The Preparation Of Photocatalysts Based On TiO₂ And The Study On The Degradation Of Contaminants

Nano titanium dioxide (TiO2) has long been regarded as the most promising photocatalyst because of its outstanding photocatalytic activity and finds its wide applications in breaking down many kinds of organic pollutants. However, the band gap of TiO2 is so wide that it greatly limits the use of sunlight as an energy source for the photoreaction since only about 3-4% of solar light falls in the UV range. In response to the defect, many attempts have been made to improve the photocatalytic efficiency of TiO2 under visible-light irradiation by shifting its optical response from the UV to the visible range. Therefore, it is important to improve its photocatalytic activity by reasonable doping or modification to realize practical application of TiO2 nanoparticles. It has been proved that metal doping would be a viable way to improve the photocatalytic activity of TiO2, and prevent the simple combination of photogenerated electrons and holes, consequently improving the photocatalytic efficiency of TiO2. Considering what mentioned above, in the present work, Fe3+, Al3+ doping and co-doping, Ni2+ doping TiO2 were prepared and characterized. Meanwhile, the photocatalytic activity of these TiO2 was investigated. Additionally, increasing the adsorption of the organic pollutants over TiO2 is considered to be an important parameter in enhancing the degradation rates of photocatalytic activity. Molecular imprinted polymer (MIP) has unique property of specific affinity for target compound. Therefore, the TiO2 was prepared by molecular imprinting technique in order to enhance its selective adsorption and photocatalytic ability towards the target contaminants. Based on the above mentioned considersations, following research works were carried out:(1) The effect of calcination temperature, calcination time and Fe3+-doped amount on the photocatalytic activity of TiO2. Pure and Fe3+-doped TiO2 nanoparticle photocatalysts were prepared by the sol-gel method using Ti(OC4H9)4 as precursor and characterized by X-ray diffraction (XRD) and UV-Vis. The effect of calcination temperature, calcination time and Fe3+-doped amount on the photocatalytic activity of TiO2 were investigated by photocatalytic degradation of methyl orange irradiated by sunlight. The optimal calcination time for pure TiO2 and Fe3+-doped TiO2 was 4h and 3h, respectively. The optimal calcination temperature was 773K for both pure TiO2 and Fe3+-doped TiO2. The amount of Fe3+-doped can remarkably increase the catalytic activity of TiO2 under nature light irradiation, the optimal amount of Fe3+ in Fe3+-doped TiO2 was 1.0%, and the corresponding decolorization efficiency was 28.37%.(2) Preparation and photocatalytic activity of Fe3+/Al3+-TiO2 composite photocatalyst and its the photocatalytic activity Fe3+ and Al3+ co-doped TiO2 (Fe3+/Al3+-TiO2) nanoparticle photocatalysts were prepared by the sol-gel method using Ti(OC4H9)4 as precursor and characterized by X-ray diffraction (XRD) and UV-Vis. The effect of calcination temperature, H2O2 and salts in photocatalytic system on the photocatalytic activity of Fe3+/Al3+-TiO2 were investigated by photocatalytic degradation of methyl orange irradiated by sunlight. The photocatalytic activity of Fe3+/Al3+-TiO2 was enhanced with increasing temperature. H2O2 can increace the photocatalytic activity of Fe3+/Al3+-TiO2, but HCO3-and NO2- decreased its photocatalytic activity.(3) Photocatalytic degradation of methyl orange by Ni2+-doped anatase TiO2/CoFe2O4 composites under solar light irradiation. Ni2+-doped anatase TiO2/CoFe2O4 (Ni2+-TiO2/CoFe2O4) composites with core-shell structure were prepared by an ultrasonic method. The core CoFe2O4 nanoparticles were synthesized via co-precipitation method, and the photoactive shell Ni2+-doped TiO2 nanoparticles were directly coated on the CoFe2O4 by the ultrasonic-induced hydrolysis reaction of tetrabutyl titanate in a nickel (11) sulfate aqueous solution, then the composites were calcined at different temperature. The resultant Ni2+-TiO2/CoFe2O4 composites exhibited good magnetic response. The photocatalytic activities of Ni2+-TiO2/CoFe2O4 composites were evaluated by the photocatalytic degradation of methyl orange under solar light irradiation. The results showed that Ni-doping concentration and calcined temperature had effect on the photocatalytic activities of Ni2+-TiO2/CoFe2O4 composites. Ni2+doping effectively improved photocatalytic activities of TiO2/CoFe2O4 composites, and the photocatalytic activities of +4 with an optimal doping concentration of 1.5% were four times that of undoped TiO2/CoFe2O4. Moreover, H2O2 assisted Ni2+-TiO2/CoFe2O4 composites under solar light irradiation was an effective and promising process for decolorization of dye-containing wastewater.(4) Preparation of conductive polypyrrole/TiO2 nanocomposite via surface molecular imprinting technique and its photocatalytic activity under simulated solar light irradiation. Conductive polypyrrole/TiO2 nanocomposites were successfully prepared by surface molecular imprinting technique (MIP-PPy/TiO2) using methyl orange as template molecule. The samples were characterized by means of SEM, XRD, BET and UV-vis diffuse reflectance spectroscopy. Compared with conductive polypyrrole/TiO2 nanocomposites prepared by in situ method (Control-PPy/TiO2), the absorption edge of MIP-PPy/TiO2 red-shifts 10 nm, indicating that the band gap energy of MIP-PPy/TiO2 is narrower than Control-PPy/Ti02. Moreover, MIP-PPy/TiO2 nanocomposites show higher adsorption capacity for template molecule than Control-PPy/TiO2 nanocomposites, and the photocatalytic activity of MIP-PPy/TiO2 is two times of Control-PPy/Ti02, which is attributed to the introduction of the imprinted cavities on the surface of MIP-PPy/TiO2 nanocomposites. Therefore, surface molecular imprinting method may be considered as a novel technology for the preparation of PPy/TiO2.(5) Direct systhesis of molecularly imprinted TiO2 via sol-gel method and its selective phtocatalytic degradation towards template molecule. A Novel type of molecularly imprinted TiO2 was prepared directly via sol-gel method instead of coating photocatalysts with a molecularly imprinted layer. Compared with non-imprinted TiO2, the molecularly imprinted TiO2 not only exhibits a much higher adsorption capacity for the target contaminant but also shows an enhanced photocatalytic activity in degrading the target contaminant. This enhanced photocatalytic selectivity can be attributed to selective adsorption of target molecules on the molecularly imprinted TiO2.(6) Direct systhesis of molecularly imprinted TiO2/WO3 nanocomposite via sol-gel method and its selective phtocatalytic degradation towards template molecule. A Novel type of molecularly imprinted TiO2/WO3 was prepared directly via sol-gel method instead of coating photocatalysts with a molecularly imprinted layer. The adsorption capacity of the molecularly imprinted TiO2/WO3 for the target contaminant is higher than the non-imprinted TiO2/WO3. and the adsorption dynamics fit well with the pseudo-first-order kinetic model. Moreover, the molecularly imprinted TiO2/WO3 shows an enhanced photocatalytic activity in degrading the target contaminant. This enhanced photocatalytic selectivity can be attributed to selective adsorption of target molecules on the molecularly imprinted TiO2/WO3.