Potassium fluoride,anhydrous
           Potassium fluoride,extra pure
           Potassium fluoride,Granular
           Silicon Dioxide
           Hydrofluoric acid
           Synthetic Cryolite
           Potassium Fluoaluminate
           Ammonium bifluoride
           Potassium Bifluoride
           Aluminium fluoride
           Sodium fluoride
           Potassium Fluorosilicate
           Fluorosilicic Acid
           Sodium silicofluoride
           Potassium Hydroxide Flakes
           Magnesium Fluoride
           Magnesium fluorosilicate
           Barium Fluoride
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To address these problems, we use a Hydrofluoric acid solution to etch SiO2 spheres. The effect of HF amounts on the structure and performance of TiO2 catalysts were investigated. The size of SiO2 templates decreased at some extent when the amounts of HF solution below 0.1 mL, and were not completely etched away. With increasing the amounts of HF solution, the SiO2 cores were completely removed, meanwhile, the anatase TiO2 nanocaps were produced when the amounts of HF solution more than 0.2 mL. The HRTEM images of sample EST-3. The results indicate anatase TiO2 nanocaps consisted of small TiO2 nanoparticles with an average size of 50 nm in diameter. The well crystallinity of particle shown in Fig. 3f is ascribed to high calcination temperature. The noticeable lattice fringes spacing of 0.33 nm is consistent with the (101) facet of anatase phase TiO2. HF-assisted chemical etching does not change its phase composition and peak positions, suggesting that there is no F-doping process occurred. Elemental mapping of EDX spectra for EST-4 was further confirmed, which only containing Ti and O elements.

When the amounts of  Hydrofluoric acid solution reached to 0.2 mL, the peak of Si--O--Si nearly disappeared, which indicates SiO2 templates have been cleared away. The result is consistent with the SEM images of all etched samples.In order to make a qualitative analysis, sample ST-700 ℃ and all corresponding etched samples were characterized by FTIR measurement. Powerful and wide absorption peak in the vicinity of 1119 cm-1 is attributed to the antisymmetric stretching vibration of Si--O--Si. Two peaks centering around 3500 cm-1 and 1640 cm-1, were all ascribed to the absorption of water in the air. With increasing the amount of Hydrofluoric acid solution, the peak intensity of Si--O--Si weakened. All samples revealed type III isotherms with a hysteresis loop, manifesting the existence of mesoporous structure. The photocatalytic activity of samples was measured by monitoring the degradation of Rh B under UV light irradiation. It can be concluded into two parts including the influences of calcination temperature and the Hydrofluoric acid amounts for etching SiO2 cores on the degradation of RhB.

Anatase TiO2 nanocaps were prepared by  Hydrofluoric acid assisted chemical etching method. The influence of  Hydrofluoric acid amounts on photocatalysis. Compared with the sample of ST-700 ℃, EST-3 has relatively high adsorption capacity, which is consistent with the BET tests. The destroyed structure of EST-1 and the existence of large amounts of SiO2 spheres lead to a low photocatalytic property. All other etched samples exhibit excellent degradation ability than commercial P25. The sample EST-3 can reach to 80% within 30 min for the degradation of Rh B under UV light irradiation. Meanwhile, to clarify the real degradation of RhB or just dark adsorption, ST- 700 ℃ and EST-3 were conducted for the same time in the absence of light.