Study On Modification And Performance Of Cu₂WS₄ Photocatalyst

Environmental degradation and energy shortages have become two major problems facing mankind.As a new and friendly technical means,photocatalysis can perfectly solve these problems.Photocatalytic technology has incomparable advantages over other methods,so it has been extensively studied by many scientific researchers.Although the application of photocatalytic technology does not require a lot of manpower and material resources,studies have shown that the main influencing factors that limit its practical application are the light absorption capacity of the photocatalyst and the recombination of internal photogenerated carriers.Therefore,researchers have also tried many modification methods to solve these two bottlenecks,such as defect engineering,construction of heterojunctions,and introduction of promoters etc.,so that photocatalysis technology has seen the dawn of practical applications.The current photocatalytic technology in the actual field is mainly dedicated to the treatment of sewage in the printing and dyeing industry and the photolysis of water to produce hydrogen.Therefore,scientific research is also mainly devoted to improving the reaction efficiency of photocatalytic technology in the above fields.Most sulfides have a certain absorption capacity in the visible light band.For this reason,this paper takes the ternary sulfide Cu₂WS₄ as the research object.In order to solve the shortcomings of its single material Cu₂WS₄ with high photogenerated carrier recombination rate,the introduction of cocatalysts and structural differences the two control methods were combined.Finally,the reaction efficiency of Cu₂WS₄ in dye degradation and light splitting water to produce hydrogen are improved.The first method is to prepare the series of Cu₂WS₄/Ag₂S composites by adjusting the content of Ag NO₃ in the system based on the successful preparation of Cu₂WS₄ by hydrothermal method.A series of tests such as photoelectric show that the introduction of Ag₂S improve the transmission of photogenerated carriers in Cu₂WS₄,the CA25 sample with the best composite ratio has the strongest photocurrent response and the smallest Electrochemical Impedance Spectroscopy.For this reason,the photocatalytic degradation of Rh B dye was tested under LED white light,which was found that compared with Cu₂WS₄ alone,the degradation rate of Rh B dye in the CA25 sample increased by 1.27 times.By testing the hydrogen production of Ag₂S,Cu₂WS₄ and series Cu₂WS₄/Ag₂S composites under visible light,it was found that pure Ag₂S did not detect hydrogen production,and the gas yield of the best composite sample CA25 was19.8umol/h,which was 9.4 times of Cu₂WS₄.Through tested under simulated sunlight found that CA25 sample still have excellent hydrogen production capacity.By free radical capture test and binding energy band structure investigation,the flow of electrons and holes in the Cu₂WS₄/Ag₂S composites is confirmed.It is believed that Ag₂S only acts as the cocatalyst in the composite system,which accelerating the transfer of electrons in the system.Consequently,the Cu₂WS₄/Ag₂S composites has the better photocatalytic activity.The second method is to prepare Cu₂WS₄/Cu_7.2S₄ heterojunction composites by one-step hydrothermal method by changing the content of Cu in the raw material.PL and electrochemical tests show that compared with pure Cu₂WS₄,the one-step hydrothermal method is used to prepare the Cu₂WS₄/Cu_7.2S₄ heterojunction composites has the lower recombination rate of photogenerated electrons and holes and smaller internal transmission resistance,which is more favorable for electrons and holes to participate in the photocatalytic reaction.The photocatalytic performance of the prepared samples was evaluated by degrading two dyes of Rh B and MB.The results showed that the degradation rate of Rh B and MB of the Cu₂WS₄/Cu_7.2S₄ heterojunction composites was increased by 3.67 times and 11 times,respectively,which compared with pure Cu₂WS₄.Therefore,the results proves that the composite sample has stronger photocatalytic performance.Through free radical capture experiments and energy band analysis,it is deduced that the Cu₂WS₄/Cu_7.2S₄ composites prepared by the one-step hydrothermal method forms Type-II heterojunction,which further shows that the transmission and separation of photogenerated carriers in the composite sample has been strengthened.Finally,the photocatalytic activity of the composite sample is improved.