| Nowadays,about 80%of the energy that people use is based on unrenewable fossil fuels.However,with the development of society,the continuous consumption of unrenewable fossil fuels has brought some serious problems such as the depletion of energy and greenhouse effect caused by increasing C02 emission.Therefore,developing new types of clean and renewable energy sources is of great significance for solving the energy crisis and preventing environmental pollution.Photosynthesis refers to that higher plants employ chlorophyll as a carrier to convert CO2 and H2O to hydrocarbons and release oxygen under the sunlight irradiation.Obviously,photosynthesis is an effective way to solve the greenhouse effect.However,the ability of photosynthesis to convert CO2 is limited because of the rapid increasing of CO2 emissions.Therefore,simulating and establishing an artificial photosynthesis system with photocatalytic technology provide new possibilities for preventing and controlling environmental pollution.Meanwhile,the hydrocarbons produced by the conversion of CO2 can also be used as fuel,which also has an important contribution to mitigate the energy crisis.Ti-based catalytic materials are widely used in artificial photosynthesis systems due to the advantages of high stability,non-toxicity,and low cost.However,the poor photo-response,low electron transfer rate and fast carrier recombination rate of traditional Ti-based photocatalysts make it difficult to maximize the catalytic performance.In order to improve the efficiency of artificial photosynthesis,this paper proposes a new idea to enhance the photocatalytic performance by constructing ultrathin Ti-based photocatalytic composites,which enhancethe light absorption ability and improve the photocarrier transfer rate by increasing the specific surface area and the dispersion of the active components.Futhermore,the mechanism of ultrathin Ti-based photocatalysts in the photocatalytic CO2 conversion is elucidated through the structure-activity relationship study.Layered double hydroxides(LDHs)are a typical two-dimensional layered inorganic functional materials.In this paper,based on the cation-tunability on the LDHs brucite-like layer,Ti,as a photoactive metal cation,was introduced into the layer of MgAl-LDH to synthesize a TiMgAl-LDH precursor by co-precipitation method.The ultrathin TiMgAl-LDH nanosheets were obtained by exfoliating in formamide solution and immobilized on the surface of graphite oxide(GO)with high-speed electron transfer performance by electrostatic self-assembly.In this way,a series of TiMgAl-LDH/GO composite photocatalysts with different LDH and GO ratios were obtained.The photocatalytic results showed that TiMgAl-LDH/GO composites exhibit higher CO2 reduction activity than bulk TiMgAl-LDH catalysts.A combined study showed the enhanced photocatalytic activity was attributed to increasing Vo-Ti active sites during LDHs exfoliation process,which are benefit to capture electrons and activate reactants.Besides,coupling TiMgAl-LDH with GO can enhance light adsorption and improve separation ability of photoinduced electron-hole pairs.Among the TiMgAl-LDH/GOcomposites,the catalytic activity exhibited a volcanic curve along with the ratios of LDH and GO.When the proportion of GO was 5%,the catalytic activity was optimal,the yields of CH4 and CO were 3.78 ?mol h-1·gcat-1 and 4.64?mol h-1·gcat-1.This is due to the fact that,too much GO can mask some of active sites and thus affects the photocatalytic performance.In-situ DRIFTS spectroscopy was used to understand the active radicals during the reaction.Compared with bulk TiMgAl-LDH catalyst,TiMgAl-LDH/GO composites produced two new active radicals of HCO32-and CO2-indicating the reaction path were changed by GO coupling.The ultrathin TiO2 nanosheets are excellent catalyst supports owing to their high specific surface area and atomic thickness.In this paper,ethylene glycol was used as template agent to synthesize ultrathin TiO2 nanosheets by hydrothermal method.Then Photoinduced reduction method was used to immobilize Pt nanoparticles on the surface,and a novel Pt/Ti02 composite photocatalytic materials was obtained.The Pt/TiO2 exihibited an efficient CO2 photoreduction activity.The yields of reduction products CH4 and CO were 66.35 ?mol·h-1·gcat-1 and 54.22 ?mol·h-1 gcat-1 respectively.The high photocatalytic performance mainly attributes to that ultrathin TiO2 has large specific surface area to enhance light absorption and promote photo-carriers generation,meanwhile the high concentration of Vo-Ti3+ defect sites on the ultrathin TiO2 surface can anchor metal nanoparticles during photoinduced reduction process,resulting in higher dispersion of metal components and enhanced interaction between metal and TiO2 support.Besides,Pt on the catalyst surface also is reactive site which can effectively trap electrons and activate reactants.It is not only inhibit the recombination of photoelectron-hole pairs but also promotes reaction process.The in situ FTIR was carried out to understand the photocatalytic mechanism.The result show that Vo-Ti3+ active sites can activate CO2 to CO2,Pt reactive site splitt H20 to H and OH.CO2 react with H',OH and electron reaction to generate products of CH4 and CO. |
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