Layered Double Hydroxides With Rare Earth Doping Toward Highly-Efficient Photocatalytic Oxygen Evolution

Recently, layered double hydroxides （LDHs） materials have attracted considerable attentions due to their excellent photocatalytic activity, stability, and environmentally friendliness. However, the poor charge mobility of LDHs that suppresses separation of photo-induced charge carriers, restricts their further development in the photocatalysis area. To solve this problem, herein, Tb³⁺was incorporated into LDH brucite host layers with photo-response activity, so as to improve the charge transfer property and thus enhance the photocatalytical performance of the catalysts. Moreover, we explored the influence of different rare earth ions on the photocatalytical activity of NiTi-LDH. The mechanism of photocatalytic reaction by using rare earth ions doping has also been systematically investigated. This work provides an effective approach to prepare efficient and stable LDHs-based photocatalysts. The details are as follows:（1） A series of Tb³⁺ doped ZnTi-LDH photocatalysts with different amount of Tb were prepared by urea decomposition method. The sample with doping ratio of 1% gives the best performance with 1334 μmol h^-1 g^-1 in the gas production rate for photocatalytic oxygen evolution from water, which is amostly twice higher than that of pure ZnTi-LDH. Moreover, various Tb³⁺ doped ZnCr-LDH were synthesized and evaluaed in the reaction of oxygen evolution from water under visible light irradiation. The Tb-ZnCr-LDH with doping content of 0.5% exhibits the highest activity with an oxygen evolution rate of 1022 μmol h^-1 g^-1 under visible light, which was nearly twice of the pure ZnCr-LDH. X-ray photoeletron spectra, UV-vis diffuse reflectance spectra, electron spin resonance and electrochemical tests were applied to study the properties of electronic structure, band gap, charge separation and injection efficiency of the catalysts.（2） On the basis of the research above, a series of NiTi-LDH doped by various rare earth metal ions (Tb³⁺, Gd³⁺, La³⁺, Y³⁺) with different doping content were sythesized by dynamic urea reflux method, and were devoted to the photocatalytical water splitting under visible light irradiation. It is found that rare earth element demonstrates distinct impact on the NiTi-LDH. The sample of La³⁺ doped NiTi-LDH with a doping ratio of 10% shows the best performance with oxygen production rate of 1270 μmol h^-1 g^-1. Various characterizations have been used to study the properties of the electron structure, seperation of electrons and holes, and charge injection efficiency. The results demonstrated that the incorporation of rare earth ions improves charge transfer properties of NiTi-LDH, facilitates the separation of photoinduced electron-hole pairs and injection processes, and therefore enhances the photocatalytic activity significantly.