查看更多>>摘要：Catalyst poisoning is a core research topic in the field of heterogeneous catalysis. Despite its importance, however, the catalytic properties of Ag–M bimetallic nanoparticle (biNP) catalysts have not been investigated with regards to the effect of precursor-induced silver halide byproducts. To address this issue, we demonstrated the synthesis of Ag-Pd and Ag-Pt biNPs of controlled and uniform shapes, sizes, and compositions using chlorometallate and Cl-free precursors and investigated their catalytic properties. Importantly, we discovered that the catalytic properties of the biNPs were significantly enhanced upon AgCl removal using ascorbic acid, which could increase their exposed surface area. Moreover, the structures of the biNPs were maintained after AgCl removal using ascorbic acid, which is a significant advantage over AgCl removal using conventional NH3. This study is the first to report AgCl-induced biNP catalyst poisoning caused by the use of chlorometallate precursors and its chemical regeneration, and can be used as a guideline for the controlled synthesis of biNPs of high purity and their efficient applications in catalysis, plasmonics, biomedical detection, and energy conversion.
查看更多>>摘要：Sub-10 nm Bi nanoparticle (NP) is employed herein as an alternative plasmonic nanomaterial to those made of precious Au and Ag, exhibiting localized surface plasmon resonance (LSPR) at wavelengths from the UV to the visible regions. Upon attaching to the ZnO nanorod array (NRA), near-field enhanced photogeneration of charge carriers and heterojunction-rectified charge transfer are observed under broadband sunlight illumination. The synergistic effect renders the derived Bi/ZnO composite attractive for solar water splitting, of which the photocurrent density reaches ~0.8 mA cm?2 at 0.6 VAg/AgCl (~1.23 VRHE). Upon further decorated with proline, electric field-enhanced Raman spectrum is additionally seen under visible light irradiation, highlighting the great promise of this Bi/ZnO composite also for bioanalytical application.
查看更多>>摘要：Fatigue-induced grain growth was observed in ultrafine-grained (UFG) metals processed by the severe plastic deformation technique, and the slip bands (SLBs) formed on coarse grains served as potential crack initiation sites. The SLBs in conventional grain-sized materials are characterized as parallel linear-like configuration along with primary slip orientation. By contrast, four typical configurations of SLBs were commonly observed in UFG materials, including granular, square lattice-like, triangular lattice-like, and parallel linear-like configurations. In the present study, stress-controlled fatigue tests were conducted on oxygen-free copper processed by equal-channel angular pressing under constant stress amplitudes. In addition, two-step block loading fatigue tests were carried out to observe the formation behavior of SLBs in a large dynamically recrystallized grain subjected to a higher cyclic stress. The objective of this study was to investigate the formation process of SLBs with a variety of configurations in UFG high-purity copper based on the microstructural evolution and the change in surface morphology because of cyclic stressing.
查看更多>>摘要：This article opens a series of publications devoted to the preparation and stabilization of new high-temperature (HT) semiconductor phases A (III) – B (VI), which have a large number of vacancies and possess a number of unique properties. In this first work from the proposed series, the T-x-diagram of the Ga–S system was investigated in the composition range x = (30.0–60.7) mol% S, and then the structural identification of new HT phases was carried out. For the Ga–S system, four polymorphic (α-, α′-, β-, γ-) Ga2S3 phases of different symmetry were found and displayed on the phase diagram near the Ga2S3 composition (x ～ 60.0 mol% S). For the first time, it became possible to obtain in-situ a reliable direct proof for the existence of equilibrium in narrow temperature range for the re-opened cubic phase γ-Ga2+δS3 (x ≈ 59.0 mol% S), which was isolated at room temperature in a fairly pure form. We also confirmed the presence of another hexagonal β(α)-Ga2S3 modification, existing at much higher temperatures than the cubic γ-Ga2+δS3 phase. It was shown that the polymorphic α-Ga2S3 and α′-Ga2S3 phases mentioned in the literature form superstructures from the parent β-Ga2S3 phase. The observed structural variants for all four Ga2S3 polymorphic phases, containing up to 1/3 of vacancies in the Ga sub-lattices, are closely related to different methods of ordering Ga vacancies. The reliability of our studies follows from the combination of the methods used: differential thermal analysis (DTA), microstructural local analysis (TEM, HREM, SAED), powder X-ray diffractometry (XRD), including high-temperature synchrotron XRD.
查看更多>>摘要：Sub-stoichiometric tungsten oxide (i.e., WO3-x) materials are advanced multipurpose semiconducting materials. However, it is still a challenge to tune their structure and morphology. Here we report the structural and morphological conversion and the photoluminescence (PL) enhancement of the WO3-x materials synthesized in the mixed acetic and oleic acids using tungsten hexachloride precursor. We demonstrate the structural conversion from nanorods to nanodots, accompanied by the morphological change from the mushroom-like particles to the spherical particles. Importantly, the PL emission from the particles aggregated by the WO3-x nanodots is much stronger than the particles aggregated by the WO3-x nanorods. The structural and morphological conversion mechanism is related to the growth rate reduction of WO3-x nuclei and the steric repulsion effect, which are caused by oleic acid. The PL enhancement arises from the reduction of non-radiative recombination caused by the structural conversion and the surface passivation of WO3-x nanodots caused by oleic acid. These results contribute to the commonly needed ability to control the structure of metal oxide nanomaterials and to the development of next-generation functionalities and devices for energy, electronics, optics, and other fields.
查看更多>>摘要：Cu30Cr10W and GO/CeO2-Cu30Cr10W composites were fabricated by the spark plasma sintering (SPS). The isothermal compression tests of the Cu30Cr10W and GO/CeO2-Cu30Cr10W composites were carried out on the Gleeble-1500 thermo-mechanical simulator under the deformation temperatures of 600–900 °C and strain rates of 0.001–1 s?1. The effects of graphene doped CeO2 on the thermal deformation behavior and microstructure of the composites were investigated. The results show that a trace amount of Cr7C3 layers/nanoparticles was in-situ formed at the interface between graphene and metal matrix, and the interfacial adhesion of composites improved significantly. The Cr particles grew in strip shape perpendicular to the compression direction, and the edge of tungsten carbide particles deformed slightly. With the increased of deformation temperature from 700 ℃ to 900 ℃, the texture component changed to fiber texture. In addition, the constitutive equations of the three composites were obtained. Compared with Cu30Cr10W composites, the addition of GO/CeO2 and the accompanying twinning mechanism increased the flow stress, and the activation energy increased by 8.4% and 33.1%, respectively. Furthermore, the hot working performance is obviously improved.
查看更多>>摘要：Multi-metal oxide materials have gained increasing attention due to their superior electrochemical performance for supercapacitors. In this work, Ni-Co-Mo oxides composite materials (NiCoMo/NF) are synthesized and anchored on Ni foam in the form of vertically aligned nanosheet arrays using a two-step hydrothermal method. It has confirmed that good electrochemical performance stems from a synergic interaction effect between the hybrid Ni-Co-Mo composite materials and the co-existence of Ni-Co and Co-Mo oxide, which can be attributed to a unique nanostructure in the hybrid Ni-Co-Mo composite materials and Ni-Co/Co-Mo oxide intersections with each other. The NiCoMo/NF binder-free electrode shows an enhanced specific capacitance of 1837.7 F g?1(3.31 F cm?2) at a current density of 1 A g?1 and maintains capacitance retention of 81.2% after 6000 cycles at 5 A g?1. Meanwhile, the fabricated hybrid capacitor achieves high specific energy of 41.1 W h kg?1. The results indicate that NiCoMo/NF has the potential for application in supercapacitors. Moreover, our work provides a practical approach for fabrication of multi-metal oxide materials and hold promise for high-power energy storage devices.
查看更多>>摘要：The pristine and antimony (Sb) doped tin selenide (SnSe) has been prepared by vacuum melting followed by ball milling process. The crystallographic pattern of both doped and undoped samples shows the formation of orthorhombic SnSe without any impurities. The influence of Sb on SnSe were confirmed from Projected Density of States (PDOS) and electron density analysis. The Elemental Probe Micro Analyzer (EPMA) technic used to confirm the presence of Sn, Se and Sb elements along with homogenous distribution. HR-TEM micrographs reveal highly crystalline nature of the samples as well as the formation of defects and distinguishable grains and grain boundaries, which helps to reduce the thermal conductivity of 10 wt% Sb doped SnSe samples to 0.55 W/mK at 600 K. Seebeck coefficient analysis has been discloses the double charge polarity switching in Sb substituted samples. Thus, 10 wt% Sb doped SnSe samples achieved a comparable negative Seebeck coefficient with respect to pristine SnSe, which can be a breakthrough in thermoelectric devices.
查看更多>>摘要：A large coercivity increment of 11.63 kOe is obtained by grain boundary diffusion with composite powders of Pr80Al20 surface-coated DyF3. The coercivity increases from the original 12.76 kOe to 24.39 kOe and 23.28 kOe in PA-0.7 and PA-0.9 diffused magnets (Pr80Al20:DyF3 = 7:3, 9:1 in wt%), which shows an increase of 91.15% and 82.45%, respectively. The temperature coefficient of coercivity of diffused magnets is improved due to the high magnetic anisotropy field (HA) of (Nd, Pr, Dy)2Fe14B and the optimized microstructure. Excellent diffusion efficiency and Dy diffusion depth are obtained owing to the betterment of Pr-Al-rich grain boundary (GB) phases. Microstructural features show that the combined strengthening effect of magnetic isolation by the continuous Pr-Al-rich GB phases and magnetic hardening by Dy-Pr-rich shells significantly improve the coercivity of the PA-0.7 and PA-0.9 diffused magnets. Especially, no accumulation of Dy element occurs in the PA-0.9 diffused magnet. The composite diffusion sources provide a new method to improve diffusion efficiency of Dy.
查看更多>>摘要：Innovation of an excellent microwave absorber with a wide effective absorption bandwidth, high conductivity, and easy processability has become a hard dare, which obstructs its prospective applications. Thus, three microwave absorbers of Bi2Te3 based on different size (labelled BT1 ~30.7 μm, BT2 ~43.1 ± 3 nm and BT3 ~20.1 ± 3 nm) have been designed for this purpose, for the first time. BT3 absorbers have shown a surface area (70.9 m2/g) larger than BT2 (41.39 m2/g) and BT1 (2.34 m2/g). The size of the Bi2Te3 based absorbers has shown a great impact on the microwave absorbing features. The smaller size/diameter of Bi2Te3 has displayed a higher EM absorption, whereas the BT3 (20.1 ± 3 nm) absorber with thickness 1.51 mm exhibits a minimum reflection loss (RL= ─ 60 dB) at f = 15.47 GHz while the BT2 (43.1 ± 3 nm) exhibits a (RL = ─ 34.9 dB at 6.59 GHz for 4.1 mm) and (RL= ─25 dB at 7 GHz for 4.1 mm) for BT1 (30.7 μm). Also, the BT3 absorber shows an effective absorption bandwidth (8 GHz at 2.1 mm) extending from 10 to 18 GHz better than the other two shields (7.01 GHz at 2.1 mm) for the BT2 and (6.01 GHz at 2.6 mm) for the BT1. The dielectric loss is the prevailing factor participates in the strong EM absorption mode. The smaller size Bi2Te3 (BT3) absorber has recorded the highest thermal conductivity k = 1.41 W/mK, proving the larger thermal energy storages of these absorber. Finally, these Bi2Te3 particles based EM absorbers may have potential applications as an efficient EM absorption material in broad bandwidth of frequency in electronic, electrical and military devices thanks to their lightweight, small size and smart features.
NSTL
Elsevier