High-performance chitosan/blue-green algae (Cyanobacteria) nanocomposite for rapid and optimized removal of organic pollutant from wastewater

This work explores the synthesis and utilization of a green composite material based on chitosan and blue-green algae biomass for the effective removal of Acid Red 35, a recalcitrant anionic dye, from aqueous solutions. Chitosan-Blue-Green Algae (Ch-BGA) nanocomposite was prepared by cross-linking chitosan with glutaraldehyde and subsequent BGA biomass incorporation, which resulted in gel-like nanoparticles (16.3-19.6 nm). FTIR characterization confirmed the presence of the key functional groups (O-H, N-H, C = O) involved in adsorption. Measurement of the zeta potential revealed a positive surface charge (+ 27.8 mV) that facilitates electrostatic attraction for the anionic AR35 dye. SEM imaging revealed a rough, irregular surface morphology conducive to adsorption and EDX confirmed the main C, O, N composition. Optimum dye removal (> 96%) was achieved at acidic pH (pH 3). Adsorption equilibrium was reached in approximately 150 min. The Langmuir isotherm model best fitted the equilibrium data (R² = 0.999), indicating monolayer adsorption with a maximum adsorption capacity (q_m) of 38.2 mg/g. Kinetic studies showed that the pseudo-second-order model accurately described the adsorption process (R² = 0.970), suggesting that chemisorption could be involved alongside physisorption, although intraparticle diffusion was also suggested as a factor. Thermodynamic calculation showed an exothermic process and a spontaneous (ΔG° = -7.603 kJ mol^{- 1}) and entropy-reducing (ΔS° = -0.1736 Jmol K^{- 1}) process, characteristic of physisorption. Definitive Screening Design (DSD) was effectively applied for optimization, and initial dye concentration and contact time were determined to be the most influential variables. DSD modeling predicted maximum 97-98% removal rates at optimized conditions (e.g., pH 3, 0.1 g dosage).