Morphology Control And Photocatalytic Performance Of TiO₂ Based Nano-Materials

Titanium dioxide(TiO2)is realized as the most popular photocatalyst due to the unique photocatalytic-related properties such as high oxidation activity,good chemical stability,non-toxic,low cost and easy manufacture.However,conventional TiO2 has some drawbacks such as low utilization rate of sunlight,lack of reactive sites and high electron-hole recombination rate.In order to resolve this problem,we synthesized a series of morphologies of TiO2 with higher specific surface area to increase the reaction active sites.In addition,to reduce the recombination of electron-hole pairs,novel Au@TiO2 yolk-shell nanostructures(Au@TiO2-YS)were also prepared by a hard template method with an open-air hydrothermal process..The morphology,composition,and optical properties of the products were characterized by several advanced techniques such as TEM,XRD,and UV-vis spectroscopy,respectively.Finally,the photocatalytic properties of the products were evaluated by degrading organic contaminant.The main results can be summarized as below:(1)The TiO2 hollow structures were successfully synthesized by the aid of a hard template(uniform silica nanospheres)as a sacrificial layer.After removal of the template by the dissolution of sodium hydroxide,TiO2 hollow structures(TiO2-HS)with uniform size and good dispersion were obtained by high-temperature calcination.The cavity diameters could be adjusted by controlling the size of the template.The UV-vis spectra indicate that the absorption peak of the product shows a gradually red shift with the increase in the cavity size.The red shift is favor for the utilization of sunlight,further promoting photocatalytic performance.The TiO2-HS with the cavity size of 220 nm shows the highest kinetic constant(0.00521 min-1),which is 1.35 times higher than that of pure TiO2 nanoparticles(0.00384 min-1).(2)The sheet-like TiO2 hollow structures(SL-TiO2-HS)were successfully prepared by the hydrothermal treatment of the TiO2 hollow precursors.The results show that such a structure exhibits strong adsorption capacity and good photocatalytic performance.Moreover,the adsorption performance and photocatalytic performance increase with the diameter of the cavity.The best adsorption and photocatalytic performance can be found from the product with the cavity diameter of 250 nm.(3)The dendritic branched TiO2(D-TiO2)was prepared by a sol-gel method and a hydrothermal method.It is found that the absorption peak of the D-TiO2 was also red-shifted,compared to pure TiO2 nanoparticles.The photocatalytic performance has been greatly improved,and its kinetic constant(0.01567 min-1)is 4 times higher than that of pure TiO2 nanoparticles.(4)The Au@TiO2-YS structures were successfully synthesized by the aforementioned hard template in which various Au sizes served as a core.The yolk-shell structures show tunable absorption bands based on different Au core size.Moreover,Au@TiO2-YS structures exhibit enhanced photocatalytic activities toward MB under solar light irradiation compared to the TiO2 nanoparticles.The 50 nm Au@TiO2-YS structures show the highest kinetic constant(0.00704 min-1),which is 1.83 times higher than that of TiO2 nanoparticles.