Piezo-potential induced molecular oxygen activation of defect-rich MoS₂ ultrathin nanosheets for organic dye degradation in dark

As a new concept, single-and odd-numbered layer of molybdenum disulfide (MoS₂) is a piezocatalyst semiconductor. Herein, we report the created odd numbered layer of defect-rich MoS₂ (DR-MoS₂) with high sulfur (S) vacancy concentration (S/Mo ratio-0.83) which can strongly interact with adsorbed oxygen molecules for highly efficient generation of reactive oxygen species (ROS) in the piezocatalytic degradation process. DR-MoS₂ presents far superior piezocatalytic activity for Eriochrome Black T dye degradation which is 2.14 and 18.12 times higher than that of defect-free MoS₂ (DF-MoS₂) and bulk MoS₂. The abundant native S vacancies induced the enhanced carrier density (electron density) of DR-MoS₂ is to be 4.6 × 10¹⁷ cm^-3 and is roughly 15 times higher than that the 2.9 × 10¹⁶ cm^-3 of DF-MoS₂. The S vacancies induced the increased flat-band potential and the vast majority of charge density strengthens the electron transfer dynamics and increases the surface band bending, which drive the charge carrier separation efficiently along with piezopolarization. More importantly, Mo active sites created by S vacancy defects can facilitate the two-electron reduction of molecular oxygen activation by introducing Mo⁴⁺/Mo⁶⁺ redox couple. In addition, based on the experimental results, a tentative mechanism was proposed to explain the origin of the piezocatalytic enhancement in DR- MoS₂.