Bimetallic Ni–Co functionalized bentonite for sustainable dye removal: an experimental and DFT approach

The increasing discharge of dye-containing industrial wastewater requires efficient and sustainable adsorbents for water treatment. In this study, nickel (Ni)-, cobalt (Co)-, and Ni–Co-modified bentonite adsorbents were synthesized and evaluated for the removal of methyl orange (MO) from aqueous solutions. Structural and elemental characterization confirmed the preservation of the montmorillonite framework after metal incorporation and the successful dispersion of nickel and cobalt species on the bentonite surface. Adsorption performance was investigated as a function of pH, contact time, adsorbent dosage, initial dye concentration, and temperature. The adsorption process was pH-dependent and endothermic, with removal efficiency increasing at higher temperatures. Among the prepared materials, 5 wt.%Ni–5 wt.%Co/bentonite exhibited the highest performance, achieving up to 98% MO removal, compared with approximately 94% and 91% for Ni/bentonite and Co/bentonite, respectively. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) confirmed the spontaneous and endothermic nature of adsorption and demonstrated the superior performance of the bimetallic adsorbent. Density functional theory calculations provided molecular-level insight into the adsorption mechanism and revealed favorable adsorbate–surface interactions. The combined experimental and theoretical results highlight Ni–Co-modified bentonite as a promising adsorbent for wastewater treatment applications.