Preparation,Characterization And Property Of Mesoporous TiO₂ Microspheres

Environmental pollution and energy shortage are the biggest problems that plague human progress and development in the 21st century.Photocatalysis is one of the most promising technologies to solve this problem.As the most studied photocatalyst,TiO₂ is one of the best candidates due to the advantages of its good chemical stability,non-toxicity and low cost.However,the disadvantages of TiO₂,such as easy aggregation leading to fewer active sites,fast recombination between photogenerated electron and hole resulting in low quantum efficiency,limiting its further application.Therefore,it is very important to fabrication TiO₂ with high photocatalytic efficiency.The problems of small specific surface areas and few active sites could be solved by preparation of spherical mesoporous TiO₂ and thus the photocatalytic efficiency could be improved.In addition,spontaneous separation of photogenerated electron-hole pairs could be realized by fabrication of TiO₂ with specific high-energy facets and thus improve the photocatalytic efficiency.The photocatalytic activity of TiO₂ would be improved significantly if these two methods were combined together,i.e.,by preparation of spherical mesoporous TiO₂ with specific high-energy facets.However,the traditional method for preparation of mesoporous TiO₂ is relatively cumbersome and easily introduce impurities,which could influence the subsequent processing and application.The fluoride ion is usually introduced as a capping agent during the preparation of TiO₂with specific high-energy facets,while the compounds of fluoride ion are usually toxic,which is harmful to the environment.In order to solve the above problems,the following studies were conducted.Firstly,the mesoporous TiO₂ microspheres were prepared from tebutyl titanate?TBOT?without template agent and surfactant by using the modified St?ber method.The influences of various experimental factors on the preparation of mesoporous TiO₂microspheres were investigated,and finally the obtained samples were calcined.The morphology,specific surface area and crystalline phase of the samples were characterized by SEM,BET and XRD,respectively,the photocatalytic activity was evaluated by photodegradation of methyl orange.The result shows that the obtained powder without calcination is amorphous monodisperse mesoporous spherical TiO₂,which basically has no photocatalytic activity.The crystalline phase was changed after the calcination process and the photocatalytic activity increased first and then decreased with the increase of calcination temperature,and the degradation rate reached the maximum at 700°C.Subsequently,the above-mentioned amorphous mesoporous TiO₂ microspheres were used as the precursor,and mesoporous TiO₂ microspheres with high energy facets were prepared without other additives by a hydrothermal/solvothermal method using an ethanol/water mixed system.The morphology,crystalline phase and specific surface area of the obtained samples were characterized by SEM,XRD,and BET,and the photocatalytic activity was evaluated by hydrogen evolution.The experimental results show that the product after hydrothermal treatment is mesoporous TiO₂ microspheres with high energy facets which assembled from nanocrystals,the crystalline phase is anatase,and the morphology of nanocrystals could be adjusted by the volume ratio of ethanol to water.Its photocatalytic activity increased first and then decreased with the increase in the amount of deionized water,and the photocatalytic activity reached the maximum when the amount of deionized water was 6 m L,which is nearly 40 times that of commercial P25.Additionally,the ethanol was replaced by isopropanol during the hydrothermal/solvothermal method,and the influences of various experimental parameters on the product morphology under the isopropanol system were investigated.The experiment result shows that the variation pattern of the isopropanol/water mixture system was similar to that of the ethanol/water mixture system,but the nanocrystals on the surface of the microspheres show unique morphology by the isopropanol mixture system.