ZnO/reduced graphene oxide thin-film photocatalysts immobilized on flexible polyurethane foam for toluene degradation

A new hybrid photocatalytic system was designed for the gas-phase degradation of toluene by immobilizing reduced graphene oxide (rGO)-modified zinc oxide (ZnO) thin films on polyurethane foam (PUf). ZnO was selected for its high redox potential and electron mobility, while rGO was incorporated as a conductive carbon component to enhance adsorption and improve charge carrier utilization. The interconnected three-dimensional (3D) PUf structure provided mechanical stability, additional accessible surface area, and improved gas diffusion within the reactor. The hybrid catalysts were fabricated via a multi-stage dip-coating process, enabling uniform deposition of ZnO thin films followed by rGO functionalization. Morphological analysis confirmed the homogeneous coating of ZnO on the PUf struts and the subsequent decoration with rGO sheets, while optical and photoluminescence (PL) analyses indicated enhanced light response and suppressed charge recombination in the hybrid system. Efficient toluene removal and mineralization were achieved at different initial concentrations (43, 86, and 129 ppm), as confirmed by real-time concentration decay and CO₂ formation in a plug-flow reactor under UVA, UV-LED, and UV-vis light irradiation. The optimal catalyst (ZnO/rGO/PUf) achieved a maximum removal efficiency of 81% under UVA light, compared with 68% for the bare ZnO/PUf catalyst under the same conditions, confirming the beneficial role of rGO hybridization. The ZnO/rGO/PUf hybrid also exhibited higher adsorption capacity (27%) compared to ZnO/PUf (17%), indicating synergistic integration of adsorption and photocatalytic oxidation. Reusability tests confirmed the structural stability of the hybrid photocatalysts, with less than 6% efficiency decrease over ten consecutive cycles.