Mechanical-vibration-driven piezocatalytic degradation of organic pollutants over microcrystalline SnSe with selenium vacancies

Two-dimensional piezoelectric materials are attractive candidates to trigger piezoelectric catalytic reactions for organics degradation. Microcrystalline structures can endow them with enhanced piezocatalytic activity due to their large surface area and abundant defect structures. In this work, microcrystalline SnSe with selenium vacancies (mc-SeVs SnSe) was synthesized and employed for piezocatalytic degradation of aqueous organics for the first time. Various instrumental testing results demonstrated that this unique microcrystalline SnSe has strong piezoelectric responses, abundant selenium vacancy defects and large active edges. Compared with crystalline SnSe, mc-SeVs SnSe showed superior piezocatalytic activity for the degradation of various organics in water. More importantly, mc-SeVs SnSe could induce the piezoelectric effect through mild mechanical energy to facilitate the efficient degradation of organic pollutants. The degradation efficiency of Crystal violet, p-nitrophenol, Malachite green, Congo red and Rhodamine B approached 100 % within 60 min reaction time. Superoxide and hydroxyl radicals were detected as the main reactive oxygen species generated in the piezocatalytic process. The degradation pathways of Rhodamine B were proposed based on high performance liquid chromatography-quadrupole-time of flight mass spectrum. The impact of strain on the alterations of dipole moment and electronic structure was investigated using density functional theory. The change in electron band structure induced by the polarized electric field was the underlying reason for the generation of hydroxyl radicals. This work will enrich the piezoelectric materials for organics degradation and provide fresh light on the mechanism of mechanically driven piezoelectric catalytic reactions.