The Carboxyl Functionalized UiO-66-(COOH) for Selective Adsorption of Sr.

Efficient and selective removal of Sr is an important process for the safe use of nuclear energy. Herein, we investigate and assess the Sr adsorption properties of a metal-organic framework UiO-66-(COOH) functionalized by non-bonded carboxylic groups. This MOF is an exciting class of free carboxylic functionalized MOFs that combine chemical stability with gas sorption, dye elimination, and conductivity. Specifically, we show that uniformly distributed carboxyl and water stability make it accessible for loading Sr without structural changes. The FTIR spectroscopy, PXRD analysis, XPS, and SEM-EDS studies show excellent stability as well as the strong affinity between -COOH active site and Sr. This strong coordination interaction guarantees a high adsorption capacity of 114 mg g within 5 h (pH 5 and 298 K). Combined kinetic and thermodynamic studies show that the surface complexation is strong chemisorption and cost-effective spontaneous process (ΔG = -5.49 kJ mol~-2.16 kJ mol). The fact that UiO-66-(COOH) not only possesses a high adsorption capacity, but also enables selectivity to Sr in the presence of similar radius ions Na and K, prefigures its great potential for the practical treatment of radioactive Sr in polluted water.