Preparation And Photocatalytic Activity Of Rare Earth Elements Codoped TiO₂Photocatalysts

As a kind of functional semiconductor material, nano-TiO2has a verywide range of applications in the fields of environmental protection,photoelectric conversion and industrial catalysis. However, the narrowabsorption range of spectra, and the low quantum efficiency are the maindrawbacks that limit the practical applications of TiO2. Therefore, it isimportant to broaden the spectrum absorption range and improve thequantum efficiency in order to enhance the photocatalysis property. In thispaper, rare earth elements codoped TiO2photocatalysts were synthesizedwith La and Gd as the host doping elements. First, Sol-gel method wasadopted to obtain the best co-doping proportion of La and Gd elements,and then other preparation methods were tried to further optimize thephotocatalytic properties. The research details were as follows:(1) First, TiO2nanoparticles were prepared using sol-gel method bymono-doping with La or Gd. The mono-doping amount of La or Gd isoptimized as2.0%and0.4%(molar ratio), respectively. Secondly, La-Gdcodoped TiO2photocatalysts were also prepared by sol-gel method and thephotocatalytic performances were measured by photodegradation ofmethyl orange (MO). When the doping molar ratio of Gd, La and Ti isoptimized as0.004:0.015:1, the degradation rate of MO was reached to97%under ultraviolet light irradiation for30min, which is3.2timescompared to that of the undoped TiO2. And the degradation rate wasreached to40%under visible light irradiation for2h, while the result ofthe pure TiO2was almost no change. The results indicated that codopingby double rare earth elements will widen spectral absorption range, improve the utilization of sunlight and increase the photocatalyticperformance.(2) La-Gd codoped TiO2microspheres were synthesized using P123and urea as templates, respectively. The microspheres with diameter of1.5-3.5μm, large pore volume and high surface area were composed ofnanoparticles by using P123as template. The influence of calcinationtemperature on photocatalytic performance was studied and the samplecalcined at350℃for2h was found to be the best photocatalyst：thedegradation rate of MO can reach100%after20min ultraviolet lightirradiation and83%after2h visible light irradiation, respectively.under ultraviolet light irradiation: The nanospheres with a narrowpore size distribution of100nm were synthesized using urea as template.The influence of hydrothermal temperature and time on photocatalyticactivities of the nanospheres evaluated by photodegrading MO undervisible light were investaged, revealing the best photocatalyticperformance for the one synthesized at110℃for36h, which can degrade80%of MO after60min, giving a strong response to visible light.(3) La-Gd codoped TiO2nanotubes were synthesized by hydrothermalmethod for the first time. The nanotubes with an average diameter of15~20nm have plenty active sites in the rough surface. The preparedsamples were all anatase phase. With the increasing calcinationtemperature, the nanotubes increased in diameter and length due to theexpansion effect. However, nanotubes were damaged when the calcined at600℃. The calcination temperature also affected photocatalysis activities:sample calcined at500℃showed best photocatalytic activity, which canphotodegrade Rhodamine B up to71%after210min under visible lightirradiation, increasing twice than the uncalcined one.