The Synthsis Of Composite Nano-sized Photocatalysis Material For Visible Light Photocatalytic Reduction Of CO₂

With the rapid development of industrialization and modernization, the need for energy is increasing. The excessive consumption of coal, oil and natural gas and other fossil fuels which are the main energy source is the primary reason for the increase of greenhouse gases like CO2 in the atmosphere, broking the balance of the natural carbon cycle, and then leading to global warming. At the same time, the shortage of fossil fuels results in energy crisis. Photocatalytic reduction of CO2 into useful hydrocarbon fuel is an ideal way to reduce carbon emissions and provide new energy, and it is one of the effective ways to achieve the carbon cycle. In recent years, inspired by the photosynthesis of green plants, a technology that using CO2 as a raw material and semiconductors as catalysts, converting CO2 to hydrocarbon fuel under the irradiation of sunlight has attracted extensive attention. A lot of semiconductor materials can be used as photocatalysts, but each have their own disadvantages. At present, the full researched TiO2 that owns the advantages of cheapness, non-toxic, stabilization, and easy preparation is widely used in photocatalytic splitting of H2O, photocatalytic reduction of CO2 and degradation of organic pollutants. But the high recombination rate of photo-generated electron-hole pairs and lack of utilization of visible light limit its application in photocatalytic reaction. Suporting noble metals on the surface of semiconductors to increase light absorption and assembling other semiconductor on the surface of semiconductors to regulate the energy band structure are helpful to improve the photocatalytic properties of semiconductor materials. In this dissertation, we prepared two composite photocatalytic materials and applied them to photoreduction of CO:. The details are summarized as follows:(1) Au nanoplates were synthesized with use of surfactant under the condition of the oil bath, and TiO2 nanosheets with high activity{001} plane exposed were synthesized under hydrothermal condition. The Au-TiO2 nanocomposite consisting of {001} exposed TiO2 nanosheet-anchored Au nanoplate was successfully fabricated by using bifunctional linker molecules. Being applied for photocatalytic reduction of CO2 into hydrocarbon fuels, this unique nanocomposite benefits for the combination of higher photocatalytic activity of TiO2 (001) and the visible to near-infrared region plasma resonances of the anisotropic Au nanostructure. Several carbon fuels were selectively produced over the Au-TiO2 nanocomposite, including CO, CH4, CH3OH, and CH3CH2OH and so on under different light irradiation and reaction systems.(2) An all-solid-state Bi2WO6/Au/CdS Z-scheme system was constructed for the photocatalytic reduction of CO2 into methane in the presence of water vapor. This Z-scheme consist of Bi2WO6 and CdS as photocatalysts, and Au nanoparticle as solid electron mediator offering a high speed charge transfer channel and leading to the more efficient spatial separation of electron-hole pairs. The photocatalytic efficiency of the Z-scheme exhibits remarkable enhancement relative to pure Bi2WO6, Bi2WO6/Au and Bi2WO6/CdS.