Electrochemical fabrication of ZnO nanoparticles on rGO sheets: Optical, antioxidant, dye pollution control, and biological studies

This work reports a low-temperature electrochemical route for synthesizing ZnO nanoparticles and their subsequent integration with reduced graphene oxide (rGO) via a reflux method to form an rGO/ZnO nanocomposite (1:1). Structural and surface analyses (XRD, XPS, HR-TEM, SEM/EDAX, FTIR, and PL) confirmed the successful anchoring of crystalline wurtzite ZnO (≈21–26 nm) onto rGO sheets with strong interfacial interaction and uniform dispersion. Optical studies revealed a significant band-gap narrowing from 3.38 eV (ZnO) to 3.05 eV (rGO/ZnO), accompanied by a reduction in photoluminescence intensity, indicating efficient charge separation and reduced electron–hole recombination. The rGO/ZnO nanocomposite exhibited superior antioxidant performance compared to ZnO, achieving a maximum DPPH radical scavenging efficiency of 83.6% with a reduced IC₅₀ value of 176.7 μg/mL. Photocatalytic evaluation using Fast Green dye under UV irradiation demonstrated markedly enhanced activity, with rGO/ZnO achieving ∼91% degradation within 105 min, compared to ∼73% for pristine ZnO. The improved performance is attributed to rGO's enhanced role as an electron acceptor and a conductive network, which promotes the generation of reactive oxygen species. Additionally, the rGO/ZnO nanocomposite demonstrated significantly enhanced antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as notable cytotoxicity toward HeLa cancer cells, outperforming the individual components. Overall, the results establish electrochemically derived rGO/ZnO as a multifunctional nanocomposite with strong potential for environmental remediation, antioxidant applications, and biomedical research.