Regulating the Electronic Structure of Cu Single-Atom Catalysts toward Enhanced Electro-Fenton Degradation of Organic Contaminants via 1O2 and •OH.

Heterogeneous electro-Fenton degradation with 1O2 and •OH generated from O2 reduction is cost-effective for the removal of refractory organic pollutants from wastewater. As 1O2 is more tolerant to background constituents such as salt ions and a high pH value than •OH, tuning the production of 1O2 and •OH is important for efficient electro-Fenton degradation. However, it remains a great challenge to selectively produce 1O2 and improve the species yield. Herein, the electronic structure of atomically dispersed Cu-N4 sites was regulated by doping electron-deficient B into porous hollow carbon microspheres (CuBN-HCMs), which improved *O2 adsorption and significantly enhanced 1O2 selectivity in electro-Fenton degradation. Its 1O2 yield was 2.3 times higher than that of a Cu single-atom catalyst without B doping. Meanwhile, •OH was simultaneously generated as a minor species. The CuBN-HCMs were efficient for the electro-Fenton degradation of phenol, sulfamethoxazole, and bisphenol A with a high mineralization efficiency. Its kinetic constants showed insignificant changes under various anions and a wide pH range of 1-9. More importantly, it was energy-efficient for treating actual coking wastewater with a low energy consumption of 19.0 kWh kgCOD-1. The superior performance of the CuBN-HCMs was contributed from 1O2 and •OH and its high 1O2 selectivity.

Steering CO2 electroreduction toward ethanol production by a surface-bound Ru polypyridyl carbene catalyst on N-doped porous carbon.

Electrochemical reduction of CO2 to multicarbon products is a significant challenge, especially for molecular complexes. We report here CO2 reduction to multicarbon products based on a Ru(II) polypyridyl carbene complex that is immobilized on an N-doped porous carbon (RuPC/NPC) electrode. The catalyst utilizes the synergistic effects of the Ru(II) polypyridyl carbene complex and the NPC interface to steer CO2 reduction toward C2 production at low overpotentials. In 0.5 M KHCO3/CO2 aqueous solutions, Faradaic efficiencies of 31.0 to 38.4% have been obtained for C2 production at -0.87 to -1.07 V (vs. normal hydrogen electrode) with 21.0 to 27.5% for ethanol and 7.1 to 12.5% for acetate. Syngas is also produced with adjustable H2/CO mole ratios of 2.0 to 2.9. The RuPC/NPC electrocatalyst maintains its activity during 3-h CO2-reduction periods.

Improvement of Antifouling and Antimicrobial Abilities on Silver-Carbon Nanotube Based Membranes under Electrochemical Assistance.

Excellent fouling resistance to various foulants is crucial to maintain the separation performance of membranes in providing potable water. Antimicrobial modification is effective for antibiofouling but fails to mitigate organic fouling. Improving surface charges can improve the resistance to charged foulants, but the lack of antimicrobial ability results in bacterial aggregation. Herein, a silver nanoparticle modified carbon nanotube (Ag-CNT)/ceramic membrane was prepared with enhanced antifouling and antimicrobial properties under electrochemical assistance. The presence of silver nanoparticles endows the composite membrane with antimicrobial ability by which biofilm formation is inhibited. Its steady-state flux is 1.9 times higher than that for an unmodified membrane in filtering bacterial suspension. Although the formation of organic fouling did weaken the biofouling resistance, the negatively charged bacteria and organic matter can be sufficiently repelled away from the cathodic membrane under electrochemical assistance. The flux loss under a low-voltage of 2.0 V decreased to <10% from >35% for the membrane alone when bacteria and organic matter coexisted in the feedwater. More importantly, silver dissolution was significantly inhibited via an in situ electroreduction process by which the Ag+ concentration in the effluent (<1.0 µg/L) was about 2 orders of magnitude lower than that without voltage. The integration of antimicrobial modification and electrochemistry offers a new prospect in the development of membranes with high fouling resistance in water treatment.

Enhanced Perfluorooctanoic Acid Degradation by Electrochemical Activation of Sulfate Solution on B/N Codoped Diamond.

Electrochemical oxidation based on SO4•- and •OH generated from sulfate electrolyte is a cost-effective method for degradation of persistent organic pollutants (POPs). However, sulfate activation remains a great challenge due to lack of active and robust electrodes. Herein, a B/N codoped diamond (BND) electrode is designed for electrochemical degradation of POPs via sulfate activation. It is efficient and stable for perfluorooctanoic acid (PFOA) oxidation with first-order kinetic constants of 2.4 h-1 and total organic carbon removal efficiency of 77.4% (3 h) at relatively low current density of 4 mA cm-2. The good activity of BND mainly originates from a B and N codoping effect. The PFOA oxidation rate at sulfate electrolyte is significantly enhanced (2.3-3.4 times) compared with those at nitrate and perchlorate electrolytes. At sulfate, PFOA oxidation rate decreases slightly in the presence of •OH quencher while it declines significantly with SO4•- and •OH quenchers, indicate both SO4•- and â€¢OH contribute to PFOA oxidation but SO4•- contribution is more significant. On the basis of intermediates analysis, a proposed mechanism for PFOA degradation is that PFOA is oxidized to shorter chain perfluorocarboxylic acids gradually by SO4•- and •OH until it is mineralized.

Improving Ion Rejection of Conductive Nanofiltration Membrane through Electrically Enhanced Surface Charge Density.

Nanofiltration (NF) is considered a promising candidate for brackish and seawater desalination. NF exhibits high multivalent ion rejection, but the rejection rate for monovalent ions is relatively low. Besides, great challenges remain for conventional NF membranes to achieve high ion rejection without sacrificing water flux. This work presents an effective strategy for improving the ion rejection of conductive NF membrane without decreasing the permeability through electrically assisted enhancement of surface charge density. When external voltage is increased from 0 to 2.5 V, the surface charge density of the membrane increases from 11.9 to 73.0 mC m-2, which is 6.1× higher than that without external voltage. Correspondingly, the rejection rate for Na2SO4 increases from 81.6 to 93.0% and that for NaCl improves from 53.9 to 82.4%; meanwhile, the membrane retains high permeabilities of 14.0 L m-2 h-1 bar-1 for Na2SO4 filtration and 14.5 L m-2 h-1 bar-1 for NaCl filtration. The Donnan steric pore model analysis suggests that the Donnan potential difference between the membrane and bulk solution is increased under electrical assistance, leading to increased ion transfer resistance for improved ion rejection. This work provides new insight into the development of advanced NF technologies for desalination and water treatment.

Degradation of phenol by coal-based carbon membrane integrating sulfate radicals-based advanced oxidation processes.

Phenol, as a representative organic pollutant in aquatic environments, has posed a serious threat to humans and ecosystem. In this work, a novel integration system combined coal-based carbon membrane with sulfate radicals-based advanced oxidation processes (SR-AOPs) was designed for degradation of phenol. The integrated system achieved 100% removal efficiency under the optimal condition (peroxydisulfate dosage is 0.2 g/L, at alkaline condition with 2 mL/min flow velocity). The quenching experiments revealed that the efficient removal of phenol by the integrated system were attributed to the co-existence of radical and nonradical mechanisms. This study proposes a green and efficient technique for the removal of phenol.

Highly Permeable Thin-Film Composite Forward Osmosis Membrane Based on Carbon Nanotube Hollow Fiber Scaffold with Electrically Enhanced Fouling Resistance.

Forward osmosis (FO) is an emerging approach in water treatment, but its application is restricted by severe internal concentration polarization (ICP) and low flux. In this work, a self-sustained carbon nanotube hollow fiber scaffold supported polyamide thin film composite (CNT TFC-FO) membrane was first proposed with high porosity, good hydrophilicity and excellent electro-conductivity. It showed a specific structure parameter as low as 126 µm, suggesting its weakened ICP. Against a pure water feed using 2.0 M NaCl draw solution, its fluxes were 4.7 and 3.6 times as high as those of the commercial cellulose triacetate TFC-FO membrane in the FO and pressure retarded osmosis (PRO) modes, respectively. Meanwhile, the membrane showed excellent electrically assisted resistance to organic and microbial fouling. Its flux was improved by about 50% during oil-water simulation separation under 2.0 V voltage. These results indicate that the CNT TFC-FO membrane opens up a frontier for stably and effectively recycling potable water from electrochemical FO process.

Combined Effects of Surface Charge and Pore Size on Co-Enhanced Permeability and Ion Selectivity through RGO-OCNT Nanofiltration Membranes.

Nanofiltration (NF) has received much attention for wastewater treatment and desalination. However, NF membranes generally suffer from the trade-off between permeability and selectivity. In this work, the coenhancement of permeability and ion selectivity was achieved through tuning the surface charge and pore size of oxidized carbon nanotube (OCNT) intercalated reduced graphene oxide (RGO) membranes. With the increase of OCNT content from 0 to 83%, the surface charge and the pore size were increased. The permeability increased to 10.6 L m-2 h-1 bar-1 and rejection rate reached 78.1% for Na2SO4 filtration at a transmembrane pressure of 2 bar, which were 11.8 and 1.3 times higher than those of pristine RGO membrane. The composite membrane also showed 11.1 times higher permeability (11.1 L m-2 h-1 bar-1) and 2.9 times higher rejection rate (35.3%) for NaCl filtration. The analyses based on Donnan steric pore model suggest that the increased permeability is attributed to the combined effects of enlarged pore size and increased surface charge, while the enhanced ion selectivity is mainly dependent on the electrostatic interaction between the membrane and target ions. This finding provides a new insight for the development of high-performance NF membranes in water treatment and desalination.

Selective Electrochemical Reduction of Carbon Dioxide to Ethanol on a Boron- and Nitrogen-Co-doped Nanodiamond.

Electrochemical reduction of CO2 to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO2 to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B- and N-co-doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO2 to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (-1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co-doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO2 reduction revealed by DFT computation was CO2 →*COOH→*CO→*COCO→*COCH2 OH→*CH2 OCH2 OH→CH3 CH2 OH.

A controlled wet-spinning and dip-coating process for preparation of high-permeable TiO2 hollow fiber membranes.

In order to improve the permeate flux of photocatalytic membranes, we present an approach for coupling TiO2 with ceramic hollow fiber membranes. The ceramic hollow fiber membranes with high permeate flux were fabricated by a controlled wet-spinning process using polyethersulfone (PESf) and ceramic powder as precursors and 1-methyl-2-pyrrolidinone as solvent, and the subsequent TiO2 coating was performed by a dip-coating process using tetra-n-butyl titanate as precursor. It has been found that the PESf/ceramic powder ratio could influence the structure of the membranes. Here the as-prepared TiO2 hollow fiber membranes had a pure water flux of 4,450 L/(m(2)·h). The performance of the TiO2 hollow fiber membrane was evaluated using humic acid (HA) as a test substance. The results demonstrated that this membrane exhibited a higher permeate flux under UV irradiation than in the dark and the HA removal efficiency was enhanced. The approach described here provides an operable route to the development of high-permeable photocatalytic membranes for water treatment.

Enhanced permeability, selectivity, and antifouling ability of CNTs/Al2O3 membrane under electrochemical assistance.

Membrane filtration provides effective solutions for removing contaminants, but achieving high permeability, good selectivity, and antifouling ability remains a great challenge for existing membrane filtration technologies. In this work, membrane filtration coupled with electrochemistry has been developed to enhance the filtration performance of a CNTs/Al2O3 membrane. The as-prepared CNTs/Al2O3 membrane, obtained by coating interconnected CNTs on an Al2O3 substrate, presented good pore-size tunability, mechanical stability, and electroconductivity. For the removal of a target (silica spheres as a probe) with a size comparable to the membrane pore size, the removal efficiency and flux at +1.5 V were 1.1 and 1.5 times higher, respectively, than those without electrochemical assistance. Moreover, the membrane also exhibited a greatly enhanced removal efficiency for contaminants smaller than the membrane pores, providing enhancements of 4 orders of magnitude and a factor of 5.7 for latex particles and phenol, respectively. These results indicated that both the permeability and the selectivity of CNTs/Al2O3 membranes can be significantly improved by electrochemical assistance, which was further confirmed by the removal of natural organic matter (NOM). The permeate flux and NOM removal efficiency at +1.5 V were about 1.6 and 3.0 times higher, respectively, than those without electrochemical assistance. In addition, the lost flux of the fouled membrane was almost completely recovered by an electrochemically assisted backwashing process.

High-yield electrosynthesis of hydrogen peroxide from oxygen reduction by hierarchically porous carbon.

H2O2 production by electroreduction of O2 is an attractive alternative to the current anthraquinone process, which is highly desirable for chemical industries and environmental remediation. However, it remains a great challenge to develop cost-effective electrocatalysts for H2O2 synthesis. Here, hierarchically porous carbon (HPC) was proposed for the electrosynthesis of H2O2 from O2 reduction. It exhibited high activity for O2 reduction and good H2O2 selectivity (95.0-70.2%, most of them >90.0% at pH 1-4 and >80.0% at pH 7). High-yield H2O2 generation has been achieved on HPC with H2O2 concentrations of 222.6-62.0 mmol L(-1) (2.5 h) and corresponding H2O2 production rates of 395.7-110.2 mmol h(-1) g(-1) at pH 1-7 and -0.5 V. Moreover, HPC was energy-efficient for H2O2 production with current efficiency of 81.8-70.8%. The exceptional performance of HPC for electrosynthesis of H2O2 could be attributed to its high content of sp(3)-C and defects, large surface area and fast mass transfer.

Constructing all carbon nanotube hollow fiber membranes with improved performance in separation and antifouling for water treatment.

Manipulating carbon nanotubes (CNTs) through engineering into advanced membranes with superior performance for disinfection and decontamination of water shows great promise but is challenging. In this paper, a facile assembly of CNTs into novel hollow fiber membranes with tunable inner/outer diameters and structures is developed for the first time. These free-standing membranes composed entirely of CNTs feature a porosity of 86±5% and a permeation flux of about 460±50 L m(-2) h(-1) at a pressure differential of 0.04 MPa across the membrane. The randomly oriented interwoven structure of CNTs endows the membranes considerable resistance to pore blockage. Moreover, the adsorption capability of the CNT hollow fiber membranes, which is crucial in the efficient removal of small and trace contaminant molecules, is about 2 orders of magnitude higher than that of commercial polyvinylidene fluoride hollow fiber membranes. The unique advantage of the CNT hollow fiber membranes over other commercial membranes is that they can be in situ electrochemically regenerated after adsorption saturation.

Promoting Electrocatalytic Reduction of CO2 and Nitrate to Urea on N-Doped Porous Hollow Carbon Spheres.

The electrocatalytic coreduction of CO2 and nitrate is a green method for urea synthesis, mitigating CO2 emission and nitrate contamination. However, its slow kinetics and high energy barrier result in a poor urea production performance. Herein, we reported N-doped porous hollow carbon spheres (N-PHCS) for promoting CO2 and nitrate conversion to urea via nanoconfinement and N-doping from both reaction kinetics and thermodynamics. A high urea yield of 12.0 mmol h-1 gcat-1 with Faradaic efficiency of 19.1% was achieved on N-PHCS at -1.0 V (vs Ag/AgCl), which was comparable to or even higher than those of metal-based electrocatalysts reported. The experimental and theoretical calculation results revealed that carbon spheres with an appropriate interior void and pore size were favorable for confining reactants and intermediates to accelerate urea production, while N-doping can reduce the energy barrier for urea synthesis. By regulating the microstructure and N doping of N-PHCS, it showed a superior performance for urea electrosynthesis. The energy favorable pathway for urea synthesis was through the C-N coupling reaction of *NO and *CO, and pyridinic N can reduce the reaction energy barrier.

Efficient electro-Fenton degradation of organic pollutants via the synergistic effect of 1O2 and •OH generated on single FeN4 sites.

The electro-Fenton with in situ generated 1O2 and •OH is a promising method for the degradation of micropollutants. However, its application is hindered by the lack of catalysts that can efficiently generate 1O2 and •OH from electrochemical oxygen reduction. Herein, N-doped stacked carbon nanosheets supported Fe single atoms (Fe-NSC) with FeN4 sites were designed for simultaneous generation of 1O2 and •OH to enhance electro-Fenton degradation. Due to the synergistic effect of 1O2 and •OH, a variety of contaminants (phenol, 2,4-dichlorophenol, sulfamethoxazole, atrazine and bisphenol A) were efficiently degraded with high kinetic constants of 0.037-0.071 min-1 by the electro-Fenton with Fe-NSC as cathode (-0.6 V vs Ag/AgCl, pH 6). Moreover, the superior performance for electro-Fenton degradation was well maintained in a wide pH range from 3 to 10 even with interference of various inorganic salt ions. It was found that FeN4 sites with pyridinic N coordination were responsible for its good performance for electro-Fenton degradation. Its 1O2 yield was higher than •OH yield, and the contribution of 1O2 was more significant than •OH for pollutant degradation.

A 2.5-Dimensional biomimetic dual-functional bifacial-evaporator for high efficient evaporation and water purification.

Nowadays, solar-driven interfacial steam generation (SISG) is a sustainable and green technology for mitigating the water shortage crisis. Nevertheless, SISG is suffering from the enrichment of volatile organic compounds in condensate water and non-volatile organic compounds in feed water in practical applications. Herein, taking inspiration from nature, a dual-functional bifacial-CuCoNi (Bi-CuCoNi) evaporator with a special biomimetic urchin-like microstructure was successfully prepared. The unique design with 2.5-Dimensional bifacial working sides and urchin-like light absorption microstructure provided the Bi-CuCoNi evaporator with remarkable evaporation performance (1.91 kg m-2 h-1 under 1 kW m-2). Significantly, due to the urchin-like microstructure, the adequately exposed catalytic active sites enabled the Bi-CuCoNi/peroxydisulfate (PDS) system to degrade non-volatile organic pollutants (removal rate of 99.3 % in feed water, close to 100 % in condensate water) and the volatile organic pollutants (removal rate of 99.1 % in feed water, 98.2 % in condensate water) simultaneously. Moreover, the Bi-CuCoNi evaporator achieved non-radical pathway degradation at whole-stages. The dual-functional evaporator successfully integrated advanced oxidation processes (AOPs) into SISG, providing a new idea for high-quality freshwater production from polluted wastewater. ENVIRONMENTAL IMPLICATION: Inspired by nature, a dual-functional bifacial CuCoNi evaporator with a special biomimetic urchin-like microstructure formed by CuCoNi oxide nanowires grown on nickel foam by the hydrothermal synthesis method was successfully prepared. The prepared Bi-CuCoNi evaporator can effectively degrade organic pollutants in feed water and condensate water simultaneously during SISG, thus generating high-quality fresh water. Meanwhile, the health risks associated with the accumulation of organic pollutants in water during traditional SISG were reduced via green and sustainable way. The spatial 2.5-Dimensional structural design of Bi-CuCoNi provided new insights for achieving efficient water evaporation and fresh water generation from various polluted wastewater.

Activating peroxymonosulfate with MOF-derived NiO-NiCo2O4/titanium membrane for water treatment: A non-radical dominated oxidation mechanism.

Traditional peroxymonosulfate (PMS) catalytic membranes dominated by radical pathways often face interference from complex components in water bodies. Herein, we employed a controlled electro-deposition technique to coat a Ni-Co metal-organic framework (MOF) precursor onto titanium hollow fiber membrane (THFM), followed by high-temperature calcination to synthesize a MOF-derived NiO-NiCo2O4/THFM (M-NNCO-THFM) PMS catalytic membrane. Then, the M-NNCO-THFM filtration integrated with PMS activation (MFPA process) for water treatment. Experimental results demonstrated that the M-NNCO-THFM MFPA process successfully achieved complete phenol (PE) removal via a non-radical-dominated degradation pathway, involving singlet oxygen (1O2) and electron transfer, while exhibiting wide pH adaptability and exceptional stability in complex water matrices. Mechanism analysis revealed that the electron transfer process was significantly enhanced by the MOF-derived heterojunction structure, which increased the flat-band potential from 0.39 eV to 0.56 eV, thereby facilitating efficient electron transfer for PE removal. The non-radical 1O2 pathway was primarily due to the cycling of metal valence states (Ni2+/Co3+), leading to the reduction of Co2+ and its reaction with PMS, resulting in the generation of reactive species. Furthermore, electrochemical measurements indicated that the M-NNCO-THFM exhibited lower charge transfer resistance and enhanced charge transfer efficiency compared to non-MOF-derived NNCO-THFM, corresponding to the superior catalytic performance and electrochemically active surface area of M-NNCO-THFM.

Enhanced persulfate activation by nitrogen-doped mesoporous carbon for efficiently degrading organic matters.

Nitrogen-doped carbon materials (NMC) are widely used in peroxymonosulfate-based advanced oxidation processes (PMS-AOPs). Despite great efforts to improve the specific surface area of and the content of N atoms in catalysts for enhancing catalytic performance, this does not mean that the catalytic performance will improve with the increasing specific surface area and nitrogen content. Therefore, it is the key to optimize pore structure of NMC for maximizing the catalytic performance of nitrogen active sites. Herein, we synthesized the NMC as an efficient catalyst to activate PMS for the phenol removal. It can be found that the mesopore structure significantly accelerated the diffusion of reactants and might build the spatial confinement effect to improve the utilization of short life free radicals for further improving the removal efficiency. The removal efficiency of 1NMC750 (95%) with abundant mesopore channels was much higher than that of 1NMC750-0F127 (20%) with abundant micropore channels. Furthermore, the mechanism was confirmed to be radical (SO4•-, •OH) and non-radical (1O2, electron transfer) pathways. This study proposed a new insight for improving the catalytic performance of carbon materials by coordinating the pore structure.

Metal-free electro-Fenton degradation of perfluorooctanoic acid with efficient ordered mesoporous carbon catalyst.

Heterogeneous electro-Fenton with in situ generated H2O2 and •OH is a cost-effective method for the degradation of refractory organic pollutants, in which the catalyst is an important factor affecting its degradation performance. Metal-free catalysts can avoid the potential risk of metal dissolution. However, it remains great challenge to develop efficient metal-free catalyst for electro-Fenton. Herein, ordered mesoporous carbon (OMC) was designed as a bifunctional catalyst for efficient H2O2 and •OH generation in electro-Fenton. The electro-Fenton system showed fast perfluorooctanoic acid (PFOA) degradation with kinetics constant of 1.26 h-1 and high total organic carbon (TOC) removal efficiency of 84.0 % after 3 h reaction. The •OH was the main species responsible for PFOA degradation. Its generation was promoted by the abundant oxygen functional groups such as C-O-C and the nano-confinement effect of mesoporous channels on OMCs. This study indicated that OMC is an efficient catalyst for metal-free electro-Fenton system.

Bifunctional Solar Evaporator with Co/N-Doped Graphene Oxide for Synergistic Steam Generation and Organic Pollutant Degradation.

Solar-driven interfacial steam generation (SISG) is a promising technology for alleviating freshwater shortage. However, when the SISG technology is applied to wastewater treatment, the contaminant would be enriched in residual bulk water. Herein, a dual-functional evaporator was constructed via tactfully decorating Co/N-doped graphene oxide (GO) on melamine foam (MF), which can simultaneously achieve efficient vapor production and source water purification. N-doped carbon nanotubes (NCNTs) endowed evaporators with powerful light absorption and water transport performance, guaranteeing an evaporation rate of 2.02 kg m-2 h-1 under 1 sun irradiation. Meanwhile, the catalytic activity of the carbon layer was adjusted by the N dopant and embedded Co particles, providing abundant active sites to activate peroxymonosulfate (PMS). When treating the solution containing sulfamethoxazole (SMX), no SMX residues were detected in the remaining bulk water (up to 100% SMX degradation efficiency within 60 min), demonstrating that reactive oxygen species (ROS) were generated to attack SMX in the source water. The bifunctional evaporator successfully combined SISG and advanced oxidation processes (AOPs), providing an ingenious strategy for solving the problem of wastewater enrichment during SISG.