| Hydrotalcite(LDHs)is a kind of multi-function material,and is widely used in the fields of adsorption,degradation,catalysis,photoelectric chemistry and so on.With the continuous progress of technology,its application in photocatalysis is particularly outstanding.Single LDHs photocatalytic activity is very limited,so the researchers use various methods to improve.At present,the effective improving measures are sythesis of LDHs-semiconductor composite materials,which formed heterogeneous structure composite photocatalyst.The main principle is based on the synergistic effect between LDHs and semiconductor material.The main application fields of LDHs composite photocatalysts are dye degradation,wastewater treatment,hydrogen and oxygen production,etc.But their use on the photocatalytic desulfurization of fuel has seldom been reported.In this work,a composite photocatalyst composed of different LDHs and carbon nitride materials was constructed,and its photocatalytic reaction mechanism and desulfurization performance for model oils were discussed.A green desulfurization system was formed with LDHs composite as catalyst,air as oxidant and acetonitrile as extraction agent.This provides an idea and valuable exploration for the photocatalytic desulfurization of model oil and the construction of new photocatalyst.The main research content is as follows:(1)Ten LDHs/g-C3N4 composite photocatalysts were prepared,and their photocatalytic oxidation desulfurization performance was compared with pure LDHs for model oil.Two kinds of ZnM-LDHs/g-C3N4(M=Al,Cr)composite photocatalysts with the best desulfurization activity were selected,by which 100%of desulfurization can be achieved within 3 hours.(2)Taking ZnM-LDHs/g-C3N4(M=Al,Cr)as the example,the effect of catalyst's heterostructure on the photocatalytic oxidation desulfurization performance of model oil was investigated.The catalytic mechanism of the two composite catalysts and their catalysis difference were analyzed by XPS,PL,TRPL,ESR,photocurrent and sideband position.It was found that a Z-Scheme heterostructure was formed between the LDHs and the semiconductor,which not only effectively inhibited the recombination of electron holes,but also provided a high redox potential,promoted the photocatalytic oxidation activity and realized the bicomponent collaborative desulfurization.The difference in desulfurization activity between the two composites is mainly attributed to their difference in energy band structure,resulting in different electron migration rate,carrier life and the number of active species.This kind of catalyst has good reusability and good removal performance for other thiophene sulfides.(3)Four C3N4 with different structure of g-C3N4,g-C3N4(550),pg-C3N4 and pg-C3N4(550),was synthesized by different preparation methods.XRD,UV-Vis DRS,PL and other characterization methods were used to analyze their crystal types,light absorption range,electron hole separation efficiency,as well as their photocatalytic oxidation desulfurization activity.Among them,pg-C3N4 shows the highest diffraction peak intensity,the best crystal shape,the smallest band gap width,fast electron migration rate,low electron and hole recombination rate,the best photocatalytic oxidation desulfurization performance,and greatly enhanced visible light activity.A series of CoAl-LDHs/pg-C3N4 composite photocatalysts were synthesized by in situ growth method.When the light source was xenon lamp,81.2%of desulfurization rate can be achieved in 3h.The desulfurization reaction mechanism was discussed in terms of XPS,TRPL,Mott-Schottky and other characterization ways.The results show that the visible light absorption efficiency and electrochemical properties of CoAl-LDHs/pg-C3N4 composite are superior to that of ZnM-LDHs/g-C3N4(M=Al,Cr).The heterostructure formed by the two components has significant synergistic effect and greatly improves the photocatalytic desulfurization activity.At the same time,CoAl-LDHs/pg-C3N4 has good reusability and removal capacity for different thiophenic sulfur substrates. |
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