The Preparation, Mechanism And Properties Of Nanosized Anatase TiO₂ With High Phase Stability

Because of its advantages, such as big specific surface area, high surface activity and chemical resistance, nanosized TiO₂ is applied in photocatalytic materials. However, the titania nanocrystal grew up and resulted in poor photocatalytic properties when it was used in the environment of high temperature. So the preparation of nanometer titania with high phase stabilization has attrcted extensive interest.In this paper, the preparation and the mechanism and properties of nanosized anatase TiO₂ with high phase stabilization were studied. the product was attained by boiling reflux and hydrothermal method using TiCl₄ as raw material. The effect of additive on the product by XRD, IR,TEM, HRTEM, XPS and Raman spectra. The main research aspects are as follows:Firstly, the preparation of nanometer anatase titania with high phase stabilization were investigated.The nanometer titania powders were prepared by forced hydrolysis under boiling reflux method. In the experiment, the influences of different additives were studied. It considered that phosphate was in favor of forming anatase structure. When the ratio of the concenrtration of Ti4+ and H₂PO₄^- ions was more than 1:0.01, the product was pure anatase structure. The product prepared by forced hydrolysis using 1.0M Ti⁴⁺ included 38% anatase titania. When calcined at 600oC, the percent of anatase was 2.7%.Appending 0.08M phosphate , the product, which had higher temperature of phase stabilization, was still with anatase structure when calcined at 1000 oC.Secondly, the mechanism of preparation and the phase stabilization of nanometer anatase titania were studied. The influences of H₂PO₄^- was studied by phosphomolybdate blue spetrophotometric method. The mechanism of phase stabilization of anatase titania was studied by IR and XPS. The result was as follows: Ti⁴⁺ and H₂O first become TiO₆^2-. The TiO₆^2- octahedron formed two different structures by combining in different way. The existance of H₂PO₄^- influence the position of the third octahedron. Because of the blocking of H₂PO₄^-, the third octahedron formed anatase titania by zigzag. when calcined H₂PO₄^- ion was moved to the surface of the titania and prevented the transformation of structure. With higher temperature, H₂PO₄^- reduced in inner part of anatase titania, the product transform to rutile.Thirdly, the photocatalytic properties of titania as prepared were investigated. 30-50nm TiO₂ were synthesized by forced hydrolysis method with boiling reflux using TiCl₄ as raw materials. The photocatalytic degradation of methyl orange was studied using nano-TiO₂ powders as catalyst. Calcining the product can increase the photocatalysic. The results show that the degradation rate of methyl orange was 90.87%, with the solution pH=2, TiO₂ calcined at 600oC, the amount of catalyst was 0.8g/L.The last, the preparation of anatase titania by hydrothermal method were studied.As the product prepared by forced hydrolysis under boiling reflux method needed calcination. The well crystalline TiO₂ were prepared by hydrothermal method. The effects of the temperature, the quantity of additive, the concentration of H+ on the crystal structure and shape of the product were discussed.