Photocatalytic Degradation of Toluene by Three-dimensional Monolithic TiO2/Cu2O Heterojunction Foams

Abstract

In the photocatalytic degradation of volatile organic compounds (VOCs), the powdered catalysts have insufficient contact with gas and are prone to detachment from the support. To address this challenge, we present a sacrificial template and in-situ growing approach to fabricate a three-dimensional (3D) monolithic photocatalyst. The design combines the n-type TiO₂ and p-type Cu₂O semiconductors using foamed copper as a substrate. The 3D monolithic TiO₂/Cu₂O heterojunction foam was used to evaluate its toluene removal efficiency under simulated sunlight and a 15 W UV disinfection lamp. The results show that the photocatalyst outperforms conventional TiO₂ and Cu₂O in toluene removal under both simulated sunlight and UV light. After 180 min of exposure to a 500 W Xe lamp, the TiO₂/Cu₂O foam achieved a removal rate of 90.2% for toluene. This performance improvement is attributed to the unique 3D open internal structure, which enhances the gas-solid mass transfer efficiency. In addition, the formation of p-n junctions between TiO₂ and Cu₂O prolongs the lifetime of the photogenerated carriers, resulting in higher catalyst activity. After four cycles of experiments, its degradation rate is 88.0%, indicating its stability. The degradation pathway, toxicity analysis and catalytic mechanism of the catalytic degradation of toluene by the TiO₂/Cu₂O foam were explored. Furthermore, this study demonstrates the feasibility of fabricating highly active monolithic catalysts by in-situ growing of semiconductor photocatalysts onto metal foams. This approach offers a promising solution to enhance reactant contact area and minimize mass transfer resistance in gas-solid reactions.