Enhanced photocatalytic degradation of methyl orange dye under UV light using Cu and Ni-doped CdS nanocomposites: Insights into reactor performance and kinetic analysis

The inefficient treated wastewater poses a significant environmental challenge, which drives intensive research toward the development of novel photocatalysts. While CdS photocatalysts have been widely studied, their limited stability and fast charge carrier recombination hinder photocatalytic performance. In this study, Cu and Ni-doped CdS nanocomposites were synthesized via a simple chemical precipitation route to improve photocatalytic efficiency under UV irradiation. The structural, morphological, and optical properties were characterized using XRD, SEM-EDX, FTIR, and XPS, confirming a hexagonal wurtzite structure (average crystalline size: 22.0–30.0 nm), spherical morphology with homogeneous elemental dispersion, O–H stretching bands, and the presence of new chemical states. Photocatalytic degradation of methyl orange dye (MO) (10 mg l^-1) showed efficiencies of 77.7 % (CdS), 81.3 % (CdS-Cu), 93.8 % (CdS-Ni), and 83.0 % (CdS-Cu-Ni) after 3.0 h of UV exposure. Notably, CdS-Ni achieved 100 % degradation upon the addition of 1.0 mL of H₂O₂. The reaction followed pseudo-second-order kinetics, with a reaction rate constant of 0.0079 min^-1, and the catalyst demonstrated good stability over multiple reuse cycles. The enhanced photocatalytic activity was primarily attributed to the narrowed bandgap, increased light-harvesting capability, and reduced electron-hole pair recombination. These outcomes demonstrate the potential of CdS-Ni nanocomposites as effective photocatalysts for the treatment of dye-contaminated wastewater.