Carbon Fiber Film with Multi-Hollow Channels to Expedite Oxygen Electrocatalytic Reaction Kinetics for Flexible Zn-Air Battery.

The high oxygen electrocatalytic overpotential of flexible cathodes due to sluggish reaction kinetics result in low energy conversion efficiency of wearable zinc-air batteries (ZABs). Herein, lignin, as a 3D flexible carbon-rich macromolecule, is employed for partial replacement of polyacrylonitrile and constructing flexible freestanding air electrodes (FFAEs) with large amount of mesopores and multi-hollow channels via electrospinning combined with annealing strategy. The presence of lignin with disordered structure decreases the graphitization of carbon fibers, increases the structural defects, and optimizes the pore structure, facilitating the enhancement of electron-transfer kinetics. This unique structure effectively improves the accessibility of graphitic-N/pyridinic-N with oxygen reduction reaction (ORR) activity and pyridinic-N with oxygen evolution reaction (OER) activity for FFAEs, accelerating the mass transfer process of oxygen-active species. The resulting N-doped hollow carbon fiber films (NHCFs) exhibit superior bifunctional ORR/OER performance with a low potential difference of only 0.60 V. The rechargeable ZABs with NHCFs as metal-free cathodes possess a long-term cycling stability. Furthermore, the NHCFs can be used as FFAEs for flexible ZABs which have a high specific capacity and good cycling stability under different bending states. This work paves the way to design and produce highly active metal-free bifunctional FFAEs for electrochemical energy devices.

Chemical characteristics of long-term acid rain and its impact on lake water chemistry: A case study in Southwest China.

The chemical composition of acid rain and its impact on lake water chemistry in Chongqing, China, from 2000 to 2020 were studied in this study. The regional acid rain intensity is affected jointly by the acid gas emissions and the neutralization of alkaline substances. The pH of precipitation experienced three stages of fluctuating decline, continuous improvement, and a slight correction. Precipitation pH showed inflection points in 2010, mainly due to the total control actions of SO2 and NOx implemented in 2011. The total ion concentrations in rural areas and urban areas were 489.08 µeq/L and 618.57 µeq/L, respectively. The top four ions were SO42-, Ca2+, NH4+ and NO3-, which accounted for more than 90% of the total ion concentration, indicating the anthropogenic effects. Before 2010, SO42- fluctuated greatly while NO3- continued to rise; however, after 2010, both SO42- and NO3- began to decline rapidly, with the rates of -12.03 µeq/(L·year) and -4.11 µeq/(L·year). Because the decline rate of SO42- was 2.91 times that of NO3-, the regional acid rain has changed from sulfuric acid rain to mixed sulfuric and nitric acid rain. The lake water is weakly acidic, with an average pH of 5.86, and the acidification frequency is 30.00%. Acidification of lake water is jointly affected by acid deposition and acid neutralization capacity of lake water. Acid deposition has a profound impact on water acidification, and nitrogen (N) deposition, especially reduced N deposition, should be the focus of future research.

Brominated flame retardants in surface sediment from Western Guangdong, South China: Occurrence, distribution and toxicity in Caenorhabditis elegans.

Sediment is the ultimate sink of environmental pollutants. A total of 128 surface sediment samples were collected from 8 rivers and 3 reservoirs in Maoming City, Guangdong Province. This study assessed the content and distribution of brominated flame retardants in sediments. The acute toxicity effects of tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCDs) in sediments were evaluated using Caenorhabditis elegans as model organisms. The concentration of TBBPA in sediments ranged from not detected (ND) to 12.59 µg/kg and was mainly distributed in the central area, which was affected by the emission of TBBPA from residential and factory. The concentration of HBCDs ranged from ND to 6.31 µg/kg, and the diastereoisomer distribution was consistent, showing a trend close to the South China Sea. The composition pattern of HBCDs in the surface sediments from rivers were 41.73%-62.33%, 7.89%-25.54%, and 18.76%-40.65% for α-, ß-, and γ-HBCD, respectively, and in the sediments from reservoirs were 26.15%-45.52%, 7.44%-19.23%, and 47.04%-61.89% for α-, ß-, and γ-HBCD, respectively. When the sum of concentrations of TBBPA and HBCD in sediments were above high levels, reactive oxygen species in nematodes significantly increased, resulting in an oxidative stress response. Intestinal permeability was also enhanced, causing intestinal damage. In addition, in terms of this study, TBBPA had a greater impact on biotoxicity compared to HBCDs, and more attention should be paid to the toxic effects of the river ecosystem organisms in Maoming City, Guangdong Province. This study can complement the pollution database in the study area and provide basic data for pollution control.

Two-dimensional type-II g-C3N4/SiP-GaS heterojunctions as water splitting photocatalysts: first-principles predictions.

Hydrogen production from water splitting by sunlight is a promising approach to solve the increasing energy and environmental crises, and the two-dimensional (2D) g-C3N4 monolayer is a red star in this realm. However, it suffers from low quantum efficiency caused by the fast combination of photogenerated electrons and holes. In this work, we investigate the electronic and photocatalytic properties of three newly proposed g-C3N4/SiP-GaS-α, -ß and -γ heterojunctions via first principles predictions. Theoretical results demonstrate that the three g-C3N4/SiP-GaS heterojunctions exhibit direct bandgaps of ∼2.2 eV, and have a type-II band alignment with the valence band maximum (VBM) located at the g-C3N4 layer and the conduction band minimum (CBM) at the SiP-GaS layer. Furthermore, their band edges straddle the redox potential of water in a wide range of biaxial strain. Their absorption coefficients are several times larger than that of most previously discovered 2D heterojunctions. Moreover, the in-built electric field adds a driving force to separate photogenerated electrons and holes. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) successfully take place on the g-C3N4 and SiP-GaS layers, respectively. Briefly, separated charge carriers, suitable band edges and strong visible-light absorbance, successful OER and HER enable the three g-C3N4/SiP-GaS heterojunctions to be promising water-splitting photocatalysts.

Transformation of algal-dissolved organic matter via sunlight-induced photochemical and microbial processes: interactions between two processes.

Algal-dissolved organic matter (ADOM) is an important fraction of dissolved organic carbon (DOC) in eutrophic water. Although ADOM is known to be readily transformed by microbes, the role of sunlight-induced photochemical process and the interactions between two processes on ADOM transformation remains unclear. In this study, three types of treatments for ADOM, including photochemical process under natural solar light (L treatment), microbial process (M treatment), and the simultaneous photochemical plus microbial process (L&M), were performed for 18 days. Our results showed that M treatment was more effective for the loss of DOC, chromophoric DOM (CDOM) at short wavelengths (a254 and a280), than L treatment, while L treatment was more effective for the transformation of a350 and the fluorescent components of the ubiquitous humic-like component and the tryptophan-like component. Comparison in the decay kinetics of DOC and CDOM in the three treatments showed that the simultaneous photochemical and biological processes exhibited an inhibitory effect on DOC decay rate but not the percentage of labile DOC fraction. Higher relative abundance of protein-like substances was found after L&M treatment, while the relative abundance of humic-like substance and aromaticity increased after M treatment, and the low molecular-weight compounds were produced after L treatment. Our results emphasized the importance of photochemistry in processing ADOM to mediate the chemodiversity in natural water.

Effects and mechanism on cadmium adsorption removal by CaCl2-modified biochar from selenium-rich straw.

As every-one knows, cadmium contamination poses a significant and permanent threat to people and aquatic life. Therefore, research on how to remove cadmium from wastewater is essential to protect the natural environment. In this study, agricultural and forestry waste straw sprayed with selenium-enriched foliar fertilizer was prepared as biochar, which was altered by calcium chloride (CaCl2) to remove Cd2+ from water. The outcomes demonstrated that biochar generated by pyrolysis at 700 °C (BC700) had the best adsorption effect. Secondly, pseudo-second-order kinetics and Langmuir adsorption models were used to predict the Cd2+ adsorption. Finally, electrostatic adsorption, ion exchange, and complexation of oxygen functional groups (OFGs) were demonstratedto be the main adsorption mechanisms. These conclusions indicate that selenium-rich straw biochar is a novel adsorbent for agroforestry waste recovery. Meanwhile, this work will offer a promising strategy for the overall utilization of rice straw.

Mass Production of Sulfur-Tuned Single-Atom Catalysts for Zn-Air Batteries.

Single-atom catalysts (SACs) show great potential for rechargeable Zn-air batteries (ZABs); however, scalable production of SACs from sustainable resources is difficult owing to poor control of the local coordination environment. Herein, lignosulfonate, a by-product of the papermaking industry, is utilized as a multifunctional bioligand for the mass production of SACs with highly active MN4 S sites (M represents Fe, Cu, and Co) via strong metalnitrogen/sulfur coordination. This effectively adjusts the charge distribution and promotes the catalytic performance, leading to highly durable and excellent performance in oxygen reduction and evolution reactions for ZABs. This study paves the way for the industrial production of cost-effective SACs in a sustainable manner.

[Risk Assessment and Source Analysis of Heavy Metal Pollution in Surface Sediments from Major River Systems in Maoming City, Guangdong Province].

In order to understand the spatial distribution and sources of heavy metals in surface sediments of MaoMing city and to reasonably evaluate the ecological risk of heavy metals in sediments of the study area, the contents of heavy metals (As, Hg, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) in surface sediments of eight rivers and three reservoirs were detected, and the risks of heavy metals were assessed using the geo-accumulation index (Igeo), potential ecological disk index (RI), and potential adverse biological impacts (ΣTUs). The sources of heavy metals were analyzed via correlation, principal component analysis (PCA), and positive matrix factorization (PMF). The results showed that the ω(Zn) (147.56 mg·kg-1) and ω(Hg) (0.20 mg·kg-1) were 3.72 and 2.25 times the background value, respectively, and the spatial distributions of Cd, Co, Cu, Mn, Ni, and Zn were in the order of northern>central>western>southeast. The geo-accumulation index results showed that Zn was at a moderate pollution level, 76.6% of the sampling sites of Hg were at a light-heavy pollution level, and other heavy metals were at a non-light pollution level. The results of potential ecological risk and potential adverse biological impacts indicated that the potential ecological risk index and toxicity effect of Gaozhou Reservoir were higher than those of other rivers, and Hg was the major contributor to heavy metal pollution. The three factors extracted from principal component analysis and positive matrix factorization represented natural sources, agricultural sources, and industrial sources, respectively. Therefore, in order to reduce the health hazards caused by heavy metals in sediments, a prevention and control system for the Hg element should be established.

Insights into gold-catalyzed formation of aza-heterocycles using benzofuroxans as nitrene transfer reagents: mechanism and origins of chemoselectivity.

Density functional theory (DFT) calculations have been performed to reveal the mechanism of gold(i)-catalyzed annulation of N-allylynamides and benzofuroxans as nitrene transfer reagents to construct azaheterocyclic compounds. The calculated results revealed that the reaction mechanism mainly undergoes eight processes. Among the reaction steps, intramolecular nucleophilic attack of the imino N atom on the α-position of activated gold keteniminium is a rate-determining process, which is different from that proposed previously by experiment. The chemoselectivity of the products is controlled by competition between the cyclopropanation of α-imino gold carbenes and intramolecular nucleophilic attack of the phenyl ring on α-imino gold carbenes, and could be explained by NPA charge. The different yields of cyclopropanated product in different solvents are dictated by the relative polarity leading to the different energy barriers of the rate-determining steps. The present work expounds the experimental observation at the molecular level and is informative for exploring efficient syntheses of 3-azabicyclo[3.1.0]hexanes.

Chiral rhodium(III)-azobenzene complexes as photoswitchable DNA molecular locks.

Chiral rhodium(III)-azobenzene complexes that are able to intercalate into DNA were developed. Upon light exposure, the azobenzene moiety of the metal complexes can photoisomerize from the trans-form to the cis-form, and strongly stabilize the DNA double-helix and modulate DNA transcription. This study presents the first example of metal-based photoswitchable DNA molecular locks.

A novel nomogram for anastomotic leakage after surgery for rectal cancer: a retrospective study.

Background: Anastomotic leakage remains one of the most common serious complications after rectal cancer surgery. How to predict its occurrence and prevent it remains largely elusive. Objective: This study aimed to identify the risk factors of anastomotic leakage and construct a nomogram for predicting postoperative anastomotic leakage in patients with rectal cancer. Methods: The data of 406 patients with rectal cancer after gastrointestinal surgery in the Third Affiliated Hospital of Sun Yat-sen University from January 2011 to May 2020 were collected (243 in the training set and 163 in the testing set). Logistic regression was applied to determine the risk factors of postoperative anastomotic leakage of rectal cancer, and a nomogram prediction model was thus established. Predictive performance of the nomogram was evaluated by C-index and area under the receiver-operating characteristic (ROC) curve. Results: Logistic regression analysis showed that preoperative bowel obstruction (odds ratio [OR] = 12.846, 95% confidence interval CI [1.441-114.54], p = 0.022) and early first defecation after surgery (OR = 0.501, 95% CI [0.31-0.812], p = 0.005) were independent risk factors, which could be used to develop a nomogram to predict the occurrence of anastomotic leakage accurately. The evaluation of the prediction model shows that the C-index value of the model was 0.955, the area under the ROC curve (AUC) of the training set was 0.820, and the testing set was 0.747, whereas the optimal cut-off point based on the nomogram score was 174.6. Conclusion: This nomogram had a good prediction ability for postoperative anastomotic leakage in patients with rectal cancer. It can provide a reference for perioperative treatment and the selection of surgical methods to promote individualized and accurate treatment.

Characteristics and health risks of benzene series and halocarbons near a typical chemical industrial park.

Health risks of typical benzene series and halocarbons (BSHs) in a densely populated area near a large-scale chemical industrial park were investigated. Ambient and indoor air and tap water samples were collected in summer and winter; and the concentration characteristics, sources, and exposure risks of typical BSH species, including five benzene series (benzene, toluene, ethylbenzene, o-xylene, m,p-xylene) and five halocarbons (dichloromethane, trichloromethane, trichloroethylene, tetrachloromethane, and tetrachloroethylene), were analysed. The total mean concentrations of BSHs were 53.32 µg m-3, 36.29 µg m-3, and 26.88 µg L-1 in indoor air, ambient air, and tap water, respectively. Halocarbons dominated the total BSHs with concentrations relatively higher than those in many other industrial areas. Industrial solvent use, industrial processes, and vehicle exhaust emissions were the principal sources of BSHs in ambient air. The use of household products (e.g., detergents and pesticides) was the principal source of indoor BSHs. Inhalation is the primary human exposure route. Ingestion of drinking water was also an important exposure route but had less impact than inhalation. Lifetime non-cancer risks of individual and cumulative BSHs were below the threshold (HQ = 1), indicating no significant lifetime non-cancer risks in the study area. However, tetrachloromethane, benzene, trichloromethane, ethylbenzene, and trichloroethylene showed potential lifetime cancer risk. The cumulative lifetime cancer risks exceeded the tolerable benchmark (1 × 10-4), indicating a lifetime cancer risk of BSHs to residents near the chemical industry park. This study provides valuable information for the management of public health in chemical industrial parks.

Nitrogen wet deposition in the Three Gorges Reservoir area: Characteristics, fluxes, and contributions to the aquatic environment.

Measurements of nitrate nitrogen (NO3--N), ammonia nitrogen (NH4+-N), and dissolved organic nitrogen (DON) in precipitation were conducted at six different sites in the hinterland of the Three Gorges Reservoir (TGR) area from January 2016 to December 2017. The characteristics and the sources of nitrogen (N) species were identified. N flux of wet deposition in the hinterland of the TGR area were 13.56 ± 2.95 kg N ha-1 yr-1, of which the proportions of NO3--N, NH4+-N and DON were 60.9%, 25.1% and 14.0%, respectively. N flux in urban area was significantly higher than those in suburban, agricultural, and wetland areas. Industrial activities, biomass burning, and secondary transformation were the main contributors of N in urban area. In agricultural area, biomass burning, crustal, and manure were main sources of N. In suburban area, mixed emissions from industry, agriculture, and crustal sources were primary contributors of N. For wetlands, the major contributions were from industrial sector and biomass burning. Additional, analysis of regional distribution of dissolved N deposition in the TGR area was conducted by combining current study data and previously published data between 2000 and 2017. N flux of wet deposition in the entire TGR area ranged from 12.17 to 51.93 kg N ha-1 yr-1, with an average of 26.81 kg N ha-1 yr-1. Regional N distribution was greatest in the tail region, followed by the head region, and then the hinterland in the TGR area. The amount of N entering the TGR directly through atmospheric wet deposition was 2906 t yr-1, accounting for 2.1% of the total N inputs. N load from wet deposition had exceeded the critical loads from that of the water, forest, and even some farmland ecosystems in the TGR area. Decreasing NH3 emissions from agricultural activities is the key to alleviate the regional N deposition.

An Iron-Decorated Carbon Aerogel for Rechargeable Flow and Flexible Zn-Air Batteries.

Mechanically stable and foldable air cathodes with exceptional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities are key components of wearable metal-air batteries. Herein, a directional freeze-casting and annealing approach is reported for the construction of a 3D honeycomb nanostructured, N,P-doped carbon aerogel incorporating in situ grown FeP/Fe2 O3 nanoparticles as the cathode in a flexible Zn-air battery (ZAB). The aqueous rechargeable Zn-air batteries assembled with this carbon aerogel exhibit a remarkable specific capacity of 648 mAh g-1 at a current density of 20 mA cm-2 with a good long-term durability, outperforming those assembled with commercial Pt/C+RuO2 catalyst. Furthermore, such a foldable carbon aerogel with directional channels can serve as a freestanding air cathode for flexible solid-state Zn-air batteries without the use of carbon paper/cloth and additives, giving a specific capacity of 676 mAh g-1 and an energy density of 517 Wh kg-1 at 5 mA cm-2 together with good cycling stability. This work offers a new strategy to design and synthesize highly effective bifunctional air cathodes to be applied in electrochemical energy devices.

Planar graphitic ZnS, buckling ZnS monolayers and rolled-up nanotubes as nonlinear optical materials: first-principles simulation.

Nonlinear optical (NLO) materials have an ability to generate new coherent light. At the present stage, three dimensional (3D) mid-infrared NLO materials suffer from various deficiencies such as low laser damage thresholds (LDTs) for AgGaQ2 (Q = S, Se); the band gaps of most intensively studied two-dimensional (2D) NLO materials are not wide enough to avoid two-photon absorption (TPA); a steady NLO property regardless of diameter and chirality is absent in one-dimensional (1D) single-walled nanotubes (SWNTs). In this research, the electronic and second harmonic generation (SHG) properties of planar graphitic ZnS (g-ZnS) monolayer, buckling reconstructed ZnS (R-ZnS) monolayer which is synthesized in a recent experiment, and rolled-up SWNTs are investigated with first-principles simulations. Theoretical results suggest the SHG coefficients of planar g-ZnS, buckling R-ZnS and rolled-up SWNTs are comparable with that of AgGaS2 crystals. The band gaps of planar g-ZnS and ZnS SWNTs are ∼3.8 eV, and that of buckling R-ZnS is as wide as ∼4.0 eV, indicating high LDTs and reduced TPA as NLO materials. The TPA edges can be further blue shifted by using incident light beams with a polarized electric field perpendicular to buckling R-ZnS. On the other hand, the TPA edges of ZnS SWNTs are nearly not affected by diameter and chirality. The SHG coefficients of ZnS SWNTs are much less influenced by chirality and diameter than those of SiC, GeC and BN SWNTs. Therefore, they are superior ultrathin NLO materials, and especially have a potential application in the mid-infrared regime where high-quality NLO crystals are emergently needed.

Mobility and potential risk of sediment-associated heavy metal fractions under continuous drought-rewetting cycles.

Ecological decline in the water level fluctuating (WLF) zone of the Three Gorges Reservoir (TGR) has been well established over the past decades. However, the effect of heavy metal fractions present in the sediment and their potential ecological risk under the anti-seasonal hydrological regime are still unclear. The Pengxi River is a tributary of the Yangtze River and it has a typical annual water level fluctuation ranging from 145 to 175m above sea level. The current study examined heavy metal fractions in sediments containing Cr, Cd, Cu, Pb and Mn collected along the WLF zone using the Tessier sequential extraction scheme. The total organic carbon (TC), total nitrogen (TN), carbon/nitrogen ratio (C/N), pH, particle size composition and content of nitrate (NO3--N), and ammonium (NH4+-N) differed dramatically among the sampled altitudes and depths and was significantly correlated with the flooding time of the WLF zone. At lower altitudes of the WLF zone, the amounts of the exchangeable (EXC), carbonate-bound (CA) and total heavy metal contents of the surface sediment were much higher compared to those of higher altitudes of the WLF zone. The risk assessment code (RAC) for Cd and Mn showed an opposite trend to that of Cr, Cu, and Pb and mainly depended on the organic matter-bound fraction (OM). The modified RAC (mRAC) indicated a very high potential adverse effect for the whole WLF zone, although the risk value was much lower at the lower altitudes and upper depths of the WLF zone. Our results showed that the positive response of the loosely bound fractions (LOS) of heavy metals to the drought-rewetting (DRW) process minimizes the risk of heavy metals in the WLF zone sediment.