Synthesis and photocatalytic performance of ZnO/NiO-decorated reduced graphene oxide nanohybrids for methylene blue degradation

The photocatalytic properties of semiconductors play a crucial role in eliminating water pollutants helping to mitigate significant health risks to humans and ecosystems. This study aims to synthesize rGO/ZnO/NiO nanohybrids (RZN) using the hydrothermal method which demonstrates promising photocatalytic properties for environmental remediation. FESEM and TEM reveal that RZN agglomerated and that rGO exhibited a stacked layer structure. ZnO and NiO were evenly deposited onto the surface of rGO during the hydrothermal synthesis as confirmed by FESEM imaging. The size of RZN was determined to be 24.4 nm from XRD and the band gap was found to be 3.12 eV from UV-DRS analysis. RZN demonstrated superior efficiency in degrading methylene blue (MB) dye compared to pure and binary materials. RZN achieved a remarkable MB degradation rate of 90.24% within 90 min under UV light at pH 11. The degradation of RZN follows pseudo first-order kinetics with a rate constant of 0.0258 min⁻¹. The photocatalytic degradation mechanism was found to involve hydroxyl radicals (•OH) and superoxide anions (O2∙-) as the primary active species. Furthermore, the RZN nanohybrids exhibited excellent reusability maintaining high degradation efficiency over five consecutive cycles demonstrating their stability and long term usability. These findings suggest that RZN is a highly efficient sustainable solution for environmental remediation particularly in the degradation of organic dye pollutants making them a promising candidate for real world applications in water treatment.