Adsorptive removal of toxic crystal violet dye using copper sulfide‐filled sodium alginate microspheres: Equilibrium, kinetic, and thermodynamic evaluation

The discharge of crystal violet (CV)‐containing wastewater poses serious environmental and health risks due to its toxicity, persistence, and resistance to biodegradation. Therefore, the development of efficient and sustainable adsorbents for CV removal is of significant importance. Copper sulfide‐filled sodium alginate (SA/CuS) composite microspheres were synthesized and characterized using FT‐IR, SEM, XRD, and ζ potential analyses. Batch adsorption experiments were conducted to investigate the effects of pH, adsorbent dosage, contact time, temperature, and initial dye concentration. Equilibrium, kinetic, and thermodynamic studies were performed to elucidate the adsorption behavior. The SA/CuS/10 composite exhibited the best adsorption performance under optimum conditions (pH 7, 298 K, 0.075 g adsorbent dosage, and 60 min contact time), achieving 80.45% CV removal efficiency. Equilibrium data were best fitted by the Langmuir isotherm model with a maximum adsorption capacity of 47.28 mg/g at 298 K. Kinetic studies demonstrated that the adsorption process followed the pseudo‐second‐order model ( R 2 = 0.999). Thermodynamic parameters confirmed that the adsorption process was spontaneous and exothermic, with ΔG° values ranging from −25.62 to −26.64 kJ/mol and ΔH° of −10.48 kJ/mol. The enhanced adsorption performance is attributed to the synergistic interaction between CuS nanoparticles and alginate functional groups through electrostatic interactions, hydrogen bonding, and surface complexation. The developed SA/CuS composite microspheres represent an efficient, reusable, and environmentally friendly adsorbent for the removal of cationic dyes from wastewater.