Mg-doped OMS-2 nanorods: a highly efficient catalyst for purification of volatile organic compounds with full solar spectrum irradiation

Abstract

Mg-doped OMS-2 nanorod catalysts with different Mg doping amounts were prepared using a hydrothermal redox reaction with Mn(NO₃)₂, Mg(NO₃)₂, and KMnO₄. We find that a small amount of Mg doping considerably promotes the catalytic activity of OMS-2 for the catalytic oxidation of carcinogenic and recalcitrant benzene (typical VOCs). The optimum Mg-doped OMS-2 sample has a much higher catalytic activity than the pure OMS-2 catalyst and a commercial precious metal catalyst (0.5% Pt/Al₂O₃). Its turnover frequency (TOF) at 200 °C is 3.8 times higher than that of the pure OMS-2 nanorods. The considerable enhancement of the catalytic activity of OMS-2 upon Mg doping is attributed to the significant enhancement of the lattice oxygen activity of OMS-2. Very importantly, the Mg-doped OMS-2 sample demonstrates highly efficient photothermocatalytic activity and very good stability for benzene oxidation with full solar spectrum (UV-vis-IR) irradiation from a Xe lamp. Its initial rate of CO₂ production is as high as 575.8 μmol min⁻¹ g⁻¹, which is 3.8 and 171 times higher than that of pure OMS-2 and TiO₂ (P25), respectively. The Mg-doped OMS-2 sample also demonstrates efficient photothermocatalytic activity with visible-infrared (IR) irradiation. Remarkably, even with λ > 690 nm vis-IR irradiation, it still demonstrates efficient photothermocatalytic activity with a r_CO2 of 103.9 μmol min⁻¹ g⁻¹. The highly efficient catalytic activity of the Mg-doped OMS-2 catalyst with UV-vis-IR irradiation arises from the efficient solar light-driven (SLD) thermocatalysis, which is attributed to its very good thermocatalytic activity as well as the efficient photothermal conversion due to its strong absorption across the whole solar spectrum. A novel photo-activation effect, which is completely different from the well-known photocatalysis on semiconducting photocatalysts such as TiO₂, is found to promote the SLD thermocatalytic activity of the Mg-doped OMS-2 nanorods.