(528d) Remediation of Uranium-Contaminated Groundwater By Functionalized Magnetic Mesoporous Silica Nanoparticles

U(VI) species display limited adsorption onto sediment minerals and synthetic sorbents in pH < 4 or pH > 8 groundwater. In this work, magnetic mesoporous silica nanoparticles (MMSNs) with magnetite nanoparticle cores were functionalized with various organic molecules using post-synthetic methods. The functionalized MMSNs were characterized using N₂ adsorption-desorption isotherms, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), ¹³C cross polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy, and powder X-ray diffraction (XRD). The functionalized MMSNs were effective for U removal from pH 3.5 and 9.6 artificial groundwater (AGW). Functionalized MMSNs removed U from the pH 3.5 AGW by as much as 6 orders of magnitude more than unfunctionalized nanoparticles or silica and had adsorption capacities as high as 38 mg/g. They removed U from the pH 9.6 AGW as much as 4 orders of magnitude greater than silica and 2 orders of magnitude greater than the unfunctionalized nanoparticles with adsorption capacities as high as 133 mg/g. These results provide an applied solution for treating U contamination that occurs at extreme pH environments and a scientific foundation for solving critical industrial issues related to environmental stewardship and nuclear power production.

Further, after U adsorption, U L₃-edge XANES and EXAFS spectra of all functionalized MMSNs were collected using the Materials Research Collaborative Access Team (MRCAT) Sector 10-ID beamline at the Advanced Photon Source (APS) in order to understand molecular mechanisms of different U species binding with functional organic ligands. Such molecular mechanistic studies can further guide the future selection of organic ligands to develop more robust nano sorbent materials that are more efficient and cost-effective for U extraction from environmental aqueous systems.