Nanostructured ZnO, CuO and Zn-Cu mixed metal oxides for enhanced photocatalytic performance

Semiconductor metal oxides, particularly zinc oxide (ZnO) and copper oxide (CuO), have attracted considerable attention as photocatalysts for the degradation of organic pollutants because of their favorable electronic properties, chemical stability, and low cost. In this study, ZnO and CuO nanoparticles were synthesized by wick-assisted solution combustion, while Zn-Cu mixed oxide composites were prepared by thermal decomposition of oxalate precursors. Their structural, morphological, and photocatalytic properties were systematically compared with those of commercial materials. X-ray diffraction analysis showed that the synthesized ZnO possessed a highly crystalline hexagonal wurtzite structure, whereas the commercial ZnO exhibited a predominantly amorphous nature. The photocatalytic activity was evaluated by the degradation of Orange G dye under UV irradiation. Commercial ZnO exhibited superior photocatalytic performance compared with the synthesized ZnO, while the synthesized CuO showed enhanced activity relative to commercial CuO. The Zn-Cu mixed oxide composite demonstrated improved photocatalytic performance owing to the synergistic interaction between ZnO and CuO, which promotes charge separation and suppresses electron-hole recombination. Electron paramagnetic resonance (EPR) spectroscopy confirmed the generation of hydroxyl (˙OH) and superoxide (˙O₂ ^-) radicals during UV irradiation, and radical trapping experiments identified ˙OH as the dominant reactive species responsible for Orange G degradation. These findings provide direct experimental evidence for the proposed photocatalytic mechanism and establish a clear relationship between crystallinity, reactive oxygen species generation, and photocatalytic performance. The results provide useful insights into the design of efficient ZnO-CuO-based photocatalysts for environmental remediation applications.