Facile construction of composition-tuned ruthenium-nickel nanoparticles on g-C3N4 for enhanced hydrolysis of ammonia borane without base additives

Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C₃N₄) as a NP support without additional stabilizing ligands. The optimized Ru₁Ni_7.5/g-C₃N₄ catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min^?1 and an activation energy of 28.46 kJ mol^?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru₁Ni_7.5/g-C₃N₄ is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru₁Ni_7.5/g-C₃N₄ has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru₁Ni_7.5/g-C₃N₄ should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen.     

寻找城中村与城市的罅隙——以广州市为例

随着城市的扩张,城中村不知不觉地被卷入这场城市化运动中.文章以广州城中村为例,寻找城中村与城市存在罅隙的原因,进一步具体阐释了其在物质形态、文化意识形态、经济社会结构方面与城市存在的罅隙,以找到解决问题的办法,达成城中村与城市融合共生的目的,不赞成以"一刀切"的方式进行大拆大建.     

Simple and novel synthesis of zirconia whiskers from a phosphate flux

High quality zirconia whiskers have been successfully prepared by molten salt method, using zirconium oxychloride (ZrOCl₂·8H₂O) and sodium phosphate tribasic dodecahydrate (Na₃PO₄·12H₂O) as precursor and molten salt, respectively. The effects of types of molten salt and heat treatment temperature on the formation of zirconia whiskers were characterized by XRD, Raman, DTA-TG, FE-SEM, TEM, SAED and HR-TEM. When Na₃PO₄·12H₂O is utilized as molten salt and the heat treatment temperature is 900?°C, the as-prepared zirconia whiskers with length ranging from 4?µm to 8?µm show an average aspect ratio of 25. The obtained ZrO₂ whiskers with monoclinic structure are elongated along [010] direction and exhibit a smooth surface with no distinct defects. The XRD and Raman results reveal that the phase transformation from tetragonal zirconia to monoclinic zirconia occurs with the increased crystal size and the water quenching treatment can significantly reduce the content of sodium zirconium phosphate [Na_9–4×Zr_x(PO₄)₃] in the final product. The growth mechanism of zirconia whiskers is supposed to be a dissolution-precipitation process. Since the sodium zirconium phosphate [Na_9–4×Zr_x(PO₄)₃] effectively promotes the dissolution of zirconia in liquid molten salt, zirconia can grow into zirconia whiskers according to its anisotropy.     

The peptides in oat and malt extracts that are preferentially absorbed by Lactobacillus plantarum and stimulates its proliferation in milk

Lactobacillus plantarum proliferates inefficiently in milk, mainly because of its lack of cell envelope proteases and its inability to hydrolyse proteins in milk. Our previous study showed that this strain could grow well in milk with the addition of oat and malt extracts. To investigate the usage and preference for polypeptides and oligopeptides for this strain, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), o-phthaldialdehyde (OPA), high-performance liquid chromatography (HPLC), plate counting and other methods were used in this study. The results showed that proteins in fermented milk cannot be absorbed and utilised by L. plantarum, whereas polypeptides and oligopeptides provide available nitrogen sources for their growth. Short-chain peptides were more conducive to absorption and utilisation than long-chain peptides. In particular, peptides with molecular weights in the range of 200–1400 Da in the oat extract and 100–700 Da in the malt extract were preferentially absorbed and utilised.     

Porous nitrogen-enriched hollow carbon nanofibers as freestanding electrode for enhanced lithium storage

One-dimensional porous carbons bearing high surface areas and sufficient heteroatom doped functional-ities are essential for advanced electrochemical energy storage devices, especially for developing free-standing film electrodes. Here we develop a porous, nitrogen-enriched, freestanding hollow carbon nanofiber (PN-FHCF) electrode material via filtration of polypyrrole (PPy) hollow nanofibers formed by in situ self-degraded template-assisted strategy, followed by NH3-assisted carbonization. The PN-FHCF retains the freestanding film morphology that is composed of three-dimensional networks from the entanglement of 1D nanofiber and delivers 3.7-fold increase in specific surface area (592 m2·g-1) com-pared to the carbon without NH3 treatment (FHCF). In spite of the enhanced specific surface area, PN-FHCF still exhibits comparable high content of surface N functionalities (8.8％, atom fraction) to FHCF. Such developed hierarchical porous structure without sacrificing N doping functionalities together enables the achievement of high capacity, high-rate property and good cycling stability when applied as self-supporting anode in lithium-ion batteries, superior to those of FHCF without NH3 treatment.     

Fabrication of fine-grained undoped Y2O3 transparent ceramic using nitrate pyrogenation synthesized nanopowders

Y₂O₃ ceramic is a promising optical material for mid-infrared (IR) windows and domes. Improvements in the mechanical and thermal performance of this material have become urgent if it is to perform adequately under extreme conditions. Herein, Y₂O₃ nanopowders were produced through the nitrate pyrogenation method. The final Y₂O₃ transparent ceramics were fabricated with a hybrid sintering method combining low temperature presintering and a subsequent hot isostatic pressing (HIP) treatment. The synthesis of nanopowders and the fabrication of the final ceramic products were investigated in detail. The Y₂O₃ ceramic sample that was presintered at 1350?°C provided the optimum microstructure for HIP treatment and resulted in an average grain size of 0.5?µm. Owing to the reduced grain size, the flexure strength and Vickers hardness of the sample were improved to 180?MPa and 8.4?GPa, respectively. Furthermore, the achieved pure Y₂O₃ ceramic demonstrated an excellent thermal conductivity at high temperature.     

Structure variation and energy storage properties of acceptor-modified PBLZST antiferroelectric ceramics

Energy storage capacitors with high recoverable energy density and efficiency are greatly desired in pulse power system. In this study, the energy density and efficiency were enhanced in Mn-modified (Pb_0.93Ba_0.04La_0.02)(Zr_0.65Sn_0.3Ti_0.05)O₃ antiferroelectric ceramics via a conventional solid-state reaction process. The improvement was attributed to the change in the antiferroelectric-to-ferroelectric phase transition electric field (E_F) and the ferroelectric-to-antiferroelectric phase transition electric field (E_A) with a small Mn addition. Mn ions as acceptors, which gave rise to the structure variation, significantly influenced the microstructures, dielectric properties and energy storage performance of the antiferroelectric ceramics. A maximum recoverable energy density of 2.64 J/cm³ with an efficiency of 73% was achieved when x = 0.005, which was 40% higher than that (1.84 J/cm³, 68%) of the pure ceramic counterparts. The results demonstrate that the acceptor modification is an effective way to improve the energy storage density and efficiency of antiferroelectric ceramics by inducing a structure variation and the (Pb_0.93Ba_0.04La_0.02)(Zr_0.65Sn_0.3Ti_0.05)O₃-xMn₂O₃ antiferroelectric ceramics are a promising energy storage material with high-power density.     

岩土工程勘察设计常见问题与解决对策

勘察数据的准确性关乎建筑架构的稳定性及后期运营周期.分析了目前在岩土勘察设计上的不足之处,分别从技术、管理及人员3个层面来展开,并且列举实例进行分析,从滑动面、物探、电法勘探以及钻探等方面进行研究,提出解决问题的对策,可为类似工程提供借鉴.     

Rapid screening of DON contamination in whole wheat meals by Vis/NIR spectroscopy and computer vision coupling technology

This work intends to develop an online experimental system for screening of deoxynivalenol (DON) contamination in whole wheat meals by visible/near-infrared (Vis/NIR) spectroscopy and computer vision coupling technology. Spectral and image information of samples with various DON levels was collected at speed of 0.15 m s⁻¹ on a conveyor belt. The two-type data were then integrated and subjected to chemometric analysis. Discriminant analysis showed that samples could be classified by setting 1000 μg kg⁻¹ as the cut-off value. The best correct classified rate obtained in prediction was 93.55% based on fusion of spectral and image features, with reduced prediction uncertainty as compared to single feature. However, quantification of DON by quantitative analysis was not successful due to poor model performance. These results indicate that, although not accurate enough to provide conclusive result, this coupling technology could be adopted for rapid screening of DON contamination in cereals and feeds during processing.