Study On The Performance Of Organic Conjugated Polymer Photocatalytic Decomposition Of Water To Produce Hydrogen

The various aspects of human life and scientific progress are closely related to energy.Traditional energy systems are mainly based on fossil fuels,which lead to environmental pollution because of the emission of greenhouse gases from the burning of fossil fuels.On the other hand,fossil fuels,as a kind of non-renewable energy,would be exhausted by overexploitation.These are the two major problems that limit the development of human.As a result,it is highly desirable to develop efficient and environmentally friendly energy systems to address energy crisis and environmental pollution.Solar energy has the advantages of plentiful and renewable,the focus of scientific research workers has gradually shifted to the usage and conversion of solar energy.Photocatalytic hydrogen production from water is an ideal way to the conversion of solar energy,in which the key issue is how to synthesis a kind of catalysts with strong visible light response and high quantum yield while low costs.In the past decades,most studies have mainly focused on metal-based inorganic semiconductor photocatalysts,which suffer from the low photocatalytic activity under visible light,toxicity,and the limitation of resource,reduced the possibility of large-scale industrialization.Great progress has been made in the inorganic metal sulfides for photocatalytic hydrogen production.However,these catalysts show photocatalytic activity only in the ultraviolet region.Compared to traditional inorganic semiconductor photocatalyst,conjugated polymers feature with ? electrons along the polymer chain,high physicochemical stability,tunable chemical and electronic structures and strong absorption to visible light,which make conjugated polymers great potential as photocatalysts for hydrogen evolution.In this thesis,a series of linear conjugated polymers and conjugated microporous polymers photocatalysts have been designed and synthesized through structural design.The influences of polymer structure,band gap and electronic property on the photocatalytic performance were studied in detail:(1)A series of novel linear conjugated polymers was synthesized by Pd(0)-catalyzed Suzuki-Miyaura coupling reaction using nitrogen-containing species as acceptor and pyrene as the basic building block.Photocatalytic performance has been improved by increasing of nitrogen content.The polymer PyPm,in which the nitrogen atoms are in the m-position,exhibits the highest photocatalytic hydrogen production activity of 18.7 ?mol h-1 and good photocatalytic stability.PyDZ and PyPz with nitrogen atoms in the o-position and p-position show weak photocurrent and photocatalytic hydrogen production activity due to the different internal dipole orientation which against charge transport.The results reveal that the construction of an electronic push-pull system is an efficient strategy to produce linear conjugated polymer photocatalysts with high photocatalytic performance.The structure-performance relationships revealed in this work offer a fundamental understanding in the rational design of organic polymer photocatalysts.(2)Three dibenzothiophene dioxide-containing conjugated microporous polymers(DBTD-CMPs)were synthesized via Pd(0)-catalyzed Suzuki-Miyaura coupling reaction.A study on the effect of the comonomer linker length on the photocatalytic performances for hydrogen evolution was conducted by changing the comonomers from benzene to biphenyl,and to p-terphenyl with four polymerizable functional groups.It was found that the increasing of the comonomer linker length leads the decreasing of photocatalytic activity of the resulting polymers due to the increased twisted polymer skeleton leading to the decreased conjugation degree and planarity of the polymer,which block the light-induced charge carriers transport and separation.As a result,DBTD-CMP2 with the comonomer of benzene exhibited an enhanced photocatalytic efficiency with a high hydrogen evolution rate(HER)of 2460 ?mol h-1 g-1 under visible light irradiation(?>420 nm)without Pt co-catalyst.Remarkably,the Pt-loaded DBTD-CMP2 showed an attractive HER of 9200 ?mol h-1 g-1 under UV-Vis light irradiation with an apparent quantum yield(AQY)of 3.3%at 400 nm,demonstrating that these dibenzothiophene dioxide-containing CMPs are great promising organic photocatalysts for hydrogen evolution from water.