Efficient Co-Adsorption and Highly Selective Separation of Cs + and Sr 2+ with a K + -Activated Niobium Germanate by the pH Control.

137 Cs and 90 Sr are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs + and Sr 2+ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K + -activated niobium germanate (K-NGH-1) presents efficient Cs + /Sr 2+ coadsorption and highly selective Cs + /Sr 2+ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs + and Sr 2+ (q m Cs  = 182.91 mg g -1 ; q m Sr  = 41.62 mg g -1 ). In 1 M HNO 3 solution, K-NGH-1 still possesses q m Cs of 91.40 mg g -1 for Cs + but almost no adsorption for Sr 2+ . Moreover, K-NGH-1 can effectively separate Cs + from 1 M HNO 3 solutions with excess competing Sr 2+ and M n + (M n +  = Na + , Ca 2+ , Mg 2+ ) ions. Thus, efficient separation of Cs + and Sr 2+ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs + /Sr 2+ coadsorption and selective separation.