Direct Electron Transfer Coordinated by Oxygen Vacancies Boosts Selective Nitrate Reduction to N₂ on a Co–CuO_<i>x</i> Electroactive Filter

Atomic hydrogen (H*) is used as an important mediator for electrochemical nitrate reduction; however, the Faradaic efficiency (FE) and selective reduction to N2 are likely compromised due to the side reactions (e.g., ammonia generation and hydrogen evolution reactions). This work reports a Co–CuOx electrochemical filter with CoOx nanoclusters rooted on vertically aligned CuOx nanowalls for selective nitrate reduction to N2, utilizing the direct electron transfer between oxygen vacancies and nitrate to suppress the contribution by H*. At a cathodic potential of −1.1 V (vs Ag/AgCl), the Co–CuOx filter showed 95.2% nitrate removal and 96.0% N2 selectivity at an influent nitrate concentration of 20 N−mg L–1. Meanwhile, the energy consumption and FE were 0.60 kW h m–3 and 53.5%, respectively, at a permeate flux of 60 L m–2 h–1. The presence of abundant oxygen vacancies on Co–CuOx was due to the change in the electron density of the Cu atom and a decrease of the coordination numbers of Cu–O via cobalt doping. Theoretical calculations and electrochemical tests showed that the oxygen vacancies coordinated nitrate adsorption and subsequent reduction reactions, thus suppressing the contribution of H* to nitrate reduction and leading to a thermodynamically favorable process to N2 via direct electron transfer

Particle size distribution and fractal dimension of DM layers at various TMPs.

<p>(A) median particle size by number, (B) fractal dimension. Error bars represent standard deviations of triplicate tests.</p

Variations of soluble EPS during short-term batch tests.

<p>(A) AS1, (B) AS2, (C) AS3. PS-polysaccharides, PN-proteins, HS-humic substances. Error bars represent standard deviations of triplicate tests.</p

Variations in (A) specific resistance and (B) porosity of DM layer at the end of filtration.

<p>Error bars represent standard deviations of triplicate tests.</p

Fouling resistance with time at different TMPs.

<p>(A) 10 kPa, (B) 20 kPa, (C) 30 kPa. Error bars represent standard deviations of triplicate tests.</p

Schematic of anaerobic DM formation with EPS extraction and re-addition.

<p>Schematic of anaerobic DM formation with EPS extraction and re-addition.</p

CLSM images of AS1 (A1-A4), AS2 (B1-B4) and AS3 (C1-C4).

<p>Symbols 1–4: 1 exhibits combination of individual images in 2–4, 2 represents CLSM image of α-polysaccharides (Con A), 3 represents CLSM image of β-polysaccharides (Calcofluor white), and 4 represents CLSM image of proteins (FITC).</p

Table_1_Effective Removal of Sulfanilic Acid From Water Using a Low-Pressure Electrochemical RuO2-TiO2@Ti/PVDF Composite Membrane.DOCX

Removal of sulfanilic acid (SA) from water is an urgent but still challenging task. Herein, we developed a low pressure electrochemical membrane filtration (EMF) system for SA decontamination using RuO2-TiO2@Ti/PVDF composite membrane to serve as not only a filter but also an anode. Results showed that efficient removal of SA was achieved in this EMF system. At a charging voltage of 1.5 V and a electrolyte concentration of 15 mM, flow-through operation with a hydraulic retention time (HRT) of 2 h led to a high SA removal efficiency (80.4%), as expected from the improved contact reaction of this compound with ROS present at the anode surface. Cyclic voltammetry (CV) analysis indicated that the direct anodic oxidation played a minor role in SA degradation. Electron spin resonance (ESR) spectra demonstrated the production of •OH in the EMF system. Compared to the cathodic polarization, anodic generated ROS was more likely responsible for SA removal. Scavenging tests suggested that adsorbed •OH on the anode (>•OH) played a dominant role in SA degradation, while O2•- was an important intermediate oxidant which mediated the production of •OH. The calculated mineralization current efficiency (MCE) of the flow-through operated system 29.3% with this value much higher than that of the flow-by mode (5.1%). As a consequence, flow-through operation contributed to efficient oxidation of SA toward CO2 and nontoxic carboxylic acids accounting for 71.2% of initial C. These results demonstrate the potential of the EMF system to be used as an effective technology for water decontamination.</p

Total interaction energy curves of (A) sludge and (B) EPS.

<p>Total interaction energy curves of (A) sludge and (B) EPS.</p

Trade-off between Endocrine-Disrupting Compound Removal and Water Permeance of the Polyamide Nanofiltration Membrane: Phenomenon and Molecular Insights

The polyamide (PA) nanofiltration (NF) membrane has the potential to remove endocrine-disrupting compounds (EDCs) from water and wastewater to prevent risks to both the aquatic ecosystem and human health. However, our understanding of the EDC removal–water permeance trade-off by the PA NF membrane is still limited, although the salt selectivity–water permeance trade-off has been well illustrated. This constrains the precise design of a high-performance membrane for removing EDCs. In this study, we manipulated the PA nanostructures of NF membranes by altering piperazine (PIP) monomer concentrations during the interfacial polymerization (IP) process. The upper bound coefficient for EDC selectivity–water permeance was demonstrated to be more than two magnitudes lower than that for salt selectivity–water permeance. Such variations were derived from the different membrane–solute interactions, in which the water/EDC selectivity was determined by the combined effects of steric exclusion and the hydrophobic interaction, while the electrostatic interaction and steric exclusion played crucial roles in water/salt selectivity. We further highlighted the role of the pore number and residual groups during the transport of EDC molecules across the PA membrane via molecular dynamics (MD) simulations. Fewer pores decreased the transport channels, and the existence of residual groups might cause steric hindrance and dynamic disturbance to EDC transport inside the membrane. This study elucidated the trade-off phenomenon and mechanisms between EDC selectivity and water permeance, providing a theoretical reference for the precise design of PA NF membranes for effective removal of EDCs in water reuse