Regional haze which triggered both public anxiety and official concerns has been one of the most disastrous weather events in China in recent years. Haze not only had negative impact on daily life, ...but also an indicator of high concentrations of PM2.5 with the potential to adversely impact public health by damaging people's respiratory, cardiovascular, blood vessel of brain and nervous system. The dust-haze is an accumulated result for a long time of both natural factors and unhealthy economic growth model. In order to tackle air pollution, a number of policies and measures which target at reducing pollution emission and promoting alternative energy production had been implemented. Although significant improvement has occurred in China, change the development mode of "high growth, high pollution" and balance environmental conservation with the well-being of the population remains a challenge for China.
Hydrogen and oxygen evolution reactions (HER and OER) are important for many electrochemical systems. Besides traditional noble-metal-based catalysts, carbon-based materials have been found to be ...effective for catalyzing these reactions. Various carbon structures doped with heteroatoms (N, S, P, B, and transition metals) and graphitic-layer-encapsulated metal and compound particles have shown good activities toward HER and OER at universal pHs. In this Perspective, recent research on the development of carbon-based electrocatalysts for HER and OER, as well as their challenges and opportunities are discussed.
NiFe‐based layered double hydroxides (LDHs) are among the most efficient oxygen evolution reaction (OER) catalysts in alkaline medium, but their long‐term OER stabilities are questionable. In this ...work, it is demonstrated that the layered structure makes bulk NiFe LDH intrinsically not stable in OER and the deactivation mechanism of NiFe LDH in OER is further revealed. Both operando electrochemical and structural characterizations show that the interlayer basal plane in bulk NiFe LDH contributes to the OER activity, and the slow diffusion of proton acceptors (e.g., OH−) within the NiFe LDH interlayers during OER causes dissolution of NiFe LDH and therefore decrease in OER activity with time. To improve diffusion of proton acceptors, it is proposed to delaminate NiFe LDH into atomically thin nanosheets, which is able to effectively improve OER stability of NiFe LDH especially at industrial operating conditions such as elevated operating temperatures (e.g., at 80 °C) and large current densities (e.g., at 500 mA cm−2).
The interlayer basal plane in bulk NiFe layered double hydroxide (LDH) contributes to the oxygen evolution reaction (OER) activity. Restricted diffusion of proton acceptors within the interlayers of bulk NiFe LDH causes catalyst dissolution. Exfoliating multilayered NiFe LDH into single‐layered nanosheets greatly improves the catalytic stability of NiFe LDH in alkaline OER.
We developed a method to engineer well-distributed dicobalt phosphide (Co2P) nanoparticles encapsulated in N,P-doped graphene (Co2P@NPG) as electrocatalysts for hydrogen evolution reaction (HER). We ...fabricated such nanostructure by the absorption of initiator and functional monomers, including acrylamide and phytic acid on graphene oxides, followed by UV-initiated polymerization, then by adsorption of cobalt ions and finally calcination to form N,P-doped graphene structures. Our experimental results show significantly enhanced performance for such engineered nanostructures due to the synergistic effect from nanoparticles encapsulation and nitrogen and phosphorus doping on graphene structures. The obtained Co2P@NPG modified cathode exhibits small overpotentials of only −45 mV at 1 mA cm–2, respectively, with a low Tafel slope of 58 mV dec–1 and high exchange current density of 0.21 mA cm–2 in 0.5 M H2SO4. In addition, encapsulation by N,P-doped graphene effectively prevent nanoparticle from corrosion, exhibiting nearly unfading catalytic performance after 30 h testing. This versatile method also opens a door for unprecedented design and fabrication of novel low-cost metal phosphide electrocatalysts encapsulated by graphene.
Flexible and thin energy storage devices have attracted enormous attentions. An easy and large-scale method has been employed to fabricate flexible and interwoven N, P dual-doped carbon ...fibers/graphitic carbon nitride (huCP/g-C3N4) using filter paper as a precursor. The huCP/g-C3N4 composite as self-supporting anode for lithium ion batteries exhibits high reversible capacities of 1030 mAh g−1 after 1000 cycles at 1 A g−1 and 360 mAh g−1 after 4000 cycles at 10 A g−1 along with excellent rate performance (133 mAh g−1 at 30 A g−1). For sodium ion batteries, huCP/g-C3N4 as anode delivers high reversible capacities of 345 mAh g−1 after 380 cycles at 0.1 A g−1 and 110 mAh g−1 after 4000 cycles at 1 A g−1. This excellent electrochemical performance can be attributed to the high contents of doped N and P in huCP/g-C3N4 and graphitic carbon nitride network, which not only create more defects and active sites but also expand the layer planes and provide interconnected conductive network.
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The world's largest afforestation programs implemented by China made a great contribution to the global “greening up.” These programs have received worldwide attention due to its contribution toward ...achieving the United Nations Sustainable Development Goals. However, emerging studies have suggested that these campaigns, when not properly implemented, resulted in unintended ecological and water security concerns at the regional scale. While mounting evidence shows that afforestation causes substantial reduction in water yield at the watershed scale, process‐based studies on how forest plantations alter the partitioning of rainwater and affect water balance components in natural vegetation are still lacking at the plot scale. This lack of science‐based data prevents a comprehensive understanding of forest‐related ecosystem services such as soil conservation and water supply under climate change. The present study represents the first “Paired Plot” study of the water balance of afforestation on the Loess Plateau. We investigate the effects of forest structure and environmental factors on the full water cycle in a typical multilayer plantation forest composed of black locust, one of the most popular tree species for plantations worldwide. We measure the ecohydrological components of a black locust versus natural grassland on adjacent sites. The startling finding of this study is that, contrary to the general belief, the understory—instead of the overstory—was the main water consumer in this plantation. Moreover, there is a strict physiological regulation of forest transpiration. In contrast to grassland, annual seepage under the forest was minor in years with an average rainfall. We conclude that global long‐term greening efforts in drylands require careful ecohydrologic evaluation so that green and blue water trade‐offs are properly addressed. This is especially important for reforestation‐based watershed land management, that aims at carbon sequestration in mitigating climate change while maintaining regional water security, to be effective on a large scale.
A process‐based “Paired plot” study suggests that conversion of croplands to forests and grasslands in a dryland region resulted in a complex change of precipitation partitioning between green and blue flows. Forest plantations use more water than grasslands. Increased green flows in artificial forests are at the expenses of blue flows. We conclude that ensuring adequate levels of water supply for both ecosystems and people at both local and regional scales, large‐scale tree planting effort must be carefully planned.
Photoacoustic (PA) imaging holds great promise for preclinical research and clinical practice. However, most studies rely on the laser wavelength in the first near-infrared (NIR) window (NIR-I, ...650–950 nm), while few studies have been exploited in the second NIR window (NIR-II, 1000–1700 nm), mainly due to the lack of NIR-II absorbing contrast agents. We herein report the synthesis of a broadband absorbing PA contrast agent based on semiconducting polymer nanoparticles (SPN-II) and apply it for PA imaging in NIR-II window. SPN-II can absorb in both NIR-I and NIR-II regions, providing the feasibility to directly compare PA imaging at 750 nm with that at 1064 nm. Because of the weaker background PA signals from biological tissues in NIR-II window, the signal-to-noise ratio (SNR) of SPN-II resulted PA images at 1064 nm can be 1.4-times higher than that at 750 nm when comparing at the imaging depth of 3 cm. The proof-of-concept application of NIR-II PA imaging is demonstrated in in vivo imaging of brain vasculature in living rats, which showed 1.5-times higher SNR as compared with NIR-I PA imaging. Our study not only introduces the first broadband absorbing organic contrast agent that is applicable for PA imaging in both NIR-I and NIR-II windows but also reveals the advantages of NIR-II over NIR-I in PA imaging.
•Carbon encapsulated MnMoO4 microrods are realized in this work.•The MnMoO4@C microrods show excellent performance in SIBs and PIBs.•A sodium ion capacitor (SIC) based on MnMoO4 and Na3V2(PO4)3 is ...employed.•The SICs display energy densities of 168 and 88 Wh kg−1 at 240 and 4000 W kg−1.
Mixed transition metal molybdate oxides (AMoO4 where A= Ni, Co, Fe, Mn) manifest high capacities (≈ 980 mAh g − 1) via the multiple redox reactions, with the Mo ranging from Mo6+ to Mo0. What's more, this dual metal oxides exhibit superior performance to single transition metal oxide, as a result of the synergic effects of multiple transition metals and the better electrical conductivity than that of single metal oxide. Bimetallic MnMoO4 shows satisfied performance in lithium ion batteries (LIBs), but its performance in sodium ion batteries (SIBs) and potassium ion batteries (PIBs) has not been exploited. On account of this, a carbon encapsulated MnMoO4 microrod is designed as the anode material in SIBs and PIBs. It is detected that the electrochemical performance of the carbon encapsulated MnMoO4 microrods in SIBs is highly boosted with respect to the bare MnMoO4. In view of the pseudocapacitance effect of MnMoO4 microrods in SIBs, a sodium ion capacitor (SIC) based on MnMoO4 capacitor-type anode and Na3V2(PO4)3 battery-type cathode is employed and displays high energy densities of 168 and 88 Wh kg−1 at 240 and 4000 W kg−1.
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Electrocatalytic reactions invariably occur in the electrochemical double layer (EDL) whose properties are markedly dictated by the excess free charge on the electrode surface. The peroxodisulfate ...(PDS) reduction has long served as a model reaction to understand the surface charge effect on electrocatalytic reactions. Herein, we develop a mechanistic model for the PDS reduction at Pt(111) based on a mechanism consisting of a dissociative chemisorption step and two one-electron reduction steps. The electron-transfer step is described using the Marcus–Hush–Chidsey theory considering the double-layer structure and the metal electronic structure. The model reveals that considering the metal electronic structure in the kinetic rate expression is essential to explain the experimental observation that the reduction current first increases as the electrode potential decreases and is then suppressed when the electrode potential is lower than the potential of zero charge (pzc). In addition, a quantitative match with experimental data requires electrostatic interactions that are much stronger than that described by the mean-field Poisson–Boltzmann equation. Furthermore, hydroxyl adsorption forms surface dipoles at the metal surface and changes the surface-charging behavior, leading to a second pzc in high potential range that coincides with the onset potential of PDS reduction.
Abstract
Background
The emergence of coronavirus disease 2019 (COVID-19) is a major healthcare threat. The current method of detection involves a quantitative polymerase chain reaction (qPCR)–based ...technique, which identifies the viral nucleic acids when present in sufficient quantity. False-negative results can be achieved and failure to quarantine the infected patient would be a major setback in containing the viral transmission. We aim to describe the time kinetics of various antibodies produced against the 2019 novel coronavirus (SARS-CoV-2) and evaluate the potential of antibody testing to diagnose COVID-19.
Methods
The host humoral response against SARS-CoV-2, including IgA, IgM, and IgG response, was examined by using an ELISA-based assay on the recombinant viral nucleocapsid protein. 208 plasma samples were collected from 82 confirmed and 58 probable cases (qPCR negative but with typical manifestation). The diagnostic value of IgM was evaluated in this cohort.
Results
The median duration of IgM and IgA antibody detection was 5 (IQR, 3–6) days, while IgG was detected 14 (IQR, 10–18) days after symptom onset, with a positive rate of 85.4%, 92.7%, and 77.9%, respectively. In confirmed and probable cases, the positive rates of IgM antibodies were 75.6% and 93.1%, respectively. The detection efficiency by IgM ELISA is higher than that of qPCR after 5.5 days of symptom onset. The positive detection rate is significantly increased (98.6%) when combining IgM ELISA assay with PCR for each patient compared with a single qPCR test (51.9%).
Conclusions
The humoral response to SARS-CoV-2 can aid in the diagnosis of COVID-19, including subclinical cases.
The time kinetics of humoral responses against the novel coronavirus (SARS-CoV-2) are characterized in patients with COVID-19 by nucleocapsid-based enzyme-linked immunosorbent assay. The antibody testing can aid in the diagnosis of COVID-19 when combined with quantitative polymerase chain reaction, including in subclinical cases.
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