Extraordinary terahertz absorption bands observed in micro/nanostructured Au/polystyrene sphere arrays

Terahertz (THz) time-domain spectroscopy is carried out for micro/nanostructured periodic Au/dielectric sphere arrays on Si substrate. We find that the metal-insulator transition can be achieved in THz bandwidth via varying sample parameters such as the thickness of the Au shell and the diameter of the Au/dielectric sphere. The Au/polystyrene sphere arrays do not show metallic THz response when the Au shell thickness is larger than 10 nm and the sphere diameter is smaller than 500 nm. This effect is in sharp contrast to the observations in flat Au films on Si substrate. Interestingly, the Au/polystyrene sphere arrays with a 5-nm-thick Au shell show extraordinary THz absorption bands or metallic optical conductance when the diameter of the sphere is larger than 200 nm. This effect is related to the quantum confinement effect in which the electrons in the structure are trapped in the sphere potential well of the gold shell.     

A high density of vertically-oriented graphenes for use in electric double layer capacitors

The growth, capacitance and frequency response of vertically-oriented graphenes grown by radio frequency plasma-enhanced chemical vapor deposition on nickel substrates and used as electrodes in electric double layer capacitors (EDLCs) are presented. The graphenes grown on the grain boundary of substrates show a faster growth rate, but less ordered structure than in the center of the nickel grain. At a few nanometers away from the grain boundaries the graphenes grow vertically at the rate of 70–80 nm per minute. The film height increased linearly with growth time from 700 nm (10 min sample) to 3.1 μm (40 min sample). Raman spectra show that the intensity ratio of the D band to G band gradually decreased with growth time to a value of 0.5, indicating that the crystalline order of the graphene increases with height. The specific capacitance of symmetric, parallel plate EDLC devices fabricated with these films was found to increase in a linear fashion with growth time up to values greater than 120 μF/cm² at 1 kHz. An impedance phase angle of ?45° was reached at 30 kHz. Specific capacitance normalized to growth height suggests that mechanisms other than double layer charge storage on planar surface area were operative.     

The adsorption feature and photocatalytic oxidation activity of K1−2xMxTiNbO5 (M = Mn,Ni) for methyl mercaptan in methane

The novel photocatalytic ceramics material K_1?2xM_xTiNbO₅ (M = Mn, Ni) were prepared through Mn²⁺ and Ni²⁺ ion-exchange of KTiNbO₅, which was synthesized by a hydrothermal method. The influence of the ion-exchange process on the structure and morphology of prepared ceramics material were investigated by such physicochemical methods as powder X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), UV–visible diffuse reflectance spectroscopy (UV–vis DRS) and Fourier-transform infrared (FT-IR) microscopy. The adsorption and photocatalytic oxidation of methyl mercaptan (MM) in methane were used to evaluate the catalytic performance of different constitutes. The results revealed that K_1?2xNi_xTiNbO₅ exhibited better adsorption and photocatalytic oxidation activity for MM in methane under both visible and UV light radiation. While the photocatalytic oxidation activity of K_1?2xMn_xTiNbO₅ is similar to that of K_1?2xNi_xTiNbO₅, however it has little adsorption activity for MM in dynamic state.     

Dense Bi3Fe0.5Nb1.5O9 ceramics prepared by spark plasma sintering

Bi₃Fe_0.5Nb_1.5O₉ ceramics have attracted much attention due to its interesting dielectric and magnetic properties. However, the Bi₃Fe_0.5Nb_1.5O₉ ceramics prepared by the conventional solid state reaction method have a maximum density of about 60% of the theoretical density. Decomposition at temperatures higher than 850 °C precluded the preparation of a more highly dense sample. In the present research, dense ferroelectric Bi₃Fe_0.5Nb_1.5O₉ ceramics with a density of more than 97% of the theoretical one were prepared by spark plasma sintering. XRD data shows that Bi₃Fe_0.5Nb_1.5O₉ has an orthorhombic Aurivillius-type structure.     

离子液体水热法辅助合成稀土Ce掺杂ZnO纳米材料的制备及其应用研究

以1-甲基咪唑和氯代正丁烷为原料,合成1-丁基-3-甲基咪唑氯盐离子液体;以醋酸锌[Zn(Ac)2]、硫酸锌(ZnSO4)和氯化锌(ZnCl2)为锌源,在1-丁基-3-甲基咪唑氯盐离子液体和丙氨酸体系中与硝酸铈反应,经水热合成法制备得到Ce掺杂的纳米ZnO。采用扫描电子显微镜(SEM)、紫外-可见光吸收光谱(UV-Vis)、X射线衍射仪(XRD)、X射线光电子能谱分析(XPS)和红外光谱(FT-IR)对产品进行表征。以亚甲基蓝(MB)为目标降解物,采用UV-Vis检测,考察了Ce掺杂的纳米ZnO的光催化活性。研究表明,焙烧温度对光催化的晶体结构和光催化活性产生较大的影响;2%Ce/ZnO、焙烧温度为500℃、催化时间为30 min、亚甲基蓝用量0.05 g、pH值为10时降解率可达99.5%以上。     

A polyvinyl alcohol-based mixed matrix membrane with uniformly distributed Schiff base network-1 for ethanol dehydration

In this study, Schiff base network (SNW)-1 nanoparticles with high hydrophilicity and large specific surface area were used to prepare polyvinyl alcohol (PVA)-based mixed matrix membranes (MMMs), which were evaluated for ethanol dehydration. Because of the low difference of density between SNW-1 and PVA, the as-prepared nanoparticles can be uniformly distributed into the PVA active layer. The effects of SNW-1 loading, feed temperature, and water concentration on pervaporation (PV) performance were further studied. The results showed the MMM with 10 wt% of SNW-1 loading exhibited a separation factor of 1,501 and a permeation flux of 187 g m⁻² h⁻¹ for feeding 95 wt% ethanol/water binary solution at 75°C. Overall, the SNW-1/PVA MMMs showed great prospect in ethanol dehydration via PV.     

Synergistic effects of modified TiO2/multifunctionalized graphene oxide nanosheets as functional hybrid nanofiller in enhancing the interface compatibility of PLA/starch nanocomposites

The aim of this study is to investigate the synergistic effects of modified TiO₂/multifunctionalized graphene oxide nanosheets at different ratios on the interface compatibility between starch and poly(lactic acid) (PLA). To this end, silanylated nano-TiO₂ (MTiO₂, 1 and 2%) and alkylated maleic anhydride grafted graphene oxide (f-GO, 0.1, 0.2, and 0.4%) at different combinations are blended with the PLA-starch composites using solution blending technique. Then, the synergistic effects of MTiO₂ and f-GO on PLA/starch matrix are investigated in terms of the morphology, crystallinity, structural characterization, thermal stability, dynamic mechanical, and antiaging properties, and the related mechanisms. The Raman and Fourier transform infrared spectroscopy spectra verify the successful synthesis of the two modified nanofillers (f-GO and MTiO₂) and the formation of strong hydrogen bond within the PLA-starch nanocomposites. Due to the strong interfacial interaction and the synergistic effect from the combination of 1% MTiO₂ and 0.2% f-GO, obvious improvement was observed in PLA-starch versus other nanocomposites in terms of morphology, thermal stability, surface hydrophobicity, storage modulus, ultraviolet-shielding capacity, and aging-resistance. Furthermore, differential scanning calorimeter (DSC), isothermal crystallization kinetic, and X-ray diffraction analysis demonstrate that f-GO and the M-TiO₂ significantly synergize in enhancing the crystallization rate and crystallinity of PLA/starch matrix. These results provide novel insights for constructing high-performance nanocomposites and facilitate their applications in food packaging.     

Poly(vinyl alcohol)/carboxyl graphene mixed matrix membranes: High-power ultrasonic treatment for enhanced pervaporation performance

High-power ultrasonic treatment was conducted during the mixing process to obtain poly(vinyl alcohol) (PVA)/carboxyl graphene (CG) mixed matrix membranes (MMMs). Results from X-ray photoelectron spectrometer and thermogravimetric analysis confirmed the enhanced esterification reaction. The increased amorphous region and free volume were investigated by wide-angle X-ray diffraction and positron annihilation lifetime spectroscopy. Scanning electron microscope and atomic force microscope measurements suggested that ultrasonic could uniformly disperse CG in PVA polymer matrix. The mechanical properties and hydrophilicity of as-prepared membrane were enhanced due to ultrasonic treatment. The permeation flux and separation factor of PVA/CG-US membrane for 90 wt % ethanol aqueous solution were 0.79 kg m⁻² h⁻¹ and 860, respectively. For methanol (15 wt %)/methyl tert-butyl ether mixture, its permeation flux and separation factor were also increased significantly compared with membranes without ultrasonic treatment. Due to the simplicity of the ultrasonic process and the versatility of the inorganic fillers, this method may contribute to the design of various MMMs and extend the application of these membranes in different uses. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48526.     

废热锅炉服役后筒体环焊缝处的断裂失效研究

某氮肥公司合成氨系统的一台合成废热锅炉筒体环焊缝周围发生多处开裂。利用JB30B冲击试验机对废锅筒体环焊缝处材料的断裂韧性进行实验分析,同时结合断裂力学的基本理论对服役后废热锅炉筒体环焊缝处的开裂失效进行分析。结果表明：由于废锅焊缝区组织的晶界性能变差,使得材料的冲击韧性显著下降,抵抗裂纹扩展的能力降低,最终在机械应力、热应力及腐蚀环境的作用下,筒体环焊缝处发生多处晶间腐蚀开裂,从而导致筒体失效。