161.png"},{"id":58355536,"identity":"84c18dee-a910-4998-8f14-6e1df309a319","added_by":"auto","created_at":"2024-06-14 09:53:59","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":40014,"visible":true,"origin":"","legend":"\u003cp\u003eImpact of initial concentration and kinetic model regressions of MV2B removal by CS/Alg/FA (CS/Alg/FA dose=0.1g/100mL; pH=10; temperature=25°C; agitation speed=80 strokes/min)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/07fe00c563bd3ba2ffb79e8c.png"},{"id":58354803,"identity":"f7e943ac-6944-4c1d-8cb0-5d93b8cc6600","added_by":"auto","created_at":"2024-06-14 09:45:59","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":30722,"visible":true,"origin":"","legend":"\u003cp\u003eLangmuir, Freundlich and Temkin isotherm regressions for MV2B removal by CS/Alg/FA (CS/Alg/FA dose=0.1g/100mL; pH=10; temperature=25°C; agitation speed=80strokes/min)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/8894cd1b7d7512b1677165c9.png"},{"id":58354798,"identity":"89ba1831-f573-4071-ab6a-3c1960cdedc5","added_by":"auto","created_at":"2024-06-14 09:45:59","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":22768,"visible":true,"origin":"","legend":"\u003cp\u003eVan't Hoff plot of MV2B removal by CS/Alg/FA (CS/Alg/FA dose=0.1g/100mL; pH=10)\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/867e31b69757d7da40dd3b60.png"},{"id":58354802,"identity":"039353f6-71d2-482c-bf92-7e9d9d06c9ae","added_by":"auto","created_at":"2024-06-14 09:45:59","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":33431,"visible":true,"origin":"","legend":"\u003cp\u003eSuggested mechanism of adsorption for the removal of MV2B dye by CS/Alg/FA\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/b30f2548ede6bef144b69912.png"},{"id":67149759,"identity":"0b7df77b-ac5a-4b46-9dbc-abe0a0be2e99","added_by":"auto","created_at":"2024-10-21 16:14:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1565855,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/86f58e1a-7eec-46e7-9bd0-da38bfd94951.pdf"},{"id":58355534,"identity":"b3496141-6fa0-49ca-951c-5672d8ac4bf1","added_by":"auto","created_at":"2024-06-14 09:53:59","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":48548,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-4508283/v1/da21eba0da37a046c0c1bd96.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Organic and inorganic polymeric matrix of modified chitosan with algae and coal fly ash for cationic toxic dye removal: Multivariable optimization by Box-Behnken Design","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSynthetic dyes are increasingly employed across various industries, and the discharge of their effluents significantly contributes to water pollution [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These deleterious dyes pose severe threats to aquatic organisms and may exhibit teratogenic, mutagenic, or carcinogenic hazards to humans [\u003cspan additionalcitationids=\"CR3 CR4\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Consequently, the development of advanced technologies capable of effectively removing these pollutants has become imperative. Various treatment methods such as coagulation and flocculation [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], photocatalytic degradation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], electro flocculation [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], adsorption [\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], advanced oxidation processes [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], and anaerobic degradation [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] have been employed for the removal of organic pollutants from wastewater. Among these methods, adsorption stands out as the preferred method due to its cost-effectiveness and high efficiency [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe second most prevalent biopolymer following cellulose is chitosan (CS), a cationic biomaterial derived from the partial deacetylation of chitin [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. CS is a distinguished biopolymer due to its non-toxicity, biodegradability, abundant sources, preferable adsorption capacity, and biocompatibility [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The adsorption efficacy of CS can be ascribed to the abundant hydroxyl (-OH) and amine (NH\u003csub\u003e2\u003c/sub\u003e) functional groups on its polymeric backbone [\u003cspan additionalcitationids=\"CR21 CR22 CR23 CR24\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Nevertheless, CS faces challenges such as susceptibility to dissolution and swelling in acidic environments, a limited specific surface area, and inadequate mechanical stability, drawbacks that significantly constrain its practical utility in adsorption processes [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Given these limitations, enhancing the physicochemical properties of CS becomes imperative.\u003c/p\u003e \u003cp\u003eThe capability of chitosan (CS) hybrid composites to amalgamate the benefits of CS with biomaterials rich in functional groups, thereby enhancing surface area, porosity, chemical stability, mechanical stability, and reducing internal diffusion resistance, has garnered considerable attention [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In the fabrication of CS hybrid composites, materials with multifunctional moieties, including titanium dioxide nanoparticles [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], silica nanoparticles [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], clays [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], fly ash particles [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], algae [\u003cspan additionalcitationids=\"CR32 CR33\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], cellulose [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], and starch [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], have been employed to augment the adsorption and physicochemical properties of the composites.\u003c/p\u003e \u003cp\u003eNotably, coal fly ash (FA), a by-product from coal combustion in thermal power plants, primarily comprises metal oxides such as silica, and alumina in addition to unburned carbon [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Due to its chemical composition, preferable surface area, and porosity, FA can engage with CS biopolymers, making it a valuable component for the removal of organic water pollutants [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Moreover, algae (Alg) are a diverse group of aquatic organisms that have the capability to conduct photosynthesis. However, the surface functional groups of Alg species indicate the existence of various acidic/oxygenated functional groups in its biological molecular structure such as hydroxyl (-OH), carboxyl (-COOH), sulphate (SO\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), phosphate (-PO\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), and amino (\u0026minus;\u0026thinsp;NH\u003csub\u003e2\u003c/sub\u003e) groups. These acidic functional groups of Alg exhibit high affinity towards capturing toxic cationic dye species [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTherefore, the main aim of this study is to synthesize a chitosan (CS) based composite adsorbent by incorporating CS with algae (Alg) and fly ash (FA) (CS/Alg/FA). The incorporation of Alg into polymeric backbone of CS will enrich the CS functionality with acidic functional groups, and as a result improve its affinity towards capturing cationic dye molecules. Moreover, incorporating FA into the polymeric backbone of CS will improve its chemical stability, surface properties, and functionality. Thus, the efficacy of CS/Alg/FA composite was assessed for the removal of cationic methyl violet 2B dye (MV2B) from aqueous environment. To achieve optimal removal of MV2B dye, the adsorption key parameters of MV2B dye were optimized using response surface methodology and Box-Behnken design (RSM-BBD). Furthermore, various characterization methods (FTIR, FE-SEM, XRD) as well as equilibrium adsorption data (adsorption isotherm model, adsorption kinetic data, and thermodynamic parameters) were utilized to derive the plausible pathways to the adsorption of MV2B dye by CS/Alg/FA.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Materials\u003c/h2\u003e\n \u003cp\u003eThe fly ash (FA) utilized in this study was obtained from a thermal power station located in Kapar, Klang, Selangor, Malaysia. Algae (Alg) was procured from Henan Yuzhong Bioengineering in China. Methyl violet 2B (MV 2B) was acquired from R\u0026amp;M Chemicals, possessing a molecular formula of C\u003csub\u003e24\u003c/sub\u003eH\u003csub\u003e28\u003c/sub\u003eClN\u003csub\u003e3\u003c/sub\u003e with a molecular weight of 393.94 g/mol and a maximum absorption wavelength (\u0026lambda;\u003csub\u003emax\u003c/sub\u003e) of 584 nm. The chitosan (CS) powder used, with a degree of deacetylation of 80, was sourced from Tianjin Damao Chemical Reagent Factory in China. High analytical grade chemical reagents, such as acetic acid, hydrochloric acid, and sodium hydroxide, were supplied by R\u0026amp;M Chemicals.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Synthesis of Chitosan/Algae/Fly ash\u003c/h2\u003e\n \u003cp\u003eThe chitosan/algae/fly ash (CS/Alg/FA) biocompsite was formed by mixing 2 g CS powder, 1g algae powder, and 1 g fly ash powder in a glass beaker containing 80 mL of acetic acid solution (5% v/v) and stirred at room temperature for 24 h to form a viscous gel solution of CS/Alg/FA. Then, by injecting droplets of the CS/Alg/FA viscous solution into a beaker containing 1000 mL of sodium hydroxide solution (0.5 M) the viscous solution was transformed into beads form. To completely remove all traces of NaOH from the CS/Alg/FA beads, deionized water was used. Then the beads were left to oven-dry at 50\u0026deg;C overnight. The CS/Alg/FA sample was ultimately crushed to achieve a final consistent particle size (150 \u0026micro;m\u0026thinsp;\u0026lt;\u0026thinsp;particle size\u0026thinsp;\u0026lt;\u0026thinsp;250) for future investigations.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Characterization\u003c/h2\u003e\n \u003cp\u003eThe properties of CS/Alg/FA, including surface charge, surface area, surface morphology, elemental composition, surface crystalline and amorphous nature, and surface functional groups, were investigated using various techniques. These techniques include zero point of charge (pH\u003csub\u003epzc\u003c/sub\u003e) for surface charge analysis, a Micromeritics ASAP 2060 analyzer for surface area determination, scanning electron microscopy-energy dispersive X-ray (SEM-EDX, BRUKER, model: Apreo 2 S) for surface morphology and elemental composition analysis, X-ray diffractometer (XRD; X\u0026rsquo;Pert PRO, PANalytical) for examining crystalline and amorphous nature of the surface, and Fourier transform infrared spectroscopy (FTIR, Perkin-Elmer, Spectrum RX I) for studying surface functional groups.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4 Statistical optimization methodology\u003c/h2\u003e\n \u003cp\u003eBox-Behnken design (BBD) in response surface methodology RSM was used to optimize the adsorption process of MV2B by the CS/Alg/FA. Thus, three independent variables including solution pH, CS/Alg/FA dosage, and contact time were optimized by BBD. The design of the experiments and data processing was accomplished using Design-Expert 13.0 (Stat-Ease, USA). Values of inputs (factors) at various BBD levels are shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The relationship between the inputs (adsorption parameters) and output (MV2B removal) to determine the optimal operational conditions is essentially represented by the following expression (Eq. 1).\u003c/p\u003e\n \u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$\\mathbf{Y}={\\varvec{\\beta }}_{0}+\\sum _{}^{}{\\varvec{\\beta }}_{\\mathbf{i}}{\\mathbf{X}}_{\\mathbf{i}}+\\sum _{}^{}{\\varvec{\\beta }}_{\\mathbf{i}\\mathbf{i}}{\\mathbf{X}}_{\\mathbf{i}}^{2}+\\sum _{}^{}\\sum _{}^{}{\\varvec{\\beta }}_{\\mathbf{i}\\mathbf{j}}{\\mathbf{X}}_{\\mathbf{i}}^{}{\\mathbf{X}}_{\\mathbf{j}} \\left(1\\right)$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere \u003cem\u003eY\u003c/em\u003e represents the predicted MV2B removal % (output), \u0026beta;\u003csub\u003e0\u003c/sub\u003e is the constant coefficient, X\u003csub\u003ei\u003c/sub\u003e and X\u003csub\u003ej\u003c/sub\u003e are inputs (factors), and \u0026beta;\u003csub\u003eij\u003c/sub\u003e, \u0026beta;\u003csub\u003eii\u003c/sub\u003e, and \u0026beta;\u003csub\u003ei\u003c/sub\u003e are the coefficients of interaction, quadratic, and linear terms, respectively. The BBD matrix and results for the removal of MV2B are detailed in Table\u0026nbsp;2. For the MV2B removal experiments, 100 mL of MV2B solutions with fixed concentration 50 mg/L were introduced into a 250 mL Erlenmeyer flask along with a fixed amount of CS/Alg/FA. Subsequently, the flasks containing MV2B solutions were stirred for a specified duration in a shaking water bath at 80 rpm. Following the completion of the adsorption process, CS/Alg/FA was separated from the mixture using a 0.45 \u0026micro;m syringe filter. The quantity of MV2B in the solution was determined using a UV-Vis analyzer at the wavelength of 584 nm. The percentage of MV2B removal was calculated using the following equation (Eq.\u0026nbsp;2).\u003c/p\u003e\n \u003cdiv id=\"Equb\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e$$\\text{R} \\text{%}=\\frac{\\left({\\text{C}}_{\\text{o}}-{\\text{C}}_{\\text{e}}\\right)}{{\\text{C}}_{\\text{o}}} \\times 100 \\left(2\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cp\u003eThis equation calculates the percentage of MV2B removal, where C\u003csub\u003ee\u003c/sub\u003e represents the equilibrium concentration of MV2B in mg/L, and C\u003csub\u003e0\u003c/sub\u003e is its initial concentration.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Adsorption study of MV2B by CS/Alg/FA\u003c/h2\u003e\u003cp\u003eThe optimal values for the adsorption variables were determined using the Box-Behnken design (BBD), and these values were subsequently employed in the isotherm, kinetic, thermodynamic, and batch adsorption study [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. As indicated in Table\u0026nbsp;2, the optimal conditions leading to the maximum removal of MV 2B (78.4%) were a CS/Alg/FA dosage of 0.10 g/100 mL, a pH of 10, and a duration of 100 min. Following the methodology outlined in Section \u003cspan class=\"InternalRef\"\u003e2.4\u003c/span\u003e, optimal input parameters (dosage: 0.10 g/100 mL, pH: 10) and initial concentrations (C\u003csub\u003eo\u003c/sub\u003e) of MV 2B ranging from 20 to 250 mg/L were utilized for kinetic and isothermal studies in batch adsorption equilibrium experiments. Furthermore, the optimal input parameters (dosage: 0.10 g/100 mL, pH: 10) were employed for the removal of MV 2B (initial concentration\u0026thinsp;=\u0026thinsp;100 mg/L) using the CS/Alg/FA adsorbent material at various temperature ranges (25\u0026deg;C, 35\u0026deg;C, 45\u0026deg;C, 55\u0026deg;C). The adsorption capacity (q\u003csub\u003ee\u003c/sub\u003e, mg/g) of the CS/Alg/FA adsorbent for MV2B dye was calculated according to the following Eq.\u0026nbsp;(3).\u003c/p\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e$${\\text{q}}_{\\text{e}}=\\frac{\\left({\\text{C}}_{\\text{o}}-{\\text{C}}_{\\text{e}}\\right)\\text{V}}{\\text{W}} \\left(3\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cp\u003ewhere W (g) represents the CS/Alg/FA\u0026apos;s weight, and V (L) stands for the dye solution\u0026apos;s volume.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Characterization of CS/Alg/FA\u003c/h2\u003e\n \u003cp\u003eThe specific surface area results obtained through the Brunauer, Emmett, and Teller (BET) analysis are presented in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Specifically, the specific surface area (BET) was measured to be 1.43 (m\u003csup\u003e2\u003c/sup\u003e/g), Langmuir surface area at 16.5 (m\u003csup\u003e2\u003c/sup\u003e/g), pore volume at 0.0023 (cm\u003csup\u003e3\u003c/sup\u003e/g), with an average pore size of 14.4 (nm) which indicates a mesoporous structure of CS/Alg/FA composites in accordance with the International Union of Pure and Applied Chemistry (IUPAC) classification [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. Moreover, the N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherm of CS/Alg/FA (depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) aligns with the type IV isotherm, providing additional confirmation of the mesoporosity of CS/Alg/FA. Notably, the curve exhibits the H3 hysteresis loop associated with the presence of macropores in the pore network, further supporting the mesoporous pore size range (2\u0026ndash;50 nm) of CS/Alg/FA [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. This observation is reinforced by the inset in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The average pore size of CS/Alg/FA being significantly larger than that of MV2B dye molecules implies that MV2B molecules can easily access the pores of CS/Alg/FA [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe crystalline/amorphous structure of the synthesized CS/Alg/FA composite was investigated by XRD analysis as depicted in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The XRD spectra of CS/Alg/FA shows two broad and weak peaks corresponding to the characteristic peaks of chitosan (CS) and algae (Alg) at distinct 2\u0026theta; values (10.7\u0026deg;, 20.7\u0026deg;) [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. Additional peaks observed at 2\u0026theta;\u0026thinsp;=\u0026thinsp;27\u0026deg;, 38.4\u0026deg;, 44.7\u0026deg;, 64.8\u0026deg;, and 78\u0026deg; were attributed to fly ash (FA) particles [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e], including alumina (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) and quartz (SiO\u003csub\u003e2\u003c/sub\u003e). The XRD bands of CS/Alg/FA encompass all the characteristic peaks of CS, Alg, and FA, confirming the successful integration of algae and fly ash with the chitosan matrix.\u003c/p\u003e\n \u003cp\u003eThe FTIR spectra of CS/Alg/FA biocomposites before and after MV2B dye adsorption are presented in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea and Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, respectively. In the FTIR spectrum of CS/Alg/FA (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea), the peaks at 545 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicated a weak phosphate group attributed to the vibration of the O-P-O bond, originating from Algae [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. Additionally, characteristic peaks at 1070 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 790 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e represented asymmetric Si-O-Si bond and symmetric Si-O-Si bond stretching, respectively [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e], corresponding to the SiO\u003csub\u003e2\u003c/sub\u003e band in the fly ash. The FTIR spectra of CS/Alg/FA biocomposites also exhibited the main peaks of CS polymers, with assignments at 1155 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (skeletal vibration of C-O), 1400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (stretching vibration of C-N), 1560 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (stretching vibration of C-C), 1650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (N-H bending vibration), and 2880 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (symmetric and asymmetric C-H stretching vibrations of aliphatic groups) [\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e]. The FTIR spectra of CS/Alg/FA biocomposite after the adsorption of MV2B dye (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb) showed the same bands as observed in the spectra before adsorption (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea). Notably, the band at 3770 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is enhanced after MV2B adsorption, possibly attributed to hydrogen bonding interactions formed between CS/Alg/FA and dye molecules [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. Furthermore, the intensities of other relevant peaks corresponding to surface functional groups decreased, indicating that the enriched functional groups of CS/Alg/FA biocomposites were effectively engaged in the decolorization of MV2B dye.\u003c/p\u003e\n \u003cp\u003eSEM images of FA, CS, Alg, CS/Alg/FA, and CS/Alg/FA after the adsorption process (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea-e) were employed to assess changes in the surface morphology of CS/Alg/FA following the adsorption of MV2B dye. Fly ash (FA) particles exhibited embedded spherical objects of various sizes (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea). The surface of Chitosan (CS) appeared relatively smooth (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb). Algae particles displayed an amorphous nature (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec). In contrast, the surface of physically composited CS/Alg/FA (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed) exhibited roughness, slits, cavities, and pores, favorable for the effective adsorption of dye molecules. Faintly visible small-sized FA particles, representing spherical objects embedded in the surface of CS/Alg/FA biocomposite, indicated the successful incorporation of FA particles into the molecular structure of CS/Alg/FA. EDX analysis demonstrated that CS/Alg/FA biocomposite primarily contained elements C, O, N, Si, Al, and Ca, confirming the successful doping of FA particles into the polymeric structure of CS. Following the adsorption of MV2B dye, the surface of CS/Alg/FA (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee) became smoother and denser, with reduced roughness and particles. This indicated that MV2B molecules were trapped by the surface functional groups of CS/Alg/FA, filling in uneven surface areas and pores, resulting in a smoother surface [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. EDX analysis after MV2B adsorption on CS/Alg/FA revealed an increase in the elemental content of C, further confirming the effective adsorption of MV2B dye on the surface of CS/Alg/FA.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 ANOVA validation\u003c/h2\u003e\n \u003cp\u003eANOVA is a crucial analysis in assessing the applicability of the model, and the characteristics of ANOVA are presented in Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. The significance of the correlation coefficient was indicated by the F-value and the p-value, with higher F-values and lower p-values suggesting a more significant correlation. In the ANOVA analysis (Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e), the model exhibited an F-value of 165.47 and a corresponding p-value of \u0026lt;\u0026thinsp;0.0001, indicating the statistical significance of the model [\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e]. The coefficient of determination (\u003cem\u003eR\u003c/em\u003e\u0026sup2;) value, close to 1 at 0.9953, suggested a high correlation between actual and predicted values [\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e]. In general, model terms with p-values less than 0.05 (Prob\u0026thinsp;\u0026gt;\u0026thinsp;F\u0026thinsp;\u0026lt;\u0026thinsp;0.0500) were considered significant for MV2B dye removal under the chosen conditions [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e]. As per Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, BBD model terms A, B, C, AB, AC, and B\u0026sup2; were found to be significant for MV2B dye removal. Terms with p-values greater than 0.05 were excluded from the second-order polynomial model to achieve a better fit. Consequently, the second-order polynomial model equation describing the relationship between the test factors and MV2B dye removal (response) was expressed as follows (Eq. 4):\u003c/p\u003e\n \u003cdiv id=\"Equd\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e$$\\text{M}\\text{V}2\\text{B} \\text{r}\\text{e}\\text{m}\\text{o}\\text{v}\\text{a}\\text{l} \\left(\\text{%}\\right){=+63.96+17.90\\text{A}+15.40\\text{B}+11.08\\text{C}-7.40\\text{A}\\text{B}-10.95\\text{A}\\text{C}+4.25\\text{B}\\text{C}+3.90{\\text{A}}^{2}-13.50{\\text{B}}^{2} -21.0{\\text{C}}^{2} \\left(4\\right)}_{}$$\u003c/div\u003e\u003c/div\u003e\u003cp\u003eModel validation can be accomplished by examining the relationship between the model predicted MV2B dye removal values and the actual MV2B dye removal values, along with assessing the nature of the residual distribution [\u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e]. In Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea, a normal probability plot of the model residuals is presented. The residuals exhibit a nearly perfect normal distribution, with points appearing closely aligned to a straight line. This observation affirms the accuracy of assumptions and the independence of the residuals [\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e]. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb illustrates the relationship between predicted and actual MV2B dye removal (%), revealing a proximity between predicted and actual values. This alignment confirms the statistical validity of the model [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Interactive impact of factors on MV2B removal\u003c/h2\u003e\u003cp\u003eThe pH\u003csub\u003epzc\u003c/sub\u003e test (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eg) confirms the net surface charge of the adsorbent over a pH range of 3\u0026ndash;11. Specifically, CS/Alg/FA maintained its functionality and adsorption capacity across a spectrum of pH conditions. The pronounced influence of pH on MV2B adsorption was ascribed to the variation in the surface charge of CS/Alg/FA at different pH values. Illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eg, the pH\u003csub\u003epzc\u003c/sub\u003e value for CS/Alg/FA was determined to be 8.0. When the pH exceeds the pH\u003csub\u003epzc\u003c/sub\u003e (8.0), the surface charge of CS/Alg/FA composites shifts to a negative state, thereby enhancing the adsorption of cationic MV2B dye. To further explore the interactive effects of dose and pH on MV2B dye removal, 3D response surface plots and 2D contour curves were employed, as depicted in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e (a, b) pertaining to the significant interaction of dose and pH (AB) at a retention time of 100 minutes revealed that MV2B dye removal (%) escalated from 4.8\u0026ndash;78.4% as the solution pH increased from 4 to 10. This phenomenon can be attributed to the negative surface charge of CS/Alg/FA at high pH (10), which facilitates the adsorption of MV2B cations by CS/Alg/FA through electrostatic forces, as described in Eq. (5).\u003c/p\u003e\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e$${ {\\text{C}\\text{S}/\\text{A}\\text{l}\\text{g}/\\text{F}\\text{A}}_{ }^{-} + {\\text{M}\\text{V}2\\text{B}}^{+} ⟷ {\\text{C}\\text{S}/\\text{A}\\text{l}\\text{g}/\\text{F}\\text{A}}_{ }^{-}\\dots {}^{+}\\text{M}\\text{V}2\\text{B} \\left(5\\right)}^{}$$\u003c/div\u003e\u003c/div\u003e\u003cp\u003eAs the dosage of CS/Alg/FA increased from 0.02g to 0.1g, there was a gradual improvement in the removal of MV2B dye in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e (a, b). This enhancement could be attributed to the correlation between the CS/Alg/FA dosage and the availability of active adsorption sites, with a higher dosage resulting in an increased number of active sites. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(c, d) illustrates 3D and 2D plots depicting the impact of adsorbent dosage (A) and time (C) on MV2B dye removal (%). The findings indicate a rise in dye removal (%) as the adsorption time extended from 20 to 180 min. This phenomenon could be explained by the prolonged time facilitating the accumulation of MV2B dye molecules within the pores of CS/Alg/FA. Furthermore, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e (e, f) demonstrates that the simultaneous increase in pH (B) and adsorption time (C) led to a gradual augmentation in dye removal (%). This occurrence could be attributed to both electrostatic attractions, as described earlier, and the continuous accumulation of MV2B dye molecules within the pores of CS/Alg/FA.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Adsorption study\u003c/h2\u003e\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates the adsorption capacity (\u003cem\u003eq\u003c/em\u003e\u003csub\u003et\u003c/sub\u003e, mg/g) as a function of time, considering various initial concentrations of MV2B (20, 40, 60, 80, 100, 150, and 200 mg/L), while maintaining optimal conditions (adsorbent dosage of 0.10 g/100 mL, temperature at 25\u0026deg;C, and solution pH at 10). As the initial MV2B dye concentration increased from 20 mg/L to 200 mg/L, the quantity of MV2B dye molecules adsorbed onto the surface of CS/Alg/FA composites rose from 14.5 mg/g to 61.4 mg/g. This observation can be attributed to the concentration gradient acting as a driving force, compelling MV2B molecules towards the active adsorption sites and thereby enhancing the adsorption of CS/Alg/FA [\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Adsorption kinetics\u003c/h2\u003e\u003cp\u003eThe rate parameters of the adsorption process for various initial MV2B dye concentrations on CS/Alg/FA composite were analyzed using the nonlinear pseudo-primary (PFO) [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e] and nonlinear pseudo-secondary (PSO) [\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e] kinetic models. The expressions of the nonlinear equations for the kinetic models PFO and PSO are summarized in Table 5. The kinetic model parameters and \u003cem\u003eR\u003c/em\u003e\u0026sup2; values were documented in Table \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. The adsorption of MV2B dye molecules by CS/Alg/FA aligns with the PSO model, as evidenced by the high values obtained for the coefficient of determination (R\u0026sup2;). Additionally, the computed \u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e (\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e,\u003csub\u003e\u003cem\u003ecal\u003c/em\u003e\u003c/sub\u003e) values closely matched the experimental \u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e (\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ee,exp\u003c/em\u003e\u003c/sub\u003e) values [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. This observation suggests that the adsorption process is through chemisorption of MV2B dyes onto the surface of CS/Alg/FA composite which primarily involves electrostatic interactions between negatively charged CS/Alg/FA particles and MV2B cations, along with the influence of electron sharing by the active functional groups on the adsorbent\u0026apos;s surface.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.6 Adsorption isotherms\u003c/h2\u003e\u003cp\u003eThe interaction between MV 2B and CS/Alg/FA adsorbent was evaluated using Freundlich, Langmuir, and Temkin isotherms [\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e58\u003c/span\u003e]. The nonlinear equations and descriptions for each isotherm model are provided in Table 5. Parameters for the various isothermal models have been determined and summarized in Table \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, while the graphical display of the nonlinear curves of the isothermal models for the equilibrium adsorption data is depicted in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. Figure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e clearly illustrated that both the Langmuir and Temkin isotherm models exhibit a superior fit to the experimental data, as indicated by the high coefficient of determination of 0.94 for both, as presented in Table \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. This finding suggests that the MV 2B molecules adsorbed on the CS/Alg/FA surface form a monolayer with a uniform distribution of active sites, facilitated by the presence of various functional groups on the CS/Alg/FA surface [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e]. The 1/n exponential term in the Freundlich model displays a value of 0.20, indicating that the adsorption process was favorable, and the adsorbed dye did not readily desorb from the solid surface [\u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e]. The Langmuir model estimates a monolayer adsorption capacity (\u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003emax\u003c/em\u003e\u003c/sub\u003e) of 63.4 mg/g for MV 2B using the CS/Alg/FA. This capacity was comparable to or higher than values reported for other adsorbents investigated by various researchers (Table \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e). Consequently, CS/Alg/FA could be considered a preferable adsorbent for toxic cationic dyes such as MV2B.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.7 Thermodynamic study\u003c/h2\u003e\u003cp\u003eThermodynamic analyses of adsorption were conducted under ideal conditions (0.10 g/100 mL CS/Alg/FA, pH 10) at four different temperatures (298.15 to 328.15 K) to assess the spontaneity and irregularities of MV 2B adsorption on CS/Alg/FA. The equations and descriptions for the adsorption thermodynamic parameters are detailed in Table\u0026nbsp;5. The analysis of Van\u0026rsquo;t Hoff plot (\u003cem\u003elnK\u003c/em\u003e\u003csub\u003e\u003cem\u003ed\u003c/em\u003e\u003c/sub\u003e versus 1/T) (Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e) facilitated the determination of \u0026Delta;S\u0026deg; and \u0026Delta;H\u0026deg;, represented by the intercept and slope of the resultant trend lines, respectively, as summarized in Table \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e. Negative \u0026Delta;G\u0026deg; values affirmed the favorable spontaneous adsorption of CS/Alg/FA on MV2B dye [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. Moreover, the positive \u0026Delta;H\u0026deg; value (42.6 kJ/mol) indicated the heat-absorbing nature of the adsorption process, enhancing the adsorption rate and capacity of CS/Alg/FA with the increase of temperature. This phenomenon was attributed to the accelerated diffusion of MV2B dye molecules into the structural interstitials of CS/Alg/FA facilitated by heat transfer to the system [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. Additionally, the positive \u0026Delta;S\u0026deg; value (0.15 kJ/mol K) suggested that the rise in ambient temperature augments the degree of freedom for MV2B to bind to the surface of CS/Alg/FA [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.8 MV2B adsorption mechanism\u003c/h2\u003e\u003cp\u003eThe adsorption mechanism of MV2B dye on the surface of CS/Alg/FA involving various types of interactions is illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e. The surface of CS/Alg/FA encompasses diverse functional groups (-OH, -COOH, Si-O-Si, and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e), which, in alkaline environments at pH\u0026thinsp;\u0026gt;\u0026thinsp;8, could become negatively charged and form electrostatic interactions with positively charged MV2B dye molecules. Furthermore, the abundant amino (NH\u003csub\u003e2\u003c/sub\u003e) and hydroxyl (OH) groups in the CS/Alg/FA adsorbent provide opportunities for hydrogen bonding between these groups and the nitrogen atoms of MV2B dye molecules [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. Additionally, Yoshida hydrogen bonding (Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e) can occur between -OH on the surface of CS/Alg/FA composites and the aromatic ring in the structure of MV2B dye [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. Moreover, the adsorption of MV2B dye on the CS/Alg/FA surface involves n-\u0026pi; interactions (Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e) which facilitated by the lone-pair electron delocalization of the N and O heteroatoms of the CS/Alg/FA adsorbent to the \u0026pi; orbitals of the dye\u0026apos;s aromatic ring [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e]. In summary, the adsorption mechanism of MV2B on CS/Alg/FA involved electrostatic interactions, hydrogen bonding, and n-\u0026pi; interactions (Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e). These interactions collectively contributed to the effective enhancement of MV2B dye adsorption on the CS/Alg/FA surface.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eChitosan/algae/fly ash (CS/Alg/FA) adsorbent was successfully fabricated through physical modification for efficient removal of MV 2B dye. Optimization of adsorption parameters using Box-Behnken design resulted in the identification of optimum conditions (dose: 0.10 g/100 mL; pH: 10) for subsequent adsorption equilibrium studies. Owing to the diverse functional groups on the CS/Alg/FA surface, MV2B formed a monolayer with a uniform distribution of active sites on the CS/Alg/FA surface, primarily undergoing a chemisorption mechanism. The Langmuir model estimated the maximum adsorption capacity of CS/Alg/FA at 63.4 mg/g. Thermodynamic analysis revealed a negative ΔG\u0026deg; value, confirming the spontaneous nature of MV dye adsorption on CS/Alg/FA. The substantial adsorption of MV2B on CS/Alg/FA primarily arises from electrostatic forces between the negatively charged CS/Alg/FA and MV2B cations, as well as n-π and H-bonding interactions. This study underscores the promise of CS/Alg/FA as a potent adsorbent for the removal of organic dyes from aqueous systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors are thankful to the Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia for the research facilities. The author (Ruihong Wu) would like to thank Hengshui University for its scientific research funding (2023ZRZ01). The author (Zeid A. ALOthman) is grateful to the Researchers Supporting Project No. (RSP2024R1), King Saud University, Riyadh, Saudi Arabia.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e-Ethical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e- Competing interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e-Authors Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Ruihong Wu, Elmira Kashi, Ali H. Jawad, Salis Awal Musa, and Zeid A. ALOthman, Lee D. Wilson. The first draft of the manuscript was written by Ruihong Wu, Elmira Kashi, Ali H. Jawad and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e-Funding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e-Availability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eA.M. Hameed. Synthesis of Si/Cu Amorphous Adsorbent for Efficient Removal of Methylene Blue Dye from Aqueous Media. J. Inorg. Organomet. Polym. 30(8) (2020) 2881\u0026ndash;2889.\u003c/li\u003e\n \u003cli\u003eR. Al-Tohamy, S.S. Ali, F. Li, K.M. Okasha, Y.A.-G. Mahmoud, T. Elsamahy, H. Jiao, Y. Fu, J. 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Technol. 44(7)\u003cem\u003e\u0026nbsp;\u003c/em\u003e(2023)1170-1182.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 9 are available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-inorganic-and-organometallic-polymers-and-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"joip","sideBox":"Learn more about [Journal of Inorganic and Organometallic Polymers and Materials](https://www.springer.com/journal/10904)","snPcode":"10904","submissionUrl":"https://submission.nature.com/new-submission/10904/3","title":"Journal of Inorganic and Organometallic Polymers and Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Algae, Chitosan, Coal fly ash, Methyl violet 2B dye, Box-Behnken Design","lastPublishedDoi":"10.21203/rs.3.rs-4508283/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4508283/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, a composite adsorbent of chitosan/algae/coal fly ash (CS/Alg/FA) was synthesized to be an effective and renewable adsorbent for cationic methyl violet 2B dye (MV2B) removal from synthetic wastewater. The optimization of key adsorption variables (A: CS/Alg/FA dosage (0.02-0.1 g/100 mL), B: solution pH (4-10); C: contact time (20-180 min)) was carried out using the Box-Behnken design (BBD). The Langmuir isotherm model (coefficient of determination R² = 0.94) provided a good fit for the empirical data, and the pseudo-second-order model accurately described the kinetic data. The maximum adsorption capacity (\u003cem\u003eq\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e) of CS/Alg/FA for MV2B was determined to be 63.4 mg/g at 25 ⁰C. The possible adsorption mechanism of MV2B can be assigned to electrostatic attractions along with n-π, and H-bonding interactions. Thus, this comprehensive study underscores the potential of CS/Alg/FA as a preferable adsorbent for the removal of cationic organic dyes from industrial wastewater.\u003c/p\u003e","manuscriptTitle":"Organic and inorganic polymeric matrix of modified chitosan with algae and coal fly ash for cationic toxic dye removal: Multivariable optimization by Box-Behnken Design","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-14 09:45:54","doi":"10.21203/rs.3.rs-4508283/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-06-06T08:45:30+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-06T07:30:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"84358556324791839458773475839572512926","date":"2024-06-05T02:41:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"82688126261592882170014845159177574968","date":"2024-06-04T05:49:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"98013034408963242031728773043708999658","date":"2024-06-04T03:59:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"208609363757187687588309826274784527138","date":"2024-06-04T02:14:00+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-03T21:27:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"150797603260275027452603256854811386168","date":"2024-06-03T21:27:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"86840333193034173263684446301291958584","date":"2024-06-03T21:24:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"121502556095780732261617680052769050734","date":"2024-06-03T18:55:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"251045551131832130554070597236417313424","date":"2024-06-03T17:08:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"284703169185697019128543324453352189294","date":"2024-06-03T17:08:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"71029186506897997879606620915616184127","date":"2024-06-03T17:01:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"250487790083779942910679363589122169679","date":"2024-06-03T16:51:20+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-03T16:44:35+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-03T08:39:57+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-06-03T04:22:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Inorganic and Organometallic Polymers and Materials","date":"2024-05-31T10:32:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-inorganic-and-organometallic-polymers-and-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"joip","sideBox":"Learn more about [Journal of Inorganic and Organometallic Polymers and Materials](https://www.springer.com/journal/10904)","snPcode":"10904","submissionUrl":"https://submission.nature.com/new-submission/10904/3","title":"Journal of Inorganic and Organometallic Polymers and Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e186fc70-1ea0-4d6d-9216-9a8d1e33d26b","owner":[],"postedDate":"June 14th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-10-21T16:11:55+00:00","versionOfRecord":{"articleIdentity":"rs-4508283","link":"https://doi.org/10.1007/s10904-024-03241-x","journal":{"identity":"journal-of-inorganic-and-organometallic-polymers-and-materials","isVorOnly":false,"title":"Journal of Inorganic and Organometallic Polymers and Materials"},"publishedOn":"2024-10-18 15:58:16","publishedOnDateReadable":"October 18th, 2024"},"versionCreatedAt":"2024-06-14 09:45:54","video":"","vorDoi":"10.1007/s10904-024-03241-x","vorDoiUrl":"https://doi.org/10.1007/s10904-024-03241-x","workflowStages":[]},"version":"v1","identity":"rs-4508283","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4508283","identity":"rs-4508283","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}