Characteristics of cesium ion sorption from aqueous solution on bentonite- and carbon nanotube-based composites

Highlights: • The effects of cation and hydroxyl exchanges on Cs+ sorption are investigated. • The CS-g-CNTs and the CS-g-bentonite composites are designed. • The effect of different cations on Cs+ adsorption is detected. • The cation-exchange is much more effective in Cs+ sorption than the hydroxyl group. • We give the future directions of new and selective adsorbents for Cs+ ions. - Abstract: The technology development of Cs+ capture from aqueous solution is crucial for the disposal of nuclear waste and still remains a significant challenge. Previous researches have been proven that ion exchanges with the cations and hydroxyl exchange are the main sorption mechanisms for Cs+. Therefore, how important are the cation exchange and the hydroxyl exchange mechanisms to Cs+ sorption? And whether can we improve the sorption capacity of the material by increasing the amount of hydroxyl groups? With these in mind, we herein designed the chitosan-grafted carbon nanotubes (CS-g-CNTs) and the chitosan-grafted bentonite (CS-g-bentonite) by plasma-induced grafting method. The interactions of Cs+ with CNTs, bentonite, CS-g-CNTs and CS-g-bentonite composites were investigated. The sorption of Cs+ is mainly dominated by strong cation exchange in monovalent Group I and divalent Group II. And the cation-exchange mechanism is much more effective than the hydroxyl group exchange. The effect of hydroxyl groups is dependent on the property of the matrix. We cannot improve the Cs adsorption capacity of material for Cs+ only by increasing the amount of hydroxyl groups in any case. The spatial structure and the cation-exchange capacity of the material are important factors for choosing the sorbent for Cs+ removal from radioactive waste water