Facile Synthesis of Cross-Linked Chitosan-Genipin/Algae Composite Adsorbent for Cationic Methyl Violet Dye Removal: Robust Modeling of Adsorption Using the Box–Behnken Design

A biopolymer matrix of chitosan (CTS) and algae (AGA) was chemically modified with a natural genipin (GEN) cross-linker agent via hydrothermal process. The resulting green adsorbent (CTS-GEN/AGA) was evaluated for removal of the cationic dye (methyl violet, MV) from aqueous media. The optimization of MV adsorption onto CTS-GEN/AGA was performed using the Box–Behnken design (BBD), considering the variables of adsorbent dose (0.02–0.1 g/100 mL), pH (4–10), and time (20–300 min). The CTS-GEN/AGA demonstrated the highest MV removal (76.49%) for optimal operational parameters: CTS-GEN/AGA dosage (0.0938 g/100 mL), pH (8.4), and contact time (215.3 min). The adsorption isotherm analysis revealed a close fit between the experimental data of MV adsorption and the Temkin model. Furthermore, the adsorption kinetics are well-described by the pseudo-second-order model. The maximum adsorption capacity of CTS-GEN/AGA was 71.9 mg/g at 25 °C. The probable adsorption mechanism can be assigned to H-bonding, electrostatic forces, and n–π stacking interactions. These findings highlight the potential of CTS-GEN/AGA as an effective adsorbent for treatment of wastewater for the removal of organic dyes.