Preparation And Characterization Of Phosphor-Doped Titanium Dioxide Photocatalyst

Nanometer titanium dioxide (TiO₂) can yield complete decomposition of toxic organiccontaminants into harmless carbon dioxide and water at ambient atmosphere, especiallyas for those harmful organic compounds which are hard to be decomposed usingbiological method. Due to its high photo catalytic activity, high chemical stability and lowcost, the photocatalytic TiO₂ has been widely investigated and used. However, the use ofthis photo catalyst is currently limited by two problems. One is that heat treatment at hightemperature is needed for the synthesis of the nano-sized Ti_O2 sol or thin film materials.The other is that light irradiation with rather short light wavelength is needed for theoccurrence of the photo catalytic reaction. This thesis research work focuses on resolvingthese two problems.Firstly, nano-sized TiO₂ and phosphor-doped TiO₂ sols were prepared in aqueousnitric acid below 100℃using titanium tetrachloride as precursor for TiO₂. The influencesof the preparation conditions on the structures and properties of TiO₂ sols were studied,and the optimum preparation conditions were obtained utilizing orthogonal experiments.The mechanism for the formation of the nano-sized anatase TiO₂ particles was discussedbased on the above experimental results. The microstructures and optical properties of theas-synthesized TiO₂ materials were characterized using XRD, TEM, UV-vis and FT-IRspectra analyses. The results indicate that both the TiO₂ and P-doped TiO₂ particlesremain anatase crystal phases but the latter is much more crystallized. The particle size ofthe as-obtained TiO₂ and P-doped TiO₂ samples is less than 10nm and the latter is muchmore monodisperse than the former. The UV absorption edge of the P-doped TiO₂undergoes somewhat blue-shift and high absorptivity is produced within the ultravioletregion.Secondly, the research on the stability of the sols disclose that the TiO₂ and P-dopedTiO₂ sols are acidic and no precipitates were produced after diluted with various amountsof water or kept at ambient atmosphere for long time. However, precipitation was found to immediately occur with alkali addition. The sols and the sol-gel-derived thin films onglass springs were used to degrade dyes. The results show that the P-doped TiO₂ sol andthin film samples have higher photo catalytic activities than the pure TiO₂ sols and thinfilms, and a 4-layer film has highest photo catalytic activity. With increase of the heattreatment temperature, the photo catalytic activities of the TiO₂ and P-doped TiO₂ filmsamples decrease while their adhesion to substrate is enhanced.Thirdly, nano-sized TiO₂ and p-doped TiO₂ sols were prepared in aqueous hydrogenperoxide below 100℃using titanium tetrachloride as the precursor. The effects of thepreparation conditions on the structures and performances of the sol samples were studied,followed by investigating the formation mechanism of the anatase TiO₂ particles. Thecharacterization of the as-obtained sol-gel samples shows that the TiO₂ and P-doped TiO₂sols have anatase crystal structures, and the latter has higher crystallizability than theformer. It was found that shuttle-shaped colloidal particles were highly monodispersed inthe sols. The P-doped TiO₂ has bigger band gap than TiO₂, and they exhibit highabsorptivity within visible light region and a maximum wavelength of absorbance isabout 550nm.Finally, the study of the stability of the sol samples prepared in aqueous hydrogenperoxide indicates that the TiO₂ and P-doped TiO₂ sols remained neutral and weaklyacidic, respectively. No sediments were produced after diluted with various amounts ofwater or kept at room temperature for long time but precipitation immediately occurredwith alkali or acid addition. The sols and the sol-gel-derived thin films were used todegrade dyes and phenol. The results show that the sol and film samples have high photocatalytic activities but the P-doped sample is much higher than the pure TiO₂ material. A3-layer film was found to have highest photo catalytic activity. With the increase of theheat treatment temperature, the photo catalytic activities of the films were somewhatdecreased but their adhesion to the substrates was greatly improved, especially as for theP-doped TiO₂ films. After heat treatment at 600℃and ultrasonically washed for 360minutes, this film was found to still exhibit pretty high photo catalytic activity.