Synergistic Mechanisms of Formaldehyde-Induced Radicals Enhancing Photothermal Catalytic Oxidation of Toluene

Photothermal catalysis has been extensively applied for the removal of volatile organic compounds (VOCs), typically based on performance evaluations against a single target component. However, in real situations, multiple VOCs typically coexist as complex mixtures. This study investigates the photothermal catalytic oxidation and synergistic effects of representative VOCs, consisting of formaldehyde (HCHO) and toluene over Pt/N-TiO₂. The results demonstrate that HCHO significantly promotes the photothermal catalytic performance of Pt/N-TiO₂ for toluene oxidation compared to that of toluene alone. Significantly, the conversion and CO₂ yield of toluene were enhanced by 49.6% and 56.2%, respectively. The presence of HCHO suppresses the formation of larger molecular oxidation products (e.g., benzaldehyde and benzoic acid), while promoting the formation of smaller molecular species (e.g., formic acid and acetaldehyde). Multitechnique characterizations suggest that HCHO-derived reactive species (e.g., COOH^•) may interact with toluene to form methylbenzoic acid as an alternative intermediate. This implies to a possible new aromatic-ring-opening pathway. Additionally, EPR trapping experiments further demonstrate that HCHO consumes photogenerated holes, thereby enhancing the charge separation efficiency of photoinduced electron-hole pairs in Pt/N-TiO₂. Furthermore, similar promotional effects are observed between methanol and toluene. These findings provide insights into the reaction mechanisms governing multicomponent VOCs oxidation in photothermal catalytic systems.