The retention of uranium and europium onto sepiolite investigated by macroscopic, spectroscopic and modeling techniques

The effect of Cr(VI) and bisphenol A (BPA) on U(VI) photoreduction by C3N4 photocatalyst was demonstrated by the batch experiments, electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) techniques. The batch experiments manifested that Cr(VI) and BPA enhanced the photocatalytic activity of C3N4 for U(VI) photoreduction, whereas U(VI) photoreduction was significantly diminished with increased pH from 4.0 to 8.0. According to radical scavengers and ESR analysis, U(VI) was photoreduced to U(IV) by photogenerated electrons of conduction band edge, whereas Cr(VI) was reduced to Cr(III) by H2O2. BPA and its products such as organic acid and alcohols can capture photoinduced holes, which resulted in the enhancement of U(VI) photoreduction to U(IV). XPS and XANES analyses demonstrated that U(VI) was gradually photoreduced to U(IV) by C3N4 within irradiation 60 min, whereas U(IV) was reoxidized to U(VI) with increasing irradiation time. EXAFS analysis determined that the dominant interaction mechanisms of U(VI) on C3N4 after irradiation for 240 min were reductive precipitation and inner-sphere surface complexation. This work highlights the synergistic removal of radionuclides, heavy metals, and persistent organic pollutants by C3N4, which is crucial for the design and application of a high-performance photocatalyst in actual environmental cleanup.

Enhanced Photoreduction of U(VI) on C3N4 by Cr(VI) and Bisphenol A: ESR, XPS, and EXAFS Investigation.

Memristors based on 2D layered materials could provide biorealistic ionic interactions and potentially enable construction of energy-efficient artificial neural networks capable of faithfully emulating neuronal interconnections in human brains. To build reliable 2D-material-based memristors suitable for constructing working neural networks, the memristive switching mechanisms in such memristors need to be systematically analyzed. Here, we present a study on the switching characteristics of the few-layer MoS2 memristors made by mechanical printing. First, two types of dc-programmed switching characteristics, termed rectification-mediated and conductance-mediated behaviors, are observed among different MoS2 memristors, which are attributed to the modulation of MoS2/metal Schottky barriers and redistribution of vacancies, respectively. We also found that an as-fabricated MoS2 memristor initially exhibits an analog pulse-programmed switching behavior, but it can be converted to a quasi-binary memristor with an abrupt switching behavior through an electrical stress process. Such a transition of switching characteristics is attributed to field-induced agglomeration of vacancies at MoS2/metal interfaces. The additional Kelvin probe force microscopy, Auger electron spectroscopy analysis, and electronic characterization results support this hypothesis. Finally, we fabricated a testing device consisting of two adjacent MoS2 memristors and demonstrated that these two memristors can be ionically coupled to each other. This device interconnection scheme could be exploited to build neural networks for emulating ionic interactions among neurons. This work advances the device physics for understanding the memristive properties of 2D-material-based memristors and serves as a critical foundation for building biorealistic neuromorphic computing systems based on such memristors.

MoS2 Memristors Exhibiting Variable Switching Characteristics toward Biorealistic Synaptic Emulation.

Development of 3D printable engineered cementitious composites with ultra-high tensile ductility for digital construction

Uranium extraction from seawater provides an opportunity for sustainable fuel supply to nuclear power plants. Herein, an adsorption-electrocatalysis strategy is demonstrated for efficient uranium extraction from seawater using a functionalized iron-nitrogen-carbon (Fe-Nx -C-R) catalyst, comprising N-doped carbon capsules supporting FeNx single-atom sites and surface chelating amidoxime groups (R). The amidoxime groups bring hydrophilicity to the adsorbent and offer surface-specific binding sites for UO2 2+ capture. The site-isolated FeNx centres reduce adsorbed UO2 2+ to UO2 + . Subsequently, through electrochemical reduction of the FeNx sites, unstable U(V) ions are reoxidized to U(VI) in the presence of Na+ resulting in the generation of solid Na2 O(UO3 ·H2 O)x , which can easily be collected. Fe-Nx -C-R reduced the uranium concentration in seawater from ≈3.5 ppb to below 0.5 ppb with a calculated capacity of ≈1.2 mg g-1 within 24 h. To the best of the knowledge, the developed system is the first to use the adsorption of uranyl ions and electrodeposition of solid Na2 O(UO3 .H2 O)x for the extraction of uranium from seawater. The important discoveries guide technology development for the efficient extraction of uranium from seawater.

Functionalized Iron-Nitrogen-Carbon Electrocatalyst Provides a Reversible Electron Transfer Platform for Efficient Uranium Extraction from Seawater.

Reduction of U(VI) to U(IV) on mineral surfaces is often considered a one-step two-electron process. However, stabilized U(V), with no evidence of U(IV), found in recent studies indicates U(VI) can undergo a one-electron reduction to U(V) without further progression to U(IV). We investigated reduction pathways of uranium by reducing U(VI) electrochemically on a magnetite electrode at pH 3.4. Cyclic voltammetry confirms the one-electron reduction of U(VI) to U(V). Formation of nanosize uranium precipitates on the magnetite surface at reducing potentials and dissolution of the solids at oxidizing potentials are observed by in situ electrochemical atomic force microscopy. XPS analysis of the magnetite electrodes polarized in uranium solutions at voltages from −0.1 to −0.9 V (E0U(VI)/U(V)= −0.135 V vs Ag/AgCl) show the presence of only U(V) and U(VI). The sample with the highest U(V)/U(VI) ratio was prepared at −0.7 V, where the longest average U–Oaxial distance of 2.05 ± 0.01 A was evident in the same sample...

Electrochemical and Spectroscopic Evidence on the One-Electron Reduction of U(VI) to U(V) on Magnetite

A self-consistent model describing the thermodynamics of Eu(III) adsorption onto hematite

Uranium reduction on magnetite: Probing for pentavalent uranium using electrochemical methods

The energetics and kinetics of uranyl reduction on pyrite, hematite, and magnetite surfaces: A powder microelectrode study

The mobility of toxic elements, such as lead (Pb) can be attenuated by adsorption, incorporation, and precipitation on carbonate minerals in subsurface environments. Here, we report a study of the bulk transformation of single-crystal calcite (CaCO3) into polycrystalline cerussite (PbCO3) through reaction with acidic Pb-bearing solutions. This reaction began with the growth of a cerussite shell on top of calcite surfaces followed by the replacement of the remaining calcite core. The external shape of the original calcite was preserved by a balance between calcite dissolution and cerussite growth controlled by adjusting the Pb2+ concentration and pH. The relation between the rounded calcite core and the surrounding lath-shaped cerussite aggregates was imaged by transmission X-ray microscopy, which revealed preferentially elongated cerussite crystals parallel to the surface and edge directions of calcite. The replacement reaction involved concurrent development of ∼100 nm wide pores parallel to calcite c-gl...

Ke Yuan

Papers

Electrochemical and Spectroscopic Evidence on the One-Electron Reduction of U(VI) to U(V) on Magnetite

A self-consistent model describing the thermodynamics of Eu(III) adsorption onto hematite

Uranium reduction on magnetite: Probing for pentavalent uranium using electrochemical methods

The energetics and kinetics of uranyl reduction on pyrite, hematite, and magnetite surfaces: A powder microelectrode study

Replacement of Calcite (CaCO3) by Cerussite (PbCO3).