|
A series of Halogen elements doped TiO2 photocatalysts (Fluorine doped TiO2 has been recorded as FT, the same expression of chlorine, bromine and iodine doped TiO2 were recorded as CT, BT and IT respectively) were prepared by hydrothermal method using titanium sulfate and four kinds of Halogen salt (NaF, NaCl, KBr and KIO3). Halogen elements doped TiO2 supported on SiO2 (Which have been respectively recorded as FTS, CTS, BTS and ITS) were also obtained by in-situ hydrothermal method. The samples were characterized by XRD, BET and UV-Vis absorbance spectra. The photocatalytic activity of the two series of TiO2 photocatalysts was studied by photocatalytic degradation of dyes (Weak Acid Red B and Methylene Blue) and photoreduction of Gr(Ⅵ). The studies proved that the degradation ratio was relevant to initial concentration, catalysts quantity and solution pH. The photocatalytic activity of two dyes in seawater was explored. The kinetics of photocatalytic oxidation was also further studied.If the degradation of organic matter concentration was too high, the catalyst activity will be affected. The degradation rate reaches 90% when the initial concentration less than 40mg/L. The effect of pH was very complicated. When pH value was varied between 1.0 to 11.0, the degradation rate of the two dyes remain above 90%, so IT has a better activity in a wide range of pH values scope; while FT, CT, and BT present high catalytic activity in a narrower range. The degradation rate increased first and decreased later when increasing the catalysts quantity, the optimal catalysts quantity was 0.5g/L. NaCl has prohibitive action on the photocatalytic activity of FT, CT, and BT, while the degradation rates were maintained above 95% for IT, when the concentration of NaCl changed from 0 to 1.Omol/L. The photocatalytic degradation of Weak Acid Red B and Methylene Blue accords with Langumuir-Hinshelwood kinetic model, and belongs to the first order reaction. The photocatalytic activity of samples has no significant decrease by repeated use for three times, and the degradation rate can be maintained above 80%.The research found that, Halogen elements doped TiO2 supported on SiO2 were suitable for low concentration of dye. To FTS, CTS, BTS, ITS, the optimal pH value for photocatalytic degradation of Weak Acid Red B were 6,3,3 and 1 respectively, while the optimal pH value for photocatalytic degradation of Methylene Blue were 1.0,11.0,11.0 and 1.0 respectively. NaCl has prohibitive action on the photocatalytic degradation of the dyes with the action strengthened as the concentration of NaCl increased. The photocatalytic degradation of FTS, CTS, BTS and ITS for Weak Acid Red B and Methylene Blue were according with the charateristic of the first order reaction, their photodegradation rate constants (min-1) of Weak Acid Red B were 0.0054,0.0051,0.0085 and 0.0131 respectively, while those of Methylene Blue were 0.0048,0.0105,0.0160 and 0.0121 respectively.In sea water system, IT and BTS still maintained high activity, while other catalysts and P-25 did not, and the degradation rate of dyes in sea water system decreased by 20%-50% compared to that in deionized water system. When the dyes were irradiated for 150 min in seawater system, the amount of catalyst was 1.0g/L, initial concentration was 40mg/L, and the degradation rate could reach 95%.The experiments of photocatalytic reduction of Cr(Ⅵ) showed that the reduction rate increased with the pH values. According to the order of CT→BT→FT→IT, the reaction efficiency increased. The reaction accords with L-H kinetic model, and belongs to the first order reaction.To sum up, according to the experimental results of photocatalytic degradation of dyes and photoreduction reaction of Cr(Ⅵ), it has been proved that halogen elements doped TiO2 have high catalytic property. So we wish this work may enrich the photocatalytic theory and provide the necessary information for the actual wastewater treatment.
|