LAUSR

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 Sr2+ 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+ /Sr2+ coadsorption and highly selective Cs+ /Sr2+ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs+ and Sr2+ (qm Cs  = 182.91 mg g-1 ; qm Sr  = 41.62 mg g-1 ). In 1 M HNO3 solution, K-NGH-1 still possesses qm Cs of 91.40 mg g-1 for Cs+ but almost no adsorption for Sr2+ . Moreover, K-NGH-1 can effectively separate Cs+ from 1 M HNO3 solutions with excess competing Sr2+ and Mn + (Mn +  = Na+ , Ca2+ , Mg2+ ) ions. Thus, efficient separation of Cs+ and Sr2+ 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+ /Sr2+ coadsorption and selective separation.