Improving photocatalytic activity and chlorine resistance of carbon nanolayer-wrapped TiO2 nanocomposite catalysts for dichloromethane purification†

Abstract

Developing advanced photocatalysts with excellent deep purification activity and robust chlorine resistance has always been a key focus in the photocatalytic degradation of chlorinated volatile organic compounds (CVOCs). Herein, carbon nanolayer-wrapped TiO₂ (CNWT-x) nanocomposite catalysts with tunable carbon nanolayer thickness were fabricated by controlled pyrolysis of NH₂-MIL-125(Ti) to degrade dichloromethane (DCM) under UV-vis irradiation. The results demonstrated that carbon nanolayers wrapped around TiO₂ could drastically accelerate the transfer of photogenerated electrons and prolong the photogenerated carrier lifetime, thereby producing abundant ·O₂⁻ and ·OH radicals with strong oxidation ability. These radicals rapidly oxidized DCM and intermediates to final products of CO₂ and Cl₂. The CNWT-2 sample exhibited optimal catalytic activity with 85% DCM conversion and 90% CO₂ selectivity, even after 5 h of UV-vis light irradiation. More importantly, CNWT-2 also demonstrated robust resistance to chlorine and high humidity. Furthermore, in situ NAP XPS results suggested that the dissociated chlorine species might preferentially be absorbed onto the stable outer carbon nanolayers, which significantly protected the interior TiO₂ active sites. This reduced the reaction probability of the dissociated chlorine species with TiO₂ active sites and the generated organic intermediates, thereby inhibiting the formation of toxic polychlorinated byproducts and catalyst deactivation due to chloride poisoning. This work offers a facile and efficient strategy for developing highly active and stable catalysts for the photocatalytic degradation of CVOCs.