Integrated experimental and DFT study of a GO–CuO nanocomposite with improved antifungal efficacy and photocatalytic behavior

A novel graphene oxide–copper oxide (GO–CuO) nanocomposite was successfully synthesized using Hummers’ and sol–gel/solvothermal methods and systematically investigated through combined experimental and theoretical approaches. X-ray diffraction (XRD) analysis confirmed the formation of highly crystalline monoclinic CuO nanoparticles uniformly anchored on graphene oxide (GO) sheets, with characteristic reflections at 2θ ≈ 35.9°, 39.1°, and 59.0° corresponding to the (–111), (111), and (202) planes (JCPDS No. 80–1268). The average crystallite size of CuO was estimated to be ~ 23.6 nm using the Scherrer equation. The GO (001) peak at 2θ ≈ 11.2° (d ≈ 0.79 nm) shifted to 24.97° (d ≈ 0.37 nm) in the GO–CuO nanocomposite, indicating partial reduction of GO and strong interfacial interaction between GO and CuO. UV–Vis spectroscopy revealed enhanced optical absorption of the GO–CuO nanocomposite over the 200–800 nm range, with a redshifted absorption edge compared to pristine GO and CuO. The optical bandgap values determined from Tauc plots were 3.45 eV for GO, 1.42 eV for CuO, and a reduced bandgap of 1.85 eV for the GO–CuO nanocomposite, demonstrating improved visible-light harvesting capability. Density functional theory (DFT) calculations using the B3LYP functional supported the experimental observations, revealing strong adsorption of CuO on GO, significant charge transfer (0.72 e), and modulation of the electronic structure that promotes efficient charge separation and electron transport. Antifungal studies showed superior biological activity of the GO–CuO nanocomposite against Chlorella vulgaris and Phytophthora spp., with a minimum inhibitory concentration (MIC) of 75 µg/mL, compared to 100 µg/mL for CuO and 150 µg/mL for GO. Disk-diffusion assays further confirmed enhanced inhibition zones of 16 mm for GO–CuO. These results demonstrate that the GO–CuO nanocomposite is a multifunctional material with enhanced photocatalytic performance and pronounced antifungal activity, making it a promising candidate for environmental remediation and antimicrobial applications.