Efficient removal of anionic dyes by chitosan-based hydrogels modified with SDS and NaOH: Structural optimization, adsorption performance, and mechanistic insights.

The acceleration of industrial and urban development has intensified pollution from dye-containing wastewater, while conventional adsorbents demonstrate inadequate performance for complex wastewater remediation. This study develops two chitosan (CS)-based hydrogels (CSS and CNS) through modification with sodium dodecyl sulfate (SDS) and sodium hydroxide (NaOH), for efficient removal of anionic Reactive Red X-3B. The effects of preparation conditions on hydrogel structure and adsorption performance were systematically investigated. Comprehensive characterization via FTIR, XRD, SEM, EDS and BET elucidated distinct physicochemical properties between CSS and CNS. Experimental results demonstrated marked differences in pH adaptability and adsorption capacity: CSS retained 94 % mass stability under strongly acidic conditions, while the NaOH-modified CNS developed a porous structure that exhibited a significantly higher saturated adsorption capacity for Reactive Red X-3B (1834.04 mg/g) compared to CSS (123.01 mg/g). Adsorption mechanisms follow pseudo-second-order kinetics and Langmuir isotherm models, dominated by chemisorption with enhanced efficiency at lower temperatures. In addition, the CNS exhibits a Cuadsorption capacity of 146.64 mg/g at an initial concentration of 100 mg/L. Its strong adsorption capacity (electrostatic-coordination synergy) shows its multi-pollutant treatment potential. This study offers both theoretical foundations and technical insights for the rational design of chitosan-based hydrogels and their application in dye wastewater remediation.