H<sub>2</sub>O Promoted the Photocatalytic Toluene\nOxidation at Ambient Humidity on Zn-Doped K‑OMS-2: Mechanism\nStudy

The\npoor stability of the MnO<sub>2</sub> catalyst limits its application\nin photocatalytic toluene oxidation, especially at ambient humidity.\nHerein, the doped Zn<sup>2+</sup> attached to the tunnel of K-OMS-2\nby replacing K<sup>+</sup> (Zn-KM photocatalyst) with an appropriate\nhydrophilicity surprisingly exhibits better photocatalytic performance\nand stability for the toluene oxidation at ambient humidity than that\nof KM. Especially, at a higher RH of 42%, Zn-KM shows approximately\ndouble the times of toluene removal (80%) than KM, with an excellent\nstability for at least 8 h. Comprehensive characterizations and calculations\nsuggest that on the Zn-KM photocatalyst, the H<sub>2</sub>O molecule\nsignificantly reduces the adsorption energy of toluene (from −3.38\nto −3.72 eV) via the hydrogen bond–mediated intermediate;\nsimultaneously, its enhanced average Mn–O bond (from 2.27 to\n2.20 Å) forms the intensive built-in electric field and promotes\nfaster electron transfer, leading to more oxygen radical generation,\nricher key ring-opening intermediate of alkoxide species, and an increased\nstability. However, the strongly hydrophilic KM photocatalyst has\neasier H<sub>2</sub>O adsorption (−1.19 eV), inhibiting toluene\nadsorption and oxidation. This work provides the economic viability\nof MnO<sub>2</sub>-based photocatalysts for toluene removal.