Metal-loaded Strontium Titanate For Photocatalytic Reduction Of Carbon Dioxide

As we know,the world's energy consumption mainly depends on fossil fuels,such as coal,natural gas and petroleum.However,with the excessive utilization of unrenewable fossil fuels and the rising atmospheric concentration of carbon dioxide,environmental pollution and energy crisis become two serious issues.It is extremely urgent to look for a renewable energy.As a type of abundant,clean and renewable energy,solar energy is a suitable candidate to replace traditional fossil fuel energy Photocatalytic reduction of carbon dioxide to hydrocarbon fuels using solar energy is a promising and attractive option for simultaneously solving the above two serious problems.Since CO₂ cannot absorb irradiation in the range of 200-900nm,the key to the photoreduction of CO₂ is to develop an efficient photocatalyst which has proper positions of the valence and conduction band for oxidation and reduction half-reactions of water and CO₂,respectively.SrTiO₃ is a typical perovskite-type semiconductor photocatalyst which has been widely reported for water splitting and photodegradation of organic pollutants.It has attracted lots of attentions in terms of its superior photocorrosion resistibility,nontoxicity and photochemical stability.The band gap of SrTiO₃ is about 3.2eV and the bottom of the conduction band?CB?and the top of the valence band?VB?are located at-0.88V and 2.32V?vs NHE,pH=7?,respectively,which means that the photogenerated electrons in the CB are more negative than reduction potentials of CO₂ into HCOOH,CO,HCHO,CH3OH and CH4,and the corresponding photogenerated holes in the VB can easily oxidize H2O.In other words,SrTiO₃ has the feasibility of the photocatalytic reduction of CO₂.In this paper,based on the mechanism of photocatalytic reduction of CO₂,we analyze the prerequisites that an ideal semiconductor photocatalyst for CO₂ photoreduction needs to meet,the main factors affecting photocatalytic performance,as well as some methods to improve the activity of semiconductor photocatalyst.SrTiO₃ particles were synthesized by a sol-gel method and then metal?Ag,Pt,Au?nanoparticle cocatalysts were loaded onto the surface of SrTiO₃ by a liquid-phase chemical reduction method.The structures and properties of photocatalysts were characterized by means of X-ray diffraction?XRD?,UV-visible diffuse reflectance spectra?UV-vis DRS?,BET surface-area analyzer?BET?,scanning electron microscopy?SEM?and high-resolution transmission electron microscopy?HR-TEM?.The photocatalytic activities of SrTiO₃ for CO₂ reduction in a gas phase reaction system were investigated in detail.Furthermore,we focused on studying the function of metal nanoparticle cocatalysts loaded on the surface of SrTiO₃.Based on the characterization and the photocatalytic results,pure-phased SrTiO₃ particles with a porous structure were successfully prepared,and metal?Ag,Pt,Au?nanoparticle cocatalysts obviously improved the photocatalytic activities of SrTiO₃ samples for CO₂ photoreduction.Among all the samples,SrTiO₃-lwt%Pt exhibited the best performance.In addition,SrTiO₃-lwt%Pt also exhibited a good stability after a long-time reaction process for photocatalytic reduction of CO₂.The SEM and HR-TEM results indicated that Pt nanoparticles with an average diameter of about 3-5nm were highly dispersed on the surface of SrTiO₃,where Pt site acted as the electron trapper and reaction active sites to decrease the recombination rate of photogenerated electron-hole pairs,and enhanced the photocatalytic activity finally.