Improving the performance of a solar photocatalyst for methylene blue degradation using a synthesized ZnO/activated carbon composite

Abstract Integrating biomass-derived materials with renewable energy sources is a sustainable way to develop environmentally friendly photocatalysts. In this context, the use of agricultural by-products in catalytic applications has attracted growing attention due to their abundance, low cost and environmental compatibility. This study reports on the synthesis of ZnO and ZnO/activated carbon (ZnO/AC) composites prepared from olive kernel biomass via the sol–gel method, and their subsequent structural, morphological, and textural characterization using XRD, ATR-FTIR, SEM, EDS, and BET analyses. The results confirm the successful anchoring of ZnO particles onto the activated carbon surface and indicate enhanced interfacial charge-transfer interactions. Photocatalytic performance was assessed through methylene blue (MB) degradation under solar irradiation, which was markedly more effective than UV irradiation alone. The ZnO/AC composite exhibited a degradation rate nearly four times higher than pristine ZnO. Optimal performance was achieved with a catalyst dosage of 1 g L −1 , an initial MB concentration of 25 mg L −1 , and a natural pH (∼7), with complete degradation occurring within 90 min. Experiments investigating reactive species scavenging revealed that hydroxyl radicals ( • OH) dominate MB degradation in the ZnO system, whereas superoxide radicals (O 2 •− ) are the primary active species in the ZnO/AC composite. This highlights their crucial role in enhancing charge separation and overall photocatalytic efficiency.