Evidence for non-electrostatic interactions between a pyrophosphate-functionalized uranyl peroxide nanocluster and iron (hydr)oxide minerals

摘要

The terminal oxygen atoms of the pyrophosphate groups in the uranyl peroxide nanocluster U(24)Pp(12) ([(UO2)(24)(O-2)(24)(P2O7)(12)](48-)) are not fully satisfied by bond valence considerations and can become protonated. This functionality could allow for specific interactions with mineral surfaces, as opposed to the electrostatically-driven interactions observed between non-functionalized uranyl peroxide nanoclusters and mineral surfaces. The sorption of U(24)Pp(12) to goethite and hematite was studied using batch sorption experiments as a function of U(24)Pp(12) concentration, mineral concentration, and pH. A suite of spectroscopic techniques, scanning electron microscopy, and electrophoretic mobility measurements were used to examine the minerals before and after reaction with U(24)Pp(12), leading to a proposed conceptual model for U(24)Pp(12) interactions with goethite. The governing rate laws were determined and compared to those previously determined for a non-functionalized uranyl peroxide nanocluster. The rate of uranyl peroxide nanocluster sorption depends on the charge density and functionalized component of the uranyl peroxide cage. Electrophoretic mobility and attenuated total reflectance Fourier transform infrared spectroscopy analyses show that an inner-sphere complex forms between the U(24)Pp(12) cluster and the goethite surface through the terminal pyrophosphate groups, leading to a proposed conceptual model in which U(24)Pp(12) interacts with the triply-coordinated reactive sites on the (110) plane of goethite. These results demonstrate that the behavior of U(24)Pp(12) at the iron (hydr)oxide-water interface is unique relative to interactions of the uranyl ion and non-functionalized uranyl peroxide nanoclusters.