Synthesis And Photocatalytic Properties Of Conjugated Polymers Doped With Nitrogen And Sulfur Elements

The consumption of a large amount of energy promotes the rapid and high-quality development of industrial society.Energy depletion,environmental damage and other problems are becoming increasingly prominent.Therefore,it is urgent to seek a kind of clean energy with high energy,green environmental protection and other characteristics.However,solar energy is the most abundant energy in nature,and it plays a dominant role in the development of social energy in the future.Hence,the focus of the present gradually changes to the utilization and transformation of solar energy.Therefore,the current focus is gradually shifting to the use and conversion of solar energy.Hydrogen,whose combustion value is about three times that of kerosene,and the product of combustion is water,which meets environmentally friendly requirements.Photocatalysis of water to produce hydrogen is one of the ideal ways.It is very important to prepare catalysts with high conversion efficiency and low cost.In the early days,inorganic semiconductor catalysts（such as TiO₂,Cd S）were widely concerned,but their existing problems such as narrow light absorption range,large forbidden band value,low adsorption capacity and rapid charge recombination were gradually exposed,which limited their applications.In recent years,organic conjugated polymers have attracted much attention because of their high chemical and physical thermal stability,high light trapping power,πconjugation,flexible structure and high light conversion efficiency.This graduate thesis design and preparation of a large amount of N and S elements doped organic conjugated polymer,by using the polymer pyrolysis water hydrogen production process was carried out by photocatalytic technology performance testing,and considering their chemical structure of the system,and electronic structure and optical band structure of catalytic cracking technology,and the effects of water hydrogen production process.The main research contents include:1.Triazine based conjugated microporous polymers with different linkage units for visible light driven hydrogen evolution:In this work,we synthesized two polymers,which are constructed from two different triazine derivatives as building units and FSO as linking units and Pd-catalyzed Suzuki-Miyaura coupling reaction,analyzed their structure and photocatalytic performance by relevant characterizations.The results show that CMP-1,an organic conjugated polymer with a benzene ring connected to a triazine unit,the best production rate of 9699μmol g^-1 h^-1.The hydrogen production is significantly higher than CMP-2.This work suggests that molecular design is a potent method to optimize the photocatalytic performance towards hydrogen evolution of the CMPs.2.The introduction of dual pyridinic N atoms into analogous conjugated polymer for improved hydrogen evolution:Experimental and theoretical study:with dibenzothiophen-S,S-dioxide（FSO）as linkage units and benzene derivatives as building units,several linear polymers synthesized by Suzuki-Miyaura coupling reaction are dependent on Pd catalysts.Through the characterization,it was proved that the introduction of nitrogen atom can provide more reactive sites to promote the change of the direction of the dipole in the polymer,so as to promote the process of photocatalytic hydrogen evolution.The energy barrier of H activation can be lowered by changing the electron density near Fermi level.Polymers containing the same number of nitrogen atoms（phenanthroline unit and pyridine unit）also exhibit different hydrogen production properties.Compared with BPh SO and PHTSO polymers,the nitrogen-containing polymers BPYSO and PTLSO can better adjust the structure of the polymer,reduce the band gap value,increase the specific surface area,and speed up the separation of electrons and holes.The rate of hydrogen separation in aquatic products reached 2787μmol g^-1 h^-1（PTLSO）,which was significantly higher than the three kinds of polymers(778,1680,and 1992μmol g^-1 h^-1).This work not only synthesized four kinds of photocatalysts,but also opened up a new way for converting solar energy into chemical fuel.3.Effect of thiophene branch unit changes on photocatalytic hydrogen evolution Five kinds of organic conjugated polymers:thiophene derivatives as building units,dibenzothiophene-S,S-dioxide（FSO）as connecting units,Suzuki-Miyaura coupling occurs under the condition of Pt as a co-catalyst reaction.Through structural characterization and electrochemical characterization of five polymers,it was finally found that the hydrogen evolution performance of polymers containing only thiophene structure was significantly higher than that of polymers containing other thiophene derivatives.Among the five organic conjugated polymers,the highest hydrogen production rate reached approximately 14.9 μmol g^-1 h^-1,which was approximately 27times the lowest hydrogen production rate.Obviously,reasonable and effective structure optimization is the key to improve the photocatalytic performance.