Observations of surface-mediated reduction of Pu(VI) to Pu(IV) on hematite nanoparticles by ATR FT-IR

Abstract

Previous studies have shown that mineral surfaces may facilitate the reduction of plutonium though the mechanisms of the reduction are still unknown. The objective of this study is to use batch sorption and attenuated total reflectance Fourier transform infrared spectroscopy experiments to observe the surface-mediated reduction of plutonium on hematite nanoparticles. These techniques allow for in situ measurement of reduction of plutonium with time and may lead to a better understanding of the mechanisms of surface mediated reduction of plutonium. For the first time, ATR FT-IR peaks for Pu(VI) sorbed to hematite are measured at ∼ 916 cm −1 , respectively. The decrease in peak intensity with time provides a real-time, direct measurement of Pu(VI) reduction on the hematite surface. In this work pseudo first order rate constants estimated at the high loadings (22 mg Pu /g hematite , 1.34 × 10 −6 M Pu /m 2 ) for ATR FT-IR are approximately 10× slower than at trace concentrations based on previous work. It is proposed that the reduced rate constant at higher Pu loadings occurs after the reduction capacity due to trace Fe(II) has been exhausted and is dependent on the oxidation of water and possibly electron shuttling based on the semiconducting nature of hematite. Therefore, the reduction rate at higher loadings is possibly due to the thermodynamic favorability of Pu(IV)-hydroxide complexes.

Increase in the reduction potential of uranyl upon interaction with graphene oxide surfaces

“…This is based on previous observations that the solid can be easily removed from solid surfaces with washing. 24 Uranyl stretches were observed also on the both GO electrode surfaces after exposure to CV scanning with the 1mM 238 U electrolyte. In addition to uranyl stretches at 820 cm -1 and 943 cm -1 , strong overlapping peaks were observed on the GO surfaces after CV scanning at 1011 cm -1 and 1092 cm -1 .…”

“…which can be ascribed to a hydroxide form of the uranyl, so-called scheopite type structure (UO2)8O2(OH)12•12(H2O)). 24 We hypothesize that the precipitate formed as a result of the presence of aqueous uranyl ions during drying the sample for the ATR-FTIR measuremenst and that the precipitate was not present during the CV scans. This is based on previous observations that the solid can be easily removed from solid surfaces with washing.…”

A Comparison of Adsorption, Reduction, and Polymerization of the Plutonyl(VI) and Uranyl(VI) Ions from Solution onto the Muscovite Basal Plane

“…The development of Pu IV on a mineral surface in contact with dissolved plutonium, from solutions containing trivalent through pentavalent Pu, has been previously observed. Many of the reported studies have involved iron or manganese bearing surfaces, such that the full redox couple has been assumed to involve the mineral phase itself. ,− However, similar behavior has also been observed with solutions in contact with redox-inactive mineral surfaces. ,− Related studies of Pu­(V) to Pu­(IV) reduction on montmorillonite, a redox-inactive mineral surface, show similar characteristics. The reduction was slow, and, on the basis of pH and ionic-strength dependence of the rate, it was hypothesized to involve a proton-mediated surface process .…”

“…Because of early suggestions that Pu IV may be the dominant surface species, many of these studies have focused on redox active mineral surfaces, notably those of reducing iron and manganese bearing phases. Assumed to be dependent on relative ion-surface redox couples, both oxidized − and reduced ,− Pu have been identified as surface complexes. Of particular interest are studies involving redox-inactive minerals and related surfaces in which Pu is also found as an oxidized or reduced surface complex relative to its dominant solution speciation, ,− raising questions about the complementary roles of solution and interfacial chemistry in sorbed Pu speciation.…”

High effectiveness of pure polydopamine in extraction of uranium and plutonium from groundwater and seawater

“…48 The appearance of shoulders around 1122, 1063 and 1035 cm À1 in the spectrum of PDA-U and 1101 cm À1 in the spectrum of PDA-Pu may indicate the formation of hydroxyl complexes, which exhibit the metal-OH bending mode in the region 1200-700 cm À1 . 39,46,49 In comparison to pristine PDA, PDA-U sample demonstrates a twofold enhancement of the band at 3214 cm À1 and its red shi to 3130 cm À1 . The band at 1588 cm À1 shis to 1610 cm À1 and increases distinctly in the region of C]O stretching vibrations of the carboxylic acid groups and the quinone units.…”