Design And Synthesis Of DA-type Organic Conjugated Microporous Polymer And Its Photocatalytic Water Splitting For Hydrogen Production

With the rapid development of the global economy,the energy crisis and environmental pollution are becoming more and more serious.Hydrogen is an ideal clean energy system because of its advantages of high heat of combustion,high atomic utilization and environmental protection.Using solar energy to produce hydrogen by photocatalytic decomposition of water is considered as a potential hydrogen production technology.Since the first TiO2 photocatalyst was developed in 1972,researchers have developed a variety of semiconductor photocatalysts and preparation strategies to improve the photocatalytic performance of photocatalytic hydrogen production by water decomposition.At present,most photocatalysts are mainly based on metal oxides(such as TiO2),sulfide(such as CdS),selenide(such as CdSe)and other inorganic semiconductor materials.However,most inorganic semiconductor photocatalysts have many problems,such as complex preparation procedures,large pollution emissions and weak visible light response.Therefore,the development of a new type of photocatalyst with simple preparation,low cost and high activity has become one of the important research topics in this field.Compared with inorganic semiconductors,organic semiconductors are characterized by simple synthesis,diverse synthesis methods,easy design of chemical structure,easy regulation of electronic properties,and sustainable development.Therefore,organic semiconductors are a new type of photocatalyst materials with great development potential,and have attracted extensive attention from many researchers in recent years.The activity of photocatalyst is affected by many factors,mainly in the absorption capacity of visible light,the migration capacity of photogenerated carriers,the separation efficiency of photogenerated electrons and holes.The master's thesis is mainly through the construction of electron donors-receptor(D-A)type organic conjugated polymer microporous light catalyst,through regulating the topology of the comonomer,receptor cell types and kinds of the base to realize effective control of the electronic structure,system research effect of organic conjugated polymer microporous photocatalytic performance of the main structural factors,so as to build A team with efficiency photocatalytic hydrogen production activity of organic conjugated polymer microporous photocatalyst,A new method of preparation,specific research content mainly includes the following three aspects:Effect of thiophene content on photocatalytic hydrogen production by triazinyl organic conjugated microporous polymer:A series of terpolymer containing 2,4,6-triphenyltriazine,benzene and thiophene units were designed and synthesized.The results showed that with the increase of thiophene content,the band gap of the prepared polymer decreased gradually and the absorption range of visible light was expanded.At the same time,the electron delocalization of the polymer was improved,and the separation of photogenerated electrons and holes was promoted.Therefore,in the prepared series of polymers,polymer 0DB3Th with the highest thiophene content showed the highest photocatalytic hydrogen production activity.When exposed to visible light,the hydrogen production rate reaches 1204 mol.h-1·g-1.Effects of the topological structure of the copolymer on the photocatalytic production of hydrogen from sulfoxide class organic conjugated microporous polymers:Two series of novel d-a organic conjugated microporous polymer photocatalysts were designed and synthesized by using perylene and dibenzothiophensulfone as acceptor units and dibenzothiophensulfone as acceptor units.The results showed that the hydrogen generation activity of dicarbazole-constructed polymers was higher than that of perylene polymers under the same conditions,because the lone pair electrons of nitrogen atoms on dicarbazolium had better electron giving capacity than that of perylene.In addition,the methyl-substituted unit dibenzothiophensulfone receptor unit reduces its electron pulling ability due to the electron donating property of methyl group,which reduces the separation of photoelectron and hole,resulting in low hydrogen production rate.The prepared polymer CzDOST showed a photocatalytic hydrogen production rate of 1604 mol·h-1·g-1 under visible light.Effects of substituent on photocatalytic production of hydrogen from sulfoxide class organic conjugated microporous polymers:On the basis of the above,two D-A organic conjugated polymer photocatalysts with different substituents were designed and synthesized with pyrene with good planarity and high conjugation as the donor unit and dibenzothiophensulfone with F atom or methyl group as the acceptor unit.The effects of F atom and methyl group substitution on the photocatalytic properties of polymer were studied.The results show that pyrene has good planar structure,which improves its electron-giving ability,and also promotes the photoelectron transport performance of the polymer.On the other hand,due to the strong electron-pulling effect of F atom,the electron-pulling ability of the receptor unit dibenzothiophensulfone was further improved,which promoted the separation of photogenerated electrons and holes.However,the methyl group has an electron-donating effect,so it reduces the electron-pulling capacity of the receptor unit,thus inhibiting the effective separation of photogenerated electrons and holes in the polymer.Therefore,under visible light irradiation,the polymer PyDF prepared by F atom substitution showed a photocatalytic hydrogen production rate as high as 13.47 mmol h-1 g-1,indicating that the introduction of substituent with strong electron pulling effect into the receptor unit was an effective way to improve the photocatalytic activity of organic conjugated microporous polymer.