Synthesis, characterization and photocatalytic degradation of textile dyes using ZnO, CuO and ZnO–CuO nanocomposites

Abstract Water pollution from industries, particularly from textile industries, is a major environmental and health concern due to untreated effluent containing toxic, non-biodegradable, carcinogenic dyes. Among various wastewater purification techniques, semiconductor-based photocatalysis offers a sustainable remediation strategy due to its low cost, operational simplicity, and environmental compatibility. The present study explored the photocatalytic degradation of methyl orange (MO) and methylene blue (MB) dyes using ZnO, CuO, and ZnO–CuO metal oxide nanocomposites synthesized via the co-precipitation method. Structural characterization using XRD (x-ray diffraction) confirmed the formation of highly crystalline, phase-pure nanostructures with crystallite sizes between 12–26 nm. Infrared spectroscopy revealed distinctive Zn-O and Cu-O bond stretches between 400–600 cm −1 , and Scanning Electron Microscopy (SEM) images confirmed nanostructured morphologies suitable for catalysis. The band gaps estimated by UV–Vis spectroscopy were found to be 3.14 eV for ZnO, 2.20 eV for CuO, and 2.42 eV for the ZnO-CuO nanocomposite. Photocatalytic degradation study carried out under UV light revealed that CuO exhibited the highest degradation efficiency for MB (94% in 40 min), while ZnO showed superior performance for MO (84.7% in 40 min). The 1:1 ZnO-CuO nanocomposite under the present conditions achieves the MB degradation efficiency of CuO, while exhibiting less photocatalytic activity for MO compared to ZnO. Kinetic studies and PZC (point of zero charge) values, determined by the pH drift method, confirm the correlation between surface properties and the observed dye degradation efficiencies. The varied degradation behaviour may be due to the interplay between band gap energies, surface adsorption affinities, and dye structures. The optimized synthesis of ZnO-CuO nanocomposites through band gap engineering and heterojunction formation presents a promising path for future research in enhancing photocatalytic efficiency. The study highlights the potential of low-cost binary metal oxide nanostructures as a sustainable and eco-friendly alternative for wastewater management techniques.