The Synthesis Of Sulfone Group-containing Organic Conjugated Polymer And Its Photocatalytic Performance Of Water Splitting To Produce Hydrogen

The development of hydrogen energy plays a vital role in solving the energy crisis and environmental pollution problems.Using solar photocatalytic water splitting is considered as a promising hydrogen production technology.So far,the most reported photocatalysts are inorganic semiconductor materials based on metal oxides or sulfides.However,these photocatalysts are generally limited by low visible light activity,complicated synthetic procedures and shortage of natural resources of rare metals.Therefore,from the sustainable development of perspective,it is highly desirable to develop a class of green renewable metal-free photocatalyst materials.In recent years,a new type of organic photocatalyst materials with great development potential and have been received extensive attention due to easily tuneable energry bands and electronic structures,abundantly building blocks,diversely synthetic methods and easily functional modification.At present,organic semiconductor photocatalyst materials still have defects such as weak visible light response,low transport efficiency of charge carriers,and low photocatalytic activity and poor photocatalytic stability.Therefore,developed organic polymer photocatalytic system with strong visible light response,high activity and stability has become one of the most important research topics in the field.In general,a high-efficiency organic photocatalyst should feature with a broad visible light adsorption ability,proper bandgap,and efficient photogenerated electrons and holes transport and separation capabilities,which could be finely tuned by the selection of building blocks.This master’s thesis designed and synthesized a series of linear organic conjugated polymers and three-dimensional cross-linked conjugated microporous polymer photocatalysts with electron donor and acceptor structures.The nolecular structure,band structure and electronic properties of the polymers were systematically studied for the effect on photocatalytic hydrogen production performance.The main contents were researched,including the following three aspects:（1）Light-induced charge-transfer and charge-separation abilities could be promoted by the molecular structure of electronic donor and acceptor of the building blocks.Organic linear conjugated polymers were designed and synthesized by thioxanthone as acceptor unit,benzene or biphenyl as donor unit.The effects of the length of the coupling unit and the electronic structure on the photocatalytic performance were investigated.Furthermore,the sulfur atom was oxidized to a sulfone group in the molecular structure of thioxanthone,and the effects of photophysical properties,conjugated degree,charge transfer and separation on photocatalytic performance were investigated.The results demonstrated that oxidated sulfur atoms to sulfone groups in the molecular structure of thioxanthone contributes to increasing the electron withdrawing capacity of the acceptor stmcture and strengthening the delocalization of electrons in the LUMO energy level,significantly improved the photocatalystic performance and apparent quantum yield of the prepared polymer.Under ultraviolet visible light irradiation,the photocatalytic hydrogen production rate of the prepared polymer TXO-P could reach 3774 μmol h^-1 g^-1,and the apparent quantum efficiency was 2.5%at an incident wavelength of 400 nm.（2）A series of linear organic conjugated polymers and three-dimensionally crosslinked conjugated microporous polymers were prepared by 2,7-disubstituted or 1,3,6,8-tetrasubstituted pyrene and thioxanthone-S,S-dioxide or thianthrene-5,5’,10,10’-tetraoxide,respectively.Investigated the different substituted position of electron donor building blocks and the structure type of the acceptor had influence on the photocatalytic performance.The results showed that the conjugated skeleton between the 2,7-disubstitxuted pyrene and the acceptor has higher coplanarity than the 1,3,6,8-tetrasubstituted linking pattern,which effectively promotes intramolecular charge transfer and the red-shift of optical absorption in D-A polymers skeleton.In addition,containing the sulfone unit thianthrene-5,5’10,10’-tetraoxide had stronger pull-electron effect than the molecular structure of thioxanthone-S,S-dioxide including the carbonyl group,which promote rapidly charge separation,significantly increased the photocatalytic activity and apparent quantum yield.Under the full-arc spectrum（>300 nm）,Pt modified the polymer PySEO-1 with the best optimized D-A structure exhibited photocatalytic hydrogen production rate of 9477 μmol h^-1 g^-1 and showed excellent photocatalytic stability under the visible light.（3）Conjugated microporous polymers were designed and synthesized by pyrene as donor,dibenzothiophene-S,S-dioxide as acceptor.The effect of pyrene and the linking pattern of the building block of dibenzothiophene-S,S-dioxide on the photocatalytic hydrogen evolution was studied.The results displyed that the photocatalytic activity of the polymer PyDOBT-1 with the 3,7-linked dibenzothiophene-S,S-dioxide is much higher than that PyDOBT-2 with 2,8-linking pattern.The main reason was that the 3,7-linking pattern enhances the conjugation chain length and improves the coplanarity of the polymeric backbone,which facilitate the charges migration along the polymer chains,thereby improved its photocatalytic activity.The bare PyDOBT-1 showed an impressive visible light activity with a hydrogen evolution rate（HER）of 5697 μmol h^-1 g^-1.A appealing HER of 12986 μmol h^-1 g^-1 was obtained by the Pt-modified PyDOBT-1 under the full-arc spectrum（>300 nm）,which lies toward the upper end compared to that of the reported organic photocatalysts.