Efficient removal of Ba2+, Co2+ and Ni2+ by an ethylammonium-templated indium sulfide ion exchanger

Removal of radioactive 133Ba, 60Co and 63Ni and their nonradioactive isotopes through ion exchange method would be highly beneficial for the safe disposal of liquid industrial waste, and it also bears importance for the emergency response to nuclear accident. Herein, we report the employment of an indium sulfide [CH3CH2NH3]6In8S15 (InS-2) with exchangeable ethylammonium cations for efficient and selective uptake of Ba2+, Co2+ and Ni2+. The corner-sharing linkage of P1-{In8S17} clusters in InS-2 endow the layered structure with nanoscale windows, which facilitates both transfer and accommodation of the large hydrated divalent metal ions. This results in ultrafast exchange kinetics (10-20 min) and top-level exchange capacities of 211.73 mg g-1 for Ba2+, 103.57 mg g-1 for Co2+, and 111.78 mg g-1 for Ni2+. Particularly, InS-2 achieves ultrahigh Kd values of 2.3 × 105 mL g-1 for Ba2+, 2.0 × 105 mL g-1 for Co2+ and 1.6 × 105 mL g-1 for Ni2+, corresponding to remarkable removal efficiencies larger than 99.4% (C0 ~ 6 ppm). InS-2 shows high β and γ irradiation resistance, wide pH durability (pH 3-13 for Ba2+, pH 3-11 for Co2+ and Ni2+), and outstanding selectivity against competitor ions (e.g. Na+, K+, Mg2+, Ca2+). The InS-2-filled ion exchange column exhibits a fantastic removal effect (R > 99%) for mixed Ba2+, Co2+, Ni2+, as well as Sr2+. The ultralong column-treatment on 20000 BVs of flow reveals an affinity order of Co2+ > Ni2+ > Ba2+ > Sr2+ for InS-2, which gives deep insights into the adsorption process and interaction between competitor ions. This excellent uptake of Ba2+ (Ra by analogy), Co2+ and Ni2+ ions by InS-2 highlights the great potential of metal chalcogenides as a type of promising materials for minimizing contamination in complex wastewater.