Unveiling the effect of gallic acid capping on ZnO–CuO nanocomposites for photocatalytic insight and antioxidant activity

Photocatalytic degradation of organic pollutants on biogenically synthesized nanocatalysts is a pragmatic approach. In this regard, the use of gallic acid (GA) as a capping and reducing agent is scarcely studied. Therefore, the synthesis of GA capped g-ZnO NPs, g-CuO NPs, and g-ZnO-CuO NCs is reported here for the photocatalytic and antioxidant applications. The synthesized samples were thoroughly characterized by PXRD, FTIR, SEM, EDX, ZP, and UV-Visible spectroscopy, confirming the reduction and formation of nanomaterials. Due to the visible light-responsive energy band gaps (2.68-3.14 eV), the photocatalytic activity of the g-ZnO NPs, g-CuO NPs, and g-ZnO-CuO NCs was evaluated for the photodegradation of azo dyes, <i>i.e.,</i> methylene blue (MB) and crystal violet (CV). On comparison of pristine g-ZnO NPs and g-CuO NPs, the g-g-ZnO-CuO NCs showed the best photocatalytic activity by degrading CV (91%) and MB (90%) with rate constant values of 2.43 × 10^-2min^-1 and 2.35 × 10^-2min^-1, respectively. Due to potent antioxidant GA capping, the antioxidant activity of synthesized NPs and NCs was also evaluated by DPPH assay, FRAP assay, and TPC assay. Based on experimental findings, the synthesized g-ZnO-CuO NCs have been proposed as a reliable material for a sustainable and efficient solution to tackle water contamination.