ZnO/CuO nanocomposites for enhanced photocatalytic and antibacterial applications: A comparative study of synthesis methods

ZnO/CuO nanocomposites (NCs) were prepared through a biological route using Vernonia amygdalina leaf extract as a stabilizing and reducing agent. ZnO nanoparticles (NPs) and ZnO/CuO NCs were also fabricated via the chemical precipitation method for comparison purposes. Spectroscopic, microscopic, electrochemical and XRD techniques were employed to characterize the prepared samples. In addition, first-principles calculations based on density functional theory (DFT) were utilized to elucidate the electronic characteristics of the individual ZnO and CuO NPs. The X-ray diffraction (XRD) results affirmed the purity and crystalline features of the fabricated NPs and NCs. Morphological analyses demonstrated that the particles of green-mediated ZnO/CuO NCs are smaller and less agglomerated than those of NCs synthesized without the extract. A comparison of photocatalytic and antibacterial performances of ZnO/CuO NCs synthesized with and without plant extract was also conducted. Compared to chemically synthesized NCs, the green-mediated NCs exhibited superior visible light photocatalytic performance for the decomposition of methylene blue (MB) dye. In particular, the degradation of MB over the optimized green-mediated NCs reached 98.80 % within 80 min of photocatalysis, and the degradation rate was achieved as 0.0528 ± 0.00813 min−1. The enhancement might result from the reduced particle size and thereby the enhanced surface area of the green-mediated NCs. In addition, the anti-bactericidal effects of the green-mediated ZnO/CuO NCs against two Gram-negative and two Gram-positive bacteria were significantly higher than those of chemically prepared NC samples. The highest inhibitory zone was observed as 19.0 ± 0.37 mm against E. coli in the presence of the optimized green-mediated NCs. Thus, the biosynthesized ZnO/CuO NCs can be a potential candidate for practical and sustainable antibacterial and photocatalytic applications.