Synergistic etching of nickel foam by Fe3+ and Cl- ions to synthesize nickel-iron-layered double hydroxide nanolayers with abundant oxygen vacancies for superior urea oxidation.

Urea electrolysis is an appealing topic for hydrogen production due to its ability to extract hydrogen at a lower potential. However, it is plagued by sluggish kinetics and noble-metal catalyst requirements. Herein, we developed nickel-iron-layered double hydroxide (NiFe-LDH) nanolayers with abundant oxygen vacancies (OV) via synergistically etching nickel foam with Fe3+ and Cl- ions, enabling the efficient conversion of urea into H2 and N2. The synthesized OV-NiFe-LDH exhibits a lower potential (1.30 vs. reversible hydrogen electrode, RHE) for achieving 10 mA cm-2 in the urea oxidation reaction (UOR), surpassing most recently reported Ni-based electrodes. OV provides favorable conductivity and a large surface area, which results in a 4.1-fold in electron transport and a 5.1-fold increase in catalyst reactive sites. Density Functional Theory (DFT) calculations indicate that OV can lower the adsorption energy of urea, and enhance the bonding strength of *CONHNH, giving rise to improved UOR. This study provides a viable path toward economical and efficient production of high-purity hydrogen.

MoS2-mediated active hydrogen modulation to boost Fe2+ regeneration in solar-driven electro-Fenton process.

The sluggish kinetics of Fe2+ regeneration seriously hinders the performance of Fenton process. However, the conventional Fenton system excessively stifle hydrogen-producing reactions, ignoring the significance of active hydrogen (H*) in Fe3+ reduction. Herein, a strategy of H* modulation is developed by decorating molybdenum disulfide (MoS2) on a graphite felt (GF) cathode to boost Fe2+ regeneration in solar-driven electro-Fenton (SEF) process. With MoS2 regulation, moderately dispersed MoS2 on GF can serve as a bifunctional cathode, where the H* and hydrogen peroxide (H2O2) are simultaneously generated through H+ reduction and O2 reduction, respectively. The in-situ generated H2O2 can trigger Fenton reactions with Fe2+, while the H* with robust reducing potential can significantly expedite Fe3+ reduction, consequently enhancing the HO• production. Both DFT calculations and EPR experiments confirm that H* can be activated via MoS2 decoration. The results show that Fe2+ concentration in the MoS2 @GF-SEF system remains at 15.74 mg/L (56.21%) after 6 h, which is 17.89 times that of the GF-SEF system. Moreover, the HO• content and organics degradation rate in the MoS2 @GF-SEF are 3.61 and 5.30 times those of the GF-SEF, respectively. This study provides a practical cathode strategy of H* modulation to enhance HO• production and electro-Fenton process. ENVIRONMENTAL IMPLICATION: Boosting Fe2+ regeneration is of great value for the Electro-Fenton process. Herein, report a strategy to achieve this goal based on a MoS2 @GF cathode. Remarkably, the MoS2 @GF system exhibits exceptional efficiency for both various refractory organic compounds with environmentally hazardous effects and sterilization aspects, which can also work over a wide range of pH values (3-11). Specially, this system is driven only by solar energy. These characteristics make the electro-Fenton system more suitable for practical wastewater treatment.

Keto-anthraquinone covalent organic framework for H2O2 photosynthesis with oxygen and alkaline water.

Hydrogen peroxide photosynthesis suffers from insufficient catalytic activity due to the high energy barrier of hydrogen extraction from H2O. Herein, we report that mechanochemically synthesized keto-form anthraquinone covalent organic framework which is able to directly synthesize H2O2 (4784 µmol h-1 g-1 at λ > 400 nm) from oxygen and alkaline water (pH = 13) in the absence of any sacrificial reagents. The strong alkalinity resulted in the formation of OH-(H2O)n clusters in water, which were adsorbed on keto moieties within the framework and then dissociated into O2 and active hydrogen, because the energy barrier of hydrogen extraction was largely lowered. The produced hydrogen reacted with anthraquinone to generate anthrahydroquinone, which was subsequently oxidized by O2 to produce H2O2. This study ultimately sheds light on the importance of hydrogen extraction from H2O for H2O2 photosynthesis and demonstrates that H2O2 synthesis is achievable under alkaline conditions.

Synergistic catalysis of TiO2/WO3 photoanode and Sb-SnO2 electrode with highly efficient ClO• generation for urine treatment.

Urine is the major source of nitrogen pollutants in domestic sewage and is a neglected source of H2. Although ClO• is used to overcome the poor selectivity and slow kinetics of urea decomposition, the generation of ClO• suffers from the inefficient formation reaction of HO• and reactive chlorine species (RCS). In this study, a synergistic catalytic method based on TiO2/WO3 photoanode and Sb-SnO2 electrode efficiently producing ClO• is proposed for urine treatment. The critical design is that TiO2/WO3 photoanode and Sb-SnO2 electrode that generate HO• and RCS, respectively, are assembled in a confined space through face-to-face (TiO2/WO3//Sb-SnO2), which effectively strengthens the direct reaction of HO• and RCS. Furthermore, a Si solar panel as rear photovoltaic cell (Si PVC) is placed behind TiO2/WO3//Sb-SnO2 to fully use sunlight and provide the driving force of charge separation. The composite photoanode (TiO2/WO3//Sb-SnO2 @Si PVC) has a ClO• generation rate of 260% compared with the back-to-bake assembly way. In addition, the electrons transfer to the NiFe LDH@Cu NWs/CF cathode for rapid H2 production by the constructed photoelectric catalytic (PEC) cell without applied external biasing potential, in which the H2 production yield reaches 84.55 µmol h-1 with 25% improvement of the urine denitrification rate. The superior performance and long-term stability of PEC cell provide an effective and promising method for denitrification and H2 generation.

Heteroatom substitution enhances generation and reactivity of surface-activated peroxydisulfate complexes for catalytic fenton-like reactions.

Peroxydisulfate (PDS)-based Fenton-like reactions are promising advanced oxidation processes (AOPs) to degrade recalcitrant organic water pollutants. Current research predominantly focuses on augmenting the generation of reactive species (e.g., surface-activated PDS complexes (PDS*) to improve treatment efficiency, but overlooks the potential benefits of enhancing the reactivity of these species. Here, we enhanced PDS* generation and reactivity by incorporating Zn into CuO catalyst lattice, which resulted in 99% degradation of 4-chlorophenol within only 10 min. Zn increased PDS* generation by nearly doubling PDS adsorption while maintaining similar PDS to PDS* conversion efficiency, and induced higher PDS* reactivity than the common catalyst CuO, as indicated by a 4.1-fold larger slope between adsorbed PDS and open circuit potential of a catalytic electrode. Cu-O-Zn formation upshifts the d-band center of Cu sites and lowers the energy barrier for PDS adsorption and sulfate desorption, resulting in enhanced PDS* generation and reactivity. Overall, this study informs strategies to enhance PDS* reactivity and design highly active catalysts for efficient AOPs.

Plastic wastes-derived N-doped carbon nanotubes for efficient removal of sulfamethoxazole in high salinity wastewater via nonradical peroxymonosulfate activation.

Peroxymonosulfate (PMS) catalytic activation is effective to eliminate organic pollutants from water, thus the development of low-cost and efficient catalysts is significant in applications. The resource conversion of plastic wastes (PWs) into carbon nanotubes (CNTs) is a promising candidate for PMS-based advanced oxidation processes (AOPs), and also a sustainable strategy to realize plastic management and reutilization. Herein, cost-effective PWs-derived N-doped CNTs (N-pCNTs) were synthesized, which displayed efficient activity for PMS activation through an electron transfer pathway (ETP) for sulfamethoxazole (SMX) degradation in high salinity water. The pyrrolic N induced the positively charged surface of N-pCNTs, favoring the electrostatic adsorption of PMS and subsequent generation of active PMS* . A galvanic oxidation process was developed to prove the electron-shuttle dominated ETP for SMX oxidation. Combined with theoretical calculations, the efficiency of ETP was determined by the potential difference between HOMO of SMX and LUMO of N-pCNTs. Such oxidation produced low-toxicity intermediates and resulted in selective degradation of specific sulfonamide antibiotics. This work reveals the feasibility of low-cost N-pCNTs catalysts from PWs serving as an appealing candidate for PMS-AOPs in water remediation, providing a new solution to alleviate environmental issues caused by PWs and also advances the understanding of ETP during PMS activation.

Reduction of pollution loads based on sewage treatment projects around a lake: A case study on Erhai Lake.

Erhai Lake is a highland freshwater lake in Dali, China. Rapid tourism development has generated large amounts of pollutants. Since 2015, six wastewater treatment plants (WWTPs) have been built to treat wastewater collected through sewage interception projects. In this study, reductions in the pollution load of wastewater from different sources were evaluated by considering the effects of groundwater leakage, microbial degradation, and rainfall-runoff. The results showed that the systems reduced the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) loads by 85, 83, and 85%, respectively. Discharge wastewater has the characteristics of a low concentration of domestic sewage discharge, large tourist sewage discharge, and high concentration of livestock wastewater. Due to the high groundwater level, there is groundwater infiltration in the influent water of WWTPs, which dilutes the pollutant concentration of the influent and, therefore, results in a lower treatment efficiency. Further treatment of tailwater also reduced the pollution loads discharged into the lake as well as the COD and TN by 10.25 and 22.90%, respectively. The results indicate that groundwater infiltration in the sewer network system is the primary target to be addressed in future developments.

CoN1 O2 Single-Atom Catalyst for Efficient Peroxymonosulfate Activation and Selective Cobalt(IV)=O Generation.

High-valent metal-oxo (HVMO) species are powerful non-radical reactive species that enhance advanced oxidation processes (AOPs) due to their long half-lives and high selectivity towards recalcitrant water pollutants with electron-donating groups. However, high-valent cobalt-oxo (CoIV =O) generation is challenging in peroxymonosulfate (PMS)-based AOPs because the high 3d-orbital occupancy of cobalt would disfavor its binding with a terminal oxygen ligand. Herein, we propose a strategy to construct isolated Co sites with unique N1 O2 coordination on the Mn3 O4 surface. The asymmetric N1 O2 configuration is able to accept electrons from the Co 3d-orbital, resulting in significant electronic delocalization at Co sites for promoted PMS adsorption, dissociation and subsequent generation of CoIV =O species. CoN1 O2 /Mn3 O4 exhibits high intrinsic activity in PMS activation and sulfamethoxazole (SMX) degradation, highly outperforming its counterpart with a CoO3 configuration, carbon-based single-atom catalysts with CoN4 configuration, and commercial cobalt oxides. CoIV =O species effectively oxidize the target contaminants via oxygen atom transfer to produce low-toxicity intermediates. These findings could advance the mechanistic understanding of PMS activation at the molecular level and guide the rational design of efficient environmental catalysts.

Nitrogen-containing wastewater fuel cells for total nitrogen removal and energy recovery based on Cl•/ClO• oxidation of ammonia nitrogen.

The excess nitrogen discharge into water bodies has resulted in extensive water pollution and human health risks, which has become a critical global issue. Moreover, nitrogenous wastewater contains considerable chemical energy contributed by organic pollutants and nitrogenous compounds. Therefore, the treatment of various kinds of nitrogen-containing wastewater for nitrogen removal and energy recovery is of significance. Biological methode and advanced oxidation processes (AOPs) are the main methods for nitrogen removal. However, biological treatment is easily inhibited by high-salinity, high ammonia nitrogen (NH3-N/NH4+-N), nitrite and toxic organics in wastewater, which limits its application. AOPs mainly induce in situ generation of highly reactive species, such as hydroxyl radical (HO•), sulfate radical (SO4•-) and chlorine radicals (Cl•, ClO•, Cl2•-), for nitrogen removal. Nevertheless, HO• shows low reactivity and N2 selectivity towards NH3-N/NH4+-N oxidation, and SO4•- also demonstrates unsatisfactory NH3-N/NH4+-N removal. It has been shown that Cl•/ClO• can efficiently remove NH3-N/NH4+-N with high N2 selectivity. The generation of Cl•/ClO• can be triggered by various techniques, among which the PEC technique shows great potential due to its higher efficiency for Cl•/ClO• generation and eco-friendly approach for pollutants degradation and energy recovery by utilizing solar energy. Cl•/ClO• oxidation of NH3-N/NH4+-N and nitrate nitrogen (NO3--N) reduction can be strengthened through the design of photoanode and cathode materials, respectively. Coupling with this two pathways, an exhaustive total nitrogen (TN) removal system is designed for complete TN removal. When introducing the mechanism into photocatalytic fuel cells (PFCs), the concept of nitrogen-containing wastewater fuel cells (NFCs) is proposed to treat several typical types of nitrogen-containing wastewater, achieving high-efficiency TN removal, organics degradation, toxic chlorate control, and energy recovery simultaneously. Recent research progress in this field is reviewed, summarized and discussed, and in-depth perspectives are proposed, providing new ideas for the resource treatment of nitrogen-containing wastewater.

Ni doped amorphous FeOOH layer as ultrafast hole transfer channel for enhanced PEC performance of BiVO4.

Bismuth vanadate (BiVO4), as the potential and prospective photocatalyst, has been limited by the issue of poor separation and transfer of charge carrier for photoelectrocatalytic (PEC) water oxidation. Here, a significant increase of surface injection efficiency for BiVO4 is realized by the rationally designed Ni doped FeOOH (Ni:FeOOH) layer growing on BiVO4 photoanode (Ni:FeOOH/BiVO4), in which doped Ni2+ can induce partial-charge of FeOOH to serve as ultrafast transfer channel for hole transfer and transportation at the semiconductor/electrolyte interface. In addition, the Ni:FeOOH/BiVO4 shows the ηsurface value of 81.6 %, which is 3.28-fold and 1.47-fold of BiVO4 and FeOOH/BiVO4, respectively. The photocurrent density of Ni:FeOOH/BiVO4 is 4.21 mA cm-2 at 1.23 V vs. RHE, with the onset potential cathodically shifting 237 mV over BiVO4 and a long-term stability for suppressing surface charge recombination. The UPS and UV-Vis spectra have confirmed the type-II band alignment between Ni:FeOOH and BiVO4 for promoting carrier transfer. This facile and effective spin-coating method could deposit oxygen evolution catalysts (OECs) availably onto photoanodes with enhanced PEC water splitting.

Unconventional Substitution for BiVO4 to Enhance Photoelectrocatalytic Performance by Accelerating Polaron Hopping.

Bismuth vanadate (BiVO4) as a fascinating semiconductor for photoelectrocatalytic (PEC) water oxidation with suitable band gap (Eg) has been limited by the issue of poor separation and transportation of charge carriers. Herein, we propose an unconventional substitution of V5+ sites by Ti4+ in BiVO4 (Ti:BiVO4) for the similar ionic radii and accelerated polaron hopping. Ti:BiVO4 increased the photocurrent density 1.90 times up to 2.51 mA cm-2 at 1.23 V vs RHE and increased the charge carrier density 1.81 times to 5.86 × 1018 cm-3. Compared with bare BiVO4, Ti:BiVO4 improves the bulk separation efficiency to 88.3% at 1.23 V vs RHE. The DFT calculations have illustrated that Ti-doping modification could decrease the polaron hopping energy barrier, narrow the Eg, and decrease the overpotential of the oxygen evolution reaction (OER) concurrently. With further spin-coated FeOOH cocatalyst, the photoanode has a photocurrent density of 3.99 mA cm-2 at 1.23 V vs RHE. The excellent PEC performance of FeOOH/Ti:BiVO4 is attributed to the synergistic effect of the FeOOH layer and Ti doping, which could promote charge carrier separation and transfer by expediting polaron migration.

Facile, Controllable, and Ultrathin NiFe-LDH In Situ Grown on a Ni Foam by Ultrasonic Self-Etching for Highly Efficient Urine Conversion.

As the primary source of nitrogen pollutants in domestic sewage, urine is also an alternative for H2 production via electrochemical processes. However, it suffers from sluggish kinetics and noble-metal catalyst requirement. Here, we report a non-precious ultrathin NiFe-layered double hydroxide catalyst for the remarkable conversion of urea into N2 and H2, which is in situ grown on a Ni foam via ultrasonic self-etching in Fe3+/ethylene glycol (EG). EG regulates the etching rate of Fe3+, resulting in an ultrathin nanosheet structure with the aid of ultrasonication. This structure dramatically promotes the dehydrogenation process via decreasing the nanolayer thickness from 120 to 3.4 nm and leads to a 4.8-fold increase in the generation of active sites. It exhibits record urea oxidation kinetics (390.8 mA·cm-2 at 1.5 V vs RHE) with excellent stability (120 h), which is 11.8 times better than that of commercial Pt/C catalyst (33.1 mA·cm-2). Tests with real urine at 20 mA cm-2 achieve 74% total nitrogen removal and 2853 µmol·h-1 of H2 production. This study provides an attractive landscape for producing H2 by consuming urine biowastes.

Single-Atom MnN5 Catalytic Sites Enable Efficient Peroxymonosulfate Activation by Forming Highly Reactive Mn(IV)-Oxo Species.

Four-nitrogen-coordinated transitional metal (MN4) configurations in single-atom catalysts (SACs) are broadly recognized as the most efficient active sites in peroxymonosulfate (PMS)-based advanced oxidation processes. However, SACs with a coordination number higher than four are rarely explored, which represents a fundamental missed opportunity for coordination chemistry to boost PMS activation and degradation of recalcitrant organic pollutants. We experimentally and theoretically demonstrate here that five-nitrogen-coordinated Mn (MnN5) sites more effectively activate PMS than MnN4 sites, by facilitating the cleavage of the O-O bond into high-valent Mn(IV)-oxo species with nearly 100% selectivity. The high activity of MnN5 was discerned to be due to the formation of higher-spin-state N5Mn(IV)═O species, which enable efficient two-electron transfer from organics to Mn sites through a lower-energy-barrier pathway. Overall, this work demonstrates the importance of high coordination numbers in SACs for efficient PMS activation and informs the design of next-generation environmental catalysts.

Type-II Heterojunction CdIn2S4/BiVO4 Coupling with CQDs to Improve PEC Water Splitting Performance Synergistically.

Bismuth vanadate (BiVO4) has been considered as a promising photoelectrocatalytic (PEC) semiconductor, but suffers from severe hole recombination, attributed to the short hole-diffusion length and the low carrier mobility. Herein, a type-II heterojunction CdIn2S4/BiVO4 is designed to improve the photocurrent density from 1.22 (pristine BiVO4) to 2.68 mA cm-2 at 1.23 V vs the reversible hydrogen electrode (RHE), accelerating the bulk separation of photogenerated carriers by the built-in field from the matched energy band. With the introduction of CQDs, CQDs/CdIn2S4/BiVO4 increases the photocurrent density to 4.84 mA cm-2, enhancing the light absorption and cathodically shifting its onset potential, due to the synergetic effect of the heterojunction and CQDs. Compared with BiVO4, CQDs/CdIn2S4/BiVO4 promotes the bulk separation efficiency to 94.6% and the surface injection efficiency to 72.2%. Additionally, spin-coating of FeOOH on CQDs/CdIn2S4/BiVO4 could further improve the PEC performance and keep a long stability for water splitting. The density function theory (DFT) calculations illustrated that the type-II heterojunction CdIn2S4/BiVO4 could decrease the oxygen evolution reaction (OER) overpotential and accelerate bulk charge separation for the built-in field of the aligned band structure.

Rapid Conversion of Co2+ to Co3+ by Introducing Oxygen Vacancies in Co3O4 Nanowire Anodes for Nitrogen Removal with Highly Efficient H2 Recovery in Urine Treatment.

Urine is a nitrogenous waste biomass but can be used as an appealing alternative substrate for H2 recovery. However, urine electrolysis suffers from sluggish kinetics and requires alkaline condition. Herein, we report a novel system to decompose urine to H2 and N2 under neutral conditions mediated by Cl• using oxygen-vacancy-rich Co3O4 nanowire (Ov-Co3O4) anodes and CuO nanowire cathodes. The Co2+/Co3+ cycle in Co3O4 activates Cl- in urine to Cl•, which rapidly and selectively converts urea into N2. Thus, electron transfer is boosted for H2 production, eliminating the kinetic limitations. The shuttle of Co2+ to Co3+ is the key step for Cl• yield, which is accelerated due to the introduction of Ov. Electrochemical analysis shows that Ov induces positive charge on the Co center; therefore, Co2+ loses electrons more efficiently to form Co3+. H2 production in this system reaches 716 µmol h-1, which is 320% that of non-radical-mediated urine electrolysis. The utilization of Ov-Co3O4 further enhances H2 generation, which is 490 and 210% those of noble Pt and RuO2, respectively. Moreover, urine is effectively degraded in 90 min with the total nitrogen removal of 95.4%, and N2 is the final product. This work provides new insights for efficient and low-cost recovery of H2 and urine remediation.

Novel Denitrification Fuel Cell for Energy Recovery of Nitrate-N and TN Removal Based on NH4+ Generation on a CNW@CF Cathode.

NO3- is an undesirable environmental pollutant that causes eutrophication in aquatic ecosystems, and its pollution is difficult to eliminate because it is easily converted into NH4+ instead of N2. Additionally, it is a high-energy substance. Herein, we propose a novel denitrification fuel cell to realize the chemical energy recovery of NO3- and simultaneous conversion of total nitrogen (TN) into N2 based on the outstanding ability of NH4+ generation on a three-dimensional copper nanowire (CNW)-modified copper foam (CF) cathode (CNW@CF). The basic steps are as follows: direct and highly selective reduction of NO3- to NH4+ rather than to N2 on the CNW@CF cathode, on which negative NO3- ions can be easily adsorbed due to their double-electron layer structure and active hydrogen ([H]) can be generated due to a large number of catalytic active sites exposed on CNWs. Then, NH4+ is selectively oxidized to N2 by the strong oxidation of chlorine free radicals (Cl•), which originate from the reaction of chlorine ions (Cl-) by photogenerated holes (h+) and hydroxyl radicals (OH•) under irradiation. Then, the electrons from the oxidation on the photoanode is transferred to the cathode to form a closed loop for external power generation. Owing to the continuous redox loop, NO3- completely reduces to N2, and the released chemical energy is converted into electrical energy. The results indicate that 99.9% of NO3- can be removed in 90 min, and the highest yield of electrical power density reaches 0.973 mW cm-2, of which the nitrate reduction rates on the CNW@CF cathode is 79 and 71 times higher than those on the Pt and CF cathodes, respectively. This study presents a novel and robust energy recycling concept for treating nitrate-rich wastewater.

Treatment of hazardous organic amine wastewater and simultaneous electricity generation using photocatalytic fuel cell based on TiO2/WO3 photoanode and Cu nanowires cathode.

Organic amines are regarded as high toxic, refractory chemicals due to the great damage on human body, and ecosystem. The treatment of organic amine wastewater involves the removal of total nitrogen and toxic organics simultaneously, which is one of the biggest difficulties in wastewater treatment. In this study, hazardous organic amine wastewater was purified by a photocatalytic fuel cell (PFC) with efficient nitrogen removal and organic degradation, and its chemical energy was recovered simultaneously based on hydroxyl radical (HO·) and chlorine radical (Cl·) reaction in a novel TiO2/WO3 and 3D Cu nanowires modified Cu foam (CuNWs/CF) system. TiO2/WO3 heterojunction as photoanode provided rapid charge separation and good stability, and the composite of poly-Si enhanced the light harvest and charge transfer. HO· played critical role in degrading organic amines, while Cl· was responsible for selectively oxidizing amine group or NH4+ to N2. Besides, trace amount of NO2- and NO3- formed by over-oxidation was eliminated on CuNWs/CF cathode due to large specific surface area and fast charge transfer. Moderate Cl- concentration and initial pH had vital influence on strengthening Cl· and HO· generation in the system, and the optimal conditions were 50 mM NaCl and pH = 7. For methylamine, ethylamine and dimethylamine wastewater, the system showed total nitrogen removal efficiency of 94.93%, 91.81%, 93.10% and total organic carbon removal of 58.47%, 53.57%, and 56.71% within 2 h, respectively. Moreover, the corresponding maximum power densities of 2.49, 2.40, 2.27 mW cm-2 were also generated, respectively. The study proposes an efficient, sustainable method for the treatment of hazardous organic amine wastewater and simultaneous energy recovery.

Highly efficient removal of total nitrogen and dissolved organic compound in waste reverse osmosis concentrate mediated by chlorine radical on 3D Co3O4 nanowires anode.

Reverse osmosis concentrate (ROC) from wastewater reclamation has posed significant disposal challenges due to its highly concentrated NH3-N, chloride ion and bio-refractory organics, and developing technologies for their removal are essential. Herein, we developed an efficient electrochemical system to remove total nitrogen and dissolved organic compound (DOC) simultaneously mediated by chlorine radical (Cl•), which is generated by activation of chloride ion existing in ROC on an inexpensive, three-dimensional Co3O4 nanowires. Results showed that the total nitrogen and total organic carbon removal were 98.2% and 56.9% in 60 min for synthetic ROC with 56 mg/L of NH3-N and 20 mg/L of DOC. The utilization of Co3O4 nanowires enhanced NH3-N degradation by 2.58 times compared with Co3O4 nanoplates, which were 1.69 and 17.5 times these of RuO2 and Pt. We found that structural Co3+/Co2+ acts as cyclic catalysis to produce Cl• via single-electron transfer, which convert NH3-N to N2 and lead to faster DOC degradation. This architecture provides abundant catalytic sites and sufficient accessibility of reactants. Small amount of nitrate generated by oxidation of NH3-N was further reduced to N2 on Pd-Cu/NF cathode. These findings provide new insights for utilization of waste Cl- and development of novel electrochemical system for ROC disposal.

Efficient Hydrogen Generation and Total Nitrogen Removal for Urine Treatment in a Neutral Solution Based on a Self-Driving Nano Photoelectrocatalytic System.

Urine is the main source of nitrogen pollution, while urea is a hydrogen-enriched carrier that has been ignored. Decomposition of urea to H2 and N2 is of great significance. Unfortunately, direct urea oxidation suffers from sluggish kinetics, and needs strong alkaline condition. Herein, we developed a self-driving nano photoelectrocatalytic (PEC) system to efficiently produce hydrogen and remove total nitrogen (TN) for urine treatment under neutral pH conditions. TiO2/WO3 nanosheets were used as photoanode to generate chlorine radicals (Cl•) to convert urea-nitrogen to N2, which can promote hydrogen generation, due to the kinetic advantage of Cl-/Cl• cyclic catalysis. Copper nanowire electrodes (Cu NWs/CF) were employed as the cathode to produce hydrogen and simultaneously eliminate the over-oxidized nitrate-nitrogen. The self-driving was achieved based on a self-bias photoanode, consisting of confronted TiO2/WO3 nanosheets and a rear Si photovoltaic cell (Si PVC). The experiment results showed that hydrogen generation with Cl• is 2.03 times higher than in urine treatment without Cl•, generating hydrogen at 66.71 µmol h-1. At the same time, this system achieved a decomposition rate of 98.33% for urea in 2 h, with a reaction rate constant of 0.0359 min-1. The removal rate of total nitrogen and total organic carbon (TOC) reached 75.3% and 48.4% in 2 h, respectively. This study proposes an efficient and potential urine treatment and energy recovery method in neutral solution.

High Yield of CO and Synchronous S Recovery from the Conversion of CO2 and H2S in Natural Gas Based on a Novel Electrochemical Reactor.

H2S and CO2 are the main impurities in raw natural gas, which needs to be purified before use. However, the comprehensive utilization of H2S and CO2 has been ignored. Herein, we proposed a fully resource-based method to convert toxic gas H2S and greenhouse gas CO2 synchronously into CO and elemental S by using a novel electrochemical reactor. The special designs include that, in the anodic chamber, H2S was oxidized rapidly to S based on the I-/I3- cyclic redox system to avoid anode passivation. On the other hand, in the cathodic chamber, CO2 was rapidly and selectively reduced to CO based on a porous carbon gas diffusion electrode (GDE) modified with polytetrafluoroethylene and cobalt phthalocyanine (CoPc). A high Faraday efficiency (>95%) toward CO was achieved due to the enhanced mass transfer of CO2 on the GDE and the presence of the selective CoPc catalyst. The maximum energy efficiency of the system was more than 72.41% with a current density of over 50 mA/cm2, which was 12.5 times higher than what was previously reported on the H2S treatment system. The yields of S and CO were 24.94 mg·cm-2·h-1 and 19.93 mL·cm-2·h-1, respectively. A model analysis determined that the operation cost of the synchronous utilization of H2S and CO2 method was slightly lower than that of the single utilization of H2S in the existing natural gas purification technology. Overall, this paper provides efficient and simultaneous conversion of H2S and CO2 into S and CO.