Study On The Synthesis And Photocatalytic Properties Of Co-Doped TiO₂/SiO₂

TiO₂ is one of the most promising green photocatalytic materials, which has been widely used in environmental pollution control because of its prominent behaviors such as low cost, high oxidation, chemical stability and no secondary pollution, etc. However, its wide band gap between valence band and conduction band restricts the utilization of the visible part of solar energy. Moreover, the high recombination rate of photogenerated electrons and holes also restricts its wide application in industry. Many studies show that proper doping with metal or nonmetal as a promising approach can improve its absorbance range and restrain recombination rate of photogenerated electrons and holes, which is the preferred method to improve the photocatalytic activity of TiO₂.In this paper, a series of co-doped nano- TiO₂/SiO₂ photocatalytic materials were synthesized by in-situ hydrolysis and sol-gel method, respectively, with the dopant of N, B, Co and La and using TiO₂/SiO₂ as the precursor. The crystal morphology and structure, electronic structure, optical properties and photocatalytic properties were investigated by TEM, XRD, XPS, DRS and photocatalytic experiments. The significant results are listed as follows:(1)N, Co codoped TiO₂/SiO₂/PS composite microspheres were synthesized by chemical adsorption with in-situ hydrolysis method, then burning at 600℃to prepare the hollow composite microspheres catalyst(CNT) after removing the PS. The samples were characterized by TEM, XRD, XPS, and DRS. The results showed that the samples were of anatase TiO₂; N in the TiO₂ lattice mainly existed in the form of Ti-O-N, and Co mainly CoO_x–MO₂(M=Ti, Si); the surface of CNT became more rough and the size of it was much smaller than the undoped TiO₂/SiO₂; the visible light response range of the catalyst was extended up to 600nm because of N, Co doping; the degradation experimental showed that N and Co had a synergetic effect that enhanced the photocatalytic activity in visible light.(2)B, La co-doped nano-TiO₂/SiO₂ composite photocatalyst(BLT) was synthesized by sol-gel method. The samples were characterized by TEM, XRD, SEM, DRS, SEM,TGA and BET. The results showed that, the samples were of anatase TiO₂ and doping of B and La inhibited the transformation from the anatase to rutile phase; the diameter of BLT was about 60-100nm and the specific surface area of it was twice as that of undoped sample; compared to pure TiO₂ and B or La doped TiO₂/SiO₂, the visible light response performance of BLT was enhanced because of the obvious red shift occurred at the absorption edge; the degradation experimental showed that B and La had a synergetic effect that enhanced the photocatalytic activity in visible light.(3)The photocatalytic activities of BLT were evaluated by decolorization of methyl violet, crystal violet, methyl green and basic red 9, respectively, at the 500W xenon lamp irradiation (UV under 400nm was filtered out) so as to study the effect of catalyst dosage, initial concentration and initial pH value on photocatalytic activities. The results showed that, the initial pH value was 4, the catalyst dosage was 3.0g/L and the initial concentration was 85mg/L, 32mg/L, 60mg/L, 10mg/L, respectively, when the four basic dyes reached the heightest decolorization rate. On optimum conditions, the decolorization rate of Methyl violet was 93.2% and CODcr removal rate was 68%; crystal violet was 85.4% and 71%; methyl green was 84.4% and 76%; basic red 9 was 74.7% and 68%, respectively. In visible light, photocatalytic decolorization rate and degradation of CODcr of the four dyes were in line with pseudo first order reaction kinetics model.