The Research On The Preparation And Photocatalytic Properties Of TiO₂ Doped With Rare Earth Ions

In this paper, TiO₂ doped with La³⁺, Gd³⁺, Er³⁺, Ce³⁺, Pr³⁺ (labeled as Ln/TiO₂, Ln = La³⁺, Gd³⁺, Er³⁺, Ce³⁺, Pr³⁺) photocatalysts were prepared by the modified sol-gel method. The photocatalytic degradations of RhB were used as model reactions to evaluate the photocatalytic activity under visible light and UV light irradiation. The influences of rare earth doping on the structure of catalysts and their photocatalytic performance were systematically studied by using TG/DTA,XRD,Zeta Potential,BET,UV-Vis DRS,HRTEM,PL and XPS. Together with the electron spin resonance (ERS) spectral results a reaction mechanism of RhB degradations over Pr/TiO₂ under visible light was proposed. The following results were obtained: The photocatalytic degradation of RhB on Ln/TiO₂ was significantly affected by the doping cation, calcinations temperature, the reaction atmosphere and the light source. After treated at 60℃, Ln/TiO₂ (Ln=La³⁺, Gd³⁺, Er³⁺, Pr³⁺ other than Ce³⁺) exhibited higher activity for than pure TiO2, and there is a photocatalysis downtrend of Ln/TiO₂, namely , Pr/TiO₂ >La/TiO₂ >Er/TiO₂ >Gd/TiO₂ >TiO₂ >Ce/TiO₂. The activity of Pr/TiO₂ was twice over TiO₂ for RhB photodegradation, and the RhB mineralization amount of Pr/TiO₂ was thrice over that of TiO₂. The characteristic results showed that Pr³⁺ doping induced the band edge blue shifts, improved the anatase phase crystallinity, promoted the dispersion degree of the catalyst solid in aqueos solution, increased the effective separation of photogenerated carriers, and prolonged the lifetime of the photogenerated carriers. The circle experiments showed that Pr/TiO₂ could be precipitated and peptizated through adjusting the pH of solution, and keep the durability of the catalyst. We propose a reaction mechanism in which the more rapid conversion of RhB over Pr/TiO₂ is caused principally by the localized photoexcitation of the praseodymium nitrate supported on TiO₂ surface under visible light irradiation yielding a metal-to-ligand charge-transfer state. The excited state produce Pr⁴⁺ and NO₃^2- by homolytic Pr-NO₃ bond cleavage. Then the Pr⁴⁺ intermediate abstracts an electron from the Ti-OH to form OH radicals. Thus the photocatalytic efficiency of Pr/TiO₂ is improved evidently. The innovations of this work include: Compared with TiO2, Ln/TiO₂ photocatalysts synthesized by sol-gel method at low temperature have higher photocatalytic activity and longer durability under visible light illumination. Moreover, its UV photocatalytic activity have decuple over that of TiO2. Here we provide a new method for the preparation of effective catalysts with high photocatalytic activity. At the same time, we propose a novel mechanism module of Pr ion doped titanium dioxide photodegradating RhB under visible light irradiation. Furthermore, Pr/TiO2 can be precipitated and peptizated by adjusting the pH of solution, and keep its durability. This study provided a new strategy for the TiO2 technology applied in the field of environment pollution treatment.