Facile Preparation of a Kaolin-Supported CuO Catalyst and Investigation of Its Catalytic Performance for Methylene Blue Dye Degradation in Aqueous Solution

The increasing pollution of water bodies from various industrial wastewater discharges has raised significant environmental concerns because these effluents contain toxic, nonbiodegradable compounds that pose serious risks to living organisms. In particular, the textile and pharmaceutical industries routinely use dyes that severely degrade water quality and lead to significant environmental issues. Therefore, effective removal of these dyes from industrial wastewater is crucial for mitigating pollution. In this study, copper oxide (CuO) nanoparticles supported on beneficiated kaolin (BK) clay were synthesized as heterogeneous catalysts using a simple and cost-effective wet-precipitation method. Various characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), Fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption/desorption analysis, and ultraviolet-visible (UV-vis) spectrophotometry, were used to evaluate the crystallinity, morphology, composition, structure, and surface properties of the synthesized BK/CuO nanocomposite (NC). The catalytic efficiency of the BK/CuO NC was evaluated for the oxidative degradation of methylene blue (MB) dye in an aqueous solution using sodium hypochlorite (NaOCl) as the oxidizing agent. The effects of the key reaction parameters, including the precursor-to-support ratio during synthesis, catalyst dosage, NaOCl concentration, initial MB dye concentration, and reaction temperature, were systematically examined. The results demonstrated that BK/CuO NC achieved nearly complete degradation (>97%) of an MB solution (50 mg L^-1, 50 mL) within 6 min, using a 1:2 mass ratio of the precursor to kaolin. Kinetic analysis revealed that the degradation followed a pseudo-first-order model with an apparent rate constant (<i>k</i> _app) of 0.68 min^-1. Additionally, the activation energy (<i>E</i> _a) of the reaction was determined to be 51.93 kJ mol^-1. The reusability of the BK/CuO NC was also assessed, showing remarkable stability, with the degradation efficiency remaining above 97% even after seven consecutive cycles. These findings highlight the potential of BK/CuO as a highly efficient and durable catalyst for the removal of organic pollutants from wastewater via catalytic oxidation.