Carboxylate-functionalized organic nanocrystals for high-capacity uranium sorbents

Carboxylate-functionalized organic nanocrystals (ONCs) derived from perylene diimide or naphthalene diimide were synthesized and carefully characterized as novel high-capacity uranium (U(VI)) sorbents. Adsorption studies using uranyl ions demonstrated that the carboxyl and hydroxyl groups on the surface of the ONCs play pivotal roles in U(VI) adsorption. ONCs formed from the condensation of perylene dianhydride and aminoisophthalic acid exhibit very high U(VI) adsorption capacities of 1393 mg g^-1 comparable to the highest capacity ever reported. The adsorption kinetics of the ONCs were found to obey the second-order model, indicating that chemisorption is the rate-determining step for U(VI) adsorption by these materials. Furthermore, the perylene-based ONC containing imidazole exhibited no pH dependency upon the U(VI) adsorption and the naphthalene-based ONC was able to remove up to 97.5% U(VI) from simulated nuclear industrial effluent containing many competing elements. These findings will facilitate the development of high-performance organic U(VI) sorbents with high densities of adsorption sites.