Efficient Removal of Azo-Dyes in Aqueous Solution by CeB₆Nanocrystals

Rare earth oxides have been well-developed for the treatment of synthetic dyes in wastewater, but limited information is known regarding the application of other rare earth containing materials in this field. Herein, cerium hexaborides (CeB6) were synthesized via the reaction of CeF3 and NaBH4 in molten LiCl–KCl at 900 °C. Homogeneously dispersed CeB6 nanocrystals exhibit great performances for the removal of azo-dyes such as Congo red (CR). It follows pseudo-second-order kinetics, and a maximum removal capacity of 775.6 mg g–1 was obtained. On the basis of the results from adsorption–desorption tests, TEM, and XPS, both adsorption and photocatalytic degradation contribute to the CR removal process. Hydroxyl (•OH) radicals are the major active species involved in the photocatalytic degradation while superoxide (•O2–) radicals and holes (h+) play minor roles as made evident by the radical quenching and ESR results.