Fabrication Of 3D Porous SrTiO₃ Microspheres And Their Photocatalytic Activity For Cr（Ⅵ） Reduction

During past decade,semiconductor photocatalysis technology has been developed rapidly due to its high catalytic performance,low cost,and no secondary pollution etc,which provide a sustainable method for Cr（Ⅵ）removal.SrTiO₃ semiconductor is one of the most widely used materials owing to its excellent photochemical stability and optical properties,as well as low cost.Moreover,SrTiO₃ has the higher reduction capacity than TiO2 because of its more negative conduction energy band,which is about 200 mV.However,it is difficult for pure SrTiO₃ to use visible light due to its wide band gap（3.2 eV）.Thus,we have fabricated a novel type of SrTiO₃ with three-dimensional（3D）porous SrTiO₃ microspheres,which can enhance light adsorption ability.Besides,La adopted SrTiO₃ with porous architecture has been synthesized,which can improve the visible-light photocatalytic activity of SrTiO₃.Three-dimensional（3D）porous SrTiO₃ microspheres have been fabricated by a solgel-templating method using the agarose gel bead containing SrCO₃ granules as the template.The resultant SrTiO₃ microspheres,several tens of micrometers in diameter,exhibit a bimodal pore structure,in which the macropore about 70-150 nm in size stems from SrCO₃ granules and the mesopore about 3 nm is formed via removing the agarose fiber embedded in the composite microspheres.The porous framework of SrTiO₃ microspheres is assembled by regular single-crystalline SrTiO₃ nanocubes with an edge length of 100 ± 10 nm.The highly interconnected porous network renders numerous pathways for the rapid mass transport,strong adsorption of reactants and multireflection of incident light.Moreover,the as-prepared SrTiO₃ microspheres exhibit excellent photocatalytic performance for the Cr（Ⅵ）reduction under simulated sunlight,which can reduce nearly 100% Cr（Ⅵ）at pH=2 within 2 h and retain a relatively high reduction ability after four recycles.3D porous La-doped SrTiO₃（STO-La）microspheres have been synthesized to imptove the visible-light phtocatalytic activity of SrTiO₃ using the agarose gel bead containing SrCO₃ granules and La2O₃ particles.The result STO-La microspheres have macropore about 100 nm on the surface.Based on the analysis of XPS and XRD,La3+ substitutes Sr2+ and forms an impurity energy level in the conduction band of SrTiO₃,resulting in the visible light photocatalytic activity of SrTiO₃ microspheres.The La3+ doping content can be regulated easily by changing the initial concentration of La2O₃.Furthermore,STO-La-0.5 sample behaves the highest photocatalytic activity under visible light,which can reduce about 84% Cr（Ⅵ）within 100 min at pH=2.