Study On The Preparation And Properties Of MIn₂S₄ ?M=Zn?Ca?Mg?Co? Photocatalytic Materials

In order to retard the increasingly serious greenhouse effect and solve the energy shortage problems,generation hydrogen by photocatalytic water splitting and photocatalytic reduction of CO₂ into clean fuels has received extensive attention and research.ZnIn₂S₄?CaIn₂S₄ and CoIn₂S₄ are reported as semiconductor photocatalysts with visible light response.A new semiconductor photocatalysts CoIn₂S₄ is developed firstly.The prepared MIn₂S₄?M=Zn,Ca,Mg,Co?semiconductor material can decompose water to produce hydrogen or reduce CO₂under visible light.In view of the poor photocatalttic activity of MIn₂S₄,in this thesis,MIn₂S₄ was modified by carbon doping,solid solution fabrication and constructing heterojunction to improve their photocatalytic activity.The specific research contents are as follows:?1?MgIn₂S₄,MgIn₂S₄-Cx and MgIn₂S₄-SC were prepared via hydrothermal reaction and low temperature sintering reaction.The test results showed that,for MgIn₂S₄-Cx sample,both bulk-doped carbon and surface-coated carbon exist,while the MgIn₂S₄-SC sample was only coated with carbon on the surface.The photocatalytic reduction of CO2 activity of MgIn₂S₄-Cx and MgIn₂S₄-SC samples was greatly improved compared to MgIn₂S₄.MgIn₂S₄-C2 has the highest photocatalytic activity,and its CO production rate is 20.5 times that of MgIn₂S₄sample.The CO production rate of MgIn₂S₄-SC is only 8.03 times that of MgIn₂S₄.The reason why MgIn₂S₄-Cx samples possess superior photoctallytic activity can be summarized in these three points as follow,high separation migration efficiency of photogenerated charge,strong visible light absorption and strong CO2 adsorption ability.In addition,by contrasting and analyzing the photocatalytic performance differences between MgIn₂S₄-C2 and MgIn₂S₄-SC samples,It can be deduced the function of bulk-doped carbon is to inhibit photogenerated charge recombination and promote charge separation and transfer,while the main role of surface-coated carbon is to enhance CO2 adsorption performance.?2?The crystal systems of ZnIn₂S₄ and CaIn₂S₄ prepared by the same method are trigonal and cubic,respectively.Zn_XCa_1-XIn₂S₄?x=0.8,0.6,0.4,0.2?solid solution are prepared.The CO₂ photocatalytic reduction experiments show that all Zn_XCa_1-XIn₂S₄ solid solutions exhibit better photocatalytic activity than ZnIn₂S₄ and CaIn₂S₄.In all solid solutions,Zn_0.4Ca_0.6In₂S₄exhibited the best photocatalytic performance,the CH₄ and CO evolution rate of which is 16.7and 6.8 times that of ZnIn₂S₄,and 7.2 and 3.9 times that of CaIn₂S₄,respectively.Compared with ZnIn₂S₄ and CaIn₂S₄,with the dcreasment of x value,the potention of conduction band first become more negative and then become positive,which is different from the change law of the conduction band potential in general solid solution.In addition,another heterogeneous solid solution,Zn_XCd_1-XIn₂S₄,was synthesized,and the conduction band potential of the solid solution was also more negetive than that of ZnIn₂S₄ and CdIn₂S₄.?3?A Core-shell structure heterostructural photocatalyst CoIn₂S₄/MgIn₂S_4-x with close contact was developed by using MgIn₂S₄ as the self-sacrificed template to produce CoIn₂S₄.CoIn₂S₄/MgIn₂S₄-2 sample exhibited the best photoctalytic activity among CoIn₂S₄/MgIn₂S_4-x composite photocatalysts.The CH₄ evolution rate of CoIn₂S₄/MgIn₂S₄-2 sample was 7.3 and2.1 times that of MgIn₂S₄ and CoIn₂S₄,respectively.?4?A series of x CoIn₂S₄/g-C₃N₄ composite photocatalyst was synthesized by in-situ crystallizing CoIn₂S₄ nanospheres on the matrix of g-C₃N₄.30%CoIn₂S₄/g-C₃N₄ sample has the highest photocatalytic activity,and its H₂ generation rate was 5.2 and 23.9 times that of g-C₃N₄ and CoIn₂S₄,respectively.It is indicated that the construction of heterojunction structure can promote charge separation and promote photocatalytic performance.