Conjugated Small Molecules For Photocatalytic Hydrogen/Oxygen Evolution

Solar energy and hydrogen energy are both clean energy with great utilization value.Photocatalytic water splitting provides a promising way to utilize solar energy by transferring water into hydrogen and oxygen.The development of new photocatalysts for water splitting has become a hot area in recent years.In the selection of photocatalysts,organic conjugated materials have received wide attention due to their advantages of low-cost,diverse structures and variable energy levels,all of which contribute to their versatile photocatalytic application.However,compared to inorganic materials,the photocatalytic efficiency of organic conjugated materials is still lagging behind,and the relationship between structures and properties remains to be explored.This dissertation aims to explore the photocatlytic hydrogen evolution and oxygen evolution of conjugated small molecules.The effects of structures,energy levels,aggregation states,surface charges and cocatalysts of conjugated small molecules on their performance of photocatalytic hydrogen/oxygen evolution were systematically studied.In the second chapter,we selected a series of low cost and simple process diketopyrrolopyrrole-based organic dyes as photocatalysts for hydrogen evolution and explored their structural impact on photocatalytic performance.All of the three dyes had good absorption of visible light,and had suitable energy levels for photocatalytic hydrogen evolution.It was found that the substituents in these molecules showed great impact on their photocatalytic performance.Among the three molecules,DPP-CN with cyan groups showed the best dispersibility in water,excellent interface contact with cocatalysts and the best photocatalytic hydrogen evolution efficiency of 569.26?mol g^-1h^-1.In the third chapter,we designed and synthesized a series of water/alcohol soluble perylene diimide based small molecules.The rational design of these small molecules greatly improved the driving force for charge separation,while increasing their dispersibility to enlarge the reaction interface,both of which contributed greatly to the photocatalytic performance.The small molecule with chlorine atoms and quaternary ammonium salts side chains showed the best photocatalytic oxygen evolution efficiency of 92.8?mol g^-1h^-1.Moreover,it was found that the counterions?Br^-?of perylene diimide small molecules greatly accelerate oxygen evolution by improving the generation of OH?radicals.In the fourth chapter,we introduced Co₃O₄ as cocatalyst into the oxygen evolution system in the previous chapter,and explored the impact of Co₃O₄cocatalysts on the oxygen evolution performance of different small molecules.Our research found the introduction of Co₃O₄ can effectively inhibit the recombination of photogenerated charges,and the water-soluble side chains in small molecules allow good dispersity in water and could assemble into the surface of Co₃O₄,resulting improved photocatalytic oxygen evolution rates.