Boosting oxygen reduction durability by embedding Co9S8 nanoparticles into Co single atoms anchored porous carbon frameworks.

Developing an efficient and low-cost oxygen reduction electrocatalyst is essential for the application of aqueous zinc-air batteries (ZABs). Herein, we report a facile adsorption-confined pyrolysis strategy to fabricate the hybrid electrocatalyst (denoted as Co9S8/CoSA-PC) by embedding Co9S8 nanoparticles into Co single atoms (Co-SAs) anchored porous carbon sheets for boosting oxygen reduction reaction (ORR) durability. In this strategy, the Co2+ ions are first absorbed into oxygen-rich porous carbon nanosheets and further form the Co-SAs with the help of thiourea in the following pyrolysis procedure, which is believed to be able to confine the generated Co9S8 nanoparticles into carbon frameworks due to their interface interaction. Benefiting from the synergistic effect of different components, the obtained Co9S8/CoSA-PC electrocatalyst for ORR exhibits outstanding catalytic activity with a half-wave potential of 0.82 V and a distinguished long-term durability with a current retention of 80 % after cycling 80 h under alkaline conditions, which is superior to commercial Pt/C. Moreover, the assembled ZABs with Co9S8/CoSA-PC as cathodic catalyst deliver a high specific capacity of 764 mAh gZn-1 at 10 mA cm-2 and the outstanding peak power density of up to 221.4 mW cm-2. This work provides a novel structure design strategy to prepare transition metal sulfide-based electrocatalysts with superior durability for ORR.

Accelerating Sulfur Redox Chemistry by Atomically Dispersed Zn-N4 Sites Coupled with Pyridine-N Defects on Porous Carbon Sheets.

Single-atom catalysts (SACs) with specific N-coordinated configurations immobilized on the carbon substrates have recently been verified to effectively alleviate the shuttle effect of lithium polysulfides (LiPSs) in lithium-sulfur (Li─S) batteries. Herein, a versatile molten salt (KCl/ZnCl2 )-mediated pyrolysis strategy is demonstrated to fabricate Zn SACs composed of well-defined Zn-N4 sites embedded into porous carbon sheets with rich pyridine-N defects (Zn─N/CS). The electrochemical kinetic analysis and theoretical calculations reveal the critical roles of Zn-N4 active sites and surrounding pyridine-N defects in enhancing adsorption toward LiPS intermediates and catalyzing their liquid-solid conversion. It is confirmed by reducing the overpotential of the rate-determining step of Li2 S2 to Li2 S and the energy barrier for Li2 S decomposition, thus the Zn─N/CS guarantees fast redox kinetics between LiPSs and Li2 S products. As a proof of concept demonstration, the assembled Li─S batteries with the Zn─N/CS-based sulfur cathode deliver a high specific capacity of 1132 mAh g-1 at 0.1 C and remarkable capacity retention of 72.2% over 800 cycles at 2 C. Furthermore, a considerable areal capacity of 6.14 mAh cm-2 at 0.2 C can still be released with a high sulfur loading of 7.0 mg cm-2 , highlighting the practical applications of the as-obtained Zn─N/CS cathode in Li─S batteries.

Nano silicon dioxide reduces cadmium uptake, regulates nutritional homeostasis and antioxidative enzyme system in barley seedlings (Hordeum vulgare L.) under cadmium stress.

Cadmium (Cd) toxicity is one of the most severe environmental threats inhibiting crop growth and productivity. Strategies to mitigate the adverse effects of Cd stress on plants are under scrutiny. Nano silicon dioxide (nSiO2) is an emerging material and could protect plants against abiotic stress. Can nSiO2 alleviate Cd toxicity in barley, and the possible mechanisms are poorly understood. A hydroponic experiment was conducted to study the mitigation effects of nSiO2 on Cd toxicity in barley seedlings. The results showed that the application of nSiO2 (5, 10, 20, and 40 mg/L) increased barley plant growth and chlorophyll and protein content, improving photosynthesis, compared with Cd-treated alone. Specifically, 5-40 mg/L nSiO2 addition increased net photosynthetic rate (Pn) by 17.1, 38.0, 30.3, and - 9.7%, respectively, relative to the Cd treatment alone. Furthermore, exogenous nSiO2 reduced Cd concentration and balanced mineral nutrient uptake. The application of 5-40 mg/L nSiO2 decreased Cd concentration in barley leaves by 17.5, 25.4, 16.7, and 5.8%, respectively, relative to the Cd treatment alone. Moreover, exogenous nSiO2 lowered malondialdehyde (MDA) content by 13.6-35.0% in roots, and by 13.5-27.2% in leaves, respectively, compared with Cd-treated alone. Besides, nSiO2 altered antioxidant enzyme activities and alleviated detrimental effects on Cd-treated plants, attaining maximal values at 10 mg/L nSiO2. These findings revealed that exogenous nSiO2 application may be a viable option for addressing Cd toxicity of barley plants.

Potential methane production in oligohaline wetlands undergoing erosion and accretion in the Mississippi River Delta Plain, Louisiana, USA.

Methane (CH4) is steadily increasing in the atmosphere from different sources including wetlands. However, there is limited landscape level CH4 flux data in deltaic coastal systems where the availability of freshwater is impacted by the combined effect of climate change and anthropogenic impacts. Here we determine potential CH4 fluxes in oligohaline wetlands and benthic sediments in the Mississippi River Delta Plain (MRDP), which is undergoing the highest rate of wetland loss and most extensive hydrological wetland restoration in North America. We evaluate potential CH4 fluxes in two contrasting deltaic systems, one undergoing sediment accretion as result of a freshwater and sediment diversions (Wax Lake Delta, WLD), and one experiencing net land loss (Barataria-Lake Cataouatche, BLC). Short- (<4 days) and long-term (36 days) incubations using soil and sediment intact cores and slurries were performed at different temperatures representing seasonal differences (10, 20, 30 °C). Our study revealed that all habitats were net sources of atmospheric CH4 in all seasons, and CH4 fluxes were generally the highest for the 20 °C incubation. The CH4 flux was higher in the marsh habitat of the recently formed delta system (WLD) with total carbon content of 5-24 mg C cm-3 compared to the marsh habitat in BLC, which had high soil carbon content of 67-213 mg C cm-3. This suggests that the quantity of soil organic matter might not be a determining factor in CH4 flux. Overall, benthic habitats were found to have the lowest CH4 fluxes indicating that projected future conversions of marshes to open water in this region will impact the total wetland CH4 emission, although the overall contribution of such conversions to the regional and global carbon budgets is still unknown. Further research is needed to expand the CH4 flux studies by simultaneously using several methods across different wetland habitats.

Metals geochemistry and mass export from the Mississippi-Atchafalaya River system to the Northern Gulf of Mexico.

Discharging 680 km3 of freshwater annually to the Northern Gulf of Mexico (NGOM), the Mississippi-Atchafalaya River System (MARS) plays a significant role in transporting major and trace elements to the ocean. In this study, we analyzed total recoverable concentrations of thirty-one metals from water samples collected at five locations along the MARS during 2013-2016 to quantify their seasonal mass exports. The Atchafalaya River flows through a large swamp floodplain, allowing us to also test the hypothesis that floodplains function as a sink for metals. We found that the seven major elements (Ca, Na, Mg, Si, K, Al, and Fe) constituted 99% of the total annual mass load of metals (7.38 × 107 tons) from the MARS. Higher concentrations of Al, Ba, B, Ca, Fe, Mg, Mn, Ag, and Ti were found in the Mississippi River, while significantly higher Si and Na concentrations were found in the Atchafalaya River. Significant relationships were found between daily discharge and daily loads of Ba, Ca, Fe, K, Sr, and Ti in both rivers, while significant relationships were also found for Al, Mg, Mn, V, and Zn in the Atchafalaya River and B in the Mississippi River. Overall, the Mississippi River contributed 64-76% of the total annual loading of metals from the MARS to the NGOM. Daily loads of Al, Ba, B, Fe, Li, Mn, P, K, Si, Ag, Ti, V, and Zn regularly decreased upstream to downstream in the Atchafalaya River, partially accepting the initial hypothesis on metals transport in river floodplains.

Three decadal inputs of total organic carbon from four major coastal river basins to the summer hypoxic zone of the Northern Gulf of Mexico.

This study investigated long-term (1980-2009) yields and variability of total organic carbon (TOC) from four major coastal rivers in Louisiana entering the Northern Gulf of Mexico where a large-area summer hypoxic zone has been occurring since the middle 1980s. Two of these rivers drain agriculture-intensive (>40%) watersheds, while the other two rivers drain forest-pasture dominated (>50%) watersheds. The study found that these rivers discharged a total of 13.0×10(4)t TOC annually, fluctuating from 5.9×10(4) to 22.8×10(4)t. Seasonally, the rivers showed high TOC yield during the winter and early spring months, corresponding to the seasonal trend of river discharge. While river hydrology controlled TOC yields, land use has played an important role in fluxes, seasonal variations, and characteristics of TOC. The findings fill in a critical information gap of quantity and quality of organic carbon transport from coastal watersheds to one of the world's largest summer hypoxic zones.

[Comparative study of the level and distribution of polybrominated diphenyl ethers and new brominated flame retardants in the atmosphere of typical urban].

Brominated flame retardants (BFRs) are widely used in industrial and commercial products and are frequently detected in various environmental media. It might be potential harm to the environment and the human body. This study reported the levels of 8 kinds of polybrominated diphenyl ethers (PBDEs: BDE-28, -47, -100, -99, -154, -153, -183, -209) and 3 kinds of new brominated flame retardants (NBFRs: PBT, PBEB, HBB) in the atmosphere of Binhai Development Zone, Weifang City, Shandong Province, which was taken as a BFR production source area and of Nanning City, Guangxi Province, which was taken as a contrast area. The results showed that the average concentrations of sigma8 PBDEs in the atmosphere of Weifang and Nanning were 1.4 x 10(5) pg x m(-3) and 323.0 pg x m(-3), respectively, and the average concentrations of sigma3 NBFRs were 4.2 x 10(3) pg x m(-3) and 11.9 pg x m(-3), respectively. Compared with other cities, the concentrations of BFRs in the atmosphere of the production area were at a high level in the globe, and the concentrations of BFRs in Nanning were similar with other cities in China. The distribution characteristics of PBDEs and NBFRs in the atmosphere of the production area were different from those of Nanning, and the correlations between PBEB, PBT, HBB and BDE-209 were different between Weifang and Nanning.

Polybrominated diphenyl ethers, dechlorane plus, and polychlorinated biphenyls in tree bark near the upper Yellow River, China.

Willow tree bark samples from urban and rural sites in Inner Mongolia, Ningxia Province, and Gansu Province, in the Yellow River basin, were analyzed for polybrominated diphenyl ethers (PBDEs), dechlorane plus (DP), and dioxin-like polychlorinated biphenyls (DL-PCBs) to compare their relative levels in air in these areas (i.e., treating bark as a passive air sampler). No difference was found between the pollutant concentrations in Salix matsudana and Salix babylonica bark samples. The mean concentrations of the total PBDEs, DP, and total DL-PCBs were 13000 ± 6400, 46 ± 44, and 26 ± 17 pg/g dry weight, respectively, with urban samples containing much higher concentrations (19000 ± 5700 pg/g, 51 ± 27 pg/g, and 37 ± 29 pg/g dry wt in PBDEs, DP, and DL-PCBs, respectively) than rural samples (10000 ± 5200 pg/g, 45 ± 53 pg/g, 22 ± 9 pg/g dry wt). A strong positive correlation between PBDEs and DP was found in all of the samples (r=0.712, p=0.006), but correlations between PCBs and the other pollutants were only found in the rural samples. The total DL-PCB concentration in the tree bark correlated with population density.

Concentrations and relationships between classes of persistent halogenated organic compounds in pooled human serum samples and air from Laizhou Bay, China.

Persistent halogenated organic compounds, including polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), dechlorane plus (DP), pentabromobenzene (PBBz), and pentabromotoluene (PBT), were analyzed in pooled human serum samples from different age groups and air samples from the south coast of Laizhou Bay, Shandong Province, China. The ∑25OCP and ∑8PBDE congeners were found at higher concentrations than the other compounds, with mean concentrations of 1500 and 240ng/g lipid in serum and 330 and 140,000pg/m(3) in the air, respectively. PBBz and PBT were detected in every serum and air sample, with mean concentrations of 4.9 and 1.4ng/g lipid in serum and 100 and 250pg/m(3) in air, respectively. In serum, the mean concentrations of ∑14PCBs and ∑DP were 7.1 and 3.6ng/g lipid, respectively, and in air, the mean concentrations of ∑12dioxin-like (DL-) PCBs and ∑DP were 1.7 and 1.4pg/m(3), respectively. Different relationships were observed between the concentrations of different compounds in serum and the volunteers' ages, and the concentration distributions with age were closely related to the historic production and usage volumes of each chemical in China. The ubiquity of PCBs, OCPs, PBDEs, DP, PBBz, and PBT in serum and air is potentially concerning, and effective measures should be taken to control the concentrations of these chemicals in the environment and humans. Significant correlations were found between the chemical concentrations in serum and air, suggesting that inhalation may be an important exposure route for the residents of Laizhou Bay.

[Vertical distribution of PBDEs and DL-PCBs in sediments of Taihu Lake].

Sediment core samples collected from the Zhushan Bay, Meiliang Bay, South Taihu of Taihu Lake were analyzed for 8 polybrominated diphenylethers (PBDEs) and 12 dioxin-like PCBs (DL-PCBs). The results revealed that the PBDEs levels were highest in the Zhushan Bay, followed by Meiliang Bay and South Taihu; and the DL-PCB levels were highest in the Meiliang Bay, followed Zhushan Bay and South Taihu. The vertical distribution of PBDEs level showed an exponential growth trend in Taihu Lake sediments, BDE-209 was the most abundant PBDEs congeners; and the vertical distribution of the DL-PCBs level in the sediments revealed that the contamination caused by DL-PCBs continued to increase in recent years, indicating that there were PCBs sources in the Taihu Lake region. There was significant difference in the composition of PBDEs congeners at different depths in the sediments of Meiliang Bay, however, the detailed causes remain to be investigated in further studies. The vertical distribution pattern of PCBs congeners revealed that PCB-77, -118, -105 levels significantly decreased with increasing depth in 0-15 cm upper sediments and there chang in the lower sediments.

Concentrations and trends of halogenated flame retardants in the pooled serum of residents of Laizhou Bay, China.

The south coast of Laizhou Bay, in northeastern China, is a production area for halogenated flame retardants (HFR). In 2007, the authors measured serum concentrations of polybrominated diphenyl ethers (PBDEs) in Laizhou Bay residents. To assess the PBDE concentration trend, and determine the concentrations of the emerging flame retardants Dechlorane Plus (DP) and bis(2-ethylhexyl)-3,4,5,6-tetrabromophthalate (TBPH), the authors measured the concentrations of 8 PBDE congeners, 2 DP isomers, and TBPH in 10 composite samples, which were pooled from the serum collected from 305 Laizhou Bay residents in October 2011. The average concentration of the total PBDE (∑8 PBDE) concentration in all serum pools was 240 ng/g lipid weight, and the highest serum pool concentration (in the 30- to 39-yr-old male group) was 780 ng/g lipid weight. Brominated diphenyl ether-209 was the dominant congener, accounting for 87% of ∑8 PBDE. Compared with a previous study, ∑8 PBDE serum concentrations in the present study showed no change in order of magnitude, but the relative contribution of BDE-209 to ∑8 PBDE was higher. The average concentration of ∑DP in all serum pools was 3.6 ng/g lipid weight, ranging from 1.4 ng/g lipid weight (in the 50- to 59-yr-old male group) to 11 ng/g lipid weight (in the 20- to 29-yr-old male group). The concentration of DP was lower than in other reported studies. The study also detected TBPH in the 30- to 39-yr-old female group, suggesting that TBPH, as an emerging HFR, requires further monitoring.