| The development of humankind inevitably brings energy shortage and environmental pollution issues.Despite this awareness,fossil fuels are still the main source of human development.It has paid more and more attention to explore clean energy with high efficiency and low pollution.In view of this,China has proposed the goal of emission peak and carbon neutrality.The achievement of great goals relies on green and environmentally friendly technologies.Semiconductor photocatalysis can transform renewable solar energy into chemical energy through photocatalysts,which has a very broad application prospect and is of great help to solve the energy and environmental issues,thus attracting the attention of researchers.In recent years,halide perovskites represented by MAPbI3 and CsPbBr3 have attracted extensive attention in the fields of solar cells,light-emitting diodes,photoelectric detection,lasers and so on as a new type of photoelectric conversion material.These materials have excellent optical properties,such as wide and adjustable light absorption range,high extinction coefficient,long carrier transport distance and lifetime,etc.However,common photocatalytic reactions such as water splitting need to carry out in water phase,but the thermodynamic instability of halide perovskites in water seriously hinds its application as potential photocatalysts.Therefore,it is important to design a reasonable photocatalytic reaction system.In addition,as a recognized carcinogen,the toxicity of lead seriously restricts the further development of halide perovskites.At present,the main elements that have been reported to replace lead are tin,bismuth,germanium and indium.Bismuth has similar ionic radii with lead and is more chemically stable than other mentioned elements.Therefore,although bismuth is a heavy metal element,it is the best choice to replace lead due to its non-toxic and stable characteristics.Moreover,Chinese bismuth reserves account for 75%of the world’s total reserves,which is also an advantage of developing bismuth-based perovskite in accordance with local conditions.In this thesis,bismuth-based perovskites are applied in the photocatalysis.The photocatalytic performances of them are evaluated in the gas and organic phase via photocatalytic CO2 reduction and photocatalytic selective organic oxidation,respectively.To promote their performance,measures are investigated from the aspects of perovskite properties,reaction system and photocatalytic mechanism.The particle size of perovskite is reduced through the space-confined growth,the carrier lifetime is enhanced through the components control,the photo-gernertated carrier separation efficiency is improved by the synergism of size regulation and energy band engineering,and the recombination of carriers is inhibited by constructing the suitable heterojunction.Details contents are as the follows:In chapter one,the development history,basic mechanism,applied fields of photocatalysis and the common photocatalysts were introduced.Then,the halide perovskites were introduced in detail as promising photocatalysts,including their origin and development history,structure and properties,and main research fields.The research direction and progress of halide perovskites in photocatalysis were introduced emphatically,and the significance of halide perovskites as photocatalysts in gas and organic phases was highlighted.Some problems faced by halide perovskites in photocatalysis and the current research progress of lead-free halide perovskites in photocatalysis were reviewed.Finally,the the topic and research content of the thesis were summarized.In chapter two,we used molecular sieve,a classical regular pore material.Lead-free perovskite Cs3Bi2Br9 was successfully confined growth in MCM-41 molecular sieve by a simple one-step hydrothermal process and the followed chemical impregnation.The characterizations of photocatalysts showed that MCM-41 molecular sieve could effectively reduce the size of perovskite,and the photocatalytic reaction in gas-solid condition could effectively avoid the dissolution and decomposition of perovskite.Performance measurements showed that the Cs3Bi2Br9 particles confined growth in MCM-41 molecular sieve had good photocatalytic capacity for CO2 reduction,which was 9 times higher than that of the original Cs3Bi2Br9.At the same time,the photocatalytic CO2 performances of Cs3Bi2Br confined growth in other molecular sieves were also improved,which proved that the method was universal.Theoretical analysis showed that Cs3Bi2Br9 confined growth in molecular sieve could significantly improve the BET surface area and CO2 adsorption capacity,reduce the activation energy barrier of CO2,and promote the photo-generated carriers separation efficiency.In chapter three,lead-free perovskite Cs3(BixSb1-x)2Br9 solid solution was prepared by coprecipitation method,and the performance of selective oxidation of thioanisole to methyl phenyl sulfoxide in n-hexane was studied.N-hexane could effectively protect the stability of perovskite as an organic solvent.Utilizing a series of characterizations and performance tests,we believed that the introduction of Sb atom could reduce the contribution of Bi p orbital to the conduction band,reduce the influence of Bi vacancy on the conduction band,and thus reduce the defects.Therefore,Cs3(BixSb1-x)2Br9 solid solution had a long carrier lifetime.Owing to the improved carrier migration and long lifetime,this novel lead-free perovskite solution could selectively thioanisole to methyl phenyl sulfoxide efficiently under visible light irradiation.In addition,this solid solution was superior to the most common visible photocatalysts,especially bismuth-based photocatalysts and lead-based perovskite.In chapter four,TiO2/Cs3Bi2Br9 photocatalyst was prepared by anti-solvent method,and their performances were studied via activiation C(sp3)-H bond of toluene.We found that TiO2 could effectively reduce the size of perovskite as a nucleation center.The suitable band position between TiO2 and Cs3Bi2Br9 could make them form type Ⅱ heterojunction after contact.During the photocatalytic reaction process,TiO2 could effectively transfer electrons and form Ti3+ as an important intermediate state.·O2-and H+were the main active species for activating C(sp3)H bond of toluene.We found that the construction of heterojunction could effectively prolong the lifetime of carriers,promote the separation efficiency of carriers,and ultimately improve the performance of the photocatalyst.After 5 hours of direct sunlight exposure,benzaldehyde yield can reach 590 μmol,toluene conversion amount reached 1.4%.In chapter five,we synthesized Cs3Bi2Br9/Bi2WO6 Z-scheme heterojunction composite through anti-solvent method,and continued to explore its performence via photocatalytic selective oxidation of benzyl alcohol in n-hexane.It was found that the size of perovskite could be reduced by increasing the concentration of precursor solution during the preparation process.Performance experiments showed that the Cs3Bi2Br9Bi2WO6 photocatalyst could improve the conversion of benzyl alcohol to benzaldehyde.The charge transfer mechanism in Cs3Bi2Br9/Bi2WO6 was determined to be Z-scheme by in-situ ESR test.The construction of Zscheme heterojunction could promote the space separation of photo-generated electrons and holes,and increase the lifetime of photogenerated carriers,therefore it had better photocatalytic performance.In chapter six,a comprehensive summary of the main research content of this thesis were carried out,the innovation of this thesis was put forward,and the problems and deficiencies in the current work were pointed out and discussed.Finally,the prospect of the future work of was proposed. |
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