耐热线型小分子对有机硅耐温吸波涂层的增韧改性研究

目的 采用能与有机硅单体反应的耐热小分子对苯基硅树脂基吸波涂层进行增韧改性,调控有机硅树脂的交联网络结构,并将改性树脂与耐温吸波剂复合,制备具有高柔韧、高附着力和耐温的吸波涂层。方法 将不同端基或链长的耐热增韧剂通过硅氢加成接枝到有机硅树脂基体,改变基体的交联网络结构,通过红外、扫描电镜、万能电子试验机、动态热机械分析仪和矢量网络分析仪测试其性能。结果 随着乙烯基封端聚二甲基硅氧烷含量的增加,涂层的柔韧性提高,但耐温性能和附着力降低;当乙烯基封端聚二甲基硅氧烷质量分数为45%时,1 mm涂层的柔韧性达20 mm,附着力达7.73 MPa,抗冲击性大于50 kg·cm。在300℃热处理15 h后,改性涂层挠度从未改性时的1.08 mm提升至1.35 mm,涂层在高温工作后仍保持较好的柔韧性。结论 采用耐热线型小分子对有机硅树脂交联网络结构进行改性,可有效地调控耐温吸波涂层的力学性能,为耐高温吸波涂层增韧及其工程应用提供参考。     

The effects of PVP surfactant in the direct and indirect hydrothermal synthesis processes of ceria nanostructures

CeO₂ nanostructures with completely different morphologies were successfully prepared using the same cerium source and mineralizer through the direct and indirect hydrothermal methods with different introducing strategies of PVP surfactant. The CeO₂ nanostructures tend to form the morphologies of nano-flowers and nano-cubes through the indirect and direct hydrothermal methods, respectively. X-ray diffraction (XRD) analyses revealed that both as-prepared nanostructures are composed of CeO₂ with a standard fluorite structure. The different synthesis mechanisms and corresponding chemical evolutions of the as-prepared CeO₂ nanostructures are discussed based on the different introducing strategies of PVP surfactant in the direct and indirect hydrothermal processes. Investigation of the UV-shielding ability of both CeO₂ nanostructures suggested that the UV absorbance of the nano-flowers is much higher than that of the nano-cubes.     

Logistics cost analysis of rice straw pellets for feasible production capacity and spatial scale in heat utilization systems: A case study in Nanporo town,Hokkaido, Japan

Rice straw is a promising renewable energy source because it is abundantly available in Asia. This study conducted a case study of logistics cost analysis for rice straw pellets by considering all stages in the supply chain to define the main factors affecting the selling price of rice straw pellets: collection (job-commission or employment of part-time workers), transportation, storage (vinyl greenhouses or storage buildings with larger capacity), pelletizing, and delivery to users with biomass boilers. The selling price was found to be strongly dependent on the production capacity because the investment cost for the pellet production facility had a significant effect of economies of scale. A production capacity of larger than 1500 t y⁻¹ is required for rice straw pellets to compete with wood pellets and fossil fuels in the studied Japanese context if the subsidy rate for the investment is 50%, part-time workers conduct the collection, and rice straw is stored in the storage buildings. Our sensitivity analysis also showed an economically feasible spatial scale: for example, rice straw should be collected within a 20 km radius and the users should be within a 38 km radius when the production capacity is 1500 t y⁻¹. In addition, other critical factors related to the collection of rice straw from the paddy fields and transportation of rice straw rolls to storage were identified as planning factors to further reduce the total logistics cost of rice straw pellets.     

1D ZnFe2O4 nanorods coupled with plasmonic Ag,Ag2S nanoparticles and Co-Pi cocatalysts for efficient photoelectrochemical water splitting

Improving the absorption of visible light, accelerating the separation of carries and reducing the recombination of electron-hole pairs are critical to enhance photoelectrochemical (PEC) performance of ZnFe₂O₄. Herein, the ZnFe₂O₄/Ag/Ag₂S films are firstly prepared with a photocurrent density of 0.91 mA/cm² at 1.23 V vs. RHE, which is 9.10 times higher than that of pristine ZnFe₂O₄ (0.10 mA/cm² at 1.23 V vs. RHE). On the basis, Co-Pi cocatalyst is deposited on ZnFe₂O₄/Ag/Ag₂S to further optimize PEC performance of ZnFe₂O₄, the photocurrent density of ZnFe₂O₄/Ag/Ag₂S/Co-Pi is 1.18 mA/cm² at 1.23 V vs. RHE. The improved PEC performance of ZnFe₂O₄/Ag/Ag₂S/Co-Pi films could be attributed to: (i) fast transmission of electron-hole pairs owing to 1D ZnFe₂O₄ NRs; (ii) surface plasmon resonance (SPR) effect of Ag nanoparticles; (ⅲ) visible light absorption is improved by sensitization of Ag₂S nanoparticles; (ⅳ) Co-Pi cocatalyst decreases the recombination of electron-hole pairs by capturing holes. This work provides new insights for metal plasmas, sensitizers and cocatalysts synergistically modify photoanodes for efficient PEC water splitting.     

Highly efficient metal-free phosphorus-doped platelet ordered mesoporous carbon for electrocatalytic oxygen reduction

Platinum-free electrocatalysts especially, various heteroatom-doped carbon nanostructures have attracted particular attraction as plausible solution for commercializing fuel cell technology. In this direction, novel phosphorus-doped platelet ordered mesoporous carbon (P-pOMC) is developed for the first time as metal-free electrocatalyst for alkaline oxygen reduction reaction. The P-pOMC is synthesized by nanocasting method using platelet ordered mesoporous silica as template. Various characterizations reveal that the P-pOMC materials have covalently bound P atoms with carbon framework for facilitation of oxygen reduction reaction (ORR) and also have very high surface area with uniform distribution of short mesoporous channels for unhindered mass transfer. Combination of P doping and excellent surface properties empowers the newly-developed P-pOMC catalyst to show high ORR activity nearly equal to that of state of the art Pt catalyst along with superior long-term stability and excellent methanol tolerance.     

超支化聚合物的合成及其在涂料中应用研究进展

首先介绍了超支化聚合物(HBP)的化学性质,并与传统线性聚合物的优缺点进行比较,接着对HBP的AB2单体缩聚、自缩合乙烯基聚合、自缩合开环聚合等合成方式进行了介绍,并对将来HBP的合成发展方向进行了推测.对现有HBP合成方法和末端官能团改性对比发现,在不同涂料体系中对HBP进行相应的改性是需要解决的首要问题.功能化改性HBP可作为涂料添加剂或主要成膜物质,有效地改善了涂料的流动性,降低了涂料中有机溶剂的挥发.重点结合HBP对涂料领域研究进行了概述,并介绍了近年涌现的HBP制备新策略、新方法.通过对HBP合成方法的探讨和众多末端官能团的不同修饰进行分析、对比和总结,介绍了HBP在UV固化涂料、高固体分涂料、有机-无机杂化涂料中的应用现状.结合相关研究,分析了HBP增强涂膜性能机理.最后基于HBP在涂料领域的应用现状,对今后研究侧重点提出相关建议和展望.     

Integration of nisin into nanoparticles for application in foods

Nisin and other similar food preservatives of natural origins have seen a substantial upsurge in global interest in recent years. The use of nanotechnology to regulate and manipulate nisin for enhanced capacities in the food and nutrition sector is expanding dramatically. Nanotechnology has significant food science applications in nanoparticle delivery systems, packaging, food security, and safety. However, there have been considerable issues regarding the use of nisin in the food sector, including its uncontrolled interactions with various food components, its degradation and electrostatic repulsion. These issues potentially limit its use. Alternate strategies, including a variety of nanoparticle systems such as nanoemulsions, polymeric nanoparticles, nanofibers, and combinations of nisin with other technologies, are employed to enhance the utility of nisin in the food industry. This review highlights the recent developments and new perspectives related to the uses of nisin in the food industry.Industrial relevanceThis review highlights the current status of nanotechnology in the food industry. The issues concerning use of nisin by the food industry are addressed. Nisin shows enhanced efficacy in combination with other current technologies for improved food safety.     

N,N′-Dibromo-N,N′-1,2-ethanediylbis(benzene sulfonamide) as a novel N-bromo reagent catalyzed tetrahydropyranylation/depyranylation of alcohols and phenols under mild conditions

Preparation and catalytic application of N,N′-dibromo-N,N′-1,2-dethanediylbis(benzene sulfonamide) for tetrahydropyranylation of various types of alcohols and phenols in dichloromethane and depyranylation of these compounds in methanol at room temperature is described.     

Synthesis and investigation of the properties of poly(methyl-β-cyanoethylsilylene)-methylphenylsilylene

Dichlorosilane monomer methyl-β-cyanoethyldichlorosilane, was prepared from acrylonitrile and methyl dichlorosilane in the catalytic system of N,N,N′,N′-tetramethylethylen-diamin (TMEDA)/Cu₂O by hydrosilylation reaction. Consequently, a copolysilane poly(methyl-β-cyanoethylsilylene)-methylphenylsilylene was synthesized by Wurtz-type reductive coupling reaction of methyl-β-cyanoethyldichlorosilane and methylphenyldichlorosilane using sodium as catalyst in toluene. Furthermore, UV absorption, fluorescent and thermal properties of the copolysilane were investigated. Results reveal that the copolysilane bearing β-cyanoethyl side group possesses good thermal oxidative stability and strong fluorescence emitting at 412 nm.     

Effect of additives on the WGS activity of combustion synthesized CuO/CeO2 catalysts

This paper presents a study on the role of additives (samaria, lanthana, zirconia, and zinc oxide) to ceria as a support of copper catalysts for low-temperature WGSR. A single-step urea-combustion procedure was used for preparation of highly active catalysts. The results revealed the beneficial role of Sm₂O₃ and ZnO doping in increasing BET surface area and total pore volume of the catalysts and decreasing the degree of crystallinity of ceria. TPR profiles evidenced enhanced reducibility of modified catalysts. The WGS activity of these catalysts correlates well with BET, XRD, and TPR data. By comparing the catalysts with a commercial CuO–ZnO–Al₂O₃ sample we point out the feasibility of using CuO/doped-ceria catalysts for low-temperature WGSR.