Peroxymonosulfate activation in ultrasound-driven molybdenum disulfide piezocatalysis: The effect of sulfur vacancy

Although peroxymonosulfate (PMS) can be efficiently activated by ultrasound-driven piezocatalyst, there are still uncertainties on the mechanisms. Herein, molybdenum disulfide piezocatalysts with different sulfur vacancy (VS) types were prepared by hydrothermal (MoS2–H) and solvothermal methods (MoS2–S). The configuration of Vs in MoS2 was characterized by X-ray photoemission spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and O2 diffuse reflectance infrared Fourier transform spectroscopy (O2-DRIFTS). Surface in-plane VS and edge VS dominated on MoS2–H and MoS2–S. MoS2–S exhibits higher PMS activation performance with 85.0% degradation rate of 4-chlorophenol within 2 h. Although in-plane VS feature a stronger PMS adsorption energy compared with edge VS (−1.64 vs. −0.94 eV), PMS activation is not favorable at the in-plane VS sites of MoS2 (MoS2–H). In piezo-polarized MoS2, the separated charge carriers accumulate at the edges, where edge VS (MoS2–S), as the active site, strengthens the coupling between electrons and PMS. As a result, the O–O bond length in PMS is increased from 1.467 to 1.470 Å, enabling the facile activation of PMS with the generation of more abundant ·OH and ·SO4− radicals. This work clearly explains the PMS activation mechanism from both experimental and theoretical aspects and provides directions to tailor the structure and atom vacancies of piezocatalysts.