Synthesis,Modification And Photocatalytic Performance Of ZnIn₂S₄ Photocatalyst

Semiconductor photocatalysis technology is an effective way to solve the problem of energy shortage and environmental pollution.ZnIn₂S₄（ZIS）photocatalyst has attracted much attention in the field of photocatalysis due to its suitable band structure,stable chemical properties and good visible light response.However,the photocatalytic activity of ZIS semiconductor is hampered by its shortcomings,such as the low photogenerated electron hole separation efficiency and low carrier mobility under visible light irradiation.In this thesis,we modified the ZIS photocatalysts by using several methods including the construction of semiconductor composites,the loading of co-catalyst and the decoration of quantum dots,and then explored the influence of different modification methods on the photocatalytic performance of ZIS and their photocatalytic reaction mechanism.The main research contents of this paper include:1.Preparation and photocatalytic performance of ZnIn₂S₄ photocatalystZnIn₂S₄ photocatalyst was successfully prepared by hydrothermal method using zinc chloride（ZnCl₂）,indium nitrate（In（NO₃）₃·4.5H₂O）and thioacetamide（CH₃CSNH₂）as precursors.The experimental results show that ZIS prepared by hydrothermal method had a hexagonal crystal structure with morphology of petal-like microspheres in a size of 2-5 um,which were formed by the interaction of a large number of nano-sheets.The prepared ZIS photocatalyst had a bandgap of about 2.4 eV,and exhibited good visible light response ability with an absorption edge of about 520nm.Meanwhile,the prepared ZIS photocatalyst showed a relatively low photocatalytic hydrogen production efficiency of 35μmol·h^-1·g^-1,manifesting that the photocatalytic activity of the bare ZIS was not high.2.Preparation and photocatalytic performance of WS₂ nanosheet-decorated ZnIn₂S₄ composites photocatalystsIn this paper,two-dimensional tungsten disulfide（WS₂）nanosheets were firstly synthesized by hydrothermal method using tungsten chloride（WCl₆）and thioacetamide（CH₃CSNH₂）as precursors.A series of WS₂/ZIS composite photocatalysts with different WS₂ mass percentages were then successfully prepared by hydrothermal method.The experimental results show that WS₂ nanosheets could effectively bind to ZIS in the WS₂/ZIS composite photocatalysts.Compared to pure ZIS,the decoration of WS₂ nanosheets could effectively enhance the visible light response ability of ZIS and improve the photocatalytic hydrogen production efficiencies.Among all the prepared photocatalysts,the 3%WS₂/ZIS sample exhibited the highest hydrogen production rate of 199.1μmol·h^-1·g^-1,which was almost 6 times that of pure ZIS and was even comparable to the traditional Pt/ZIS photocatalyst.Meanwhile,the photoelectrochemical（PEC）measurements reveal that the enhanced photocatalytic performance of WS₂/ZIS photocatalysts could be attributed to the formation of the traditional type II heterojunction structure at the interface of ZIS and WS₂,which could promote the efficient separation of photogenerated electron holes and the migration of photogenerated carriers,thus improving the photocatalytic activity of the WS₂/ZIS composite photocatalyst.3.Preparation and photocatalytic performance of WS₂ QDs/RGO/ZnIn₂S₄ composites photocatalystsIn this paper,WS₂ quantum dots（QDs）were firstly prepared by solvothermal method.The RGO/ZIS composite photocatalysts with different mass percentages of graphene oxide（GO）were then successfully prepared by solvothermal method,and the photocatalytic hydrogen production tests demonstrated that the 1%RGO/ZIS sample exhibited the highest photocatalytic hydrogen production activity among all the prepared RGO/ZIS composite photocatalysts.On this base,WS₂ QDs were introduced into the 1%RGO/ZIS photocatalyst to prepare WS₂ QDs/1%RGO/ZIS with different mass percentages of WS₂ QDs by a solvothermal method,labeled as 3%WS₂QDs/1%RGO/ZIS,5%WS₂ QDs/1%RGO/ZIS,7%WS₂ QDs/1%RGO/ZIS,respectively.The experimental results show that the loading of WS₂ QDs on the surface of 1%RGO/ZIS composite photocatalysts could effectively improve the photocatalytic activity of 1%RGO/ZIS.Among all the prepared QDs/1%RGO/ZIS composite photocatalysts,the 5%WS₂ QDs/1%RGO/ZIS photocatalyst exhibited the highest photocatalytic hydrogen production efficiency of about 468μmol·h^-1·g^-1,which was almost 9 times higher than that of pure ZIS.Meanwhile,the 5%WS₂QDs/1%RGO/ZIS photocatalyst also exhibited good photocatalytic activities for effective degradation of methylene blue（MB）,methyl orange（MO）and tetracycline hydrochloride（TCH）.The photocatalytic mechanism of WS₂ QDs/RGO/ZIS composite photocatalysts was further investigated by PEC measurements,PL and UV-vis spectra.It is concluded that RGO could not only effectively promote the transfer of photogenerated electrons,but also provide more active sites for redox reaction.At the same time,the favourable conductivity and light absorption properties of WS₂ QDs as well as the heterostructure formed between WS₂ QDs and ZIS would effectively promote the separation of photogenerated electrons and holes thus leading to the improved photocatalytic performance.