| At present,the energy supply of human society is excessively dependent on fossil fuels.However,fossil fuels are non-renewable energy,which will release a large amount of carbon dioxide gas in the process of use,resulting in significant greenhouse effect and serious environmental pollution.Therefore,the development of renewable energy and the development of green,sustainable and economic chemical processes is an important challenge in the field of chemistry.Among the alternatives,solar energy is particularly attractive because it is abundant,readily available and clean.Scientists have extensively studied photocatalytic reactions that use sunlight as energy.These reactions can split water to make hydrogen as clean fuel,reduce carbon dioxide to produce carbonized chemical fuels,degrade organic pollutants and sterilize efficiently,and promote organic conversion of value-added chemical feedstocks.At present,photocatalytic materials such as Ti O2,g-C3N4 and Cu2 O have been reported to have the ability of photocatalytic splitting of water and photocatalytic reduction of CO2.However,most photocatalysts are far from perfect,and they have some shortcomings,such as easy recombination of photogenerated charge,poor photoreduction potential,weak electron supply activity,lack of catalytic active sites and so on.Therefore,the design and development of new semiconductor photocatalysts with suitable performance is an important way and means to achieve high efficiency,high selectivity and high stability of water spliting and CO2 reduction.Halide perovskite semiconductors are a new class of cheap and easy-to-prepare photocatalytic semiconductors,which have excellent optoelectronic properties and extraordinary defect tolerance,showing the following advantages:(1)high optical absorption coefficient,band gap is easy to adjust;(2)long carrier diffusion distance,effectively prolong carrier lifetime;(3)there is a suitable charge transfer in the redox reaction,which is suitable for the field of photocatalysis in which solar energy is converted into chemical energy.However,essentially,halide perovskite materials are easy to form and damage,and their decomposability is homologous to the formation of low defects.Under external stimuli(such as water,polar solvents,oxygen,heat and radiation),halide perovskite is easily decomposed into its binary halide components.In practical applications,photocatalytic water decomposition and CO2 reduction need to be carried out in aqueous phase or polar solvent phase.Therefore,the relative reactivity and instability of halogenated perovskite materials limit their application as photocatalysts in the field of photocatalysis.This dissertation is devoted to developing strategies to improve the stability of halide perovskite materials,through surface encapsulation protection,phase transition recombination,and crystallographic component optimization to achieve high stability in aqueous photocatalytic water splitting and carbon dioxide reduction,which provides a new idea for the photocatalytic reaction of halide perovskites in polar solvents.First,using the surface encapsulation technology,the halide perovskite Cs Pb Br3 material was encapsulated on the surface of the nickel phosphide material to prepare a highly stable photocatalyst material,and realize the efficient photoelectric splitting of water to produce hydrogen;secondly,the two-phase perovskite material was constructed using the strategy of copper doping-induced phase transition to achieve high-efficiency photocatalytic CO2 reduction and greatly improve the selectivity of methane products;finally,a new perovskite-based catalyst oxygen-doped dimethylstanniodide(DMASn I3(O))was prepared through the optimal design of crystalline components,and a highly selective photocatalytic reduction of CO2 in aqueous phase to ethylene(C2H4)was achieved.Specifically,this thesis consists of the following four parts:Chapter 1.Overview.This chapter mainly introduces the rise,structure and properties of halide perovskite materials,the working principle and research progress of halide perovskite materials.This paper focuses on the application of halide perovskites in photocatalysis,especially the research progress of water splitting and carbon dioxide reduction.Finally,the purpose and significance of the research,the content and innovation of this paper are expounded.Chapter 2.Encapsulation of all-inorganic perovskite Cs Pb Br3 in bulk Ni2 P for stable and efficient photoelectrochemical application.In this work,nickel phosphide is used to encapsulate perovskite quantum dots to solve the stability problem,and photoelectrochemical hydrogen production in aqueous solution is realized.Here,guided by theoretical calculations,an encapsulation strategy is proposed to fabricate Cs Pb Br3/Ni2 P core/shell nanostructures.Compared with the pristine Cs Pb Br3 nanocrystals,the Cs Pb Br3/Ni2 P nanostructures exhibited remarkable increase in the photocurrent density and long-term stability in aqueous solution and exhibited excellent PEC hydrogen production activity with a Faradaic efficiency approaching 100%.The encapsulation strategy opens an avenue for rational design of perovskite-based photocathodes for efficient and stable PEC water reduction.Chapter 3.In situ preparation of copper-doped biphasic Cs Pb Br3-Cs4 Pb Br6inorganic perovskite nanocomposites for efficient and selective photocatalytic CO2 reduction.In the present work,the biphasic perovskite facilitates electron transport,the doping of copper element greatly increases the product selectivity,and the eightelectron reduction process produces methane.Converting carbon dioxide to chemical fuels using renewable energy is an attractive way to deploy carbon-harvesting technologies.Halide perovskite nanocrystals are considered be one of the most promising light-harvesting materials for photocatalytic applications.However,most perovskite-based photocatalysts promote the two-electron reduction process to CO,which is difficult for the eight-electron CH4 production pathway.Here,we developed a facile in situ transformation strategy to prepare Cu-doped biphasic Cs Pb Br3-Cs4 Pb Br6inorganic perovskite nanocomposites(Cu/Cs Pb Br3-Cs4 Pb Br6 NCs).Compared with pristine Cs Pb Br3 nanoparticles,Cu/Cs Pb Br3-Cs4 Pb Br6 NCs exhibited a 4.2-fold increase in the photocatalytic efficiency for CO2 reduction and a 303% increase in the electron consumption rate.In addition,a significant increase in the selectivity for converting CO2 to CH4 was also achieved.78.6%.The in-situ conversion strategy paves the way for the rational design of perovskite-based photocatalysts for efficient and stable redox emission.Chapter 4.Photocatalytic reduction of CO2 with perovskite-based DMASn I3(O)for selective ethylene productionThe high value-added product C2H4 was obtained by using a perovskite-based catalyst for aqueous photocatalytic CO2 reduction.Due to the gap between the relatively low multi-electron transfer efficiency in photocatalysis and the sluggish C-C coupling kinetics,it remains a great challenge to realize the reduction of C2+ hydrocarbons(such as C2H4)from CO2 in photocatalytic systems.Here,a two-dimensional flake-like oxygen-doped DMASn I3 photocatalyst(DMASn I3(O))was synthesized using DMASn I3 single crystal as the precursor.The yield of C2H4 was 10.48 μmol·g-1·h-1 and the electron selectivity was 87.02% when DMASn I3(O)was used as catalyst for CO2 reduction in aqueous environment(water as hole scavenger)under light.The results show that large number of active adsorption sites are produced through the optimization of crystal composition,and the anchored intermediates are further coupled to form C2H4.This work demonstrates a novel approach for highly selective reduction of CO2 to C2+products by perovskite-like materials in photocatalytic systems. |
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