超薄二氧化钛纳米片的合成及其光还原CO2性能的研究

摘要

Due to the peculiar intrinsic properties of ultrathin TiO2 atomic layersand theirpotential applications for photocatalytic CO2 reduction, the ultimate goal ofinvestigation elucidated in this dissertation was to reduce CO2 into hydrocarbon fuelsvia the photocatalysts.Therefore, using a facile and scalable lamellar hybrid strategy,novel atomic layers have beensynthesized and hence showed enhanced photocatalyticactivities in CO2 reduction to hydrocarbon fuels.The details of this dissertation aresummarized concisely as follows:
　　(1) In the first chapter, the author briefly interpreted the ultrathin two-dimensionalnanosheets, because during the past few years the mainresearch focus was on thetwo-dimensional ultrathin nanosheets after the impetus from the NobelPrize-winning work of graphene.These peculiar properties such as, (i) quantumconfinement, (ii) large surface area, (iii) ultrahigh level of active sites, and (iv) atomiclevel thickness, endow the ultrathin nanosheets with a new regime for deliveringauspicious prospects to fulfill people' requirements regarding the generation ofrenewablehydrocarbon fuels from CO2 reduction.The hydrocarbon fuels generatedby ultrathin nanosheets may be methane, methanol, formate etc., which could beutilized to mitigate future energycrises.
　　(2)In the second chapter, the main fascination for the research work wasmanifested in detail.Actually, carbon dioxide (CO2) being the greenhouse gas is themost notorious gas released by natural and artificial processes.Unluckily, due to theescalation of industrial progress, this balance has progressively been messed up,generating more CO2 in environment and leading to the global warming phenomena.Therefore, great attention has been paid on the CO2 conversion into useful chemicals,which seems tobe the main desire of current scenario.Hence, this environmentalissue stimulates us to trail an appropriate material model for studying the CO2
　　reduction into valuable chemicals, in which the atomically thin two-dimensional TiO2nanosheets could serve as an ideal model, owing to their (i)relatively large surfacearea, and (ii) the ultrahigh fraction of active sites for photocatalyfic CO2 reductioninto hydrocarbon fuels.
　　(3)In the third chapter, the author first clarified the synthesis strategies used forTiO2 atomic layers fabrication.Basically, these novel materials have been synthesizedby solvothermal methods using a lamellar hybridization strategy.Main benefits ofthese methods are (i) convenience,and (ii) cost effectiveness which canaugment theprobability of nanosheetssynthesis up to the industrial level.Therefore, this approachhas opened a new route in the world of materials science to tune the materialperformance.In the second part, characterizations of ultrathin nanosheets usingvarious advanced techniques and theunderstanding of their clear structure-propertycorrelation have been illustrated.
　　(4) In the fourth chapter, the author first realized the synthesis of 1.66 nm thick TiO2atomic layers byvirtue of a lamellar TiO2-octylaminehybrid precursor, followed bythe investigation of their photocatalyticCO2 reduction.Photoreduction of CO2 intofuels over TiO2 helps to relievethe increasing energy crisis and theworsening globalclimate, however, the low energetic efficiency impedes itslarge-scale applications.Herein, ultrathin TiO2 layers are first put forward to fully optimize their crucialCO2photoreduction processes through affording abundant catalyticallyactive sites andincreased two-dimensional conductivity.Ultimately, the atomic thickness of 1.66 nmendows TiO2 with ultrahigh fraction of surface atoms, which ensures stronger UVlight absorption and higher CO2 reduction ability compared with its bulk counterpart.
　　Benefitting from the increased density of states near Fermi level and the vast majorityof charge density concentrating on the surface, the TiO2 atomic layers show increasedconductivities, which is confirmed by the temperature-dependent resistivities.The 3times higher fluorescence lifetime, revealed by time-resolved fluorescencespectroscopy, accounts for the increased separate rate of photoexcited electron-holepairs.As an outcome, the TiO2 atomic layers achievea formate formation rate of 1.9μmolg-1 h-1, 450 times higher than that of bulk counterpart and also roughly2 timeshigher than that of previously reported Ag-modified BaLaaTi4O15.Briefly, this study will unlock many opportunities for designing efficient CO2photoreduction.
　　Keywords: Ultrathin nanosheets; titanium dioxide; atomic layers; CO2reduction;photocatalytic reduction; hydrocarbon fuels; formate

目录

声明

ABSTRACT

Table of Contents

Chapter 1 Introduction

1．1 Novel Functionalities of Ultrathin Nanosheets

1．1．1 Electric and Optical Properties

1．1．2 Magnetic Properties

1．1．3 Thermal Properties

1．2 Catalytic Applications of Nanosheets

1．2．1 Photocatalytic Applications

1．2．2 Water Splitting and CO2 Reduction

1．3 CO2 Reduction into Valuable Fuels

1．4 Strategies of CO2 Reduction into Hydrocarbon Fuels

1．4．1 Chemical Conversion Technology

1．5 Fame of Photocatalytic Reduction of CO2 into Fuels

1．6 Principle and Mechanism of Photocatalytic Reduction of CO2

1．7 Fundamental Reactions occurring on the Semiconductor Catalyst

1．8 Band Energy Requirements during Photocatalytic Reduction

References

Chapter 2 Motivation for Research Project ＆ Investigation Objective

2．1 Motivation for Research Project

2．2 Research Objective

References

Chapter 3 Synthesis Strategies ＆ Characterizations of Ultrathin Nanosheets

3．1 Materials and Chemicals

3．2 Materials Synthesis Routes

3．2．1 Hydrothermal Route

3．2．2 Solvothermal Route

3．3 Integrative Material Synthesis Strategies

3．3．1 In-Situ Integration of Guest Organic Moiety

3．3．2 Intercalation／Exfoliation of Organic Moiety

3．4 Characterizations for the Ultrathin Nanosheets

3．4．1 X-ray Diffractometry

3．4．2 Scanning Electron Microscopy

3．4．3 Transmission Electron Microscopy

3．4．4 Atomic Force Microscopy

3．4．5 Raman Spectroscopy

3．4．6 Fourier Transform Infra-red spectroscopy

3．4．7 X-ray Photoelectron spectroscopy

3．4．8 Thermogravimetric Analysis

3．4．9 Diffuse UV-Visible Reflectance Spectroscopy

3．4．10 Ion Chromatography

3．4．11 Time Delay Florescence Spectroscopy

3．4．12 Resistivity Measurement

References

Chapter 4 TiO2 Atomic Layers Boosting Photocatalytic CO2 Reduction into Formate

4．1 Introduction

4．2 Research Objective

4．3 Characterization

4．3．1 Calculation Details

4．4 Experimental Section Details

4．4．1 Synthesis of Lamellar TiO2-octylamine Hybrid Precursors

4．4．2 Synthesis of TiO2 Atomic Layers

4．4．3 Synthesis of Bulk TiO2

4．4．4 Photocatalytic Measurements

4．5 Results and Discussion

4．6 Conclusions

References

Chapter 5 General Conclusions ＆ Future Perspectives

5．1 Conclusions

5．2 Future Perspectives

List of Publications

ACKNOWLEDGEMENTS