Glutaraldehyde crosslinked chitosan-β-cyclodextrin/ZnO composite for the effective adsorption of Congo red anionic dye: A glimpse into adsorption performance and ANN modeling

Abstract

Removal of azo dyes is of great concern because of their large contribution in dye industry and persistent toxic nature. Congo red (CR), an anionic azo dye, poses significant environmental hazards to aquatic and terrestrial ecosystems. This study explores the use of a positively charged adsorbent composite for the effective removal of CR via adsorption. Chitosan (CS) based composite, CS-GA-β-CD/ZnO, was synthesized by grafting β-cyclodextrin (β-CD) onto cationic CS using glutaraldehyde (GA) in the presence of ZnO nanoparticles. The composite’s physicochemical characteristics were evaluated using various analytical techniques. The effects of pH, contact time, temperature, initial CR concentration, and adsorbent dosage on CR removal were systematically investigated through isotherm, kinetic, and thermodynamic analyses. The composite demonstrated high adsorption efficiency, particularly at adsorbent dosages ≥30 mg, with optimal performance under acidic conditions due to its enhanced surface positivity. The presence of salts had minimal impact on adsorption efficiency, confirming the robustness of the material. Thermodynamic studies indicated spontaneous adsorption within 300 minutes. The adsorption behavior was best described by Liu, Dubinin-Radushkevich (D-R), and Langmuir isotherm models, with a maximum capacity (i.e., Langmuir qₘ) of 337 ± 13 mg g⁻¹ at T = 30 °C. The composite retained over 93% of its adsorption efficiency after five regeneration cycles, highlighting its reusability. Moreover, an artificial neural network (ANN) model provided accurate predictive capability with an R² > 0.995. These findings underscore the potential of CS-GA-β-CD/ZnO as a cost-effective, environmentally friendly, and scalable adsorbent for CR removal from wastewater. CS-GA-β-CD/ZnO is not explored for its adsorption potential and therefore, the outcome of the present work can advance the knowledge in the field of achieving good dye removal from the aqueous solution using composite materials. The study also highlights leaching of composite adsorbent after prolonged contact period under highly acidic and basic conditions.