U(VI) reduction by Fe(II) on hematite nanoparticles
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Nanoscale size effects on U(VI) reduction by Fe(II) on hematite were investigated with four aerosol-synthesized hematite nanoparticles (12, 30, 50, 125 nm) and one aqueous-synthesized hematite (70 nm). Batch experiments were conducted at loadings of 0.01 mM U(VI) and 5 mM Fe(II) at pH 7.5 and 9.0. Rate constants for reduction of U(VI) to U(IV) were determined using a pseudo-first order reaction rate law. Reduction was faster at pH 7.5 than at pH 9.0. Rate constants were higher for aerosol-synthesized hematite than for aqueous-synthesized hematite. Rate constants were not significantly different for the 30, 50, and 125 nm particles. However, reduction was two orders of magnitude faster for the 12 nm hematite particles. Possible explanations for the dramatically faster reduction with the 12 nm hematite include the formation of a more reactive solid such as magnetite, effects on electron conduction through hematite, and quantum confinement effects.
KeywordsNanoparticles Hematite Uranium reduction Adsorption Environmental remediation Aerosols
This research was supported by the National Science Foundation (BES 0608749). The Center for Materials Innovation at Washington University provided supplemental support. Dr. Soubir Basak and Manoranjan Sahu in Dr. Pratim Biswas’ Aerosol and Air Quality Research Laboratory at Washington University provided the aerosol-synthesized hematite nanoparticles. Zimeng Wang performed selected control experiments. The valuable comments of four anonymous reviewers were helpful in revising this manuscript.