Engineering of single atomic Fe-N4 sites on hollow carbon cages to achieve highly reversible MoS2 anodes for Li-ion batteries.

Although the single atom electrocatalysts have been demonstrated as efficient catalysts for promoting Li2S/Na2S formation and decomposition in Li-S/Na-S batteries, the functional morphological and structural engineering capable of exposing more active sites is regarded as an essential factor to further enhance the catalytic activity. Here, we have synthesized a single atomically dispersed Fe sites embedded within hollow nitrogen doped carbon cages (Fe-N-HCN) using Fe3O4 spheres as an oxidant and sacrificial template, which is used as a high-efficiency catalyst for boosting the reversible capacity of MoS2 anode in lithium-ion batteries (LIBs). As expected, the electrochemical reaction of MoS2/Fe-N-HCN anode exhibits higher reversibility than pure MoS2 electrodes. Moreover, density functional theory is also employed to reveal that Fe-N-HCN can be effectively adsorbed and catalyze the rapid decomposition of Li2S. The hollow carbon cage structure can facilitate the exposure of the active Fe-N4 sites and favor the mass transfer during the electrochemical reactions, thus the synergistic effect of the Fe-N4 site and the hollow carbon cage structure together improve the catalytic activity for the conversion reaction of MoS2 anode.

Theoretical insight into the promotion effect of potassium additive on the water-gas shift reaction over low-coordinated Au catalysts.

CONTEXT: How to elucidate the effect of alkali metal promoters on gold-catalyzed water-gas shift reaction intrinsically remains a challenging, because that the complex synergy effects such as strong metal-support interactions, interfacial effects, and charge transfer of supported metal catalysts makes people difficulty in the understanding the alkali promotion phenomenon in nature. Herein, we report a systematically study of whole water-gas shift reaction mechanism on pure and the K-modified defected-Au(211) (i.e., by removing one surface Au atom from perfect Au(211) and make one model with the Au-Au coordination number is six) by using the microkinetic modeling based on first principles. Our results indicate that the presence of K can increase the adsorption ability of oxygen-containing species via the attractive coulomb interaction, has no significant effect on the adsorption of H species, but inhibits the adsorption of CO due to the steric effect. K promoter stabilizes the water adsorption by ~0.3 eV, which results in one order increasing of whole reaction rate. Interestingly, the strong promotion effect of the K can be assigned to the significant direct space interaction between K and the adsorbate H2O* through the inducted electric field, which can be further confirmed by the posed negative electric field on the unpromoted D-Au(211). Microkinetic modeling results revealed that the carboxyl mechanism is the most likely to occur, redox mechanism is the next one, and the formate mechanism is the least likely to occur. For different kinds of alkali metal additives, the adsorption strength of water molecules gradually weakens from Li to Cs, but Na shows the best promoter behavior at the low temperature. By considering the effect of K contents on the reactivity of water-gas shift reaction, we found that the K with the medium coverage (~0.2~0.3 ML) has the strongest promoting effect. It is expected that the conclusion of this work can be extended to other WGSR catalytic systems like Cu(or Pt). METHODS: All calculations were performed by using the plane-wave based periodic method implemented in Vienna ab initio simulation package (VASP, version 5.4.4), where the ionic cores are described by the projector augmented wave (PAW) method. The exchange and correlation energies were computed using the Perdew, Burke and Ernzerhof functional with the vdw correction (PBE-D3). The transition states (TSs) were searched using the climbing image nudged elastic band (CI-NEB) method. Some electronic structure properties like work function was predicated by the DS-PAW software. Microkinetic simulation was carried out using MKMCXX software.

Degradation of high concentration starch and biocathode autotrophic denitrification using photo microbial fuel cell.

In the study, a dual-chamber photo MFC was constructed with a photosynthetic bacteria consortium PB-Z and a heterotrophic nitrifier C16 as anode and cathode inoculant, respectively. The electron released from starch degradation in the anode by photosynthetic bacteria was transferred to the cathode, which was utilized by the nitrifying bacteria C16 to realize autotrophic denitrification. Lower resistance was more conducive to the electron transfer and pollutants removal. Comparing with natural light, continuous light greatly promoted starch degradation by the photosynthetic bacteria in the anode and the denitrification by the nitrifying bacteria in the cathode. Under continuous light and external resistance of 500 Ω, high concentration starch was degraded by photosynthetic bacteria PB-Z and the COD removal efficiency reached up to 88.45% within 12 d, and nitrate of 95.8% was removed within 4 d by autotrophic denitrification by heterotrophic nitrifier C16. The study provides some enlightenment and reference for the application of MFC in the field of wastewater treatment.

Towards the understanding of hyperthermophilic methanogenesis from waste activated sludge at 70 °C: Performance, stability, kinetic and microbial community analyses.

Anaerobic digestion is promising for waste activated sludge (WAS) degradation. However, conventional processes were generally stuck with limited hydrolysis and poor pathogen destruction. Hyperthermophilic digestion at 70 °C has drawn attention in overcoming those issues at a relatively low energy requirement and operating difficulties. In order to illuminate its operation characteristics, a single-stage hyperthermophilic digester was controlled at 70 °C and operated continuously to degrade WAS. 88.7 mL/g VSadded of methane yield could be achieved in the hyperthermophilic system, fourfold higher than that in the mesophilic system. Kinetic analysis revealed that hyperthermophilic digestion was advantageous in converting the non-degradable fraction. Consequently, hydrolysis under the hyperthermophilic condition was able to be significantly improved. Above 10 d was necessary for the hyperthermophilic system to gain such a high methane production. In the case of stability, the organic loading of higher than 10.2 g VS/L/d resulted in increasing limitation from methanogenesis and accumulation of propionic, butyric and valeric acids. In addition to the dominant acetoclastic genus Methanothrix for methane production in the hyperthermophilic system, two hydrogenotrophic methanogens Methanospirillum and Methanothermobacter reached 18.84% and 8.31%, respectively. The genus Coprothermobacter, affiliated with the phylum Firmicutes, made more contribution to protein hydrolysis in the hyperthermophilic digester.

Optimization of hydrothermal pretreatment conditions for mesophilic and thermophilic anaerobic digestion of high-solid sludge.

Hydrothermal pretreatment (HTP) conditions were optimized for continuous mesophilic (MAD) and thermophilic (TAD) anaerobic digestion of high-solid sludge (10-11% total solids). COD solubilization increased with prolonged HTP durations, and became not significant after 210 min. According to the methane production rate and energy consumption, the optimal HTP temperature was determined at 160 °C. Regarding continuous operation without HTP, TAD achieved higher methane yield and volatile solids (VS) reduction, at 0.12 L/g VSadded and 23.9%, respectively. After HTP, methane yield and VS reduction in MAD and TAD were increased by 400% and 191% (MAD), 67% and 72% (TAD), respectively. TAD was limited due to the inhibition from about 2800 mg/L of NH4+-N concentration. The methanogenic activity of MAD was enhanced, whereas TAD displayed a reduced value owing to ammonia inhibition. Ultimately, MAD with HTP and TAD without HTP achieved the higher energy balance, 5.25 and 3.27 kJ/g VS, respectively.

One-step acquirement of superior microbial communities from mesophilic digested sludge to upgrade anaerobic digestion.

Anaerobic digestion is a promising waste-to-energy alternative technology. However, the efficiency upgrading for conventional mesophilic digestion of organic solid waste is always indispensable. Employing hyperthermophilic or thermophilic microbial community is one of the viable upgrading alternatives. Given the unavailability of the superior microbial communities, mesophilic digested sludge was used as inoculum, and instantly controlled at 70 °C and 55 °C for acclimation of hyperthermophilic and thermophilic inocula, respectively. Waste activated sludge was continuously and synchronously fed into two digesters. After one round, thermophilic digester achieved stable biogas production rate at 0.22 L L-1 d-1, with a methane proportion over 60%, whereas fluctuation was observed in the hyperthermophilic digester, and approximately triple time was needed to reach a relatively stable biogas production rate 0.12 L L-1 d-1. Nevertheless, higher hydrolysis ratio 24.4% was observed in the hyperthermophilic digester despite the lower biogas production. Therefore, methanogenesis step limited the whole anaerobic process for the hyperthermophilic digestion, and digestion at 70 °C was appropriate as a pre-fermentation stage to enhanced hydrolysis. The genus Methanothrix proportion in the thermophilic digester gradually decreased, while another acetoclastic genus Methanosarcina ultimately was acclimated to the dominant methanogen. In addition to Methanothrix, hydrogenotrophic archaea became competitive in the hyperthermophilic digester, with Methanothermobacter dominant at 22.6%. The genus Psychrobacter, affiliated to the phylum Proteobacteria could survive better than the others at 70 °C, with a final proportion of 62.5%.

A new approach for the effective removal of NOx from flue gas by using an integrated system of oxidation-absorption-biological reduction.

A new process of NOx removal from flue gas, using an integrated system of oxidation-absorption-biological reduction (OABR), is introduced. The experimental results show that increasing the NOx oxidation ratio in flue gas can effectively improve the NOx removal efficiency of the OABR system. The NOx removal efficiency could reach 98.8% with 0.02 M NaHCO3 as the chemical absorbent and under the condition of the optimal NOx oxidation ratio of 50%. During stable operation, the OABR system could maintain a high NOx removal efficiency (above 94%) under the following conditions: 1-8 vol% (104-8 × 104 ppmv) O2, 200-800 ppmv NOx, 0.5-1.5 L/min gas flow rate and 100-800 ppmv SO2. The nitrogen equilibrium results showed that about 59% of the nitrogen in the inlet NOx were transformed to N2 through microbial denitrification, 37% of the nitrogen were converted to biological nitrogen for microbial growth, and only 1.1% of the nitrogen remained in the liquid phase. This new approach has an excellent NOx removal performance and great potential for industrial application.

Establishment and differential performance of hyperthermophilic microbial community during anaerobic self-degradation of waste activated sludge.

Hyperthermophilic anaerobic digestion, especially at 70 °C, has drawn wide attention. In order to acquire the inoculum and digestion characteristics, batch acclimation and continuous operation experiments were conducted under hyperthermophilic (70 °C), thermophilic (55 °C) and mesophilic (35 °C) conditions, respectively. Archaea at each temperature was successfully enriched from the sole-source waste activated sludge (WAS). Hyperthermophilic digestion achieved higher archaea diversity, close to the Shannon index 2.23 for the thermophilic digestion, but the population were not improved, at a 16S rRNA genes 5.99 × 105 copies mL-1. Hydrogenotrophic methanogens, Methanospirillum and Methanothermobacter, dominated in the hyperthermophilic digester, accounting for 27.15%, while the primary phylum Firmicutes was promoted to 36.31%, with the proteolytic genus Coprothermobacter in Firmicutes at 19.50%. Refractory organic fractions were converted more with a higher digestion temperature, which was demonstrated by the fact that the COD/VS increased to 5.8, 5.2 and 4.2 at 70 °C, 55 °C and 35 °C, respectively, at the end of batch acclimation. In addition, the most solubilization for the dominant fraction protein in the WAS occurred at 70 °C as well. Similar hydrolysis ratio, over 10%, and specific hydrolysis rate, around 0.025 g COD (g VSS·d)-1, were achieved at 70 °C and 55 °C. The higher hydrolysis for hyperthermophilic digestion even resulted in a higher methane yield than that for the mesophilic digestion. Nevertheless, contrary to higher hydrolysis, methanogenesis limited hyperthermophilic digestion in WAS degradation, with an ultimate methane yield 71.2 mL g-1 VSadded, despite an almost complete VFA conversion through the continuous operation.

Hollow I-Cu2MoS4 nanocubes coupled with an ether-based electrolyte for highly reversible lithium storage.

Anode materials based on transition metal sulfides suffer from poor electrochemical reversibility, which limits their cycling stability. Herein, we synthesize hollow I-Cu2MoS4 nanocubes composed of ultrathin nanosheets using a solvothermal method with Cu2O nanocubes as sacrificial templates. The presence of a surfactant is a key factor that prevents the structural collapse of the hollow cubic structure of Cu2MoS4 and the formation of nanoplates. An ether-based electrolyte shows better compatibility with the Cu2MoS4 electrode than a carbonate-based electrolyte, which is reflected in high reversible capacity, superior rate performance, and remarkably improved cycling performance. Ex-situ XRD analysis demonstrates a highly reversible electrochemical reaction in the ether-based electrolyte, which enhances the cycling stability.

Correction: Visible-light photocatalytic performance, recovery and degradation mechanism of ternary magnetic Fe3O4/BiOBr/BiOI composite.

[This corrects the article DOI: 10.1039/C9RA04412D.].

Improved bioelectricity production using potassium monopersulfate as cathode electron acceptor by novel bio-electrochemical activation in microbial fuel cell.

Potassium monopersulfate (PMS) without a catalyst as cathode electron acceptor was first established to improve the electricity generation performance of a microbial fuel cell (MFC) in this study. The work investigated the performance with pure PMS (PPMS) and compound PMS (CPMS). The concentration and initial pH of PMS had an effect on the electricity generation, which increased with higher PMS concentration and lower catholyte pH. In the PPMS-MFC system, the maximum voltage (0.972 V), power density (16.37 W/m3), optimal exchange current density (2.000 A/m3) and minimum polarization impedance (Rp: 97.33 Ω) were reached at 10 mM PMS and pH 3.0. However, the maximum power density (8.60 W/m3) was exhibited at 70 mM PMS and pH 3.0 in the CPMS system. Additionally, high COD removals of 99.41% and 98.71% in anode chambers were obtained in the two systems, respectively. Sulfate radicals (SO4-) and hydroxyl radicals (OH) played significant roles in the PPMS-MFC, while HClO was also a contributor in addition to SO4- and OH in the CPMS-MFC. Furthermore, SO4- and OH was generated in situ in the cathode to promote the reduction reaction. The inorganic anion had different effects on electricity generation. Finally, while energy was recovered, rhodamine B (RhB) was added to the cathode chamber and then removed successfully in PPMS-MFC system. This work confirmed that only PMS could be activated by bio-electrochemical method, which is an energy-saving, environmentally friendly and effective activation approach, and thus, it could be used as an efficient acceptor in a MFC.

A regularly combined magnetic 3D hierarchical Fe3O4/BiOBr heterostructure: Fabrication, visible-light photocatalytic activity and degradation mechanism.

The magnetic Fe3O4/BiOBr composites with different molar ratios were prepared by a new two-step method. The effect of different Fe3O4 contents on composites' properties was detected through XRD, SEM, TEM, HR-TEM, XPS, Uv-vis DRS, PL and BET. When the molar ratio of Fe3O4 nanospheres and BiOBr nanosheets is 0.5:1, the two are combined regularly to form 3D flower-like hierarchical heterostructure. This phenomenon is firstly found and can provide a reference for synthesizing other regularly combined magnetic heterostructure catalysts. The degradation activity for Rhodamine B (RhB) is much stronger than that of the previous studies under visible-light irradiation. 3D flower-like Fe3O4/BiOBr (0.5:1) heterostructure possesses great advantages including excellent magnetic separation, remarkable reutilization and stability. Through active species detection and liquid chromatography mass spectrometry (LC-MS) analysis, the degradation mechanisms of RhB are summarized (a) RhB photosensitization and (b) RhB moleculs attacked by radicals and a new possible degradation path was to be presented. This study offers a new method to prepare a regularly combined magnetic Fe3O4/BiOBr photocatalytic material and demonstrates its wonderful application for degradation of organic contaminants in aquatic environment.

Visible-light photocatalytic performance, recovery and degradation mechanism of ternary magnetic Fe3O4/BiOBr/BiOI composite.

The ternary magnetic Fe3O4/BiOBr/BiOI (x : 3 : 1) photocatalysts were successfully synthesized by a facile solvothermal method. The samples were characterized by XRD, SEM, EDS, ICP-AES, XPS, UV-vis DRS, PL and VSM. Nitrogen-containing dye RhB was used as a degradation substrate to evaluate the photocatalytic degradation activities of the samples. The photocatalytic performance of Fe3O4/BiOBr/BiOI (0.4 : 3 : 1) is superior to other Fe3O4/BiOBr/BiOI (x : 3 : 1). Compared with binary magnetic Fe3O4/BiOBr (0.5 : 1) prepared in our previous work, the Fe3O4/BiOBr/BiOI (0.4 : 3 : 1) has obvious advantages in photocatalytic activity and adsorption capacity. And the specific surface area (48.30 m2 g-1) is much larger than that of the previous report (Fe3O4/BiOBr/BiOI (0.5 : 2 : 2)) synthesized by a co-precipitation method. Besides, after 25 s of magnetic field, Fe3O4/BiOBr/BiOI (0.4 : 3 : 1) can be rapidly separated from water. After eight recycling cycles, the magnetic properties, photocatalytic activity, crystallization and morphology of the Fe3O4/BiOBr/BiOI (0.4 : 3 : 1) catalyst remain good. The possible photocatalytic degradation mechanism of RhB under Fe3O4/BiOBr/BiOI (0.4 : 3 : 1) photocatalyst was also proposed. The results indicate that the ternary magnetic Fe3O4/BiOBr/BiOI (0.4 : 3 : 1) composite with high photocatalytic degradation efficiency, good magnetic separation performance and excellent recyclability and stability has potential application prospect in wastewater.

A New Anode for Lithium-Ion Batteries Based on Single-Walled Carbon Nanotubes and Graphene: Improved Performance through a Binary Network Design.

Carbon nanomaterials, especially graphene and carbon nanotubes, are considered to be favorable alternatives to graphite-based anodes in lithium-ion batteries, owing to their high specific surface area, electrical conductivity, and excellent mechanical flexibility. However, the limited number of storage sites for lithium ions within the sp2 -carbon hexahedrons leads to the low storage capacity. Thus, rational structure design is essential for the preparation of high-performance carbon-based anode materials. Herein, we employed flexible single-walled carbon nanotubes (SWCNTs) with ultrahigh electrical conductivity as a wrapper for 3D graphene foam (GF) by using a facile dip-coating process to form a binary network structure. This structure, which offered high electrical conductivity, enlarged the electrode/electrolyte contact area, shortened the electron-/ion-transport pathways, and allowed for efficient utilization of the active material, which led to improved electrochemical performance. When used as an anode in lithium-ion batteries, the SWCNT-GF electrode delivered a specific capacity of 953 mA h g-1 at a current density of 0.1 A g-1 and a high reversible capacity of 606 mA h g-1 after 1000 cycles, with a capacity retention of 90 % over 1000 cycles at 1 A g-1 and 189 mA h g-1 after 2200 cycles at 5 A g-1 .

A robust, superhydrophobic graphene aerogel as a recyclable sorbent for oils and organic solvents at various temperatures.

To address oil spillage and organic contaminant problems, the preparation of efficient sorbent materials is of great importance for global environment and water source protection. Despite extensive studies, sorbents with both high efficiency and recyclability are still desired, particularly with the outstanding sorption performance for different temperature environmental conditions. Herein, we report a robust reduced graphene aerogel (rGA) as an efficient and recyclable sorbent for oils and organic solvents, which shows highly efficient absorption of various oils and organic solvents (up to 19-26 times of its own weight) and excellent recyclability (>5 times) by heat treatment. Moreover, the absorption ability of rGA can be maintained over a wide temperature range of -40°C to 240°C, which can be attributed to the inherent excellent thermal stability of graphene and goodheat dispersal of three dimensional network structure. Based on these excellent properties, the rGA is considered to be an ideal material can be employed for separation and absorption of waste oil and organic contaminants from the water surface at various temperatures.

Simultaneous removal of carbon and nitrogen by mycelial pellets of a heterotrophic nitrifying fungus-Penicillium sp. L1.

A novel heterotrophic nitrifying fungus, defined as Penicillium sp. L1, can form mycelial pellets in liquid medium in this study. The effects of inoculation method, C/N ratio, initial pH, and temperature were gradually evaluated to improve the simultaneous removal of total nitrogen (TN) and chemical oxygen demand (COD) in wastewater by Penicillium sp. L1. Results showed that compared with spore inoculation, 48 h pellet inoculum could significantly increase the pellet size (from about 1.5 mm to 3.2 mm) and improve the removal capability, particularly for COD removal (from less than 50-86.20%). The removal efficiencies of TN and COD reached 98.38% (from 136.01 mg/L to 2.20 mg/L) and 92.40% (from 10,720 mg/L to 815 mg/L) under the following conditions: C/N 36, pH 3, 30°C, and inoculation with 48 h pellets. The pellet diameter reached 4.8 mm after 4-day cultivation. In this case, Penicillium sp. L1 removed TN from 415.93 mg/L to 43.39 mg/L, as well as COD from 29,533 mg/L to 8850 mg/L. Overall, the results indicated that the pellet size was closely related to the pollutant-removal ability of Penicillium sp. L1. Furthermore, mycelial pellets (4.8 mm, dead) only adsorbed 38.08% TN (from 125.45 mg/L to 77.78 mg/L), which indicated that adsorption did not play a major role in the nitrogen-removal process.

Removal of nitrogen by heterotrophic nitrification-aerobic denitrification of a novel metal resistant bacterium Cupriavidus sp. S1.

A novel heterotrophic nitrifying and metal resistant bacterium was isolated and identified as Cupriavidus sp. S1. The utilization of ammonium, nitrate and nitrite as well as the production of N2 proved the heterotrophic nitrification and aerobic denitrification ability of S1. The ammonium, nitrate and nitrite removal efficiencies were 99.68%, 98.03% and 99.81%, with removal rates of 10.43, 8.64 and 8.36mg/L/h, respectively. A multiple regression equation well described the relationship between carbon source utilization, cell growth and nitrification. Keeping the shaking speed at 120rpm was beneficial for denitrification. Moreover, different forms of nitrogen source could be utilize in simultaneous nitrification and denitrification. Additionally, the efficient removal of ammonium occurred at 20.0mg/LZn(2+), or 10.0mg/LNi(2+) or 8.0mg/LCu(2+) or 5.0mg/LCr(6+), 33.35mmol/L sodium pyruvate, C/N 12-28. These findings demonstrate that S1 was effective for nitrogen removal in industrial wastewater containing heavy metal.

An adsorption-release-biodegradation system for simultaneous biodegradation of phenol and ammonium in phenol-rich wastewater.

The feasibility of simultaneous biodegradation of phenol and ammonium in phenol-rich wastewater was evaluated in a reusable system, which contained macroporous adsorption resin and Alcaligenes faecalis strain WY-01. In the system, up to 6000mg/L phenol could be completely degraded by WY-01; meanwhile, 99.03±3.95% of ammonium was removed from the initial concentration of 384mg/L. This is the first study to show the capability of single strain in simultaneous removal of ammonium and phenol in wastewater containing such high concentrations of phenol. Moreover, the resin was regenerated during the biodegradation process without any additional manipulations, indicating the system was reusable. Furthermore, enzyme assay, gene expression patterns, HPLC-MS and gas chromatography analysis confirmed that phenol biodegradation accompanied with aerobic nitrifier denitrification process. Results imply that the reusable system provides a novel strategy for more efficient biodegradation of phenol and ammonium contained in some particular industrial wastewater.