Synthesis and UV Absorption of La2Ce2O7 Powders by Sol-gel Method
)Abstract
La2Ce2O7 exhibits intense absorption ability in the ultraviolet (UV) region with excellent photostability, and can replace TiO2 and ZnO as an UV absorber in sunscreen formulations. Traditionally, La2Ce2O7 powder is synthesized by the solid-state method, which has problems such as high synthesis temperature, small specific surface area of the powder, and poor light absorption ability. In this study, La2Ce2O7 powder was successfully synthesized by a sol-gel method with metal nitrates, citric acid and ethylene glycol as raw materials, chelating agent and stabilizer, respectively. The conversion process of the precursor, phase change of the product, morphology of the powder, and the valence state of the elements were analyzed by TG-DSC, XRD, SEM and XPS. The UV absorption performance of the product was tested using a UV-visible spectrophotometer. The photostability of the product was evaluated by photocatalytic degradation of Rhodamine B dye. The results show that pure phase La2Ce2O7 powder can be synthesized by the sol-gel method at 250 ℃, which is more than 1000 ℃ lower than that of the traditional solid-state method. The maximum specific surface area of the La2Ce2O7 powder synthesized by the sol-gel method is 10.04 m2/g, while that of the powder synthesized by the solid-phase method is only 0.19 m2/g.The La2Ce2O7 powder synthesized at 300 ℃ shows the best UV absorption performance, 25% higher than that synthesized by the solid-state method. Compared with TiO2, La2Ce2O7 exhibits better UV absorption performance and almost no photocatalytic activity.
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