Facet-control Synthesis Of SrTiO₃ Nano-catalysts And Their Photocatalytic Properties And Mechanisms

In recent years,indoor air quality has gradually become a key factor that affects human health.The most common and harmful pollutant in indoor air pollutants is formaldehyde,which has been identified as a class of carcinogen by the world health organization.Moreover,the energy crisis has also become a major concern of people,owing to the excessive exploitation of traditional non-renewable energy sources such as coal,oil and natural gas.As a kind of green technology with broad prospects,photocatalytic technology is widely applied in the field of environment and energy.As a typical perovskite oxide,strontium titanate（SrTiO₃）has become a promising high-efficiency photocatalyst due to its unique photoelectric properties and high-efficiency photocatalytic activity.However,the exposed facet of semiconductor nanomaterials is an important factor to influence its photocatalytic activity.Therefore,three kinds of SrTiO₃ nano-catalysts with different exposed facets were prepared with the hydrothermal method in this research,and we strive to study their photocatalytic oxidation activities of HCHO as well as photocatalytic activities of hydrogen production.In addition,the photocatalytic activities of three kinds of SrTiO₃nano-catalysts were further improved by loading graphene.The main contents are shown as follows:（1）Three kinds of SrTiO₃ nano-catalysts with different exposed facets were successfully prepared with the simple and rapid hydrothermal method.Multiple characterization analyses confirm that the morphology of SrTiO₃-001 nano-catalyst is a cubic structure only with six exposed{001}facets,while the morphologies of SrTiO₃-110-1 and SrTiO₃-110-2 nano-catalysts are all octadecahedron structure with six exposed{001}facets and twelve exposed{110}facets,but the proportion of exposed{001}facets in SrTiO₃-110-2 nano-catalyst is smaller while the proportion of exposed{110}facets is larger.Furthermore,three kinds of SrTiO₃ nano-catalysts have the same valence band position,and SrTiO₃-110-1 and SrTiO₃-110-2nano-catalysts have the same conduction band position,which are much higher than that of SrTiO₃-001 nano-catalyst.（2）The photocatalytic oxidation reaction of HCHO by SrTiO₃ nano-catalysts could follow the pseudo-first order reaction kinetics.The oxidative degradation rate of HCHO by the SrTiO₃-110-2 nano-catalyst is nearly 4.1 and 6.8 times faster than that by the SrTiO₃-110-1 and SrTiO₃-001 nano-catalysts,respectively.In addition,the removal rate of HCHO and the yield of CO₂ didn’t show any decrease trend even after five cycles by SrTiO₃-110-2 nano-catalyst,which exhibited stable photocatalytic oxidation performance and favorable recycling.The capture experimental data and EPR test results indicate the exposed{110}facets of SrTiO₃ nano-catalysts could effectively activate O₂ molecules to combine with electron to produce O₂^·-,while the exposed{001}facets didn’t have this effect.The main reasons are the case that comparing with SrTiO₃-001 nano-catalyst,SrTiO₃-110 nano-catalysts possess relatively higher conduction band position,lower surface adsorption energy for O₂molecules,stronger charge separation ability as well as advantageous charge accumulation on the adsorbed O₂ molecules.（3）RGO/SrTiO₃ composite nano-catalysts with low loads were successfully prepared by one-step hydrothermal method.A variety of characterization analyses indicate that graphene was really compounded with SrTiO₃,and the SrTiO₃nanoparticles in the RGO/SrTiO₃ composite nano-catalysts were uniformly dispersed on the single-layer graphene nanosheets.The experimental results indicated that SrTiO₃-110-2 nano-catalyst exhibited the optimum performance of hydrogen production,and hydrogen production activities of RGO/SrTiO₃ composite nano-catalysts were all significantly improved after loading grapheme.Moreover,hydrogen production rate of 1wt.%of RGO/SrTiO₃-110-2 sample was the fastest,which still showed a good performance even after three cycles.（4）Noble metal auxiliary Pt nanoparticles can serve as electron reservoirs and act as active sites for hydrogen production in the hydrogen production reaction.The synergetic effects between Pt nanoparticles and graphene nanosheet can inhibit the photogenerated electron-hole pair recombination and reduce the electron-hole recombination rate,so as to enhance the photocatalytic activities for hydrogen production of RGO/SrTiO₃ composite samples.The 1wt.%RGO/SrTiO₃-110-2composite nano-catalyst exhibited the best performance of photocatalytic hydrogen production,owing to the highest electron-hole separation capacity.SrTiO₃ nano-catalyst with{110}facet,synthesised by facet-control,possessed high-efficiency properties of photocatalytic degradation of organic pollutants and hydrogen production in this reaserch,which has important reference value for the design of other high-efficient photocatalysts.