Synthesis And Photocatalytic Performance Of Lanthanum-doped TiO₂ Nanorods Through The Sol-gel-hydrothermal Method

In this paper,anatase 0.4% La-TiO2 nanorods with more regular shape,the diameter of about 20-30 nm,the length of about 200 nm and better dispersion were successfully synthesized,using tetrabutyl titanate as a precursor through the sol-gel-hydrothermal method.The effects of sol-gel process conditions,calcination temperatures,hydrothermal conditions and lanthanum doping amounts on the morphology,crystal structure,UV-Vis absorbance and photo-catalysis capability of TiO2 powders have been investigated.The results show that the optimum technological parameters for preparing TiO2 nanoparticles through the sol-gel method are listed as follows: the molar ratio of tetrabutyl titanate / deionized water / anhydrous ethanol / glacial acetic acid is 1:0.4:3.5:0.5,the PH value is 2.5,the gel temperature is 20-26 ℃,the gel time is about 8 h,and the gel calcination temperature is about 450 ℃.Since the lanthanum may inhibit the TiO2 crystal growth,the optimum gel calcination temperature after lanthanum doping is 500℃ and the optimum doping amount of lanthanum is 0.4%.The subsequent hydrothermal treatment can induce the phase transition of TiO2 from nanospheres to nanorods,which can significantly improve both the intensity and width of absorbance spectral peak.Hydrothermal treatment method shows a better capability than lanthanum doping to improve the UV-Vis light absorption intensity,as well as the light absorption range of TiO2.As a result,it can more efficiently improve the photo-catalytic degradation efficiency of methylene blue.The light-absorption threshold of TiO2 nanorods prepared at 450 ℃ gel calcination temperature and by the subsequent hydrothermal treatment was red-shifted to 548 nm,the band gap was reduced to 2.28 eV,and the photodegradation rate of methylene blue for 60 min was increased to 98.0%.The light-absorption threshold of 0.4% La-TiO2 nanospheres prepared at 500 ℃ gel calcination temperature was red-shifted to 478 nm,and the light-absorption threshold of 0.4% La-TiO2 nanorods prepared by the subsequent hydrothermal treatment was red-shifted to 555 nm,the band gap was reduced to 2.23 eV,and the photodegradation rate of methylene blue for 60 min was increased to 98.9%.The research results in this thesis are of great significance to effectively solve the problem of organic printing and dyeing wastewater.