| With the rapid development of the economy,energy and environmental problems have become increasingly serious issues.Traditional energy resources have limited storage capacity and cause a huge threat to the environment.Hydrogen energy is considered to be one of the cleanest energy sources,and how to efficiently produce hydrogen has been the focus all over the world.Semiconductor photocatalysis technology could convert solar energy into hydrogen energy,which has attracted widespread attention.Graphitic carbon nitride?g-C3N4?has a unique electronic structure and excellent stability,so it possesses great application value in photocatalysis.The structure of molybdenum disulfide?Mo S2?is similar to that of graphitic carbon nitride,and it has a good lattice match with graphitic carbon nitride that a heterojunction structure can be formed between them.Therefore,the g-C3N4/Mo S2 photocatalysts material is a very promising photocatalytic catalyst for hydrogen evolution from water.However,the preparation of g-C3N4/Mo S2photocatalysts materials usually adopts two-step method and multi-step method.The preparation process is relatively complicated and not conducive to the combination of g-C3N4 and Mo S2 at the molecular level.Therefore,in this paper,g-C3N4/Mo S2photocatalysts were prepared by one-step method,and their photocatalytic hydrogen evolution properties were studied.The main research contents include:?1?First,using a mixture of thiourea and molybdenum pentachloride as precursors,Mo S2 was prepared by the sol-gel method.The preparation process,crystal structure,morphology and chemical composition of Mo S2 were characterized by TGA,XRD and XPS.The results show that Mo S2can be prepared at 550?with molybdenum pentachloride and thiourea as precursors.By adjusting the mass of molybdenum pentachloride and thiourea in the precursor,thiourea decomposition could produce sulfur-containing gas and the decomposition product is graphitic carbon nitride at 550?.g-C3N4?T?/Mo S2photocatalysts were prepared by one-step double in-situ method.The results show that Mo S2 is successfully loaded on g-C3N4?T?,and a heterojunction structure is formed.Compared with g-C3N4?T?,the visible light absorption capacity and the recombination ratio of photo-generated electrons and holes of the prepared g-C3N4?T?/Mo S2 photocatalysts are improved.In terms of photocatalytic performance,g-C3N4?T?/Mo S2-4 decomposes water under visible light to produce hydrogen at a rate of 1004.10?mol·g-1·h-1,which is about 5.4 times the rate of hydrogen evolution from g-C3N4?T?.After cyclic hydrogen evolution,the rate of photocatalytic hydrogen evolution did not decrease significantly.?2?In order to improve the photocatalytic hydrogen evolution performance of g-C3N4?T?/Mo S2 photocatalysts,the preparation of g-C3N4?T/U?/Mo S2 photocatalysts were prepared by using the mixture of thiourea and urea instead of thiourea as the precursor.The preparation of g-C3N4?T/U?with the mixture of thiourea and urea as precursor were firstly studied.The results shows that the g-C3N4 energy band structures is different with different precursors,and when the conduction band and valence band is suitable,there is a good lattice match between them,producing the heterostructure formation.The experimental results of photocatalytic hydrogen evolution shows that g-C3N4?T/U??1:1?have the highest photocatalytic performance,and the catalytic hydrogen evolution rate is 1209.85?mol·g-1·h-1,which is about 6.51times that of g-C3N4?T?.After cyclic hydrogen evolution,the photocatalytic hydrogen evolution rate could still be kept.The study found that when the mass ratio of thiourea and urea was 1:1,g-C3N4?T/U?had the best photocatalytic hydrogen evolution.So,the mass ratio of thiourea and urea precursor were fixed to be 1:1 while the mass of molybdenum pentachloride in the precursor was changed.The g-C3N4?T/U?/Mo S2 photocatalysts were prepared by a one-step double in-situ method.The results shows that Mo S2grow on the surface of g-C3N4?T/U?,forming a heterojunction structure.Compared with g-C3N4?T/U?,the light absorption capacity of g-C3N4?T/U?/Mo S2 photocatalysts is enhanced,and the recombination ratio of photo-generated electrons and holes is effectively reduced.The experimental results of photocatalytic hydrogen evolution shows that under the condition of visible light irradiation,the photocatalytic hydrogen evolution rate of g-C3N4?T/U?/Mo S2-7 is 2201.95?mol·g-1·h-1,which is about 1.82times that of g-C3N4?T/U?and 2.19 times that of g-C3N4?T?/Mo S2-4.After cyclic hydrogen evolution,the photocatalytic hydrogen evolution rate did not decrease significantly. |
PDF Full Text Request