Direct Electrocatalytic Reduction of As(III) on CuSn Alloy Electrode: A Green and Sustainable Strategy to Recover Elemental Arsenic from Arsenic Wastewater

Arsenic contamination in groundwater and industrial wastewater poses a significant threat to human health and the ecosystem. Electrochemical reduction of highly mobile As(III) species into less toxic elemental arsenic (As(0)) has emerged as a promising method to effectively recover arsenic from water. In this study, a novel CuSn alloy nanowire array-modified copper foam (CuSn NAs/CF) electrode was fabricated for the direct electrochemical reduction of As(III) to As(0). The electrocatalytic reduction of As(III) was systematically investigated under various reaction conditions, including current densities, solution pH, electrolytes, and initial As(III) concentrations. The CuSn NAs/CF electrode was proven to effectively suppress the hydrogen evolution reaction and greatly enhance the electrochemical reduction of As(III). The recovery yield of As(0) on the CuSn NAs/CF electrode reached 3.67 mg/cm2 at 90 min of electrolysis in a 0.1 M Na2SO4 at pH 11, which was 2.75 times higher than that of the Cu NAs-modified electrode. Furthermore, the as-prepared electrode also demonstrated excellent electrochemical stability and a longer service life, maintaining a recovery yield of As(0) at 2.62 mg/cm2 even after 6 cycles. The reduction reaction mechanism of As(III) was ascribed to the synergistic effect of direct electrolysis and hydrogen radicals (·H) formation, as revealed by ESR and radical scavenger experimental results. This study not only provides convincing evidence for the direct electrochemical conversion of As(III) to As(0) on an innovative CuSn alloy electrode, but also offers a promising strategy to recover and reuse waste arsenic resources. This contributes to a sustainable and environmentally friendly approach to arsenic-containing wastewater treatment

Two superconductor-insulator phase transitions in the spinel oxide Li_1±xTi₂ O_4-δ induced by ionic liquid gating

The associations between emergent physical phenomena (e.g., superconductivity) and orbital, charge, and spin degrees of freedom of 3d electrons are intriguing in transition metal compounds. Here, we successfully manipulate the superconductivity of spinel oxide Li1±xTi2O4-δ (LTO) by ionic liquid gating. A dome-shaped superconducting phase diagram is established, where two insulating phases are disclosed both in heavily electron-doping and hole-doping regions. The superconductor-insulator transition (SIT) in the hole-doping region can be attributed to the loss of Ti valence electrons. In the electron-doping region, LTO exhibits an unexpected SIT instead of a metallic behavior despite an increase in carrier density. Furthermore, a thermal hysteresis is observed in the normal state resistance curve, suggesting a first-order phase transition. We speculate that the SIT and the thermal hysteresis stem from the enhanced 3d electron correlations and the formation of orbital ordering by comparing the transport and structural results of LTO with the other spinel oxide superconductor MgTi2O4 (MTO), as well as analyzing the electronic structure by first-principles calculations. Further comprehension of the detailed interplay between superconductivity and orbital ordering would contribute to the revealing of unconventional superconducting pairing mechanism

Supplementary information files for Two superconductor-insulator phase transitions in the spinel oxide Li_1±xTi₂ O_4-δ induced by ionic liquid gating

Supplementary files for article Two superconductor-insulator phase transitions in the spinel oxide Li1±xTi2 O4-δ induced by ionic liquid gating. The associations between emergent physical phenomena (e.g., superconductivity) and orbital, charge, and spin degrees of freedom of 3d electrons are intriguing in transition metal compounds. Here, we successfully manipulate the superconductivity of spinel oxide Li1±xTi2O4-δ (LTO) by ionic liquid gating. A dome-shaped superconducting phase diagram is established, where two insulating phases are disclosed both in heavily electron-doping and hole-doping regions. The superconductor-insulator transition (SIT) in the hole-doping region can be attributed to the loss of Ti valence electrons. In the electron-doping region, LTO exhibits an unexpected SIT instead of a metallic behavior despite an increase in carrier density. Furthermore, a thermal hysteresis is observed in the normal state resistance curve, suggesting a first-order phase transition. We speculate that the SIT and the thermal hysteresis stem from the enhanced 3d electron correlations and the formation of orbital ordering by comparing the transport and structural results of LTO with the other spinel oxide superconductor MgTi2O4 (MTO), as well as analyzing the electronic structure by first-principles calculations. Further comprehension of the detailed interplay between superconductivity and orbital ordering would contribute to the revealing of unconventional superconducting pairing mechanism

Quantum criticality tuned by magnetic field in optimally electron-doped cuprate thin films

Antiferromagnetic (AF) spin fluctuations are commonly believed to play a key role in electron pairing of cuprate superconductors. In electron-doped cuprates, a paradox still exists about the interplay among different electronic states in quantum perturbations, especially between superconducting and magnetic states. Here, we report a systematic transport study of cation-optimized La2-xCexCuO4±δ (x=0.10) thin films in high magnetic fields. We find an AF quantum phase transition near 60 T, where the Hall number jumps from nH=-x to nH=1-x, resembling the change in nH at the AF boundary (xAF=0.14) tuned by Ce doping. In the AF region a spin-dependent state manifesting anomalous positive magnetoresistance is observed, which is closely related to superconductivity. Once the AF state is suppressed by magnetic field, a polarized ferromagnetic state is predicted, reminiscent of the recently reported ferromagnetic state at the quantum end point of the superconducting dome by Ce doping. The magnetic field that drives phase transitions in a manner similar to but distinct from doping thereby provides a unique perspective to understand the quantum criticality of electron-doped cuprates