查看更多>>摘要：Nano-structured metallic oxides and carbon composites (NiO@C, Fe_3O_4@C and NiFe_3O_4@C) are successfully fabricated by the low-temperature calcinations of Ni/Fe precursors in an inert atmosphere. Density functional theory calculations show that atom rearrangements of NiFe_3O_4@C in unit cells are observed with respect to NiO@C and Fe_3O_4@C, leading to the altered exposed crystal planes and oxygen atoms redistributions on these exposed planes. Likewise, the metallic electron distributions are also changed within NiFe_2O_4@C due to bimetallic synergistic effects. In such fabricated scheme with the terephthalic acid template, the unique morphologies and structural characteristics of NiFe_2O_4@C are obtained with oxygen-rich exposed crystal planes, which are conductive to improving the conductivity, accommodating volume changes, providing rapid electron and Li ion transportations. Compared with NiO@C and Fe_3O_4@C, the fabricated NiFe_2O_4@C as lithium ion anodes can achieve the extremely high discharge capacity of 1808.8 mAh g~(-1) at 100 mA g~(-1) impressive reversible capacity of 1153.6 mAh g~(-1) after 200 cycles at 500 mA g~(-1) and average capacity of 647.1 mAh g~(-1) at 5000 mA g~(-1). The full battery is also assembled by NiFe_2O_4@C and LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2 as anode and cathode, and shows a superior high specific energy of 432.0 Wh kg~(-1), which is far higher (1.5 times) than commercial full batteries.
查看更多>>摘要：Herein, porous Si_3N_4 ceramics embracing excellent mechanical and dielectric properties were achieved via gelcasting using N, N-dimethylacrylamide (DMAA) gel system while acting as pore-former. The increase of monomer content (8.0-23.0 wt%) led to an increase in porosity (39.53-43.60%) and pore connectivity, which accelerated vapor phase mass transport and promoted p-Si_3N_4 grain growth, thereby improving flexural strength (212.33-245.30 MPa) and fracture toughness (3.60-3.89 MPa-m~(1/2)). Attributable to the pores introduced by increasing monomer content, the e' and tanδ were significantly reduced with the values of 4.18-4.29 to 3.95-4.06 and 1.83-2.38 × 10~(-3) to 0.37-1.96 × 10~(-3), respectively, demonstrating excellent microwave-transparent properties. This work proved the great application potential of porous Si_3N_4 ceramics fabricated by gelcasting employing DMAA gel system in the field of microwave-transparent materials.
查看更多>>摘要：Single step hydrothermal method was used to synthesize molybdenum disulfide (MoS_2) thin films. The hexagonal structure of MoS_2 was confirmed by X-ray diffraction techniques (XRD). The nanosheets like morphology of MoS_2 films were confirmed using scanning electron microscopy (SEM). The optical band gap of pristine MoS_2 was found to be -1.53 eV. The prepared MoS_2 films were irradiated with ion and gamma radiation at different ion fluence and doses respectively. For ion irradiation, the samples were irradiated at ion fluences of 4.7 × 10~(16) ion/cm~2, 7.1 × 10~(16) ion/cm~2, 9.5 × 10~(16) ion/cm~2,11.9 × 10~(16) ion/cm~2 and 14.3 × 10~(16) ion/cm~2. In case of gamma irradiation, the samples were irradiated for 10 kGy, 100 kGy, 300 kGy, and 500 kGy and 800 kGy doses. The tensile strain induced in the sample was studied with the help of Raman spectroscopy and XRD technique. The defect induced tensile strain in MoS_2 films due to ion irradiation is higher as compared to gamma irradiation.
查看更多>>摘要：Y_(0.9)Gd_(0.1)Fe_2, which crystallize in a C15 cubic structure, can absorb up to 5 H/f.u. and its pressure-composition isotherm displays a multiplateau behavior related to the existence of several hydrides with different crystal structures. At room temperature Y_(0.9)Gd_(0.1)Fe_2H_x hydrides (2.9 ≤x ≤ 5) crystallize in three phases with cubic structure (C1, C2 and C3), two phases with monoclinic structures (Ml and M2), and one phase with orthorhombic structure (0), with the following sequence for increasing H concentration: C1, M1, C2, M2, C3, O. Each phase exists as single phase within a H homogeneity range, and they are separated from each other by two-phase domains. The reductions of crystal symmetry are related to various hydrogen orders into interstitial sites. Weak superstructure peaks were indexed by doubling the cubic cell parameter of the cubic C2 phase. Upon heating, the monoclinic Ml and M2 and the cubic C2 phases undergo order-disorder (O-D) transitions toward a disordered cubic structure C_(Dis). These O-D transitions are reversible with thermal hysteresis effects. The cubic C3 and orthorhombic 0 phases transform into a disordered cubic phase accompanied by H desorption.
Reda M. AbdelhameedMahmoud El-ShahatMahmoud A. Abd El-Ghaffar
14页
查看更多>>摘要：Metal-organic frameworks (MOFs) have shown a great potential for producing efficient and eco-friendly photocatalysts. Furthermore, phthalocyanines (PCs) are promising materials in photocatalytic reactions because of their unique adsorption and photosensitizing properties. Here, three phthalocyanines (Pcs) derivatives with Al~(3+) and Co~(2+) ions as the central metal were prepared to attach them to the MOFs matrix. The photocatalytic decay performance of methylene blue (MB) and methyl orange (MO) and their mixtures were investigated under visible light illumination. The photocatalyst NH_2-MIL-125, Al-PcCl@NH_2-MIL-125, CoPc@NH_2-MIL-125, and CoPcPA@NH_2-MIL-125 show 0.01, 0.012, 0.035, and 0.046 min~(-1) MB degradation rate, respectively, while, the degradation rates of MO were 0.021, 0.027, 0.052 and 0.082, respectively. Amazingly, the degradation rates of MB in presence of MO showed boosted photocatalytic decomposition with the degradation rate of 0.066, 0.069, 0.085, and 0.120 min~(-1), respectively. This study illustrates a high performance for utilizing porous MOF-based materials not only as supports but as electron acceptors that enhance both photostability and photocatalytic activity.
查看更多>>摘要：The poling of macro fiber composites (MFCs) as a vital part for manufacturing usable samples, is related with but different from that of their piezoelectric phase owing to the existence of interdigitated electrodes. Herein, beginning with the quantitative relationship between effective electric field and external electric field obtained by finite element analysis, the prediction and optimization of poling condition for lead zir-conate titanate (PZT) based-MFCs was presented. The results demonstrate that the predicted values agree with the experimental results, specifically, the poling field range of the investigated MFCs is from 16.7 kV/ cm to 33.3 kV/cm. The piezoelectric and dielectric properties of MFCs are improved by adjusting the poling condition up to a suitable value, whereas are degraded due to the interaction of domain alignment and electric field concentration. The optimal poling condition of the MFCs is 26.7 kV/cm for 10 min at room temperature. This research contributes to realizing the personalized-customization of MFCs.
查看更多>>摘要：Zinc ion batteries (ZIBs) are newly emerging and widely attracted energy storage devices owing to its advantages of intrinsic safety and low-cost effectiveness. Herein, we reported a nanorod-like MnO_2 cathode material composited with carbon and pyrrolic nitrogen by in-situ co-precipitation method at room temperature, which was used as ZIB cathode to deliver a high specific capacity of 339 mAh g~(-1) at 100 mA g~(-1) and a long cycle stability over 2000 cycles at 1000 mA g~(-1), resulting in the ultrahigh coulombic efficiencies approximate to 100%. The improved performance was attributed to the enhancement of structural stability and more zinc ion insertion sites after introducing the 2-methylimidazole (2-MI) coating layer. The phase transition of α-MnO_2 @2-methylimidazole (α-MnO_2 @2-MI) and the formation of more porous architecture could be the origin of the continuous capacity increasing in the initial several cycles, which was proved by the results of the ex-situ x-ray diffraction (XRD) and the scanning electronic microscope (SEM). This method can be a more realistic choice for the further commercial applications of low-cost and easily-accessed ZIBs with excellent electrochemical performance.
查看更多>>摘要：The chemical doping of carbon and heteroatoms is expected to be a promising strategy for enhancing the absorption properties of electromagnetic waves. In this work, N-doped C/ZnO composites (CN/ZnO_x-Ts) were originally designed and synthesized by using temperature-controllable calcination engineering with zinc-based acrylate resins containing N atoms as precursors. The best electromagnetic wave absorption (EMWA) performance for the composites was obtained by changing the composition and calcination temperature of the acrylate resin precursor. A CN/ZnO_(0.064)-900 composite prepared using a precursor containing acrylonitrile (0.4 mol) and ZnO (0.064 mol) calcined at 900 °C showed a minimum reflection loss (RL_(min)) of - 43.15 dB at 3.0 mm and 9.68 GHz, with an effective absorption bandwidth (EAB) ranging from 5.1 GHz to 18 GHz achieved by adjusting the thickness of the absorber. This method for preparing novel N-doped carbon-based materials provides the possibility for the mass production of highly efficient absorbers.
查看更多>>摘要：Biomass carbon is a potential alternate for commercially expensive graphene and carbon nanotubes to fabricate nanocomposites as electromagnetic (EM) wave absorbers. Here, we systematically prepared porous biomass carbon/ferrite nanocomposites with different chemical compositions, particle sizes, and structures using rice husk ash, carbonized luffa sponge, carbonized kapok and cotton fibers. All the prepared nanocomposites show limited dielectric losses, indicating the permittivity is less affected by the micro-morphologies, chemical compositions, and structures of biomass carbon. The magnetic loss of microwaves by most samples is caused by eddy current effect. Both smaller and wider range sized particles would contribute additional natural resonance for the magnetic loss of ferrite nanoparticles. The EM wave absorption performance of the nanocomposites are controlled by both the impedance matching between the absorber and air and their magnetic/dielectric losses for incident EM waves. The maximum bandwidth of RL < -10 dB of the as-prepared nanocomposites is about 4.8 GHz, covering most of the K_u-band. Due to their low density and good impedance matching with air, the biomass carbon/ferrite nanocomposites could be promising green light-weight EM wave absorbers by adjusting the particle sizes of ferrite nanoparticles.
查看更多>>摘要：This article reports the significantly improved piezoelectric and ferroelectric properties of Cu/W co-doped Ca_2Bi_2Nb_(2-x)(Cu_(1/4)W_(3/4))_xO_9 (CBNCW-x, where 0≤ x ≤ 0.150) high Curie temperature lead-free piezoelectric ceramics. The crystal structure, microstructure, and electric properties of CBNCW-x ceramics have been systematically analyzed. The results show that ceramic samples have a bismuth layered structure of m- 2, which is a single-phase of CBN. The ceramic grains show the typical plate-like structure of the bismuth layer. Cu/W co-doped CBN ceramics increased the distortion of NbO_6 octahedron, and significantly enhanced the piezoelectric constant and the remnant polarization. When x = 0.075, it shows better comprehensive properties with an excellent d_(33) of 13.8 pC/N, a high remnant polarization of 12.10 uC/cm2, the Tc of 918 °C, a dielectric loss value of 0.57%, and the Ωm value of 7099. Moreover, CBNCW-0.075 ceramic simple maintains the d_(33) of 12.7 pC/N after annealing 900 °C for 30 min, which shows good high-temperature stability. It suggests that the Cu/W co-doped CBN ceramics have good application prospects in the high-temperature piezoelectric field.
NSTL
Elsevier