Design And Performance Of MX₂（M=W；X=S） Transition Metal Chalcogenide Nanocatalyst

Tungsten disulfide（WS₂）is a classical photocatalyst and piezoelectric catalyst in the transition metal chalcogenide group.It has a narrow band gap（1.4-1.9 e V）.It is considered to be an excellent photocatalyst.It has great potential in hydrogen evolution,carbon dioxide reduction and catalytic degradation of organic pollutants.However,due to the influence of material band gap,low carrier separation efficiency and high carrier recombination efficiency,the photocatalytic efficiency of WS₂under specific light source is low.In order to solve these problems,researchers have proposed the methods of morphology control,element doping,heterojunction recombination and crystal adjustment to overcome the above problems.These modification methods are mainly through changing the crystal structure,electronic structure and interface structure of the material itself to achieve the purpose of optimization.In this paper,due to WS₂is a typical in-plane reverse piezoelectric polarization（AB type）material,a new control method is used—piezoelectric effect.The piezoelectric effect of the material does not need to change the crystal structure of WS₂,but only needs to meet the requirements of single layer or odd few layers to achieve the purpose of modification.Therefore,it is necessary to focus on the piezoelectric properties of WS₂and its effect on catalytic performance.The main contents of this paper are as follows:1.WS₂with different layers of nanosheets were prepared by controlling the hydrothermal calcination temperature.a-WS₂（150℃）,b-WS₂（160℃）and c-WS₂（180℃）catalysts were used to degrade Methylene blue（MB）in 60 minutes,and their efficiencies were 99.7%,72.2%and 49.3%,respectively.The results show that the WS₂sheet with odd atomic layers can generate cyclic tension and compression by external mechanical force vibration,and has oscillatory piezoelectric voltage,thus achieving ultra-high piezoelectric catalytic efficiency.Under the action of mechanical stress,WS₂nanosheets can disperse a large number of hydroxyl radicals（·OH）and superoxide radicals（·O₂^-）in solution.The high repetition rate of WS₂was confirmed by cyclic experiments.The piezoelectric response force microscope（PFM）reveals the unique piezoelectric potential of WS₂nanosheets.In this work,we prepared a novel AB type in-plane reverse piezoelectric polarization WS₂nanosheets to overcome the shortcomings of traditional photocatalysis.2.WS₂nanosheets with single and odd few layers were prepared by a simple hydrothermal method.The lattice fringes were observed by high power transmission electron microscope.The number of lattice fringes was larger in single layer and three layers.The degradation efficiency of WS₂was 88.2%in 150 min,97.6%in 90 min and98.2%in 50 min under three modes of photocatalysis,piezoelectric catalysis and piezo-photocatalystic,respectively.The efficiency of the fifth cycle is 85.7%,which shows high cycle availability.The results show that the application of external piezoelectric force can significantly improve the photocatalytic efficiency of WS₂,because the built-in electric field and piezoelectric potential generated by piezoelectric force can promote the separation of photogenerated carriers,which improves the carrier separation efficiency of WS₂semiconductor,resulting in a large number of catalytic active groups（·OH and·O₂^-）,which are more conducive to the catalytic reaction the redox process in the process of oxidation and reduction.In this work,we use the piezoelectric potential of WS₂material to improve the photocatalytic activity,and propose a feasible solution for improving the catalytic efficiency of piezo-photocatalystic materials in the future.