Exploration Of New Photocatalytic Systems For Coupling Hydrogen Production And Organics Transformations

Photocatalytic technology can convert solar energy into useful chemical energy,which is one of the ideal ways to effectively solve the energy and environmental problems facing society today.The use of photocatalytic techniques to achieve organic synthesis is an emerging field in photocatalytic research.Through the photocatalytic technology,the dehydrogenation of organic matter can not only realize the directional conversion of organic matter,but also produce hydrogen at the same time.It is a green and atomic economical reaction.However,the research in this field is still in its infancy.In this thesis,a new photocatalytic system for coupled hydrogen production and organic matter conversion was explored.The thesis mainly includes the following two aspects:(1)We have developed a PtS/ZnIn2S4 reaction system that simultaneously achieves thiols dehydrogenation coupling and photocatalytic hydrogen production under visible light conditions.The co-catalyst PtS was successfully supported on ZnIn2S4 by photo reduction method to obtain the composite catalyst PtS/ZnIn2S4.The structure and composition of the composite catalyst PtS/ZnIn2S4 were studied by XRD,DRS,SEM,TEM and XPS.The catalytic performance of PtS/ZnIn2S4 for dehydrogenation of thiols to disulfides and photocatalytic hydrogen production under visible light conditions was investigated.The effects of solvent,co-catalysts and the amount of co-catalyst on the dehydrogenation of thiols to disulfides and photocatalytic hydrogen production were studied.The results show that the introduction of PtS can greatly improve the activity of ZnIn2S4 catalyzed dehydrogenation of thiols to disulfides and hydrogen.An optimum performance was observed over 0.5 wt%PtS/ZnIn2S4,with a complete transformation of thiols to disulfides in 6 h,and no other by-products are generated,with a 100%atomic economy.Based on the results of the two mechanism inquiry experiment of free radical trapping and hydrogen tracking experiments,the reaction mechanism of thiols dehydrogenation on the surface of PtS/ZnIn2S4 and photocatalytic hydrogen production was proposed.That is,the surface adsorbed RSH(RSH refers to thiols)can react with the photogenerated holes to produce sulfur-centered radicals(RS),which can couple each other to form the corresponding disulfides.In the meantime,the reduction of proton occurs on PtS,which acts as the hydrogen evolution co-catalyst.(2)We have developed a MoS2/ZnIn2S4 reaction system for the catalytic oxidation of 1,2,3,4-tetrahydroisoquinoline and photocatalytic hydrogen production under visible light conditions.The photocatalyst of MoS2 was successfully supported on Znln2S4 by photo reduction method to obtain the composite catalyst MoS2/ZnIn2S4.The structure and composition of the composite catalyst were studied in detail by means of XRD,DRS,TEM and XPS.The catalytic performance of MoS2/ZnIn2S4 for the catalytic oxidation of 1,2,3,4-tetrahydroiso-quinoline and hydrogen production under visible light conditions was investigated.The effects of solvents,co-catalysts and other factors on the oxidation of 1,2,3,4-tetrahydroisoquinoline and its products were studied.The results show that the conversion rate of 1,2,3,4-tetrahydroiso-quinoline can reach 94%within 12 hours under the visible light condition when 1.Owt%MoS2/ZnIn2S4 is used as the catalyst.The main product is 3,4-dihydroisoquinoline and hydrogen,only a small amount of completely aromatic product isoquinoline.Based on the results of the two mechanism inquiry experiment of free radical trapping and hydrogen tracking experiments,the reaction mechanism of 1,2,3,4-tetrahydroisoquinoline oxidation and photocatalytic hydrogen production was proposed.That is,the surface adsorbed 1,2,3,4-tetrahydroisoquinoline can react with the photogenerated holes and removes H+ to generate 3,4-dihydroisoquinoline.In the meantime,the reduction of proton occurs on MoS2,which acts as the hydrogen evolution co-catalyst.The innovations in this thesis are as follows:(1)We have developed a PtS/ZnIn2S4 reaction system that can simultaneously achieve dehydrogenation of thiols to form disulfides and photocatalytic hydrogen production under visible light conditions.(2)We have developed a MoS2/ZnIn2S4 reaction system that can simultaneously realize the oxidation of 1,2,3,4-tetrahydroisoquinoline and photocatalytic hydrogen production under visible light conditions.