Catalytic Degradation of 4-Nitrophenol Using CuO Nanoparticles: A Study of Structural, Optical, and Catalytic Properties

Abstract Copper oxide nanoparticles (CuO NPs) were synthesized using a simple and cost-effective chemical precipitation method, offering an alternative to high-temperature and high-pressure techniques like hydrothermal synthesis. The synthesized nanoparticles were comprehensively characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis spectroscopy, Raman spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analysis. The crystallite size was determined to be 23.28 ± 0.2153 nm, with a specific surface area of 15.4 m 2 /g. Optical studies revealed band gap values of 3.5 eV and 3.8 eV for direct and indirect transitions, respectively due to surface oxidation forming CuO/Cu₂O heterostructures. The catalytic efficiency of CuO NPs was evaluated for the degradation of 4-nitrophenol (4-NP), achieving a maximum degradation efficiency of 95% within 6 min at a catalyst concentration of 40 mg/L. The reaction followed pseudo-first-order kinetics, with a rate constant of 0.42 min −1 . Stability and reusability tests demonstrated consistent performance over five cycles, with less than 5% loss in efficiency. These results highlight the potential of CuO NPs as an efficient and reusable catalyst for environmental remediation, particularly for the degradation of toxic pollutants like 4-NP.