| With the increase of CO2 greenhouse gas emissions, seeking new sources of energy to build a low carbon society becomes more and more urgent since the 21st century. Conversion of CO2 to valuable hydrocarbon fuel driven by solar energy is a promising way to realize the global carbon balance, with great potential. The use of CO2 as a raw material containing carbon compounds conversion technologies including biological transformation, thermochemical, electrochemical conversion and photocatalytic reduction.Biotransformation is the use of algae bio catalysis conversion of CO2 carbon energy compounds; thermochemical conversion is through thermochemical conversion method, the CO2 conversion utilized as a kind of organic compounds; electrochemical conversion is used metal electrode reduction of CO2 water or non aqueous solution of hydrocarbons or alcohols chemical fuel; photocatalytic conversion is a semiconductor material in the solar light using reducing agent carbon dioxide reduction to hydrocarbons or alcohols chemical fuel. Since CO2 is thermodynamically very stable compounds, where C with+IV valence, so in these transformation processes need a high energy input to break the C=O bond, such as heat energy, electric energy, solar energy and so on. In the CO2 conversion technology, compared with other input energy, solar energy is free, clean and pollution-free, abundance and distribution of the extensive energy. Earth per second received solar radiation energy up to 173000 terawatts (TW,1012 w), about 500 million tons of standard coal combustion to provide energy. So as one of the technology of artificial photosynthesis, photocatalytic reduction of CO2 for hydrocarbon fuels is to reduce CO2 emissions and at the same time, the production of an ideal way to usable fuel, and implementation of the carbon cycle is one of the effective methods.We did the following works:(1) To obtain ultrathin Na2V6O16·xH2O nanoribbons, we uses fresh V (3+) precursor solution obtained through directly dissolving vanadium metal thread in NaNO3 solution using a solid-liquid phase arc discharge (SLPAD) route. The nanoribbon is of uniform and smooth diameter along the growth direction and a typical length of up to 500μm, a thickness of about 5 nm. And the nanoribbons were used as photocatalyst in the photocatalytic reduction of CO2 into CH4 under visible light irradiation (λ>420 nm), and extihited large enhancement of the photocatalytic activity.(2) The Ag-TiO2 double-shelled hollow sphere was synthesized through hydrothermal treatment of colloidal TiO2 obtained from TBOT and Ag mixed solutions. It is believed that the Ostwald ripening process (crystallites grow at the expense of the smaller ones) may involve the formation of the hollow spheres, through TEM images with different time of reaction. The significant increase of photocatalytic activity of Ag-TiO2 hollow spheres was confirmed with photoreduction of CO2 into renewable fuels (CH4) under visible light irradiation (λ>420 nm), relative to bare TiO2. The large enhancement of the photocatalytic activity benefits from:(1) The SPR of Ag nanoparticles greatly activate TiO2 for visible light harvesting (400-700 nm). During light irradiation, electrons generated from the SPR-induced Ag migrate to and are injected into the TiO2 CB to take part in the redox reactions (2) The hollow structure may also act as a phono trap-well to allow the multiscattering of incidence light for the enhancement of light absorption. Double-shell architecture may further strengthen this scattering process. (3) Due to the special structure, the Ag-TiO2 hollow sphere possesses high a specific surface area of about 60.87 m2/g,3 times larger than that of bare TiO2 (20.35 m2/g), which will provide more reaction sites for the photoreduction of CO2. |
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