Spectroscopic Identification of Active Sites of Oxygen-Doped Carbon for Selective Oxygen Reduction to Hydrogen Peroxide

The electrochemical synthesis of hydrogen peroxide (H₂O₂) via a two-electron (2 e⁻) oxygen reduction reaction (ORR) process provides a promising alternative to replace the energy-intensive anthraquinone process. Herein, we develop a facile template-protected strategy to synthesize a highly active quinone-rich porous carbon catalyst for H₂O₂ electrochemical production. The optimized PCC₉₀₀ material exhibits remarkable activity and selectivity, of which the onset potential reaches 0.83 V vs. reversible hydrogen electrode in 0.1 M KOH and the H₂O₂ selectivity is over 95 % in a wide potential range. Comprehensive synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with electrocatalytic characterizations reveals the positive correlation between quinone content and 2 e⁻ ORR performance. The effectiveness of chair-form quinone groups as the most efficient active sites is highlighted by the molecule-mimic strategy and theoretical analysis.     

考虑惯性效应的渗流方程及相关阻力标度律

本文基于体积平均法推导得到了多孔介质中考虑惯性效应时的局部线化宏观流动方程,由此可以递推得到较大雷诺数Re 时Navier-Stokes 方程的解,从而避免了直接求解Navier-Stokes 方程所带来的计算成本高和计算稳定性差的问题．针对正方形周期排列模型的算例表明,平均速度方向与宏观压力梯度方向并不总是一致,一般情况下,随着Re 增大,二者差异也会增大．当固定平均速度方向v ? 时,压差阻力在较大的Re 范围内存在标度律,标度指数约为3．该标度指数与弱惯性区域标度指数一致,但弱惯性区域Re 范围仅为0相似文献   

Multi-parties Controlled Dense Coding via Maximal Slice States and the Physical Realization Using the Optical Elements

An efficient scheme for controlled dense coding is presented with the aid of the introduction of auxiliary particles, appropriate local unitary operations and measurement basis. In this proposal, the four-qubits maximal slice state, which belongs to partially entangled states, is used as quantum channel. The concrete implementation procedures for our scheme with one sender, one receiver and two controllers are given in detail, and the average transmitted classical information from the sender to the receiver is calculated. Additionally, the physical realization of this proposal is discussed based on the optical elements.     

The Dirac Equation on Metrics of Eguchi-Hanson Type Ⅱ with Negative Constant Scalar Curvature

On metrics of Eguchi-Hanson type Ⅱ with negative constant Ricci curvatures,the authors show that there is no nontrivial Killing spinor.On metrics of Eguchi-Hanson type Ⅱ with negative constant scalar curvature,they show that there is no nontrivial L^p eigenspinor for 0

2 eigenspinor if either the eigenvalue has trivial real part or the eigenvalue is real,the eigenspinor is isotropic and the parameter η...     

气相色谱-三重四极杆串联质谱法同时测定焙烤食品中28种邻苯二甲酸酯

建立了气相色谱-三重四极杆串联质谱(GC-MS/MS)同时测定焙烤食品中28种邻苯二甲酸酯类(PAEs)物质残留量的方法。样品经乙酸乙酯超声提取,用中性氧化铝净化后进行检测。经程序升温气化进样口(PTV)不分流进样,TR-5MS色谱柱(30 m×0.25 mm×0.25 μ m)进行色谱分离,在选择反应监测(SRM)模式下进行质谱扫描,采用内标法定量。28种邻苯二甲酸酯的线性范围,除邻苯二甲酸二异壬酯(DINP)在0.1~20 mg/L外,其余27种均在0.05~10 mg/L范围内呈线性关系,相关系数r²≥0.9962。方法检出限范围为0.1~9.8 μ g/kg,方法定量限范围为0.4~32.6 μ g/kg。分别在面包、饼干、糕点、馅料4类样品中进行低、中、高3个添加水平的加标回收试验,加标回收率为81.0%~117%,相对标准偏差(RSD, n=6)为1.3%~13.6%。用建立的方法测定了不同焙烤食品中塑化剂的含量。该方法操作简单,可靠性高,适用范围广,适用于焙烤食品中邻苯二甲酸酯类物质残留量的检测。     

脑出血与脑梗塞患者脑脊液中微量元素含量的比较及意义

为比较脑出血和脑梗塞后脑脊液中5种微量元素的变化,用等离子体发射光谱仪测定了两种脑卒中患者脑脊液中的Zn、Cu、Fe、P、Ca含量。结果表明,脑出血组脑脊液中5种微量元素含量均高于脑梗塞组。提示脑出血在急性期对脑组织的破坏可能比脑梗塞严重;脑出血对神经细胞兴奋性的升高可能较脑梗塞严重。     

Highly shape-selective Zn-P/HZSM-5 zeolite catalyst for methanol conversion to light aromatics

A highly shape-selective and relatively long-lifetime HZSM-5-based catalyst (Zn-2P/HZSM-5) was prepared by chemical modification with both ZnSiF₆·6H₂O and H₃PO₄ solution. The phosphoric acid modification could effectively modulate the Brønsted acid strength of the HZSM-5 catalyst, which promotes the oligomerization, alkylation, cyclization, and hydrogen transfer reactions. The introduction of Zn-Lewis acid sites significantly improved the dehydroaromatization of higher olefins. All of these were very beneficial for the generation of BTX (i.e. benzene, toluene, and xylene) hydrocarbons in aromatization of methanol. The coke amount and the average rate of coke formation decreased over the Zn-2P/HZSM-5 catalysts, which may largely be ascribed to its lower strong acid sites and lower outer surface acidity. The catalytic performance of methanol aromatization showed that the Zn-2P/HZSM-5 catalyst exhibited the highest BTX selectivity of about 46.76% and the longest catalytic lifetime of about 498 h at T = 400 °C, P = 0.1 MPa, and weight hourly space velocity = 0.7 h⁻¹.     

Surface passivation effects in silicon nanowires

We report first-principles simulation results for the electronic band structure of Si nanowires (SiNWs) aligned along the ?100? and ?110? directions with H, OH, and CH₃ substituents passivating the surfaces. The ?100? wires studied have {110} faces and square cross-sections with diameters up to 1.73 nm, while the ?110? wires have {111} faces and diamond cross-sections with diameters up to 1.46 nm. We found that passivation using OH or CH₃ groups reduced the band gaps compared to H-terminated ?100? SiNWs, and passivation using CH₃ groups produced systems with indirect gaps for all ?100? SiNWs studied. All band gaps were direct in the ?110? SiNWs independent of passivation. The near-gap orbitals are greatly affected by the different substituents. We also found that the carrier effective masses of ?100? SiNWs are sensitive to the diameter and passivation, while those of ?110? SiNWs are not.     

0D–1D hybrid nanoarchitectonics: tailored design of FeCo@N–C yolk–shell nanoreactors with dual sites for excellent Fenton-like catalysis

Heterogeneous Fenton-like processes are very promising methods of treating organic pollutants through the generation of reactive oxygen containing radicals. Herein, we report novel 0D–1D hybrid nanoarchitectonics (necklace-like structures) consisting of FeCo@N–C yolk–shell nanoreactors as advanced catalysts for Fenton-like reactions. Each FeCo@N–C unit possesses a yolk–shell structure like a nanoreactor, which can accelerate the diffusion of reactive oxygen species and guard the active sites of FeCo. Furthermore, all the nanoreactors are threaded along carbon fibers, providing a highway for electron transport. FeCo@N–C nano-necklaces thereby exhibit excellent performance for pollutant removal via activation of peroxymonosulfate, achieving 100% bisphenol A (k = 0.8308 min⁻¹) degradation in 10 min with good cycling stability. The experiments and density-functional theory calculations reveal that FeCo dual sites are beneficial for activation of O–O, which is crucial for enhancing Fenton-like processes.

Novel 0D–1D hybrid nanoarchitectonics consisting of FeCo@N–C yolk–shell nanoreactors are developed for Fenton-like reaction. With the multilevel advantages of this design, FeCo@N–C nano-necklaces exhibit excellent performance for BPA removal.

Advanced oxidation processes (AOPs) are one of the most promising strategies to eliminate organic contaminants, sustainably generating reactive oxygen species (ROS) to ideally destroy all non-biodegradable, recalcitrant, toxic, or membrane-permeable organic impurities.^1–4 Among these AOPs, sulfate radical (SO₄˙⁻)-based Fenton-like processes have gained increasing attention as a water treatment strategy because of the strong oxidation potential of SO₄˙⁻ (3.1 V vs. normal hydrogen electrode) at wider pH ranges. SO₄˙⁻ is mainly produced by physical or chemical methods for activation of persulfate salts, such as peroxymonosulfate (PMS) and persulfate.^5–9 Over the past two decades, heterogeneous catalysis has emerged as the most effective approach to water treatment, with much effort dedicated to developing better catalysts, including transition metal-based and carbonaceous materials.^10,11 Unfortunately, most metal-based catalysts suffer from leaching of toxic metal ions, which can thwart their practical application,^12,13 and although carbonaceous catalysts produce no secondary pollution, their cycle performance is always depressed.¹⁴ There is therefore an urgent need to find robust catalysts with adequate activity and stability for Fenton-like processes.To achieve superior performance, an ideal Fenton-like catalyst should contain oxidants with favorably reactive centers for cleavage of peroxyl bonds (O–O), have structure optimized for target pollutant attraction, and have chainmail to protect the vulnerable active sites for long periods.^15–17 Recent studies have demonstrated Co–N–C active sites prefer to activate the O–O of PMS.¹⁸ Furthermore, introducing Fe-doping into the Co–N–C system not only suppresses Co²⁺ leaching, but also modulates the pyrrolic-N content, which is the adsorption site for capture of bisphenol A (BPA).¹⁹ We previously discovered that Co@C yolk–shell nanoreactors could enhance the catalytic activity because of the confinement effect in the nano-spaces between the core and shell, while the carbon shell acted like a chainmail protecting the Co active sites, keeping them highly reactive after five cycles.^20,21Combining different kinds of materials to generate novel hybrid material interfaces can enable the creation of new kinds of chemical and physical functionalities that do not currently exist. However, one cannot simply mix these materials in an uncontrolled manner, because the ensemble of interfaces created by random mixing tends to favour thermodynamically stable interfaces that are functionally less active. Therefore, to prepare new materials with high functionality, it is necessary to carefully control the hybridization of components in interfacial regions with nanometric or atomic precision. By further hybridization of different components e.g., zero to one dimension (0D–1D) hybrid structures, we can prepare the structure to increase not only the specific surface area but also the interfacial region between different materials.In this work, we report novel 0D–1D hybrid nanoarchitectonics (necklace-like structures) consisting of FeCo@N–C yolk–shell nanoreactors as a PMS activator for Fenton-like processes. This catalyst has multilevel advantages: (i) each FeCo@N–C unit is a well-formed yolk–shell nanoreactor, which can guarantee sufficient contact of reactants and active sites, as well as defend them for good durability; (ii) all single nanoreactors are threaded along the carbon fibers, providing a highway for electron transport; and (iii) all the carbon fibers constructed into a thin film with macroscopic structure, which overcomes the complex recyclability of powder catalysts. Benefiting from favorable composition and unique structure, the FeCo@N–C catalyst delivers excellent performance for BPA removal via activation of PMS accompanied with good stability.The synthesis processes of necklace-like nanoarchitecture containing FeCo@N–C yolk–shell nanoreactors are illustrated in Fig. 1a. First, uniform Fe–Co Prussian blue analogue (Fe–Co PBA) nanocubes with an average size of 800–900 nm (Fig. 1b) are encapsulated in polyacrylonitrile (PAN) nanofibers by electrospinning. The obtained necklace-like FeCo PBA–PAN fibers (Fig. 1c) are then pyrolyzed at 800 °C in N₂ atmosphere to produce FeCo@N–C nano-necklaces. The scanning electron microscopy (SEM) image (Fig. 1d) of the FeCo@N–C shows this necklace-like morphology with its large aspect ratio, with the FeCo@N–C particles strung along the PAN-derived carbon fibers. A broken particle (Fig. 1e) shows that the FeCo@N–C has a yolk–shell architecture, which is also identified by transmission electron microscopy (TEM). Fig. 1f and g show the well-defined space between the inner yolk and outer shell, which is attributed to the volume shrinkage of the original Fe–Co PBAs. During pyrolysis, Fe–Co PBA is reduced to FeCo (inner yolk) and PAN is carbonized (outer carbon shell), resulting in the unique necklace-like nanoarchitecture.^22–24 The high-resolution TEM in Fig. 1h shows a lattice fringe of 0.20 nm, which matches well with the (110) plane of FeCo alloy.²⁵ The scanning transmission electron microscopy (STEM) image (Fig. 1i) and corresponding elemental map (Fig. 1j) indicate that FeCo nanocrystals are well distributed in the inner core with some small FeCo nanocrystals located on external carbon shells. Furthermore, the control samples of Fe@N–C and Co@N–C nano-necklaces, prepared by only replacing the Fe–Co PBA nanocubes with Fe–Fe PB and Co–Co PBA (Fig. S1^†), also demonstrate the versatility of this synthetic strategy. The formation of hierarchical porous structure, beneficial to the PMS transportation on the surface of catalysts, could be determined by N₂ adsorption–desorption isotherms and corresponding pore volume analysis (Fig. S2 and Table S1^†).Open in a separate windowFig. 1(a) Preparation of FeCo@N–C necklace-like nanoarchitecture. SEM images of (b) Fe–Co PBA cubic particles and (c) the electrospun FeCo PBA–PAN fibers. (d and e) SEM, (f and g) TEM, and (h) high-resolution TEM images of FeCo@N–C nano-necklaces. (i) STEM and (j) the corresponding elemental mappings of C, N, Fe, and Co.The X-ray diffraction patterns of the as-prepared products are depicted in Fig. S3,^† with one prominent diffraction peak centered at 44.8° corresponding to the (110) lattice plane of FeCo alloy. All the products also have a characteristic signal at 26°, implying that graphite carbon is formed during pyrolysis. Raman spectroscopy further analyzed the crystal structures and defects of the FeCo@N–C nano-necklaces (Fig. S4^†), where peaks found at 1349 cm⁻¹ and 1585 cm⁻¹ index the disordered (D band) and graphitic carbon (G band), respectively.²⁶ X-ray photoelectron spectroscopy investigated the composition and valence band spectra of FeCo@N–C nano-necklaces. The survey spectrum (Fig. S5a^†) reveals the presence of Fe (1.4%), Co (1.2%), C (86.4%), N (4.5%), and O (6.5%) in the composite. The high-resolution N 1s spectrum (Fig. S5b^†) exhibits broad peaks at 398.1, 401.1, and 407.4 eV, corresponding to the pyridinic-N, graphitic-N, and σ* excitation of C–N, respectively.²⁷ The high-resolution Fe 2p spectrum (Fig. S5c^†) shows a broad peak at 707.4 eV, attributed to Fe⁰. Similarly, the 777.5 eV peak observed in the Co 2p spectrum (Fig. S5d^†) corresponds to Co⁰, implying that FeCo dual sites have formed.²⁸ The oxidation state of these sites was investigated by ⁵⁷Fe Mössbauer spectroscopy, which found a sextet in the Mössbauer spectrum of the FeCo@N–C nano-necklaces attributed to FeCo dual sites (Fig. 2a and Table S2^†).²⁹ The coordination environment of the FeCo dual sites was also verified by X-ray absorption fine structure (XAFS) spectroscopy. Fig. 2b shows that the X-ray absorption near-edge structure (XANES) spectra of the Fe K-edge, which demonstrates a similar near-edge structure to that of Fe foil, illustrating that the main valence state of Fe in FeCo@N–C nano-necklaces is Fe⁰. Furthermore, the extended-XAFS (EXAFS) spectra (Fig. 2c) displays a peak at 1.7 Å, which is ascribed to the Fe–N bond, and a remarkable peak at approximately 2.25 Å corresponding to the metal–metal band.^10,30 The Co K-edge and EXAFS spectra (Fig. S6^†) also confirm the presence of Co–N and the metal–metal band. These results provide a potential structure of the FeCo dual sites in the FeCo@N–C nano-necklaces, as illustrated in Fig. 2d.Open in a separate windowFig. 2(a) ⁵⁷Fe Mössbauer spectra of FeCo@N–C nano-necklaces at 298 K. (b) Fe K-edge XANES spectra of FeCo@N–C nano-necklaces and Fe foil. (c) Corresponding Fourier transformed k³-weighted of the EXAFS spectra for Fe K-edge. (d) Possible structure of the FeCo dual sites.This dual-metal center and necklace-like structure may be beneficial to enhance catalytic performance. Fig. 3a shows the Fenton-like performance for BPA degradation compared to Fe@N–C nano-necklaces, Co@N–C nano-necklaces, and FeCo@N–C particles (Fe–Co PBA directly carbonized without electrospinning). Here, the FeCo@N–C nano-necklaces display a higher catalytic performance, with BPA completely removed in 7 min. To clearly compare their catalytic behavior, the kinetics of BPA degradation was fitted by the first-order reaction. As shown in Fig. 3b, FeCo@N–C nano-necklaces exhibit the highest apparent rate constant (k = 0.83 min⁻¹), which is approximately 6.4, 2.6, and 1.2 times that of FeCo@N–C particles, Fe@N–C nano-necklaces, and Co@N–C nano-necklaces, respectively. The significantly enhanced performance of FeCo@N–C nano-necklaces suggests that the FeCo dual sites and necklace-like nanoarchitecture are crucial. Furthermore, the concentration of BPA and PMS in the solution is higher than that in yolk–shell nanoreactor, resulting a concentration gradient which helps to accelerate the diffusion rates of reactants (Fig. 3c).^31,32 For these nano-necklaces, the carbon shell acts like a chainmail protecting the FeCo active sites from attack by molecules and ions, and all the nanoreactors are threaded along the carbon fibers, providing a highway for electron transport, which is important for SO₄˙⁻ generation (SO₄˙⁻ production as eqn, HSO₅⁻ + e⁻ → SO₄˙⁻ + OH⁻). Electrochemical impedance spectroscopy further confirms the good conductivity of the FeCo@N–C nano-necklaces (Fig. 3d). In addition, the concentration of metal-ion leaching and cycling performance (Fig. 3e and f) reveal the high reusability of FeCo@N–C nano-necklaces, with 95% BPA removal in 20 min after five cycles, which is also proved by the SEM and TEM characterization (Fig. S7^†). The effect of other reaction parameters on the BPA degradation, such as pH, reaction temperature, PMS or catalysts dosage, and common anions, were investigated in detail (Fig. S8–S11^†). All the results demonstrate that FeCo@N–C nano-necklaces deliver a better performance for PMS catalysis. In addition, the turnover frequency (TOF) value of FeCo@N–C nano-necklaces is 5.5 min⁻¹ for BPA degradation, which is higher than many previously reported catalysts (detailed catalytic performance comparison as shown in Table S3^†).Open in a separate windowFig. 3(a) BPA degradation efficiency in different reaction systems and (b) the corresponding reaction rate constants. (c) Schematic illustration of PMS activation in FeCo@N–C nano-necklaces. (d) Nyquist plots of the catalysts. (e) The metal leaching in different reaction systems. (f) Cycling performance of FeCo@N–C nano-necklaces for BPA removal. Reaction conditions: [catalyst] = 0.15 g L⁻¹, [BPA] = 20 mg L⁻¹, [PMS] = 0.5 g L⁻¹, T = 298 K, and initial pH = 7.0.To examine the enhanced catalytic activity, radical quenching experiments were conducted. As shown in Fig. 4a, when NaN₃ is added to the reaction solution as a scavenger for ¹O₂, there is no significant reduction of BPA decomposition, implying that non-radicals are not the dominant reactive species. By comparison, when tert-butanol (TBA) (radical scavenger for ˙OH) is added, there is a slight (2.8%) decrease in BPA removal. However, if methanol (radical scavenger for SO₄˙⁻ and ˙OH) is added, the efficiency of BPA degradation declines by up to 59.2%, indicating that the major radicals generated from the PMS activation are SO₄˙⁻;³³ the presence of these radicals is also verified by electron paramagnetic resonance (EPR) (Fig. 4b). Furthermore, the significant inhibition ratio can be observed when KI (quencher for the surface) is added, demonstrating that BPA degradation is mainly attributed to reactions with SO₄˙⁻, which is produced by a surface catalytic process.³⁴Open in a separate windowFig. 4(a) Effects of the radical scavengers on BPA degradation. (b) EPR spectra of SO₄˙⁻ and ˙OH. (c) The energy profiles of PMS on FeCo@N–C nano-necklaces surface. (d) Optimized configurations of PMS adsorbed on FeCo@N–C nano-necklaces.Density-functional theory was applied to calculate the surface energy of PMS activation at FeCo dual sites (Fig. 4c, d and S12^†). The dissociation barrier of PMS into SO₄˙⁻ and OH⁻ is −2.25 eV, which is much lower than that on an Fe or Co single site, suggesting that cleavage of O–O bonds of PMS occurs more easily on FeCo dual sites. This is because FeCo dual sites provide two anchoring sites for the dissociated O atoms, leading to more efficient activation of O–O. The FeCo@N–C nano-necklaces can reduce the energy barrier of O–O bond breaking, which results in high activity for PMS activation and thus high productivity of SO₄˙⁻.     

胃癌和胃溃疡患者发中微量元素变化的研究

报道了湛江市胃癌患者发中微量元素的变化信息。胃癌患者与正常人相比，Zn、Zn/Cu、Mg、Ca显著降低（P＜0．05）；胃癌与胃溃疡患者相比，Zn、Zn/Cu、Mg均呈显著降低（P＜0．05）。因此，发中微量元素化学信息的变化，可作为本地区胃癌的辅助诊断和胃癌与胃溃疡的区别辅助诊断的依据之一。