Recent advances in glutaraldehyde-crosslinked chitosan for dye removal from wastewater: A review

The discharge of synthetic dyes into aquatic systems remains a significant environmental concern due to their persistence, toxicity, and resistance to conventional treatment processes. This review critically examines recent advances (2020-2025) in glutaraldehyde-crosslinked chitosan (CS-Glu) adsorbents for dye removal from aqueous solutions. The scope covers major material families, including pristine CS-Glu hydrogels, magnetic CS-Glu composites, carbon-based hybrids, and inorganic-filler nanocomposites, as well as the adsorption of representative dye classes, such as cationic dyes (e.g., methylene blue), anionic dyes (e.g., Congo red), and reactive dyes commonly found in textile effluents. Reported adsorption capacities typically range from ∼50 to mor than 800 mg/g, depending on crosslinking density, composite structure, and operating conditions, with optimal performance generally observed within pH 4-9 and moderate ionic strength. The review discusses the crosslinking chemistry of CS-Glu systems, structure-property relationships, adsorption mechanisms (electrostatic interaction, hydrogen bonding, and π-π interactions), and the influence of physicochemical parameters on adsorption efficiency. Comparative analysis indicates that nanocomposite CS-Glu systems, particularly magnetic and carbon-based hybrids, provide improved adsorption capacity, stability, and recyclability compared with conventional chitosan adsorbents. Overall, the literature suggests that controlled crosslinking can significantly enhance chitosan stability while maintaining high adsorption performance. However, future research should prioritize testing under realistic wastewater matrices, long-term regeneration performance, and scalable synthesis strategies to facilitate practical applications.