Spherical TiO₂Photocatalysts Prepared Via Template Method

The traditional TiO2was too small to recycle in pollution treatment process, and only excitated under ultraviolet light, with high recombination rate of electrons and holes. While, hollow microspheres with low density, high specific surface area, high stability and surface permeability has achieved high attention. Modification of TiO2to the visible light response was focused by researchs in recently years.Visible light respone TiO2hollow spheres were prepared by sol-gel method using hydrothermal prepared carbon spheres as template and NH4F as element N and F source. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), N2adsorption-desorption isotherm, X-ray diffraction (XRD) and UV-vis Diffuse reflectance spectra (DRS) was used for catalyst characterization. Phenol was used as model compound for photocatalytic activity test under visible light irradiation. The results showed that TiO2hollow spheres with uniform diameter of500～600nm and shell thickness75nm can be obtained. Maximum specific surface area of63.5m2/g can be achieved under the optimum conditions. N-F co-doping could improve dispersion of TiO2, inhibit particle size agglomeration and retard phase transformation. Hollow structure and N-F co-doped synergistic effect can significantly improve TiO2visible light activity. TiO2prepared at700℃exhibited the highest activity, which was4.9times and7.9times about undoped hollow TiO2and P25, respectivity.Mesoporous TiO2spheres (MS-TiO2) were prepared by sol-gel assisted hydrothermal method using double-surfactant (PEG and F127) as templates. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermal gravimetry and N2adsorption-desorption isotherm was used for catalyst structural characterization. Phenol was used as model compound for photocatalytic activity test. The results showed that mesoporous spherical TiO2with uniform diameter of200～300nm which was composed by15～20nm of TiO2crystals can be obtained. Maximum specific surface area as high as106.94m2/g, together with average pore diameter of6.5～12.6nm and pore volume of0.21cm3/g can be achieved under the optimum conditions. With the increasing of calcination temperature, specific surface area and volume of MS-TiO2decreased, pore diameter enlarged. Double templates can form a more stable spherical micelle, inhibit the growth and particle aggregation of TiO2precursor and promote its self-assembly into spherical structure. MS-TiO2prepared at500℃exhibited the highest activity with the phenol degradation of86.4%. It is about1.3times than that of TiO2without templates.The N-doped visible-light hollow sphere TiO2photocatalyst was prepared via acid catalyzed hydrolysis method by carbon spheres followed by calcinations in NH3/N2atmosphere. Phenol was used as model compound for photocatalytic activity test. The result showed that:hollow spherical TiO2with uniform diameter of600-700nm.Catalyst morphology was obvious affected on the temperature but not doped. N-doped can effectiviely improve the catalyst visible light response.TiO2prepared at600C under NH3/N24h exhibited the higtest activity with phenol degredtion of79%.