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.

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.

Coupled Effect of Sulfidation and Ferrous Dosing on Selenate Removal by Zerovalent Iron Under Aerobic Conditions.

Both the reactivity and the removal capacity of zerovalent iron (ZVI) for the target contaminant are important for applying ZVI in wastewater treatment. In this study, the feasibility of combining sulfidation treatment and Fe2+ dosing (S-ZVI/Fe2+) to enhance the performance of ZVI for Se(VI) removal was comprehensively investigated under aerobic conditions. Se(VI) was first adsorbed on the surface of ZVI particles and then reduced to Se(IV) and Se(0) with Se(0) being the final product in S-ZVI/Fe2+ system. This system bore the advantages of both sulfidation treatment (S-ZVI) and Fe2+ dosing (ZVI/Fe2+) for Se(VI) removal. The amounts and rate constants of Se(VI) removal in S-ZVI/Fe2+ system were increased by 1.8-32.8 times and 11.7-194.0 times, respectively, compared to those in pristine ZVI system. Sulfidation significantly accelerated the corrosion of Fe0 thus improved the removal rate of Se(VI). The promoting effect of Fe2+ on Se(VI) sequestration by S-ZVI should be mainly associated with the following facts: Fe2+ could maintain a relatively low pH level during Se(VI) removal by S-ZVI; Compared to S-ZVI alone, the consumption of Fe0 in S-ZVI/Fe2+ by O2/H+ was slower, and thus the electron efficiency of S-ZVI was elevated; Fe2+ dosing facilitated electron transfer by forming semiconductive Fe3O4.

Extremely Efficient Decomposition of Ammonia N to N2 Using ClO• from Reactions of HO• and HOCl Generated in Situ on a Novel Bifacial Photoelectroanode.

The conversion of excess ammonia N into harmless N2 is a primary challenge for wastewater treatment. We present here a method to generate ClO• directionally for quick and efficient decomposition of NH4+ N to N2. ClO• was produced and enhanced by a bifacial anode, a front WO3 photoanode and a rear Sb-SnO2 anode, in which HO• generated on WO3 reacts with HClO generated on Sb-SnO2 to form ClO•. Results show that the ammonia decomposition rate of Sb-SnO2/WO3 is 4.4 times than that of WO3 and 3.3 times than that of Sb-SnO2, with achievement of the removal of NH4+ N on Sb-SnO2/WO3 and WO3 being 99.2 and 58.3% in 90 min, respectively. This enhancement is attributed to the high rate constant of ClO• with NH4+ N, which is 2.8 and 34.8 times than those of Cl• and HO•, respectively. The steady-state concentration of ClO• (2.5 × 10-13 M) is 102 times those of HO• and Cl•, and this is further confirmed by kinetic simulations. In combination with the Pd-Cu/NF cathode to form a denitrification exhaustion system, Sb-SnO2/WO3 shows excellent total nitrogen removal (98.4%), which is more effective than WO3 (47.1%) in 90 min. This study provides new insight on the directed ClO• generation and its application on ammonia wastewater treatment.

Exhaustive Conversion of Inorganic Nitrogen to Nitrogen Gas Based on a Photoelectro-Chlorine Cycle Reaction and a Highly Selective Nitrogen Gas Generation Cathode.

A novel method for the exhaustive conversion of inorganic nitrogen to nitrogen gas is proposed in this paper. The key properties of the system design included an exhaustive photoelectrochemical cycle reaction in the presence of Cl-, in which Cl· generated from oxidation of Cl- by photoholes selectively converted NH4+ to nitrogen gas and some NO3- or NO2-. The NO3- or NO2- was finally reduced to nitrogen gas on a highly selective Pd-Cu-modified Ni foam (Pd-Cu/NF) cathode to achieve exhaustive conversion of inorganic nitrogen to nitrogen gas. The results indicated total nitrogen removal efficiencies of 30 mg L-1 inorganic nitrogen (NO3-, NH4+, NO3-/NH4+ = 1:1 and NO2-/NO3-/NH4+ = 1:1:1) in 90 min were 98.2%, 97.4%, 93.1%, and 98.4%, respectively, and the remaining nitrogen was completely removed by prolonging the reaction time. The rapid reduction of nitrate was ascribed to the capacitor characteristics of Pd-Cu/NF that promoted nitrate adsorption in the presence of an electric double layer, eliminating repulsion between the cathode and the anion. Nitrate was effectively removed with a rate constant of 0.050 min-1, which was 33 times larger than that of Pt cathode. This system shows great potential for inorganic nitrogen treatment due to the high rate, low cost, and clean energy source.

Dramatic enhancement of organics degradation and electricity generation via strengthening superoxide radical by using a novel 3D AQS/PPy-GF cathode.

A dramatic enhancement of organics degradation and electricity generation has been achieved in a wastewater fuel cell (WFC) system via strengthening superoxide radical with radical chain reaction by using a novel 3D anthraquinone/polypyrrole modified graphite felt (AQS/PPy-GF) cathode. The AQS/PPy-GF was synthesized by one-pot electrochemical polymerization method and used to in-situ generate superoxide radical by reducing oxygen under self-imposed electric field. Results showed that methyl orange (MO) were effectively degraded in AQS/PPy-GF/Fe2+ system with a high apparent rate constant (0.0677 min-1), which was 3.9 times that (0.0174 min-1) in the Pt/Fe2+ system and even 9.4 times that (0.0072 min-1) in the traditional WFC system (without Fe2+). Meanwhile, it showed a superior performance for electricity generation and the maximum power density output (1.130 mW cm-2) was nearly 3.3 times and 5.0 times higher, respectively, when compared with the Pt/Fe2+ system and traditional WFC. This dramatic advance was attributed to 3D AQS/PPy-GF cathode which produces more O2- via one-electron reduction process. The presence of O2- cannot only directly contribute to MO degradation, but also promotes the final complete mineralization by turning itself to OH. Additionally, O2- accelerates the Fe2+/Fe3+ couple cycling, thus avoiding continuous addition of any external ferrous ions. Inhibition and probe studies were conducted to ascertain the role of several radicals (OH and O2-) on the MO degradation. Superoxide radicals were considered as the primary reactive oxidants, and the degradation mechanism of MO was proposed. The proposed WFC system provides a more economical and efficient way for energy recovery and wastewater treatment.

Selective Degradation of Organic Pollutants Using an Efficient Metal-Free Catalyst Derived from Carbonized Polypyrrole via Peroxymonosulfate Activation.

Metal-free carbonaceous materials, including nitrogen-doped graphene and carbon nanotubes, are emerging as alternative catalysts for peroxymonosulfate (PMS) activation to avoid drawbacks of conventional transition metal-containing catalysts, such as the leaching of toxic metal ions. However, these novel carbocatalysts face relatively high cost and complex syntheses, and their activation mechanisms have not been well-understood. Herein, we developed a novel nitrogen-doped carbonaceous nanosphere catalyst by carbonization of polypyrrole, which was prepared through a scalable chemical oxidative polymerization. The defective degree of carbon substrate and amount of nitrogen dopants (i.e., graphitic nitrogen) were modulated by the calcination temperature. The product carbonized at 800 °C (CPPy-F-8) exhibited the best catalytic performance for PMS activation, with 97% phenol degradation efficiency in 120 min. The catalytic system was efficient over a wide pH range (2-9), and the reaction of phenol degradation had a relatively low activation energy (18.4 ± 2.7 kJ mol-1). The nitrogen-doped carbocatalyst activated PMS through a nonradical pathway. A two-step catalytic mechanism was extrapolated: the catalyst transfers electrons to PMS through active nitrogen species and becomes a metastable state of the catalyst (State I); next, organic substrates are oxidized and degraded by serving as electron donors to reduce State I. The catalytic process was selective toward degradation of various aromatic compounds with different substituents, probably depending on the oxidation state of State I and the ionization potential (IP) of the organics; that is, only those organics with an IP value lower than ca. 9.0 eV can be oxidized in the CPPy-F-8/PMS system.

Effects of iron and phosphorus on Microcystis physiological reactions.

OBJECTIVE: To observe the effects of iron and phosphorus on Microcystis physiological reactions. METHODS: The experimental conditions were chosen as the light dark cycles of 16 h 8 h, 12 h 12 h, and 8 h 16 h. The cell change of morphology and life history, cell number, cell color, and cell area of Microcystis were analyzed quantitatively. According to the resource competition and Monod equation, Microcystis kinetics of phosphorus and iron were also examined. RESULTS: The longer light time caused more special cell division, slower growth rate, and easier change of bigger cell area. The color of alga was changed from green to brown. Ks and micromax of phosphorus absorption were 0.0352 mircomol x L(-l) and 0.493 d(-1), respectively. Those of iron absorption were 0.00323 micromol x L(-1) and 0.483 d(-1). CONCLUSION: Microcystis bloom is more dominant than other algae.