Lin Gan,Fang-Fang Xu,Xiong-Hui Zeng,Zuo-Sheng Li,Zhi-Yong Mao,Ping Lu,Ying-Chun Zhu,Xue-Jian Liu,Lin-Lin Zhang
The critical doping structures of rare-earth atoms in the promising β-SiAlON phosphors have long been argued owing to the lack of direct evidence. Here, the exact locations and coordination of the Ce rare-earth atoms in the β-SiAlON structure have been examined using an atom-resolved Cs-corrected scanning transmission electron microscope. Three different occupation sites for the Ce atoms have been directly observed: two of them are in the structural channel coordinated with six and nine N(O) atoms, respectively; the other one is the unexpected substitution site for Si(Al). The chemical valences and stabilities of the doping Ce ions at the different occupation sites have been evaluated using density functional calculations. Correlation of the different doping structures with the luminescence properties has been investigated by the aid of cathodoluminescence (CL) microanalysis, which verifies the different contribution of the interstitial trivalent Ce ions to the light emission while no luminescence is observed for the substitutional doping of quadrivalent Ce.
A novel Ce(III) ion-implanted aluminum-trimesic metal–organic framework (Ce–MIL-96) was synthesized for the first time via alcohol-solvent incipient wetness impregnation. Compared to previously reported Ce-contained adsorbents, the fluoride adsorption performance of the new ion-implanted metal–organic framework demonstrated much higher adsorption capacity and more efficient regeneration of Ce. In a wide pH range of 3 to 10, Ce–MIL-96 maintained constant adsorption performance for fluoride, and the residual Ce and Al in the treated solution were below the safe limits in drinking water. The maximum adsorption capacity of Ce–MIL-96 was 38.65 mg g−1 at 298 K. Excluding the contribution of MIL-96, the maximum adsorption capacity of Ce ions was 269.75 mg g−1, which demonstrated that the service efficiency of cerium in Ce–MIL-96 is about 6 times that in Ce2O3, nearly 10 times that in Ce-mZrp, and double that in Mn–Ce oxides. There was no significant influence on fluoride removal by Ce–MIL-96 due to the presence of chloride, nitrate, sulfate, bicarbonate or phosphate. Moreover, the adsorption capacity of Ce–MIL-96 remained at more than 70% after nine cycles of adsorption–desorption. Due to this excellent adsorption performance and its regeneration properties, Ce–MIL-96 is a promising adsorbent for the removal of fluoride from groundwater.
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