Highly efficient removal of Cs+ from water by an ionic lamellar carbon nitride framework

Abstract

¹³⁷Cs⁺ is strongly radioactive, and has extremely high environmental mobility. It is thus a highly hazardous pollutant; meanwhile, it is also a useful resource in medical therapy processes. The technology for the adsorption of ¹³⁷Cs⁺ from water is of great significance in terms of both environmental remediation and resource recovery. Development of advanced materials with low-cost and high efficiency is critical for the efficient removal of Cs⁺ from water. Herein, an anionic lamellar carbon nitride framework (CN–Na) is constructed, and it exhibits remarkable performance in selective removal of Cs⁺ in water via an ion-exchange mechanism. The adsorption isothermal plots are fitted well with Langmuir–Freundlich isotherm models, and the maximum ion-exchange capacity reaches a high value of 278.20 mg g⁻¹. Replacement of Na⁺ by Cs⁺ from the CN–Na framework gradually decreases the crystallinity; it is worth noting that the crystalline structure could be restored during the regeneration with Na⁺. The reversibility of the structure ensures a remarkable durability of the ion-exchange materials, as verified by a long-term test of 450 h in an ion-exchange column. The work herein sheds light on the potential application of CN frameworks as a platform to realize efficient and cost-effective Cs⁺ removal.