Optimizing photocatalytic degradation of dichloromethane by MOF-derived TiO2/C catalyst: Unraveling the decisive role of carbon nanolayers and reaction mechanism

In-depth dissecting the activation of C-Cl bonds and the migration transformation of dissociated chlorine species is significant to understand the mechanism underlying the formation of polychlorinated by products and chlorine poisoning deactivation of catalyst during of the photocatalytic degradation of chlorinated volatile organic compounds (CVOCs). Herein, carbon nanolayers wrapped TiO₂ composites (CTO), and its contrastive catalysts including defective carbon nanolayers wrapped TiO₂ (DCTO) and TiO₂ without carbon nanolayer (TO) are constructed by rational pyrolysis of titanium-based MOFs. The obtained CTO exhibits a remarkable degradation efficiency of up to 91.74 % for CH₂Cl₂ after 3 h of UV–vis irradiation, robust stability as well as water resistance, far superior to that of DCTO and TO. Density functional theory calculations combined with in-situ XPS reveal that the heterogeneous interface interactions between carbon nanolayers and TiO₂ greatly facilitate the separation of photogenerated carriers, boosting the redox capacity of CTO. Simultaneously, the dissociated Cl species from the cleavage of the C-Cl bond can be preferentially adsorbed onto the outer carbon nanolayers, thereby inhibiting the occupation of TiO₂ active sites by chlorine. The preferential adsorption sites of the dissociated Cl species and optimized deep oxidation ability synergistically boost the catalytic performance and resistance of chlorine poisoning and inhibit the production of polychlorinated by-products.