Synthesis And Performance Of G-C₃N₄ And Sulfide Photocatalytic Materials

The economy,science and technology in our country have developed rapidly since the adoption of reform and open policy.Especially,the social progress has brought tremendous convenience to people’s life since the 21st,although it simultaneously resulted in the problem of energy shortage.As the population grows and people’s living standards improves,the demand for energy is gradually growing.At present,the energy used by human society such as petroleum,coal and petroleum gas are non-renewable resources and their stocks on the earth are limited.What’s more,human survival cannot be separated from these energy sources.In addition,the reserves of the fossil fuels are declining with the increasing consumption of these resources,which will be depleted sooner or later.Therefore,exploitation of new type of energy resource that does not rely on fossil fuels is urgent.Hydrogen is recognized as a clean energy and is emerging as a low-carbon and zero-carbon emissions energy source.Traditional hydrogen production methods such as the water gas method have a large output but require a lot of equipment,which results in the relatively complicated production process and high production costs.The emergence of hydrogen production from photocatalytic water splitting solves the problem exsiting in the hydrogen energy source,which provides a facile H₂ production technique and significantly reduce the production costs.In this paper,three kinds of g-C₃N₄-basedsemiconductorphotocatalyticcomposites,namelyZn_0.5Cd_0.5S/g-C₃N₄/RGO,g-C₃N₄/Cu₂（OH）₂CO₃ and ZnIn₂S₄/g-C₃N₄/MoS₂ were prepared by simple and mild methods and their structure and morphology were analyzed by XRD,XPS,SEM,TEM and other characterization techniques.The photocatalytic performance of the sample was investigated by photocatalytic decomposition of water into hydrogen.The main contents are as follows:（1）A simple hydrothermal method was used to synthesize Zn_0.5Cd_0.5S/g-C₃N₄/RGO ternary composite photocatalytic materials.The effects of the loading amouts of g-C₃N₄ and graphene on the hydrogen performance of photocatalysts were investigated by photocatalytic decomposition of water to produce hydrogen.When the loading amount of g-C₃N₄ nanosheet was 3 wt%,the hydrogen evolution rate of the obtained Zn_0.5Cd_0.5S/g-C₃N₄ composite photocatalyst reached 4955.89μmol g^-1 h^-1,which was 1.9 times higher than that of pure Zn_0.5Cd_0.5S photocatalyst.When 1 wt%of graphene was further introduced,the obtained Zn_0.5Cd_0.5S/g-C₃N₄/RGO ternary composite photocatalytic exhibited the highest H₂ evolution rate(9836.21μmol g^-1 h^-1),which was about 5.7 times than that of Zn_0.5Cd_0.5S photocatalyst.The photocatalysts were tested by means of fluorescence,transient current and other methods,and it was found that the addition of g-C₃N₄ and graphene can effectively reduce the recombination rate of photogenerated electron-hole pairs,thus significantly improving the hydrogen production performance of the photocatalysts.（2）A series of g-C₃N₄/Cu₂（OH）₂CO₃ composite photocatalysts were prepared by using anhydrous sodium carbonate,copper nitrate trihydrate and g-C₃N₄ as raw materials.The structure and morphology of the catalysts were analyzed by XRD and SEM techniques.The effect of the loading amount of Cu₂（OH）₂CO₃ on the hydrogen evolution performance of the composite photocatalysts was investigated.The results showed that the optimum photocatalytic performance of the obtained g-C₃N₄/Cu₂（OH）₂CO₃photocatalyst could be achieved when the loading amount of Cu₂（OH）₂CO₃ was 3 wt%.The hydrogen production efficiency of the optimum g-C₃N₄/Cu₂（OH）₂CO₃ photocatalyst was as high as 451.97μmol g^-1h^-1,which was about 19.3 times compared to pure g-C₃N₄.（3）A series of ZnIn₂S₄/g-C₃N₄/MoS₂ composite photocatalysts with different loading amuonts of g-C₃N₄ and MoS₂ were synthesized by a mild hydrothermal method at the reaction temperature of 80°C.The effects of the loading amount of g-C₃N₄ and MoS₂ on the performances of the ZnIn₂S₄/g-C₃N₄/MoS₂ternary composite photocatalyst were studied.The results showed that the hydrogen production efficiency of the obtained ZnIn₂S₄/g-C₃N₄/MoS₂ composite photocatalyst reached the highest(3225.91μmol g^-1 h^-1)when the loading amuonts of g-C₃N₄ and MoS₂ were 3 wt%and 1.5 wt%,respectively.The reason for the enhancement of photocatalytic activity was ascribed to the construction of a heterostructure between g-C₃N₄ and ZnIn₂S₄,which effectively reduced the recombination rate of photogenerated electrons and holes,thereby leading to the improvement of hydrogen production efficiency.In addition,MoS₂ as a cocatalyst can not only effectively promote the transfer and transport of electrons,but also enhance the absorption and utilization of visible light.Therefore,the addition of MoS₂ further improved the hydrogen production performance of the composite photocatalyst.