It is highly desirable to convert CO2 to valuable fuels or chemicals by means of solar energy, which requires CO2 enrichment around photocatalysts from the atmosphere. Here we demonstrate that a ...porphyrin-involved metal–organic framework (MOF), PCN-222, can selectively capture and further photoreduce CO2 with high efficiency under visible-light irradiation. Mechanistic information gleaned from ultrafast transient absorption spectroscopy (combined with time-resolved photoluminescence spectroscopy) has elucidated the relationship between the photocatalytic activity and the electron–hole separation efficiency. The presence of a deep electron trap state in PCN-222 effectively inhibits the detrimental, radiative electron–hole recombination. As a direct result, PCN-222 significantly enhances photocatalytic conversion of CO2 into formate anion compared to the corresponding porphyrin ligand itself. This work provides important insights into the design of MOF-based materials for CO2 capture and photoreduction.
In this work, three-dimensional (3D) hierarchical MoS2/polyaniline (PANI) nanoflowers were successfully fabricated via a simple hydrothermal method. The crystal structure and morphology of the ...MoS2/PANI nanoflowers were characterized by SEM, TEM, XRD, XPS, and FT-IR spectra, revealing that the nanoflowers were composed of ultrathin nanoplates which consisted of few-layered MoS2 nanosheets with enlarged interlayer distance of the (002) plane and PANI. The excellent electrochemical performance of the 3D hierarchical MoS2/PANI nanoflowers was demonstrated. Further 3D hierarchical MoS2/C nanoflowers can be prepared conveniently by annealing the MoS2/PANI sample in a N2 atmosphere at 500 °C for 4 h. The obtained MoS2/C sample exhibited more excellent electrochemical performance due to its excellent electronic conductivity resulting from the close integration of MoS2 nanosheets with carbon matrix. High reversible capacity of 888.1 mAh g–1 with the Coulombic efficiency maintained at above 90% from the first cycle were achieved at a current density of 100 mA g–1. Even at a current density of 1000 mA g–1, the reversible capacity of the MoS2/C sample could be retained at 511 mAh g–1. The excellent electrochemical performance of these two samples could be attributed to the combined action of enlarged interlayer distance of the ultrathin MoS2 nanosheets, 3D architectures, hierarchical structures, and conductive material. Thus, these 3D hierarchical nanoflowers are competent as promising anode materials for high-performance lithium-ion batteries.
Spectrum sensing is one of the crucial technologies used to solve the shortage of spectrum resources. In this letter, based on the short-time Fourier transform (STFT) and convolutional neural network ...(CNN), we firstly develop a STFT-CNN method for spectrum sensing. The proposed method exploits the time-frequency domain information of the signal samples and achieves the state of the art detection performance. In particular, the method is suitable for various primary users' signals and does not need any priori information. Besides, we also analyze the signal-to-noise ratio robustness and the generalization ability of the proposed algorithm. Finally, simulation results demonstrate that the proposed method outperforms other popular spectrum sensing methods. Notably, the proposed method can achieve a detection probability of 90.2% with a false alarm probability of 10% at SNR = -15dB.
This paper looks into a new direction in video content analysis - the representation and modeling of affective video content . The affective content of a given video clip can be defined as the ...intensity and type of feeling or emotion (both are referred to as affect) that are expected to arise in the user while watching that clip. The availability of methodologies for automatically extracting this type of video content will extend the current scope of possibilities for video indexing and retrieval. For instance, we will be able to search for the funniest or the most thrilling parts of a movie, or the most exciting events of a sport program. Furthermore, as the user may want to select a movie not only based on its genre, cast, director and story content, but also on its prevailing mood, the affective content analysis is also likely to contribute to enhancing the quality of personalizing the video delivery to the user. We propose in this paper a computational framework for affective video content representation and modeling. This framework is based on the dimensional approach to affect that is known from the field of psychophysiology. According to this approach, the affective video content can be represented as a set of points in the two-dimensional (2-D) emotion space that is characterized by the dimensions of arousal (intensity of affect) and valence (type of affect). We map the affective video content onto the 2-D emotion space by using the models that link the arousal and valence dimensions to low-level features extracted from video data. This results in the arousal and valence time curves that, either considered separately or combined into the so-called affect curve, are introduced as reliable representations of expected transitions from one feeling to another along a video, as perceived by a viewer.
Abstract
Two-dimensional (2D) metal-free ferromagnetic materials are ideal candidates to fabricate next-generation memory and logic devices, but optimization of their ferromagnetism at atomic-scale ...remains challenging. Theoretically, optimization of ferromagnetism could be achieved by inducing long-range magnetic sequence, which requires short-range exchange interactions. In this work, we propose a strategy to enhance the ferromagnetism of 2D graphite carbon nitride (g-C
3
N
4
), which is facilitating the short-range exchange interaction by introducing in-planar boron bridges. As expected, the ferromagnetism of g-C
3
N
4
was significantly enhanced after the introduction of boron bridges, consistent with theoretical calculations. Overall, boosting ferromagnetism of 2D materials by introducing bridging groups is emphasized, which could be applied to manipulate the magnetism of other materials.
Molybdenum disulfide (MoS2) has been widely studied as a potential earth‐abundant electrocatalyst for the hydrogen‐evolution reaction (HER). Defect engineering and heteroelemental doping are ...effective methods to enhance the catalytic activity in the HER, so exploring an efficient route to simultaneously achieve in‐plane vacancy engineering and elemental doping of MoS2 is necessary. In this study, Zinc, a low‐cost and moderately active metal, has been used to realize this strategy by generation of sulfur vacancies and zinc doping on MoS2 in one step. Density functional theory calculations reveal that the zinc atoms not only lower the formation energy of S vacancies, but also help to decrease ΔGH of S‐vacancy sites near the Zn atoms. At an optimal zinc‐reduced MoS2 (Zn@MoS2) example, the activated basal planes contribute to the HER activity with an overpotential of −194 mV at 10 mA cm−2 and a low Tafel slope of 78 mV/dec.
Zincing out loud: A method is proposed that uses zinc, a low‐cost and moderately active metal, to generate sulfur vacancies and realize zinc doping on MoS2 basal planes simultaneously.
Severe surface ozone pollution has become widespread in China. To protect public health, Chinese scientific communities and government agencies have striven to mitigate ozone pollution. However, ...makers of pollution mitigation policies rarely consider epidemiological research, and communication between epidemiological researchers and the government is poor. Therefore, this article reviews the current mitigation policies and the National Ambient Air Quality Standard (NAAQS) for ozone from an epidemiological perspective and proposes recommendations for researchers and policy makers on the basis of epidemiological evidence. We review current nationwide ozone control measures for mitigating ozone pollution from four dimensions: the integration of ozone and particulate matter control, ozone precursors control, ozone control in different seasons, and regional cooperation on the prevention of ozone pollution. In addition, we present environmental and epidemiological evidence and propose recommendations and discuss relevant ozone metrics and the criteria values of the NAAQS. We finally conclude that the disease burden attributable to ozone exposure in China may be underestimated and that the epidemiological research regarding the health effects of integrating ozone and particulate matter control is insufficient. Furthermore, atmospheric volatile organic compounds are severely detrimental to health, and related control policies are urgently required in China. We recommend a greater focus on winter ozone pollution and conclude that the health benefits of regional cooperation on ozone control and prevention are salient. We argue that daily average ozone concentration may be a more biologically relevant ozone metric than those currently used by the NAAQS, and accumulating epidemiological evidence supports revision of the standards. This review provides new insight for ozone mitigation policies and related epidemiological studies in China.
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•Review O3 control policies in China from an epidemiological perspective.•Highlight the possible problem in controlling O3 pollution in China.•Bridge the gap between O3 control policies in China and epidemiological studies.
This is the first commentary that reviews Chinese control policies and the NAAQS for ozone from an epidemiological perspective, and it highlights the importance of public health for air pollution control policies making.
Developing active, robust, and nonprecious electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is highly crucial and ...challenging. In this work, a facile strategy is developed for scalable fabrication of dicobalt phosphide (Co2P)–cobalt nitride (CoN) core–shell nanoparticles with double active sites encapsulated in nitrogen‐doped carbon nanotubes (Co2P/CoN‐in‐NCNTs) by straight forward pyrolysis method. Both density functional theory calculation and experimental results reveal that pyrrole nitrogen coupled with Co2P is the most active one for HER, while Co–N–C active sites existing on the interfaces between CoN and N‐doped carbon shells are responsible for the ORR and OER activity in this catalyst. Furthermore, liquid‐state and all‐solid‐state Zn–air batteries are equipped. Co2P/CoN‐in‐NCNTs show high power density as high as 194.6 mW cm−2, high gravimetric energy density of 844.5 W h kg−1, very low charge–discharge polarization, and excellent reversibility of 96 h at 5 mA cm−2 in liquid system. Moreover, the Co2P/CoN‐in‐NCNTs profiles confirm excellent activity for water splitting.
Dicobalt phosphide–cobalt nitride core–shell particles act as double active centers and are encapsulated into the channel of N‐doped carbon nanotubes by an in situ one‐step self‐assembly and confined pyrolysis approach, which is demonstrated to afford trifunctional performance in catalyzing hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction for Zn–air batteries and water splitting.
As a remarkable class of plasmonic materials, two dimensional (2D) semiconductor compounds have attracted attention owing to their controlled manipulation of plasmon resonances in the visible light ...spectrum, which outperforms conventional noble metals. However, tuning of plasmonic resonances for 2D semiconductors remains challenging. Herein, we design a novel method to obtain amorphous molybdenum oxide (MoO3) nanosheets, in which it combines the oxidation of MoS2 and subsequent supercritical CO2‐treatment, which is a crucial step for the achievement of amorphous structure of MoO3. Upon illumination, hydrogen‐doped MoO3 exhibits tuned surface plasmon resonances in the visible and near‐IR regions. Moreover, a unique behavior of the amorphous MoO3 nanosheets has been found in an optical biosensing system; there is an optimum plasmon resonance after incubation with different BSA concentrations, suggesting a tunable plasmonic device in the near future.
Better off amorphous: Amorphous MoO3 nanosheets were fabricated through the oxidation of MoS2 and subsequent treatment with supercritical CO2. Hydrogen‐doped MoO3 formed via a facile solar‐light‐driven process exhibits surface plasmon resonances (SPR) in the visible and NIR regions. In an optical biosensing system the SPR correlates with bovine serum albumin concentrations.
During the preparation of atomically dispersed Fe–N–C catalysts, it is difficult to avoid the formation of iron‐carbide‐containing iron clusters (“FexC/Fe”), along with the desired carbon matrix ...containing dispersed FeNx sites. As a result, an uncertain amount of the oxygen reduction reaction (ORR) occurs, making it difficult to maximize the catalytic efficiency. Herein, sulfuration is used to boost the activity of FexC/Fe, forming an improved system, “FeNC–S–FexC/Fe”, for catalysis involving oxygen. Various spectroscopic techniques are used to define the composition of the active sites, which include Fe–S bonds at the interface of the now‐S‐doped carbon matrix and the FexC/Fe clusters. In addition to outstanding activity in basic media, FeNC–S–FexC/Fe exhibits improved ORR activity and durability in acidic media; its half‐wave potential of 0.821 V outperforms the commercial Pt/C catalyst (20%), and its activity does not decay even after 10 000 cycles. Interestingly, the catalytic activity for the oxygen evolution reaction (OER) simultaneously improves. Thus, FeNC–S–FexC/Fe can be used as a high‐performance bifunctional catalyst in Zn–air batteries. Theoretical calculations and control experiments show that the original FeNx active centers are enhanced by the FexC/Fe clusters and the Fe–S and C–S–C bonds.
An “FeNC–S–FexC/Fe” bifunctional catalyst for the oxygen reduction and oxygen evolution reactions is successfully incorporated in liquid and flexible solid‐state zinc–air batteries. Based on an atomically dispersed Fe–N–C catalyst where the FeNx sites are distributed throughout a carbon framework and iron carbide cluster impurities are unavoidable, sulfuration is used to incorporate S bonds that enhance the activity of the catalytic centers in an acidic medium.
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