Preparation And Photocatalytic Performance In Visible Light Of Composite Semiconductor Based On WO₃

As an important N type semiconductor material,WO₃ has extensive research value in gas sensing,photochromic,electrochromic,superconducting and photocatalysis,etc.because of its unique physical and chemical properties.Especially in the field of photocatalysis,for the narrow gap width of 2.4².8eV,WO₃ can be directly excited by visible light and has high utilization rate of solar energy.It is one of the semiconductor photocatalysts with wide application potential.The research shows that single-phase photocatalysts,usually haing some defects which are difficult to overcome,are not conducive to the progress of photocatalytic reaction.Because of the high recombination of photogenerated charges and low conduction band potential,WO₃ has poor quantum efficiency that restricts the photocatalytic efficiency.Therefore,how to improve the separation efficiency of the electron-hole pairs and conduction band potential has become a hot topic in the field of WO₃ photocatalysis.In recent years,it has been proved that composite semiconductor photocatalysis can not only regulate the energy band,but also reduce the recombination rate of photo-generated charges by the difference of levels.It is an effective modification technology.Based on WO₃,we studied the preparation,morphology and photocatalytic degradation of RhB of composite semiconductors WO₃/Mo S₂ and WO₃/MoS₂-rGO,and the photocatalytic mechanism of WO₃/MoS₂-rGO was also discussed.The detailed work and research results of this paper are as follows:?1?Based on the effect of reaction temperature on the morphology and structure of semiconductor,we prepared WO₃ single-phase semiconductor by hydrothermal synthesis method under different temperatures.By comparing the morphology,crystal phase,UV-visible light absorption and photocatalytic degradation of RhB,we explored the growth process of WO₃ and obtained the most suitable hydrothermal temperature.?2?Based on the optimal hydrothermal temperature of WO₃ preparation,WO₃/MoS₂ compound semiconductor was synthesized by two-step hydrothermal method.The effect of MoS₂ loading and solution pH value on the photocatalytic activity of WO₃/MoS₂ was investigated.The results showed that the loading of MoS₂ should be appropriate.The increase of MoS₂ can increase the number of heterojunctions and promote the separation of electron-hole pairs,but excessive MoS₂ can hinder the contact between the catalyst and the solution and reduce the light absorption.Under the combined action of electrostatic adsorption and alkaline conditions,the catalyst has the best degradation efficiency at the pH=6.?3?OnthebasisofWO₃/MoS₂,WO₃/MoS₂-rGOcompound semiconductors was synthesized by adding GO.The effects of MoS₂-rGO loading,pH value of the solution and photocatalyst concentration on the photocatalytic activity of WO₃/MoS₂-rGO were investigated and the results were in agreement with WO₃/MoS₂.Based on the optimum loading of MoS₂-rGO and pH value of the solution,the influence of photocatalyst concentration on the degradation rate was further explored.The results show that in a certain concentration range,the degradation performance improves when the photocatalyst concentration increases,and the comparison with other semiconductors shows that the catalyst has good catalytic performance.?4?In order to verify the effect of MoS₂ and rGO on photocatalytic efficiency,the photocatalytic properties of MoS₂,WO₃,WO₃/MoS₂ and WO₃/MoS₂-rGO were compared and the order of efficiency was in sequence of MoS₂<WO₃<WO₃/MoS₂<WO₃/MoS₂-rGO.It is verified that the heterojunction formed by adding MoS₂ is beneficial to the separation of photogenerated charge.The high conductivity of rGO makes the interface charge transfer more smooth and improves the photocatalytic activity of WO₃.?5?The photocatalytic mechanism of WO₃/MoS₂-rGO compound semiconductor was initially discussed.According to the typical charge transfer method,we proposed two photocatalytic mechanisms,namely the typical type II heterojunction and Z-type system.The energy band distribution and experimental results of active species capture agent show that the typical type II heterojunction system is irrational and verify that the photocatalytic mechanism of WO₃/MoS₂-rGO conforms to the Z-type system.