The Degradation Of Organic Pollutants Catalyzed By Molecular Imprinted TiO₂

Doped TiO2with various nonmetal elements were simple and powerful ways to extendthe absorption edge from UV to the visible light region and to reduce the recombination of thephotogenerated electron-hole pairs of TiO2. Among these non-metal ions, sulfur is one of themost commonly used non-metal ions. The research results suggested that sulfur as a dopedelement replaced the lattice oxygen or titanium in TiO2. Furthermore, no matter what thesulfur oxidation state was in TiO2, the photocatalytic activity of S-doped TiO2was stillenhanced. However, there exists still ample room for improving the degradation of organicpollutants in the visible region by using S-doped TiO2。The adsorption capacity for pollutantswas one of the major factors in determining photocatalytic activity. Therefore, it is importantto enhance the adsorption capacity of TiO2for pollutants to achieve a betterphoto-degradation effect. As molecular imprinted polymers have molecular recognitionability and specific adsorption for organic pollutants, the problem concerning the lowadsorption capacity of TiO2could be resolved by molecular imprinting technique.In this paper, TiO2, S-TiO2and Cr-S-TiO2were prepared by hydrolysis method orsol-gel method. The photocatalysts were characterized by FT-IR, XRD, SEM and UV–visDRS. The results indicated that all of them were nanoparticles. The addition of S into titaniais helpful to form anatase content, reduce particle size and expand the adsorption to visibleregion．The final degradation rates of methyl orange were found to be23%，79%，98%within75min. The effects of the ratio of Cr to S and solution pH on the photocatalytie efficiency ofCr-S-TiO2were also investigated. The results showed that the2-Cr-S-TiO2exhibited thehighest photocatalytic activity, and within a certain range, the smaller pH was, the better thephotocatalytic activity became.Molecular imprinted polymer coated S-TiO2nanocomposites (MIP-S-TiO2) and nonimprinted polymer coated S-TiO2nanocomposites (NIP-S-TiO2) were synthesized by surfacemolecular imprinting technique using p-phenylenediamine as the functional monomer andsalicylic acid as the template molecule. The structure and properties of the samples wereconfirmed by FT-IR, XRD, SEM, BET, UV–vis DRS. The adsorption and degradationcapacity of S-TiO2, NIP/S-TiO2and MIP/S-TiO2nanocomposites for salicylic acid wasstudied. The influences of some factors, including the molar ratio of salicylic acid/S-TiO2,solution pH, the amount of p-phenylenediamine and reaction time, on the catalytic activity ofMIP-S-TiO2were also systematically investigated. The results indicated that the particle sizeand phase composition of S-TiO2were not changed obviously and the absorption spectra wereenhanced in the process of synthesis of MIP-S-TiO2. The adsorption and degradation capacityof S-TiO2, NIP/S-TiO2and MIP/S-TiO2nanocomposites for salicylic acid was graduallyincreased. The degradation rate of salicylic acid could reach72%within90min by usingMIP/S-TiO2, which was higher than that of NIP/S-TiO2and S-TiO2.MIP-S-TiO2/UV and NIP-S-TiO2/UV were also successfully synthesized by UVirradiation using o-phenylendiamine as the functional monomer and salicylic acid as thetemplate molecule. The photocatalysts were characterized by FT-IR, XRD, SEM. The adsorption and degradation capacity of S-TiO2, NIP-S-TiO2/UV and MIP-S-TiO2/UVnanocomposites for salicylic acid was investigated. The effects of UV time and solution pHwere studied. The results showed that the particle size and phase composition of S-TiO2werenot changed obviously in the process of synthesis of MIP-S-TiO2/UV. The adsorption anddegradation capacity of S-TiO2, NIP-S-TiO2/UV and MIP-S-TiO2/UV nanocomposites forsalicylic acid was gradually increased. The degradation rate of salicylic acid could reach81%within90min by using MIP-S-TiO2/UV, which was higher than that of NIP-S-TiO2/UV andS-TiO2.