Preparation,Characterization And Properties Of TiO₂ Photocatalysts

At present,the issues of environment and energy are the main reasons which hinder the human progress and development.Photocatalysis is one of the most promising technologies to solve these problems.TiO₂ has become the most studied photocatalysts because of its stable physical and chemical properties,high ability,non-toxic,and other advantages.But the shortcomings of the TiO₂,e.g.,only ultraviolet light could be used due to its wide band gap（3.2 e V）,the low quantum efficiency（easy recombination of photogenerated electron-hole pairs）,the few active sites（easy agglomeration）and secondary contamination（difficult to recover）,which limit its further development.The morphology of polyhedral TiO₂ could reduce the recombination possibility of photogenerated electron-hole pairs,the micron-sized spherical mesoporous and floriform TiO₂ could ameliorate the shortcomings of few active sites and secondary contamination,and modification of nobel metal could expand the range of photocatalytic response.In order to improve the property of TiO₂ based on its disadvantages,the polyhedral（octahedral,decahedral）and spherical floriform TiO₂ were prepared by one-step hydrothermal method using potassium titanate nanowires（TNWS）as precursor and the mixed solution with NH₃·H₂O and NH₄F as morphology control agent.The nobel metal Pt was deposited on the surface of TiO₂ by photochemical reduction method with polyhedral TiO₂ mesoporous microspheres as the carrier.The morphology and crystalline phase of the samples were characterized by SEM,XRD and other characterization methods.The photocatalytic properties of the samples were tested,the growth mechanism of TiO₂ and the photocatalytic mechanism were investigated.The experimental results showed that:（1）the polyhedron TiO₂ prepared by hydrothermal method had regular morphology and well mono-dispersion,and its average particle size was about 50～100 nm;（2）the optimal preparation conditions of nano polyhedron and spherical flower TiO₂ were as follows:hydrothermal temperature,time,reaction volume and TNWs’dosage was 200℃,12 h,30 m L,100 mg,respectively.（3）the morphology control agent of octahedron,decahedron and spherical flowered TiO₂ was optimized as the mixed solution of 2 mol L^-1 NH₃·H₂O with 0.1mol L^-1,0.6 mol L^-1 and 1.2 mol L^-1 NH₄F,respectively.（4）the formation of nano-polyhedron TiO₂ was a"solution-recrystallization"process,the stability of F^-1 to（001）crystal plane promotes the formation of decahedral TiO₂,and the formation process of spherical flower-like TiO₂ was a self-assembled nano-decahedron TiO₂particles and then etched into flower flakes.（5）the photocatalytic activity of Pt deposited on the surface of mesoporous TiO₂ microspheres was greatly improved.The photodegradation of methyl orange of the precursor microspheres and octahedral microspheres increased by 13.1%and 25.6%,respectively.In comparison with Pt-P25,the Pt-octahedral and Pt-decahedral microspheres was improved 1.23 and 1.94 times,respectively.The photocatalytic performance of TiO₂was greatly improved by the deposition of nobel metal Pt,due to the Pt had a large work function and the Pt on the surface of TiO₂ would form Schottky defects,which could enhance the photocatalytic response and mobility of photogenerated charges under the sunlight,thus promoting the process of photocatalytic reaction.