Nickel cobalt sulfide for the efficient adsorptive removal of malachite green dye: A modeling and thermodynamic study

Abstract

In this study, nickel cobalt sulfide (NiCo 2 S 4 ) was synthesized via a facile co‐precipitation method and evaluated for the adsorptive removal of malachite green (MG) dye from aqueous solutions. The structural and surface properties of the adsorbent were characterized using scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform‐infrared (FT‐IR), thermogravimetric analysis (TGA), point of zero charge (pH pzc ), and zeta potential analyses. The maximum monolayer adsorption capacity reached 79.03 mg/g at 298 K. Equilibrium data were best described by the Langmuir, Redlich–Peterson, and Brouers–Sotolongo isotherm models, while adsorption kinetics followed a pseudo‐second‐order model, indicating a combination of physical and chemical interactions. Thermodynamic evaluations confirmed that the adsorption process is spontaneous and endothermic. These findings demonstrate that NiCo 2 S 4 , featuring a bimetallic thiospinel structure, serves as a structurally stable and efficient alternative adsorbent for cationic dye removal in wastewater treatment applications.