Metal single-atom catalysts (MSATs), such as Fe-N coordination doped sp
2
-carbon matrices, have emerged as a promising oxygen reduction reaction (ORR) catalyst to replace their costly platinum (Pt) ...based counterparts in fuel cells. In this work, we employ density functional theory (DFT) to systematically discuss the electronic-structure and surface-stress effects of N, C configurations on Fe-N doped graphene in single and double vacancy. The formation energy (
E
f
) of Fe-N-gra dropped off with the increase of N atoms incorporated for both single and double vacancy groups. The theoretical overpotentials on Fe-N-C sites were calculated and revealed that moderate N-doping levels and doping configuration could enhance the ORR activity of Fe-N coordination structures in the double vacancy and that doping N atoms is not effective for ORR activity in single vacancy. By exploring the d-band centers, we found that ligand effects and surface tension effects contribute to the modification of the d-band centers of metal Fe atoms. An optimum Fe-N-C ORR catalyst should exhibit moderate surface stress properties and an ideal N, C ligand configuration. This study provides new insight into the effects of N atom doping in Fe-N-gra catalysts and could help guide the rational design of high-performance carbon-based ORR electrocatalysts.
An optimum Fe-N-C ORR catalyst should exhibit a moderate surface stress property and an ideal N, C ligand configurations that results in a moderate interaction between the ORR intermediates and its surface sites.
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IJS, KILJ, NUK, UL, UM, UPUK
Abstract To define the characteristics of fundus manifestations in patients after SARS-CoV-2 infection with multimodal imaging techniques. This is a retrospective multicenter and multimodal imaging ...study including 90 patients. All patients with a visual complaint occurring immediately after SARS-CoV-2 infection were referred to six clinics between December 2022 and February 2023. Demographic information and the temporal relationship between SARS-CoV-2 infection and visual symptoms were documented. The characteristics of the fundus lesions were evaluated using multimodal imaging. Ninety patients from six hospitals were included in this study, including 24 males (26.67%) and 66 (73.33%) females. Seventy-eight patients (86.66%) (146 eyes) were diagnosed with Acute Macular Neuroretinopathy (AMN). The AMN patients were primarily young women (67.95%). Sixty-eight patients (87.18%) had AMN in both eyes. Thirty-eight eyes (24.36%) included Purtscher or Purtscher-like lesions. optical coherence tomography and infrared retinal photographs can show AMN lesions well. Eleven cases were diagnosed with simple Purtscher or Purtscher-like retinopathy (2 cases, 2.22%), Vogt‒Koyanagi‒Harada (VKH) syndrome or VKH-like uveitis (3 cases, 3.33%), multiple evanescent white-dot syndrome (MEWDS) (2 cases, 2.22%), and rhino-orbital-cerebral mucormycosis (ROCM) (5 cases, 5.56%). After SARS-CoV-2 infection, diversified fundus lesions were evident in patients with visual complaints. In this report, AMN was the dominant manifestation, followed by Purtscher or Purtscher-like retinopathy, MEWDS, VKH-like uveitis, and ROCM.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The attenuation process of the oxygen reduction reaction (ORR) catalytic performance for Fe SAC@G catalysts under different discharging conditions, including KOH concentrations, solution ...temperatures, and discharging potentials, was investigated by electrochemical measurements. The ORR catalytic activity attenuation resulting from the change in KOH concentration and temperature becomes apparent in a negative discharging potential range and elevated discharging temperature. In addition, the more negative discharging potential significantly causes the ORR catalytic activity attenuation. Scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy analyses indicate that, with the prolongation of the discharge time, the nanocolumns of the as-prepared catalyst gradually dissolve, while a flowerlike discharge byproduct composed of elements C and N keeps growing on the surface of the catalyst. The weakest Fe–N bonds first break, resulting in the attenuation of the ORR catalytical performance. Then, the weak C–Cunit bonds connecting the structural units of the catalysts break, leading to the gradual collapse in the structure of the catalysts. The Fe–N4 coordination structure gradually transforms into Fe–N3, Fe–N2, and Fe–N coordination structures. Based on the analyses combined with the density functional theory (DFT) calculations of bond strength, a discharge attenuation mechanism of the structural collapse of the catalyst for the formation of the discharge byproduct with ring structure is proposed.
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IJS, KILJ, NUK, PNG, UL, UM
Xinxiang, as an important industrial city in Henan Province and one of the “2 + 26” cities, is encountering severe fine particulate matter (PM2.5) pollution. During the Beijing Winter Olympics Games, ...a series of pollution control measures were implemented in Xinxiang, which provides an excellent opportunity to investigate the local PM2.5 characteristics and formation mechanisms and assess the effectiveness of the control measures. From January 20 to February 20, 2022, samples of PM2.5 were collected in urban and rural areas of Xinxiang, and their chemical compositions were detected. Three research phases were divided according to control measures: P1, P2 and P3, representing before pollution control period, stricter pollution control period, and looser pollution control period, respectively. It was found that PM2.5 levels decreased significantly during P2 and P3, by more than 30%. There was a significant decrease in SO42−, NO3− and NH4+ (SNA) in PM2.5, but not in organic carbon (OC) and element carbon. Moreover, the secondary formations of SO42− and NO3− also decreased clearly during these two phases, especially for nocturnal NO3−. SO42− was mainly generated through the NO2 reaction pathway (SO2 oxidation by NO2 in aerosol water), and the reaction could also promote NO3− production. As NO2 is critical in this reaction, future pollution control should focus on reducing NO2. The PM2.5 in urban and rural areas had quite different compositions. Specifically, the rural area had better reaction conditions for sulfate (lower temperature). In addition, urban area had more OC that came from secondary reactions, while in rural area it comes more from biomass and coal combustion. Therefore, different pollution control measures should be taken to reduce their OC concentrations in the future. The study will provide a more scientific basis for formulating more scientific control measures of PM2.5 in Xinxiang and other cities in Central China.
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•Pollution control measures effects of Beijing Winter Olympic Games were evaluated.•SNA decreased but SOA increased at urban area of Xinxiang during pollution control.•Pollution control measures expanded the urban-rural differences in PM2.5 sources.•The secondary formation of SO42− and NO3− (especially at night) decreased clearly.•SO2 oxidation by NO2 in aerosol water is the main formation way of SO42−.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Implementing bolt supports is the main means of controlling block instability. However, the original three-dimensional discontinuous deformation analysis method (3D ODDA) is still unable to simulate ...bolt supports, making it difficult to study the control effect of bolt supports on block instabilities. Therefore, an extended three-dimensional discontinuous deformation analysis method (3D EDDA) that can simulate the effect of bolt supports is proposed in this article. Based on the 3D ODDA method, we proposed a simulation algorithm for bolt supports, which improves the constitutive model of the bolt in the original DDA method. Then, we analysed the failure process of a bolt between two blocks and compared the numerical simulation results with the theoretical analysis results to verify the accuracy of the bolt support algorithm in the 3D EDDA method. With the 3D EDDA method, we simulated the failure process of the surrounding rock in a jointed rock mass tunnel at the engineering scale under conditions with bolt supports and without bolt supports. By comparing the results of these two conditions, we deduced the evolution law of the block displacement and bolt axial force around the tunnel and determined the anisotropic characteristics of these items. Specifically, the axial force of the local bolts is relatively small and has a small control effect on the stability of the block in the area. During actual construction, the length or strength of these bolts can be reduced, which can provide a theoretical basis for the design of tunnel bolt support parameters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Low-dimensional semimetal–semiconductor (Sm-S) van der Waals (vdW) heterostructures have shown their potentials in nanoelectronics and nano-optoelectronics recently. It is an important scientific ...issue to study the interfacial charge transfer as well as the corresponding Fermi-level shift in Sm-S systems. Here we investigated the gate-tunable contact-induced Fermi-level shift (CIFS) behavior in a semimetal single-walled carbon nanotube (SWCNT) that formed a heterojunction with a transition-metal dichalcogenide (TMD) flake. A resistivity comparison methodology and a Fermi-level catch-up model have been developed to measure and analyze the CIFS, whose value is determined by the resistivity difference between the naked SWCNT segment and the segment in contact with the TMD. Moreover, the relative Fermi-level positions of SWCNT and two-dimensional (2D) semiconductors can be efficiently reflected by the gate-tunable resistivity difference. The work function change of the semimetal, as a result of CIFS, will naturally introduce a modified form of the Schottky–Mott rule, so that a modified Schottky barrier height can be obtained for the Sm-S junction. The methodology and physical model should be useful for low-dimensional reconfigurable nanodevices based on Sm-S building blocks.
Low-dimensional semiconductors have shown great potential in switches for their atomically thin geometries and unique properties. It is significant to achieve new tunneling transistors by the ...efficient stacking methodology with low-dimensional building blocks. Here, we report a one-dimensional (1D)–two-dimensional (2D) mixed-dimensional van der Waals (vdW) heterostructure, which was efficiently fabricated by stacking an individual semiconducting carbon nanotube (CNT) and 2D MoS2. The CNT–MoS2 heterostructure shows specific reconfigurable electrical transport behaviors and can be set as a nn junction, pn diode, and band-to-band tunneling (BTBT) transistor by gate voltage. The transport properties, especially BTBT, could be attributed to the electron transfer from MoS2 to CNT through the ideal vdW interface and the 1D nature of the CNT. The progress suggests a new solution for tunneling transistors by making 1D–2D heterostructures from the rich library of low-dimensional nanomaterials. Furthermore, the reconfigurable functions and nanoscaled junction show that it is prospective to apply CNT–MoS2 heterostructures in future nanoelectronics and nano-optoelectronics.
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IJS, KILJ, NUK, PNG, UL, UM
Volatile organic compounds (VOCs) are essential pollutants affecting ambient air quality. In the Pearl River Delta of China, furniture manufacturing contributes significantly to VOCs emissions, ...mainly from coatings. Therefore, the source substitution of coatings is the most effective way to reduce VOCs emissions. In this study, eight typical furniture enterprises with five different coatings types (traditional solvent coatings (solvent and solvent ultraviolet (UV) coatings) and low VOCs content coatings (waterborne, waterborne UV, and powder coatings)) were selected for field monitoring to reveal differences in VOCs emission characteristics, environmental impacts and health risks between traditional solvent coatings and low-VOCs coatings. The results showed that solvent coating VOCs have the highest concentration (143.32 mg/m3) and are much higher than that of solvent UV coating (45.96 mg/m3) and other coatings (≤11.81 mg/m3). The highest proportion of VOCs of solvent (UV) coating is aromatic hydrocarbons (50.73% (44.05%)). While oxygenated VOCs rank first in low-VOCs coatings (47.81%–59.20%). Compared with other coatings, the solvent coating has the greatest contribution to the formation potential of ozone and secondary organic aerosols. Meanwhile, the solvent coating has the highest carcinogenic risk of ethylbenzene in the spraying workshop (8.53 × 10−6), and only solvent coating in the spraying workshop has the non-carcinogenic risk of xylene (1.07). Finally, through scenario analysis, the environmental benefits of low-VOCs coatings substituting solvent coating were quantified. The study will help accelerate the process of source substitution of coatings and promote cleaner production in the furniture industry.
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•VOCs spectra of five different coating types in furniture industry were obtained.•Solvent coating has a much higher contribution to secondary pollutants than others.•Solvent (ultraviolet) coatings exist a carcinogenic risk of ethylbenzene.•Only solvent coating in spraying workshop has a non-carcinogenic risk of xylene.•The environmental benefits of low-VOCs coatings substitution were quantified.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A single-atom TM-N
x
(TM = Fe, Co, Mn,
etc.
) embedded graphene matrix is known for its excellent activity and durability in oxygen reduction reaction (ORR) catalysis. Among them, Mn-N
4
sites have ...been theoretically proved to undergo a complete 4-electron pathway with low ORR overpotentials and low activation barriers in O
2
dissociation. However, in reality there still remain significant activity gaps between such Mn-N
4
based catalysts (such as MnPc and MnP) and Fe-N
4
or Pt-group metal catalysts. The inferior ORR performance of MnPc and MnP could be attributed to the strong binding ability of Mn that causes great difficulties in removing the ORR products from the surface sites. On this basis, 17 types of Mn-N
x
models containing various three-, four- and five-coordination groups were established. Systematic density functional theory (DFT) calculations were performed to investigate the N,C coordination effects on their corresponding ORR activities. Scaling relations were found among the binding strengths of key ORR intermediates, which could be modulated by the N doping level among different coordination groups. A volcano plot for ORR overpotentials (
η
SHE
) as a function of *OH adsorption free energy (Δ
G
*OH
) was further established. The 3D five-coordination sites exhibit much higher ORR activity due to the great decrease in strong binding abilities compared with 2D three- or four-coordination sites. Particularly, (Cyan)Mn-N
4
/D is positioned near the apex of the volcano plot with an
η
SHE
of 0.33 V even lower than that of Pt(111) (0.34 V). Furthermore, the electron withdrawing/donating mechanisms among Mn, N, C, and O were investigated and related to the binding abilities of different coordination groups. Electronic structure calculations indicate that the binding abilities of Mn-N
x
well correlate with the σ-type anti-bonding components between Mn-3d and O-2p states near the Fermi energy level.
Five-coordination Mn-N
x
experiences a significant increase in ORR catalytic activity due to its moderate binding ability compared with Mn-N
4
and Mn-N
3
.
Fe-N-C single-atom catalysts usually exhibit poor ORR activity due to their unsatisfactory O
2
adsorption and activation. Here, a new design idea and tailored self-assembly synthesis method are ...reported to improve their ORR performance. DFT calculations indicate that the ORR electrocatalytic activity of Fe-N-C single-atom catalysts with an axial structure is superior to that of Fe-N-C single-atom catalysts with a Fe-N
4
active site. In order to experimentally demonstrate the difference, Fe-N-C single-atom catalysts with a Fe-N
5
active site were successfully synthesized on the surface of monolayer graphene. XANES, SEM, HRTEM, XRD, Raman and XPS analyses indicate that the synthesized Fe-N-C catalyst possessed nanofibre morphology and a curved layer-like crystal structure. For comparison, FePc powder was used as the FePc(Fe-N
4
) catalyst as its molecular structure involves a Fe-N
4
active site embedded in carbon six-membered rings. The current density of the synthesized Fe-N
5
/C@G catalyst at a potential of 0.88 V
vs.
RHE is 1.65 mA cm
−2
, which is much higher than that of the FePc(Fe-N
4
) catalyst (1.04 mA cm
−2
) and even higher than that of commercial Pt/C catalyst (1.54 mA cm
−2
). The results are very well consistent with the DFT calculations, verifying the dependability and accuracy of DFT calculations. This work reports a new synthetic idea to obtain better performance and proposes a formation mechanism to explain the process of the synthesis method.
FePc powder sublimates losing H atoms to form unstable fragments at 450 °C which self-assemble to form units with a double-layer structure. The self-assembly units are driven by argon gas at 70 °C to where the substrate is located and crystallize to form Fe-N5/C@G catalyst.
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