Food-grade algae modified Schiff base-chitosan benzaldehyde composite for cationic methyl violet 2B dye removal: RSM statistical parametric optimization

Abstract This work aims to apply the use of food-grade algae (FGA) composited with chitosan-benzaldehyde Schiff base biopolymer (CHA-BD) as a new adsorbent (CHA-BA/FGA) for methyl violet 2B (MV 2B) dye removal from aqueous solutions. The effect of three processing variables, including CHA-BA/FGA dosage (0.02–0.1 g/100 mL), pH solution (4–10), and contact duration (10–120 min) on the removal of MV 2B was investigated using the Box-Behnken design (BBD) model. Kinetic and equilibrium dye adsorption profiles reveal that the uptake of MV 2B dye by CHA-BA/FGA is described by the pseudo-second kinetics and the Langmuir models. The thermodynamics of the adsorption process (ΔG°, ΔH°, and ΔS°) reveal spontaneous and favorable adsorption parameters of MV 2B dye onto the CHA-BA/FGA biocomposite at ambient conditions. The CHA-BA/FGA exhibited the maximum ability to absorb MV 2B of 126.51 mg/g (operating conditions: CHA-BA/FGA dose = 0.09 g/100 mL, solution pH = 8.68, and temperature = 25 °C). Various interactions, including H-bonding, electrostatic forces, π-π stacking, and n-π stacking provide an account of the hypothesized mechanism of MV 2B adsorption onto the surface of CHA-BA/FGA. This research reveals that CHA-BA/FGA with its unique biocomposite structure and favorable adsorption properties can be used to remove harmful cationic dyes from wastewater. NOVELTY STATEMENT The first novel aspect of this research work comes from the utilization of food-grade algae which contains various types of negative functional groups hydroxyl, carboxyl, and phosphate to modify a cationic biopolymer (Chitosan) to improve its adsorptive property toward removal of a cationic dye such as methyl violet 2B. The second novel aspect of this research work is to use the hydrothermal process to assist the grafting of an aromatic ring of benzaldehyde into the polymer matrix of the chitosan-food grade algae composite via a Schiff base linkage to improve its chemical stability and functionality.


Introduction
Industries producing plastics, beauty products, papers, fabrics, disinfectants, leather, and food have substantially impacted the quality of aquatic environments by releasing hazardous environmental pollutants such as toxic metals, medications, insecticides, and colouring agents into aquatic habitats (Hanafi and Sapawe 2020).The carcinogenic effects, high toxicity, and non-biodegradability of organic dyes make them a major threat to aquatic life and people (Rasheed et al., 2020).Since methyl violet 2B (MV 2B) is a cationic triaryl methane colorant with mutagenic and mitotic toxin properties, its discharge into the environment can cause ecological problems (Bonetto et al., 2015).Large amounts of MV 2B, a chemical used for dyeing textiles and paper are discharged into the environment via wastewater at the rate of 15% of the total amount of dyes produced globally (Tkaczyk et al., 2020).As a result, direct damage resulting from the greater release of organic dyes into industrial wastewater has a significant and negative impact on freshwater sources.Thus, it is necessary to treat wastewater more effectively before discharge into freshwater environments (Ramalingam et al., 2022).
Several technologies, including coagulation/flocculation (Mohamed Noor et al., 2022), adsorption (El-Kammah et al., 2022), membrane filtration (Li et al., 2023), photodegradation (Shi et al., 2023), and oxidation (Nath et al., 2023), were used effectively to remove synthetic dyes from polluted water.Nevertheless, most of these techniques have downsides, including excessive use of energy, the production of secondary waste, and the production of potentially hazardous byproducts (Zamora-Ledezma et al., 2021).Adsorption stands out as the most effective way to remediate wastewater because of its many desirable qualities, including its low cost, simplicity of application, tunable operation parameters, good selectivity, and high efficiency (Rathi and Kumar 2021;Akkari et al., 2023;Beigi et al., 2023;).
Chitosan (CHA) is a cationic biodegradable polymer composed primarily of linear D-glucosamine chains, according to the level of deacetylation (Hussain et al., 2023;Emara et al., 2023).Antibacterial activity, nontoxicity, simple modification, cost-effectiveness, environmental friendliness, and biodegradability are just a few of the numerous benefits of CHA, a bioactive polymer (Bakshi et al., 2020).CHA has been favored over many other materials used as adsorbents for dyes owing to its high adsorption capacity, reactive functional groups, and relatively high rate of adsorption (T€ urker & Baran 2018;Zain et al., 2023;Mallakpour et al., 2023).CHA's drawbacks limit its use because of issues such as its weak mechanical strength, solubility in many organic acids, development of back pressure, poor surface area, and rapid swelling (Jawad et al., 2022).In view of these defects, it was necessary to find ways to improve the CHA mechanism in the adsorption process, including physical modification, chemical modifications, and photo transformation (Wang and Zhuang 2022).Cross-linking and grafting are two popular chemical modification methods used to modify CHA into CHA-composite materials (Saheed et al., 2021).Through the covalent attachment of a suitable functionality to CHA, grafting enables the structural modification of CHA and the creation of versatile derivatives (Normi et al., 2022).Additionally, CHA's hydrophilicity and adsorption properties are likely to be affected by the grafting strategy (Saheed et al., 2021).
Bio-adsorbents, derived from natural sources such as agricultural waste, biomass, or microorganisms, have gained significant attention as effective alternatives to traditional adsorbents (Mohamed et al., 2022;Solgi et al., 2023).These bio-adsorbents possess a variety of functional groups, such as hydroxyl, carboxyl, and amine groups, which enable favorable adsorption with waterborne pollutants (Shayesteh et al., 2016;Bayramo glu et al., 2017;Kheradmand et al., 2022;Bayramoglu et al., 2023;Bayramoglu et al., 2022;Steiger et al., 2023).Algae can serve as ideal biosorbents for the removal of pollutants, according to a variety of studies (Robledo-Padilla et al., 2020;Abdulhameed et al., 2022).Algal biomass is regarded as affordable, readily available, has a large surface area, reactive functional groups, and has favorable adsorption properties.Algae biomass possesses a variety of reactive functional groups (carboxyl ÀCOOH; amino ÀNH 2 ; hydroxyl ÀOH; phosphate ÀPO 4 À3 ) (Abdulhameed et al., 2022;Saket et al., 2022).These groups enable it to adsorb a wide variety of inorganic and organic contaminants by electrostatic attraction, complexation, and ion exchange (Jawad et al., 2023).However, there are a few drawbacks to previously mentioned biosorbents (CHA and algae), including weak mechanical properties, poor thermal stability, and chemical stability.Algae and CHA can be combined to provide a solution to this issue and obtained on biocomposite has good physicochemical properties and an assortment of functional groups, which provides the context of the present study.
The main objective of this research is to modify chitosan (CHA) a cationic biopolymer by food-grade algae (FGA) which is a rich biomass material with various negative functional groups that are responsible for improving the CHA's affinity toward cationic dyes.The physicochemical property of CHA was further improved by the formation of Schiff base system with benzaldehyde (BA).The potential application of a composite material consisting of chitosan-benzaldehyde/food grade algae (CHA-BA/FGA) was evaluated toward the removal of methyl violet 2B (MV 2B) dye as a model of cationic dye from an aqueous environment.Moreover, the physicochemical properties of the CHA-BA/FGA biocomposite were characterized by several methods, such as scanning electron microscopy (SEM), zero point of charge analysis (pHpzc), CHN-O analysis, Fourier transform infrared (FTIR) spectra, and X-ray diffraction (XRD).The operational parameters (CHA-BA/FGA dosage, pH, and time) influencing the MV 2B dye removal (%) were investigated using the statistical technique of response surface methodology (RSM).Kinetic and thermodynamic adsorption studies were carried out with the MV 2B dye and CHA-BA/FGA.

Synthesis of CHA/FGA
CHA/FGA biocomposite was synthesized by pouring 50 mL of 5% (v/v) CH 3 COOH into a combination of CHA (1 g) and FGA (1 g) at room temperature (RT¼ 25 ± 2 C).The sticky combination is then put in the ultrasonic device for 25 min to ensure the components are well combined.The next stage included transforming the sticky mixture into CHA/FGA beads by injecting the viscosity mixture at a rate of 1 mL/min from a syringe into a 1000 mL NaOH (0.5 M) solution.To guarantee that any residual amounts of NaOH solution were eliminated, the formed CHA/FGA beads were washed numerous times with distilled water.

Grafting of CHA/FGA with BA
The grafting reaction was performed by adding 100 mL (2% BA solution) to the fresh CHA/FGA beads inside a hydrothermal reactor.Then, the reactor was covered with a lid and left in the oven at 100 C for 12 h.The grafted beads (CHA-BA/FGA) were subsequently dried in an oven (24 h) at 60 C after having gently rinsed with distilled water.The CHA-BA/FGA beads were crushed into a powder with a particle size below 250 mm.The preparation steps of CHA-BA/FGA are presented in Figure 1.The CHA-BA/FGA biocomposite was characterized using a variety of analytical methods and procedures described in the supplementary material (Text S1).

Statistical optimization methodology
With the RSM-BBD approach, all the impacts of fundamental adsorption parameters, such as CHA-BA/FGA mass, pH, and contact duration on MV 2B removal were examined.Design Expert 13.0 software (Stat-Ease) was employed for designing the adsorption and process optimization operations as well as the statistical evaluation of the data.Table 1 provides the studied variables' levels together with their respective symbols.Therefore, the link between the input components and the efficiency of removing MV 2B dye was inferred using a second-order quadratic equation.The polynomial statistical model has a corresponding mathematical formula, according to Eq. ( 1), where Y is the estimated response;  were produced from BBD.Table 2 summarizes the studied parameter ranges and the observed responses (MV 2B dye removal).In the first experimental stage, a defined quantity of CHA-BA/FGA biocomposite was added to the Erlenmeyer flask (containing 100 mL of MV 2B).Then, the samples were moved to an orbital shaker (GFL Orbital Shaker 3017, Germany) and stirred gently (110 strokes/min) for a given period.By filtering the samples with 0.45 mm nylon syringe filters, adsorbent-free dye solutions were produced.The residual dye concentration was assessed via spectrophotometry (HACH DR 3900) at k max ¼ 575 nm (HACH DR 3900).The following Eq.( 2) was used to evaluate the efficacy (R%) of the dye removal: where C o and C e are the initial and equilibrium MV 2B dye concentrations (mg/L), respectively.
Adsorption study of MV 2B on CHA-BA/FGA Employing batch equilibration experiments, the quantity of absorbed dye onto CHA-BA/FGA was estimated.The highest dye removal (R ¼ 80.02%) employed a fixed dosage (0.1 g) CHA-BA/FGA, time ¼ 65 min, and pH ¼ 10 as per the BBD model (run 4).A comprehensive adsorption study was done at equilibrium utilizing these ideal values with a variety of dye concentrations (20, 40, 60, 80, 100, 150, and 200 mg/L).Then, to produce batch adsorption experiments for MV 2B, the identical stages of the methodology outlined in the Section for "Statistical optimization methodology" were followed.Eq. ( 3) was relied upon to calculate the dye adsorption ability (q e , mg/g) of CHA-BA/FGA.
where V (L) is the MV 2B solution volume, and W (g) is the weight of CHA-BA/FGA.

Results and discussion
Characterization of CHA-BA/FGA The estimation of the elemental composition of CHA-BA/FGA biocomposite was provided by CHN-O analysis.
Table 3 shows the findings of elemental composition for CHA-BA/FGA biocomposite.According to the CHN-O elemental results, the CHA-BA/FGA biocomposite has the following composition: 44.88% C, 6.72% H, 41.29% O, and 7.11% N.
To acquire insight on about the crystalline nature of CHA-BA/FGA, XRD analysis was conducted, where the XRD spectral profile of CHA-BA/FGA is observed in Figure 1.The Schiff base present in the CHA-BA/FGA is accountable for the peak shown at 2h ¼ 6.5 in CHI-BZA's diffraction pattern.This results from the deformation of the hydrogen bonds in the CHA skeleton and the formation of an imine (C ¼ N) bond (Normi et al., 2022).The XRD   pattern of CHA-BA/FGA displayed in Figure 2 also exhibits a distinctive peak at 22.5 , which is related to the crystalline structure of cellulose (corresponding to FGA), the semi-crystalline nature of CHA via H-bonding interactions between the CHA's -OH and -NH 2 groups (Chen et al., 2016;Normi et al., 2022).
The functional groups of the biocomposite were identified using FTIR spectra in Figure 3, where the spectra before dye adsorption (a) for CHA-BA/FGA before MV 2B dye treatment, and after adsorption (b) for CHA-BA/FGA with MV 2B dye are shown.The large peaks (3350-3670 cm À1 ) are caused by the -NH and -OH stretching vibrations (Eltabley et al., 2022;Abdulhameed et al., 2022).The band seen at (2920 cm À1 ) is due to the stretching vibrations of aliphatic bonds (C-H).The Schiff base grafting that took place in the CHA chains was demonstrated by the C¼N IR band at 1640 cm À1 .This peak also represents the C¼O stretching vibration seen in a wide variety of organics such as carboxylic acids, ketones, esters, etc. (Kurczewska et al., 2022).The peaks at 1320 cm À1 , 1030 cm À1 , and 540 cm À1 are ascribed to C-N stretching, C-O stretching, and P-O bonds, respectively (Abdulhameed et al., 2022).The IR spectra of CHA-BA/FGA after adsorption Figure 3(b) shows that is largely identical to CHA-BA/FGA, with a noticeable modification in multiple bands, indicating that the MV 2B dye adsorption process involved the participation of the fundamental functional groups of CHA-BA/FGA.
To evaluate the adsorbent morphology and chemical constituents of CHA-BA/FGA and (CHA-BA/FGA)-dye system, SEM-EDX analysis was performed.Figure 4(a and b), respectively, depict SEM-EDX data of CHA-BA/FGA and (CHA-BA/FGA)-MV 2B. Figure 3(a) reveals that the surface of the CHA-BA/FGA is heterogeneous and rough.The surface of CHA-BA/FGA became noticeably more homogenous after MV 2B adsorption, and the tiny roughness was noticeably reduced, showing that the dye molecules were adsorbed onto the CHA-BA/FGA surface.The EDX analysis indicates that the biopolymer structure of CHA-BA/FGA before and after adsorption contains several elemental species (O, C, N, and P).
The pH level at which the positive and negative surface charges of CHA-BZ/FGA's become equal is referred to as the pH pzc .Fig. S1 displays the pH pzc curve of the CHA-BA/ FGA biocomposite.The adsorbent material has a negative surface charge when the pH level exceeds the pH pzc value, making it more suited for the adsorption of positive-charged compounds (Bonetto et al., 2015).Therefore, it is possible to conclude that the uptake of MV 2B by the CHA-BA/FGA biocomposite ought to be preferred in solutions with a pH above 7.6 (pH pzc value, cf.Fig. S2).At such conditions, strong electrostatic forces can arise between the negative charge of CHA-BA/FGA composite and the positive charge of MV 2B dye in the solution (Bonetto et al., 2015).

Box-Behnken design
The BBD method was used to analyze the impacts of three independent process parameters on MV 2B removal efficiency (response variable).BBD conceived a total of seventeen trials (runs) (Table 2).These factors were the CHA-BA/FGA dose (A), pH (B), and time (C).A quadratic polynomial was adopted to describe the statistical link between the outcome and the components of the process.Eq. ( 4) provides a presentation of the empirical links between the tested component and the response: Equation ( 4) demonstrates that the coefficients for dosage (A), pH (B), and time (C) all have a positive impact on the removal efficiency (%) of MV 2B.Therefore, it follows that increasing the dosage, pH, and duration results in a higher dye removal (%).

Validation study
The model was evaluated by groups of variable combinations (adsorbent dosage, pH, and duration) within their experimental ranges to determine the precision of the optimization procedure.The robustness of the BBD model was verified using the anticipated results of the model and the actual outcomes (Table 4).According to Table 4, the highest decolorization % derived from real value was 85.28%, which is in good agreement with the anticipated value of 82.16% from the BBD model.Therefore, it is possible to employ the BBD model for increasing the level of dye removal.

Analysis of variance
A basic and crucial methodology for assessing the applicability of the model for MV 2B dye removal and its accuracy is the analysis of variance (ANOVA), where Table 5 lists the corresponding results.The F-values, sums of squares, and pvalues were used to identify significant variables.The ANOVA model exhibits statistical significance, as evidenced by the MV 2B dye model F value of 25.49 (Ashrafi et al., 2021).The MV 2B dye removal determination coefficient (R 2 ) is 0.97, where these findings show that the computed and empirical data are in very good agreement.As well as a high adjusted R 2 value of 0.93, showing a strong relationship between actual and predicted data (Rout et al., 2017).In general, according to Table 5, variables with a p-value > 0.05 are deemed insignificant for the MV 2B dye removal, and vice versa.As a result, the terms within the MV 2B model A, B, C, AC, BC, A 2 , and B 2 were found to be substantial.
The graphical technique validates the model and describes the residuals' distribution.Normal probability plots are used to evaluate model residual distributions (Moghaddam et al., 2018).The residual values in the normal probability plot, as seen in Figure 5(a), are nearly a straight line, which indicates that the residuals are independent and that the data points are regularly and fully scattered.The association between the anticipated and real levels of MV 2B dye elimination (%) by CHA-BA/FGA was demonstrated in Figure 5(b).A straight line connecting the anticipated and actual values shows that the model was statistically validated.

Effect of input variables
As illustrated in Figure 5(c), a perturbation plot was employed to examine the simultaneous impact of three input parameters on the MV 2B dye removal, where these three input factors are crucial for optimizing the effectiveness of the dye removal.The sensitivity of the MV 2B removal efficiency to the dose of CHA-BA/FGA (variable A) is indicated by the steepness of the curve for variable A. By loading additional amounts of CHA-BA/FGA into the MV 2B solution, the active sites available for the dye increase.In general, the efficiency of dye removal decreases when pH (variable B) rises.The time curve (variable C) demonstrates the response's sensitivity to working time levels.

Three-dimensional response surface
To gain an understanding of the relationships between independent parameters and dye elimination (%) effectiveness, the three-dimensional (3D) response surfaces along with twodimensional contours (2D) were constructed using the quadratic model.Every single combination of input factors shown in Table 5 was investigated in terms of their interactions.CHA-BZ/FGA dosage and time have a substantial influence on the effectiveness of the dye removal, as indicated by a pvalue of 0.029 (Table 5).The MV 2B removal (%) grew with both the amount of CHA-BA/FGA used and the period of the process to run. Figure 6 illustrates important interactions between the investigated variables impacting MV 2B dye absorption ability, including CHA-BA/FGA biocomposite vs time (AC) and pH vs time (BC).A 3D plot showing the correlation between dose and time is shown in Figure 6(a), whereas Figure 6(b) is a contour plot of the same data.This outcome may be attributable to the increase of adsorbent surfaces and active adsorption sites brought about by a higher adsorbent dose (Ali et al., 2019).Figure 6(c and d) shows the 3D plot and contour plot, respectively, for the relationship between the pH and the duration, where a high value of pH over a long period leads to an increase in dye removal (%).CHA-BA/FGA obtains a negative charge at pH 10, which favors the binding of positively charged dyes like MV 2B.

Adsorption study
By reaching a preset quantity of CHA-BA/FGA biocomposite (0.09 g/100 mL) at the initial pH of 8.68, employing various dye concentrations (20, 50, 80, 100, 150, and 200 mg/L), the significance of the contact time and initial dye concentration on the adsorption capacity of the biocomposite was identified.Figure 7(a) depicts the graphs of the adsorption capacity (q t , mg/g) of the MV 2B dye by CHA-BA/FGA at the initial levels of dye.Increasing the MV 2B dye concentration from 20 to 200 mg/L directly affects the adsorption capacity of CHA-BA/FGA as observed by the increase from 7.44 to 107.2 mg/g.The CHA-BA/FGA biocomposite will adsorb more dye species at a higher initial MV 2B concentration.Hence, MV 2B dye will fill all the unoccupied adsorption sites on the biocomposite surface to enable saturation of the adsorption sites (Trinh et al., 2021).

Kinetic dye adsorption study
Kinetic investigations are required to fully interpret the MV 2B dye uptake mode onto the CHA-BA/FGA biocomposite surface and determine the rate-controlling phase that is most responsible for it.To determine kinetic parameters, commonly, pseudo-first order (Lagergren 1898; PFO, Eq. 5) and pseudo-second order (Ho and McKay 1998; PSO, Eq. 6) kinetic models were employed.
k 1 is the rate constant of PFO, with a value of 1/min, while k 2 is the rate constant of PSO, with a value of g/mg min.
Table 6 lists the values of the kinetic factors for the PFO and PSO models.According to the findings shown in Table 6, the adsorption of MV 2B dye onto the CHA-BA/FGA biocomposite matched the PSO model adequately.The PSO illustrates higher R 2 values and a close correlation between empirical (q e,exp ) and computed (q e , cal ) values in comparison to the PFO model.Briefly, chemisorption controls the adsorption process of MV 2B dye onto the CHA-BA/FGA biocomposites (S ¸enol 2021).

Isotherm study
Adsorption isotherm results at equilibrium provide insight into the interaction between the MV 2B dye and the CHA-BA/FGA biocomposite.Isotherm models such as the Langmuir, Freundlich, and Temkin equations have been developed that describe the equilibrium features of adsorption.Isothermal behavior that follows the Langmuir model as defined by Equation ( 7), describes the monolayer adsorption process at uniform adsorption sites (Langmuir 1918).
The Langmuir maximum adsorption capacity, q max (mg/g) of the MV 2B adsorbate and K a denotes the Langmuir constant (L/mg).
For the clarification of the multilayer adsorption of adsorbate and heterogeneity of the adsorbent, the Freundlich isotherm model is adopted (Freundlich 1906).Eq. 8 outlines the Freundlich isotherm, where 1/n: adsorption intensity, K f : Freundlich constant (mg/g) (L/mg) 1/n .The Temkin isotherm model indicates that a homogeneous distribution of binding energies, to the point of maximal binding energy, characterizes adsorption and that the heat of adsorption heat for all bound species is reduced in a linear way with an increase in the adsorbate surface coverage (Temkin 1940).Eq. 9 outlines the Temkin isotherm.
Parameter values for the MV 2B dye adsorption isotherms are included in Table 7, whereas the nonlinear graphs (C e versus q e ) are noted in Figure 7(b).Since Table 7 shows that the results provide support that monolayer  adsorption of the MV 2B dye occurs on the CHA-BA/FGA biocomposite surface, where the Langmuir model has a higher R 2 (0.97) than the Freundlich and Temkin models (0.93) (Ahmad and Ansari 2021).In Table 8, the q max value for MV 2B (126.51 mg/g) dye adsorption onto CHA-BA/FGA is compared with other adsorbents that have been recently investigated from the literature.The present study highlights the utility of synthetic CHA-BA/FGA with its favorable adsorption properties for removal of toxic cation dyes from industrial effluent.

Thermodynamic study
MV 2B dye adsorption onto the CHA-BA/FGA biocomposite surface was investigated in terms of spontaneity and practicality by determining the adsorption thermodynamic parameters and analyzing the degree of molecular disorder at the CHA-BA/FGA/liquid interface.The following Eqs.
(10-12) can be used to compute the standard difference for various thermodynamic adsorption parameters: entropy change (DS ), enthalpy change (DH ), and Gibbs free energy change (DG ) (Suhaimi et al., 2022): The plot of ln K d versus 1/T (Figure 8) provides information on the numerical values of the thermodynamic variables (DH and DS ).The negative value for DG in Table 9 indicates that the MV 2B dye is bound favorably and spontaneously onto the CHA-BA/FGA biocomposite surface.In fact, the positive values of DS and DH show that the adsorption of the MV 2B dye onto the CHA-BA/FGA biocomposite  was endothermic and that there was a noticeable rise in molecular disorder throughout that process (Suhaimi et al., 2022).The enhanced diffusion of adsorbate (MV 2B) inside the interspaces structure of the CHA-BA/FGA at elevated temperatures may also be connected to the role of temperature on the internal structure of CHA-BA/FGA.

Adsorption mechanism of MV 2B dye
The active groups of the CHA-BA/FGA biocomposite are capable of adsorbing cationic contaminants since the adsorbent is comprised of CHA and FGA, both of which naturally contain abundant active groups.The active groups of CHA-BA/FGA having negative surface charges in basic media interact electrostatically with the positive group of the MV 2B dye (Figure 9).The H-atom sites that exist on the CHA-BA/FGA's surface, which interacts with the nitrogen in the MV 2B dye's structure likely serves as a vital element to the MV 2B's adsorption.The aromatic rings of the MV 2B dye engage with the N and O groups in the CHA-BA/FGA to create n-p interactions, which enhance the adsorption of the MV 2B dye, which provides another account for the binding effectiveness of CHA-BA/FGA in the adsorption process (Normi et al., 2022).Interactions between the aromatic system of the MV 2B and the BA ring present in CHA-BA/FGA led to the development of the p-p stacking as shown in Figure 9.

Conclusion
MV 2B dye was efficiently removed from aquatic environments using a unique hybrid multifunctional biocomposite denoted as CHA-BA/FGA.According to the BBD model, the CHA-BA/FGA dosage (0.1 g), pH 10, and contact period (65 min) parameters led to high removal of MV 2B (80.2%).
With MV 2B removal, the derived models had an average Fvalue of 25.49, where it was found that the R 2 value for the BBD model (MV 2B removal) was 0.97.The kinetic and isotherm data showed that the adsorption behavior of MV 2B dye was attributed mainly to monolayer chemisorption.
According to the Langmuir model, the CHA-BA/FGA has a q max of 126.51 mg/g.Many interactions, including p-p stacking, electrostatic forces, n-p stacking, and H-bonding account for the MV 2B dye adsorption by CHA-BA/FGA.The CHA-BZ/FGA material prepared herein demonstrates the potential of this adsorbent for a wide range of applications, including the removal of heavy metal ions, cationic dyes, and pharmaceuticals from aqueous environments.The blending of FGA and CHA, along with surface functionalization with BA provide favorable surface interactions and stability that impart favorable properties, which make the biocomposite suitable for efficient and effective remediation of water contaminated with these types of pollutants.

Figure 4 .
Figure 4. SEM images and EDX results of (a) CHA-BA/FGA and (b) CHA-BA/FGA after adsorption of MV 2B.

Figure 5 .
Figure 5. (a) Normal probability plot of residuals for (a) MV 2B removal; (b) plot of the relationship between the theoretical and real values of MV 2B; (c) perturbation plot showing the effect of factors (A) dose, (B) pH, and (C) time) on MV 2B removal.

Figure 9 .
Figure 9. Illustration of the possible interaction between CHA-BA/FGA and MV 2B including electrostatic forces, hydrogen bonding, p-p stacking, and n-p interactions at alkaline pH (8.7) and 25 C.

Table 1 .
Codes and actual variables and their levels in BBD.

Table 2 .
The 3-variables BBD matrix and experimental data for MV 2B dye removal.

Table 4 .
The predicted value and actual value of the validity of BBD model.

Table 8 .
Comparison of the adsorption capacity of the MV 2B dye with different types of adsorbent materials.