Designing N-Confused Metalloporphyrin-Based Covalent Organic Frameworks for Enhanced Electrocatalytic Carbon Dioxide Reduction

Electrochemical conversion of carbon dioxide (CO₂) into value-added products is promising to alleviate greenhouse gas emission and energy demands. Metalloporphyrin-based covalent organic frameworks (MN₄-Por-COFs) provide a platform for rational design of electrocatalyst for CO₂ reduction reaction (CO₂RR). Herein, through systematic quantum-chemical studies, the N-confused metallo-Por-COFs are reported as novel catalysts for CO₂RR. For MN₄-Por-COFs, among the ten 3d metals, M = Co/Cr stands out in catalyzing CO₂RR to CO or HCOOH; hence, N-confused Por-COFs with Co/CrN₃C₁ and Co/CrN₂C₂ centers are designed. Calculations indicate CoN_xC_y-Por-COFs exhibit lower limiting potential (−0.76 and -0.60 V) for CO₂-to-CO reduction than its parent CoN₄-Por-COFs (−0.89 V) and make it feasible to yield deep-reduction degree C₁ products CH₃OH and CH₄. Electronic structure analysis reveals that substituting CoN₄ to CoN₃C₁/CoN₂C₂ increases the electron density on Co-atom and raises the d-band center, thus stabilizing the key intermediates of the potential determining step and lowering the limiting potential. For similar reason, changing the core from CrN₄ to CrN₃C₁/CrN₂C₂ lowers the limiting potential for CO₂-to-HCOOH reduction. This work predicts N-confused Co/CrN_xC_y-Por-COFs to be high-performance CO₂RR catalyst candidates. Inspiringly, as a proof-of-concept study, it provides an alternative strategy for coordination regulation and theoretical guidelines for rational design of catalysts.     

Synthesis of ultrafine single-component oxide particles by the spray-ICP technique

Ultrafine oxide particles were synthesized by introducing aqueous solutions of metal salts into a high-temperature r.f. inductively coupled plasma (the spray-ICP technique). The particles synthesized were spherical for ZrO₂, Y₂O₃, Sm₂O₃, La₂O₃, δ-Al₂O₃, TiO₂ (anatase), β-Bi₂O₃ and CuO, plate-like for Nd₃O₂, Cr₂O₃ and Pr₂O₃, polyhedral for PrO₂, CeO₂ and γ-Fe₂O₃, cubical for NiO, MgO, CaO, Co₃O₄ and Mn₃O₄, bar-like for SnO₂ and ZnO, and foil-like for β-PbO and MoO₃. The products of the alkaline earth group except for magnesium, were hydroxides and/or carbonates, spoiled by atmospheric H₂O and/or CO₂. The particle morphology suggests that particle growth is controlled predominantly by the gas-solid reaction occurring on the surface of nuclei condensed from the gas phase. Some of the oxides revealed a particle morphology characteristic of their crystal structures.     

Devitrification of rapidly quenched Al-Cu-Ti amorphous alloys

X-ray diffraction, transmission electron microscopy and differential scanning calorimetry were carried out to study the transformation from amorphous to icosahedral/crystalline phases in the rapidly quenched Al₅₀Cu₄₅Ti₅ and Al₄₅Cu₄₅Ti₁₀ alloys. In the present investigation, we have studied the formation and stability of amorphous phase in Al₅₀Cu₄₅Ti₅and Al₄₅Cu₄₅Ti₁₀ rapidly quenched alloys. The DSC curve shows a broad complex type of exothermic overlapping peaks (288- 550†C) for Al₅₀Cu₄₅Ti₅ and a well defined peak around 373†C for Al₄₅Cu₄₅Ti₁₀ alloy. In the case of Al₅₀Cu₄₅Ti₅ alloy amorphous to icosahedral phase transformation has been observed after annealing at 280†C for 73 h. Large dendritic growth of icosahedral phase along with α-Al phase has been found. Annealing of Al₅₀Cu₄₅Ti₅ alloy at 400†C for 8 h results in formation of Al₃Ti type phase. Al₄₅Cu₄₅Ti₁₀ amorphous alloy is more stable in comparison to Al₅₀Cu₄₅Ti₅ alloy and after annealing at 400†C for 8 h it also transforms to Al₃Ti type phase. However, this alloy does not show amorphous to icosahedral phase transformation.     

Flux growth of some complex oxide materials

This paper describes the preparation of the following complex oxide crystals which have not previously been grown by the flux method: FeNbO₄, MnWO₄, CoWO₄, NiWO₄, RMn₂O₅ (R = Er to Sm, and Y), RMnO₃ (R = Er to Gd), LaOCl, La₂Ti₂O₇₁, Bi₂Sn₂O₇, and PbTiP₂O₈. Single crystal X-ray diffraction data are reported for the latter material, the preparation of which has not previously been reported, and for La₂Ti₂O₇ and Bi₂Sn₂O₇₁, for which only powder data were previously available. Improved methods for the growth of Mn₃O₄, LaCoO₃, RPO₄ (R = Yb to Gd), RCrO₃ (R = Lu, Yb), ErOF and NaNbO₃ are also reported.     

城市高架桥爆破拆除起爆网路可靠性研究

本文针对城市高架桥爆破拆除的长距离、长延时,目前只能采用非电起爆网路进行起爆的现状,研究了多发并联起爆网路的接力点雷管延期特性,提出了并联后的接力点起爆时间期望值的简易计算公式。针对不同规模的非电起爆网路提出了相应的可靠度标准,研发了既可保证高架桥倾倒过程不发生侧翻又能提高接力点起爆可靠度并可无限分段的复式交叉接力起爆网路,并推导了其起爆可靠度计算公式。相关成果为高架桥拆除爆破起爆网路设计提供了科学依据。     

Tuning the temperature coefficient of resonant frequency for 8-layer twinned hexagonal perovskite Ba<Subscript>8</Subscript>ZnTa<Subscript>6</Subscript>O<Subscript>24</Subscript> ceramics

High-Q dielectric materials ilmenite MgTiO₃, columbite MgNb₂O₆ and cubic perovskite Ba₃NiTa₂O₉ with negative temperature coefficient of resonant frequency (τ _f ) were selected as candidates for compensating the τ _f of hexagonal perovskite Ba₈ZnTa₆O₂₄. X-ray diffraction data shows that Ba₈ZnTa₆O₂₄ coexists with Ba₃NiTa₂O₉ but is not compatible with MgTiO₃ and MgNb₂O₆ at high temperature. The τ _f for the mixed hexagonal/cubic perovskite Ba₈ZnTa₆O₂₄–Ba₃NiTa₂O₉ system is tunable via the temperature compensation effect and its quality factor may be improved via annealing the ceramics at high temperature to enhance the cation ordering in the cubic component. Permittivity ε _r  ~ 22–25, Q×f > 30,000 GHz and tunable τ _f within ±10 ppm/°C were achieved in the range of about 50–80 wt% Ba₃NiTa₂O₉ for the hexagonal/cubic perovskite composite Ba₈ZnTa₆O₂₄–Ba₃NiTa₂O₉ ceramics, which is suitable for the application as dielectric resonators and filters.     

Dielectric properties of K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3

Dielectric constant (ɛ), dielectric loss (tan δ) and conductivity (σ) for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ have been measured over the frequency range 100 Hz — 100 kHz and in temperature range 30°C — 400°C. The values of static dielectric constant at room temperature are 7.67 and 4.80 for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively. The plots of log σ against reciprocal temperature at different frequencies of these samples merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0.67 eV and 1.98 eV for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively.     

Comparison of the magnetotransport properties between (La0.7Pb0.3MnO3)1−xAgx and (La0.7Pb0.3MnO3)1−x(Fe2O3)x composites

Ceramic composites of (La_0.7Pb_0.3MnO₃)_1−xAg_x and (La_0.7Pb_0.3MnO₃)_1−x(Fe₂O₃)_x are prepared by using chemical and solid-sate sintering route. The structural and magnetotransport properties are studied for these composites. Ferromagnetism is gradually suppressed with the increase of Ag or Fe₂O₃ mole percentage for both systems. The resistivity decreases significantly for (La_0.7Pb_0.3MnO₃)_1−xAg_x while resistivity increases dramatically for (La_0.7Pb_0.3MnO₃)_1−x(Fe₂O₃)_x. It is suggested that the introduction of Ag into the niche of grain boundaries forms artificial conducting network and improve the carriers to transport. Contrarily, the Fe₂O₃ in (La_0.7Pb_0.3MnO₃)_1−x(Fe₂O₃)_x composite acts as a separation layer between two grains and forms the artificial tunneling junction. However, the enhancement of magnetoresistance has been observed for both systems.     

Charge Transfer Modulation in Vanadium-Doped WS2/Bi2O2Se Heterostructures

The field of photovoltaics is revolutionized in recent years by the development of two–dimensional (2D) type-II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)-doped WS₂ is investigated, hereafter labeled V-WS₂, in combination with air-stable Bi₂O₂Se for use in high-performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS₂/Bi₂O₂Se, 0.4 at.% V-WS₂/Bi₂O₂Se, and 2 at.% V-WS₂/Bi₂O₂Se, respectively, indicating a superior charge transfer in V-WS₂/Bi₂O₂Se compared to pristine WS₂/Bi₂O₂Se. The exciton binding energies for WS₂/Bi₂O₂Se, 0.4 at.% V-WS₂/Bi₂O₂Se and 2 at.% V-WS₂/Bi₂O₂Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS₂. These findings confirm that by incorporating V-doped WS₂, charge transfer in WS₂/Bi₂O₂Se heterostructures can be tuned, providing a novel light-harvesting technique for the development of the next generation of photovoltaic devices based on V-doped transition metal dichalcogenides (TMDCs)/Bi₂O₂Se.     

Synthesis of Ti3Si0.8Al0.4C1.8 solid solution from Ti-Si-Al-C powder mixture

In this study, free Ti/Si/Al/C powder mixtures with molar ratios of 3:0.8:0.4:1.8 were heated in argon with various schedules, in order to reveal the possibility for the synthesis of high Ti₃Si_0.8Al_0.4C_1.8 content powder. X-ray diffraction (XRD) was used for the evaluation of phase identities of the powder after different treatments. Scanning electron microscopy (SEM) was used to observe the morphology of the Ti₃Si_0.8Al_0.4C_1.8 solid solution. XRD results showed that predominantly single phase samples of Ti₃Si_0.8Al_0.4C_1.8 were prepared after heating at 1450 °C for 5 min in argon and the lattice parameters of Ti₃Si_0.8Al_0.4C_1.8 lay between those of Ti₃SiC₂ and Ti₃AlC₂. SEM observation showed that the grains of Ti₃Si_0.8Al_0.4C_1.8 solid solution exhibited a lamellar shape, which is a characteristic feature of Ti₃SiC₂ and Ti₃AlC₂.     

Characterisation of high purity rare-earth oxides by x-ray fluorescence methods

X-ray fluorescence methods for the determination of individual rare earth impurities in high purity rare earth oxidesviz., Y₂O₃, La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃ and Er₂O₃ have been developed in our laboratory. The samples are converted to oxalate form and double-layer pellets are prepared using boric acid as binding material. A semiautomatic x-ray spectrometer is used for the analyses. Choice of instrumental parameters and analysis lines is discussed. The determination range varies from 0.005% to 1.0% for most elements with good precision and adequate accuracy.     

Mass Spectrometric Study of Photoionization. I. Apparatus and Initial Observations on Acetylene,Acetylene-d2, Benzene,and Benzene-d6

A windowless vacuum ultraviolet monochromator and mass spectrometer are combined for the study of photoionization processes in the energy range 2000 to 600 A (6 to 21 eV). Details of the apparatus and techniques of operation are given and results are reported for an initial study of acetylene, acetylene-d₂, benzene, and benzene-d₆. Ionization energies of 11.406 and 11.416 eV are obtained for the 1π_u electron of C₂H₂ and C₂D₂, respectively. Vibrational levels of the ground state of the ion are observed with quantum intervals of 1855 cm⁻¹(C₂H₂) and 1775 cm⁻¹(C₂D₂). Ionization energies for the e_1g(π) electron of C₆H₆ and C₆D₆ are determined to be 9.24₂ and 9.24₅ eV, respectively. Quantum intervals for vibrational levels of the ground state ions are apparently equal for the two isotopic molecules and estimated to be 800 cm⁻¹. A second onset of ionization is observed at 11.5₃ eV for C₆H₆ and at 11.5₉ eV for C₆D₆. Results agree well with spectroscopic data.     

Cu7.2S4 nanosheets decorated on the {3 3 2} high index facets of Cu2O with controllable oxygen defects and enhanced photocatalytic activity

The heterostructure of Cu_7.2S₄ nanosheets/trisoctahedron Cu₂O were successfully constructed on the {3 3 2} high-index facets of Cu₂O. The results show that oxygen defects amount of the Cu_7.2S₄/Cu₂O samples are closely related to the thickness of Cu_7.2S₄ nanosheets. Compared with the unmodified cuprous oxide and the Cu_7.2S₄/Cu₂O modified with thick Cu_7.2S₄ nanosheets, the Cu_7.2S₄/Cu₂O grafted with 10 nm thickness of Cu_7.2S₄ show higher oxygen defects content and photocatalytic performance for MO decoloration. UV–VIS DRS and PL detection show that the Cu_7.2S₄ nanosheets grafting on Cu₂O with high-index facets accelerates the charge carrier separation, which results in an elevated degradation properties for MO.     

Influence of different materials on the microstructure and optical band gap of α-Fe2O3 nanoparticles

Composites of hematite (α-Fe₂O₃) nanoparticles with different materials (NiO, TiO₂, MnO₂ and Bi₂O₃) were synthesized. Effects of different materials on the microstructure and optical band gap of α-Fe₂O₃ nanoparticles were studied. Crystallite size and strain analysis indicated that the pure α-Fe₂O₃ nanoparticles were influenced by the presence of different materials in the composite sample. Crystallite size and strain estimated for all the samples followed opposite trends. However, the value of direct band gap decreased from ～2.67 eV for the pure α-Fe₂O₃ nanoparticles to ～2.5 eV for α-Fe₂O₃ composites with different materials. The value of indirect band gap, on the other hand, increased for all composite samples except for α-Fe₂O₃/Bi₂O₃.     

Development of nanostructured ZnO thin film sensor for NO2 detection

In this work, we report on the performance of a NO₂ sensor based on nanocrystalline zinc oxide (ZnO) operating at 200°C. The sensor was fabricated using spin coating technique on glass substrates. ZnO film was characterised for their structural as well as surface morphologies and NO₂ response was studied. The XRD analysis showed formation of nanocrystalline ZnO. Morphological analysis using SEM revealed formation of a diffusion free surface. The ZnO film showed selectivity for NO₂ over methanol compared to ethanol, H₂S, Cl₂ and NH₃ (S_NO2 /S_CH3OH?=?18.6, S_NO2 /S_C2H5OH?=?12.4, S_NO2 /S_Cl2 ?=?9.3, S_NO2 /S_H2S?=?3.32 and S_NO2 /S_NH3 ?=?5.32). The maximum NO₂ response of 37.2% with 78% stability for the film annealed at 700°C at gas concentration of 100?ppm at 200°C operating temperature was achieved.     

Equations for the second virial coefficient of polar molecules

It is shown how an accurate series expansion for the range $\text{0.7 <}\text{T}{}^1\text{< 5.0}$ and $\text{t}{}^1\text{< 1.2}$ can be obtained for the classical integral for B for molecules interacting with a Barker Bobetic potential and a non-polarizable dipole interaction (the BBD potential). The expressions obtained in this way are used to calculate force constants for the BBD potential from data for the second virial coefficient for H₂O, NH₃, SO₂, CH₃F, CH₃Cl, CH₃Br, CH₃l, CH₃NO₂, CH₃NH₂, CCl₃H, CClF₃, CH₃CHO, and (CH₃)₂CO. The calculated values for B generally agree with the experimental data within the experimental error, even for water.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

Abstract

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

Optical properties and band gap characterization of high dielectric constant oxides

The optical characterization of amorphous and crystalline HfO₂, SrHfO₃, BaZrO₃, BaHfO₃, BaHf₀.₅Ti₀.₅O₃, SrTiO₃, Sr₂Ta₂O₇ and Ta₃Ti₂O_x high dielectric constant thin (15-50 nm) films was performed using a combination of spectroscopic ellipsometry and reflectometry in the photon-energy range 1.5-6.8 eV. The optical dielectric function, absorption coefficient, optical band gap energies E_g, Urbach energy E_u and 3D interband critical point energies were obtained from these studies. The E_g as well as the E_u of the dielectric materials are important for device performance. Indirect E_g was obtained for all materials investigated. Lower E_g tends to result in higher value of permittivity κ. The results obtained deliver the necessary information for the selection of alternative high-κ dielectrics with adequate E_u, E_g and κ values and additionally provide optical metrology for such films.     

Unique 1D Cd1−xZnxS@O‐MoS2/NiOx Nanohybrids: Highly Efficient Visible‐Light‐Driven Photocatalytic Hydrogen Evolution via Integrated Structural Regulation

Development of noble‐metal‐free photocatalysts for highly efficient sunlight‐driven water splitting is of great interest. Nevertheless, for the photocatalytic H₂ evolution reaction (HER), the integrated regulation study on morphology, electronic band structures, and surface active sites of catalyst is still minimal up to now. Herein, well‐defined 1D Cd_1?xZn_xS@O‐MoS₂/NiO_x hybrid nanostructures with enhanced activity and stability for photocatalytic HER are prepared. Interestingly, the band alignments, exposure of active sites, and interfacial charge separation of Cd_1?xZn_xS@O‐MoS₂/NiO_x are optimized by tuning the Zn‐doping content as well as the growth of defect‐rich O‐MoS₂ layer and NiO_x nanoparticles, which endow the hybrids with excellent HER performances. Specifically, the visible‐light‐driven (>420 nm) HER activity of Cd_1?xZn_xS@O‐MoS₂/NiO_x with 15% Zn‐doping and 0.2 wt% O‐MoS₂ (CZ_0.15S‐0.2M‐NiO_x) in lactic acid solution (66.08 mmol h^?1 g^?1) is about 25 times that of Pt loaded CZ_0.15S, which is further increased to 223.17 mmol h^?1 g^?1 when using Na₂S/Na₂SO₃ as the sacrificial agent. Meanwhile, in Na₂S/Na₂SO₃ solution, the CZ_0.15S‐0.2M‐NiO_x sample demonstrates an apparent quantum yield of 64.1% at 420 nm and a good stability for HER under long‐time illumination. The results presented in this work can be valuable inspirations for the exploitation of advanced materials for energy‐related applications.     

Aluminium doped ceria–zirconia supported palladium-alumina catalyst with high oxygen storage capacity and CO oxidation activity

The Ce_0.5Zr_0.3Al_0.2O_1.9/Pd-γ-Al₂O₃ catalyst prepared by a mechanochemical route and calcined at 1000 °C for 20 h in air atmosphere to evaluate the thermal stability. The prepared Ce_0.5Zr_0.3Al_0.2O_1.9/Pd-γ-Al₂O₃ catalyst was characterized for the oxygen storage capacity (OSC) and CO oxidation activity in automotive catalysis. For the characterization, X-ray diffraction, transmission electron microscopy and the Brunauer–Emmet–Teller (BET) technique were employed. The OSC values of all samples were measured at 600 °C using thermogravimetric-differential thermal analysis. Ce_0.5Zr_0.3Al_0.2O_1.9/Pd-γ-Al₂O₃ catalyst calcined at 1000 °C for 20 h with a BET surface area of 41 m² g⁻¹ exhibited the considerably high OSC of 583 μmol-O g⁻¹ and good OSC performance stability. The same synthesis route was employed for the preparation of the CeO₂/Pd-γ-Al₂O₃ and Ce_0.5Zr_0.5O₂/Pd-γ-Al₂O₃ for comparison.