Enhanced piezocatalysis of polymorphic few-layered MoS2 nanosheets by phase engineering

Molybdenum disulfide (MoS2) with diverse crystal phase shows different symmetry, which may exhibit distinct piezoelectric properties. In this work, a series of few-layered MoS2 with 1T/2H, 1T/3R and 2H phases were obtained and identified to investigate the relationship between the piezoelectric activities and crystal phases. It is firstly proved by finite element simulation that 3R phase with even layers exhibited out-of-plane piezoelectricity not shown in 2H phases. Among them, 1T/3R-MoS2 showed 100% degradation efficiency for bisphenol A (BPA) in water within 45 min under ultrasonic vibration, whose removal rate was 1.36 and 3.95 times higher than that of 1T/2H-MoS2 and 2H-MoS2, respectively. The higher activity of 1T/3R-MoS2 can be attributed to the combination of metal and semiconductor phase as well as the cooperation with in-of-plane and out-of-plane piezoelectricity of arbitrary multilayer 3R phase, which can accelerate the transfer and separation of free carriers. Herein, the piezoelectric effect of MoS2 was studied from the perspective of crystal structure, which might provide a new insight of piezocatalysis with layered transition metal dichalcogenides (TMDs) for environmental purification and energy conversion.