Polymeric Matrix of Modified Chitosan with Algae and Coal Fly Ash for a Toxic Cationic Dye Removal: Multivariable Optimization by Box-Behnken Design

Herein, a composite adsorbent of chitosan/algae/coal fly ash (CS/Alg/FA) was synthesized to be an effective and renewable adsorbent for the removal of cationic dye (methyl violet 2B dye: MV2B) from synthetic wastewater. The physicochemical characteristics of CS/Alg/FA were assessed utilizing various analytical techniques, such as XRD, BET, FTIR, pH_pzc, and SEM–EDX. 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). Based on the BBD model, the optimal removal of MV 2B (78.4%) was achieved by employing a dosage of 0.1 g of CS/Alg/FA at a pH of 10 and a contact time of 100 min. 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 ℃. The possible adsorption mechanism of MV 2B 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.