Research On Photocatalytic Activity Of Lanthanum-Cerium Co-doped Titanium Dioxide Nanotubes With Mixed Crystal

Nano-TiO₂is a new type of semiconductor material, due to the chemicalproperties:stability,non-toxic, sparingly soluble, low price.It has a wide application inthe photoelectric conversion, storage and utilization of solar energy, photochromic andphotocatalytic degradation of pollutants in the water and atmosphere.TiO₂crystallinephase mainly includes three types: anatase, rutile and brookite type.Anatase and rutileTiO₂have photocatalytic activity while Brookite doesn’t. The catalytic activity ofanatase is greater than rutile, due to the anatase’s band gap width is greater thanrutile’s,so that the hole-electron pair with corrections has more negative potentials.Butthe band width of the anatase TiO₂is about3.2eV, with only UV light irradiation cangenerate the electron-hole pairs, the charge carrier recombination’s rate is very rapidalso, approximately in the picosecond and nanosecond time,leading to the lowphotocatalytic activity,which restricts its wide application.At present, improvingphotocatalytic performance is one of the main studies directions. TiO₂nanotubes’preparation is one of the new approaches to improve the photocatalyticperformance,because of TiO₂nanotubes with larger specific surface area thannano-powders and thin films, but now the research on it is rarely, relevant study showsthat:the metal or nonmetal ion doping contributes to improving the photocatalyticperformance.This experiment used sol-gel method,then calcinated at different treatmenttemperatures combined with microwave methold to preparate TiO₂nanotubes dopedrare earth lanthanum and cerium with mixed crystals,then used field emission scanningelectron microscopy, transmission electron microscope and X ray diffraction tocharacterize and analysis TiO₂nanotube formation mechanism.The degradationobjection was methyl orange,for studying its photocatalytic properties,we have studiedTiO₂nanotubes and nanometer powders with mixed crystal （undoped,the lanthanumdoped, lanthanum and ceriem co-doped）, analysis the mechanism of degradation andthe rare earth element performance influence of photocatalytic mechanism when dopedin TiO₂mixed crystal nanotubes. The main work of this thesis includes the preparationand research on mixed crystal nanotubes：When the rare earth lanthanum and cerium doping amount is respectively0.5%,using sol-gel method, calcinating at different temperatures,we can prepare different crystals consist of TiO₂powders.The pure TiO₂crystal transition temperatureis lower than700℃, the TiO₂doped with rare earth lanthanum crystal transitiontemperature is at about800℃while lanthanum and cerium co-doped TiO₂crystaltransition temperature is at about900℃. Contrast to rare earth lanthanum doping TiO₂,rare earth lanthanum and cerium co-doped has a greater suppression of thetransformation from anatase to rutile;By sol-gel method and the heat treatment,the prepared mixed crystal TiO₂nano-powder’s particle size was between15-20nm and had uniform form.Withmicrowave method to preparate TiO₂nanotubes, outside diameter is about15nm, whilethe diameter10nm, and had uniform form;Under the irradiation of ultraviolet light（15W）, the photocatalytic degradationexperiments showed that: TiO₂nanotubes had a higher photocatalytic propertiesthannano-powders; rare earth element doped in TiO₂nanotube,the photocatalyticperformance is better than the pure TiO₂nanotubes; when0.5%lanthanum and0.5%cerium doped,calcination temperature at900℃, the anatase contentis91.8%while rutilecontent is8.2%, the photocatalytic activity is the best.Rare earth element has reduced the electron-hole pairs composite probability,sothat make a better photocatalytic performance;At the same time,TiO₂nanotubes hadgreatly increased the surface area, the mixed crystal’s effect, had improved thephotocatalytic performance.This research provides a kind of new approach to improve for the photocatalyticactivity of TiO₂and made the application of nano-TiO₂to become extensive andsubstantive in many fields.