Synthesis Of Novel Fluorene-based Organic Conjugated Materials And Study On The Performance Of Photocatalytic Hydrogen Production

With the rapid development of society,the consumption of energy is increasing day by day.The problem of energy shortage and the ensuing consequent environmental problems have become the focus of public attention.It is imperative to develop an environmentally friendly and sustainable new energy.The inexhaustible solar energy and the clean characteristics of hydrogen energy make researchers focus on the research of converting solar energy into hydrogen energy.Photocatalytic decomposition of water to produce hydrogen becomes the most ideal way.The inexhaustible solar energy and the clean hydrogen energy have allowed researchers to focus their attention on the research of converting solar energy into hydrogen energy.Photocatalytic decomposition of water to produce hydrogen has become the most ideal way.Compared with inorganic semiconductor photocatalysts,organic conjugated polymers have become current research central issue due to their outstanding advantages such as adjustable structure,easy modification,high light/thermal stability,and high visible light utilization.In this paper,a series of conjugated linear/network polymerizations with different donors and acceptors were designed for the reasons that restrict the photocatalytic activity of organic polymers,such as the interface reaction of materials,the transfer efficiency of photogenerated carriers and the position of the energy band.The structure-activity relationship between the structure,conjugation length,hydrophilicity,etc.of the polymer and the photocatalytic activity of hydrogen production from water was studied through the experimental characterization of the material structure,hydrogen evolution activity,thermodynamics and photoelectrochemical properties.（1）Fluorene is modified by introducing a hydrophilic group sulfonate on the side chain.Linear conjugated polymers FBT and FOBT were constructed by combining fluorene with benzothiadiazole through Suzuki coupling strategy.The composite photocatalysts FBT@66 and FOBT@66 were obtained by loading with UIO-66（Zr）as the framework.Under the conditions of full spectrum and Pt as the co-catalyst,the hydrogen evolution rate of FOBT@66 can reach 1204.3μmol-h^-1·g^-1,which is 10.2 times that of polymer FOBT.The material exhibited better photocatalytic activity in different concentrations of salt water than in pure water,and the hydrogen evolution rate reached 9304.9,umol·h^-1·g^-1 in 0.1 M NaCl solution.The results show that the linear conjugated polymer FOBT containing sulfonate has better hydrophilicity and enhanced photocurrent response.After being loaded by UIO-66,the charge transfer resistance of the material is further reduced.It indicats that the introduction of sulfonate and MOFs materials is beneficial to reduce the charge transfer resistance,improve the interface reaction efficiency of the materials,and enhance the photocatalytic water hydrogen production performance of the polymer.（2）The conjugated porous polymers FSO3T and FS3T were synthesized by the copolymerization of 1,3,5-tris（5-bromothiophene-2-yl）benzene with the electron acceptor dibenzothiophene modified by the introduction of sulfone group.The effect of sulfone group on the photocatalytic hydrogen evolution activity of the polymer was studied.The results show that the polymer FSO3T containing sulfone group has a wider light absorption range,better dispersion,higher optical band gap and lower charge transfer resistance.Without the addition of any co-catalyst,the hydrogen evolution rate of FSOTT can reach 44101μmol-h^-1·g^-1,which is higher than most reported values in the literature.It indicates that the introduction of sulfone group is beneficial to increase the lifetime of the excited state electron,reduce the electronhole recombination rate,and improve the photocatalytic hydrogen evolution activity of the polymer（3）Based on the basic units of thiophene and thiophene structures with different conjugate lengths,they are copolymerized with dibenzothiophene sulfone to form a series of new organic conjugated porous polymers FSOTT and FSOT.The effect of polymer conjugate length on photocatalytic activity was discussed.It is found that the polymer FSOTT with a longer conjugation length exhibits higher hydrogen evolution activity through experiments.It is worth mentioning that different types of iron,cobalt and nickel metal salts all have a promoting effect on the photocatalytic hydrogen evolution performance of FSOTT,among which cobalt salts perform the most obvious enhancement effect.Under the same conditions,the hydrogen evolution rate of polymer FSOTT with the addition of cobalt nitrate as cocatalyst can reach 13428.5μmol·h^-1·g^-1,which is about 2.31 times of that without the addition of co-catalyst.The results of experiments show that increasing the conjugation length can extend the optical absorption of the polymer and enhance the electronic lifetime of the excited state,and effectively enhance the photocatalytic activity of the polymer to produce hydrogen by water splitting.