共查询到20条相似文献，搜索用时 31 毫秒
1.
Miaudet P Derré A Maugey M Zakri C Piccione PM Inoubli R Poulin P 《Science (New York, N.Y.)》2007,318(5854):1294-1296
Shape-memory polymers can revert to their original shape when they are reheated. The stress generated by shape recovery is a growing function of the energy absorbed during deformation at a high temperature; thus, high energy to failure is a necessary condition for strong shape-memory materials. We report on the properties of composite nanotube fibers that exhibit this particular feature. We observed that these composites can generate a stress upon shape recovery up to two orders of magnitude greater than that generated by conventional polymers. In addition, the nanoparticles induce a broadening of the glass transition and a temperature memory with a peak of recovery stress at the temperature of their initial deformation. 相似文献
2.
为了有效地评估纳米粒子对植物潜在的生物毒性,选取玉米和氧化铁纳米粒子为研究对象,探讨氧化铁纳米粒子（nailo-Fe2O3）对玉米生理效应的影响。同时,测定抗氧化酶体系的酶活性和丙二醛（MDA）含量,结果表明当受到氧化铁纳米粒子胁迫时,玉米会发生氧化应激反应,但这会激发玉米本身的保护机制,导致整个机体的抗氧化预防能力增强,使得机体的超氧阴离子自由基含量降低,减少对机体的损害。同时,通过玉米根的荧光切片和透射电镜切片,可以得出氧化铁纳米粒子从上皮层运输到皮质层主要是通过质外体途径．并且能够进入玉米细胞中、、这些为评估纳米粒子对植物的影响奠定基础。 相似文献
3.
Nearly quantitative conversion of nitric oxide (NO) into N(2)H(4)CO has been obtained in the reduction of NO with carbon monoxide and hydrogen over platinum and rhodium catalysts. Depending on the temperature of collection, N(2)H(4)CO is isolated as ammonium cyanate or its isomer, urea. The process is an effective way of recovering fixed nitrogen from dilute industrial streams containing NO. Ammonium cyanate may play a role in the reduction of NO in automotive exhaust control. 相似文献
4.
Feng X Sayle DC Wang ZL Paras MS Santora B Sutorik AC Sayle TX Yang Y Ding Y Wang X Her YS 《Science (New York, N.Y.)》2006,312(5779):1504-1508
Ceria nanoparticles are one of the key abrasive materials for chemical-mechanical planarization of advanced integrated circuits. However, ceria nanoparticles synthesized by existing techniques are irregularly faceted, and they scratch the silicon wafers and increase defect concentrations. We developed an approach for large-scale synthesis of single-crystal ceria nanospheres that can reduce the polishing defects by 80% and increase the silica removal rate by 50%, facilitating precise and reliable mass-manufacturing of chips for nanoelectronics. We doped the ceria system with titanium, using flame temperatures that facilitate crystallization of the ceria yet retain the titania in a molten state. In conjunction with molecular dynamics simulation, we show that under these conditions, the inner ceria core evolves in a single-crystal spherical shape without faceting, because throughout the crystallization it is completely encapsulated by a molten 1- to 2-nanometer shell of titania that, in liquid state, minimizes the surface energy. The principle demonstrated here could be applied to other oxide systems. 相似文献
5.
Predicting structure from the attributes of a material's building blocks remains a challenge and central goal for materials science. Isolating the role of building block shape for self-assembly provides insight into the ordering of molecules and the crystallization of colloids, nanoparticles, proteins, and viruses. We investigated 145 convex polyhedra whose assembly arises solely from their anisotropic shape. Our results demonstrate a remarkably high propensity for thermodynamic self-assembly and structural diversity. We show that from simple measures of particle shape and local order in the fluid, the assembly of a given shape into a liquid crystal, plastic crystal, or crystal can be predicted. 相似文献
6.
The high performance of Au-CeO2 and Au-TiO2 catalysts in the water-gas shift (WGS) reaction (H2O + CO-->H2 + CO2) relies heavily on the direct participation of the oxide in the catalytic process. Although clean Au(111) is not catalytically active for the WGS, gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(111) or Cu(100). In TiO(2-x)/Au(111) and CeO(2-x)/Au(111), water dissociates on O vacancies of the oxide nanoparticles, CO adsorbs on Au sites located nearby, and subsequent reaction steps take place at the metal-oxide interface. In these inverse catalysts, the moderate chemical activity of bulk gold is coupled to that of a more reactive oxide. 相似文献
7.
为了研究纳米氧化铜（nCuO）对砷（As）胁迫下水稻种子发芽以及幼苗生长的影响，在培养皿中进行12 d的种子发芽试验。结果表明：2 mg·L-1砷处理下，添加低浓度纳米氧化铜（0.5和1 mg·L-1）可以缓解水稻幼苗的砷毒害，添加高浓度的纳米氧化铜（10、20和50 mg·L-1）会抑制水稻种子的发芽率和根长，降低干重。与单独砷处理相比，添加纳米氧化铜可以提高水稻叶片SOD活性(0.5、1和20 mg·L-1)及CAT活性（1、10、20和50 mg·L-1）。水稻地上部和根部砷含量随着纳米氧化铜的加入而降低。由此可见，不同浓度的纳米氧化铜对砷胁迫下种子发芽和幼苗生长的影响不同。 相似文献
8.
在比较了各种合成方法后，我们采用固相合成法来制备纳米氧化锌，并对其提出了改进．通过在固相反应过程中加入表面活性剂对纳米氧化锌进行了表面改性，制备出了粒径更小、分散性更好的氧化锌．用X-射线粉末衍射仪、扫描电镜表征产物的结构和形貌，用分光光度计研究其分散性．结果表明，改性后产物的分散性得到了显的改善，较之未改性样品，其吸光度均有不同程度的增加，且在不同极性溶剂中的分散性随表面活性剂种类和用量的不同而不同． 相似文献
9.
The prevailing view of CO oxidation on gold-titanium oxide (Au/TiO(2)) catalysts is that the reaction occurs on metal sites at the Au/TiO(2) interface. We observed dual catalytic sites at the perimeter of 3-nanometer Au particles supported on TiO(2) during CO oxidation. Infrared-kinetic measurements indicate that O-O bond scission is activated by the formation of a CO-O(2) complex at dual Ti-Au sites at the Au/TiO(2) interface. Density functional theory calculations, which provide the activation barriers for the formation and bond scission of the CO-O(2) complex, confirm this model as well as the measured apparent activation energy of 0.16 electron volt. The observation of sequential delivery and reaction of CO first from TiO(2) sites and then from Au sites indicates that catalytic activity occurs at the perimeter of Au nanoparticles. 相似文献
10.
Superlattices of iron nanocubes synthesized from Fe[N(SiMe3)2]2 总被引：1，自引：0，他引：1
The reaction of the metal-organic precursor Fe[N(SiMe3)2]2 with H2 in the presence of a long-chain acid and a long-chain amine in various proportions produces monodisperse zerovalent iron nanoparticles. These Fe particles display magnetic properties that match those of bulk iron as evidenced by magnetic and M?ssbauer measurements. The nanoparticles adopt a cubic shape with edges of 7 nanometers and are incorporated into extended crystalline superlattices containing nanocubes in close proximity and with their crystallographic axes aligned. These superlattices are formed in solution, precipitate in high yield, and may be redissolved and redeposited as two-dimensional arrays. 相似文献
11.
Brown SS Ryerson TB Wollny AG Brock CA Peltier R Sullivan AP Weber RJ Dubé WP Trainer M Meagher JF Fehsenfeld FC Ravishankara AR 《Science (New York, N.Y.)》2006,311(5757):67-70
Nitrogen oxides in the lower troposphere catalyze the photochemical production of ozone (O3) pollution during the day but react to form nitric acid, oxidize hydrocarbons, and remove O3 at night. A key nocturnal reaction is the heterogeneous hydrolysis of dinitrogen pentoxide, N2O5. We report aircraft measurements of NO3 and N2O5, which show that the N2O5 uptake coefficient, g(N2O5), on aerosol particles is highly variable and depends strongly on aerosol composition, particularly sulfate content. The results have implications for the quantification of regional-scale O3 production and suggest a stronger interaction between anthropogenic sulfur and nitrogen oxide emissions than previously recognized. 相似文献
12.
The self-assembly of particles at fluid interfaces, driven by the reduction in interfacial energy, is well established. However, for nanoscopic particles, thermal fluctuations compete with interfacial energy and give rise to a particle-size-dependent self-assembly. Ligand-stabilized nanoparticles assembled into three-dimensional constructs at fluid-fluid interfaces, where the properties unique to the nanoparticles were preserved. The small size of the nanoparticles led to a weak confinement of the nanoparticles at the fluid interface that opens avenues to size-selective particle assembly, two-dimensional phase behavior, and functionalization. Fluid interfaces afford a rapid approach to equilibrium and easy access to nanoparticles for subsequent modification. A photoinduced transformation is described in which nanoparticles, initially soluble only in toluene, were transported across an interface into water and were dispersed in the water phase. The characteristic fluorescence emission of the nanoparticles provided a direct probe of their spatial distribution. 相似文献
13.
14.
Understanding the factors that influence the growth and final shape of noble metal nanostructures is important for controlling their properties. However, relative to their single-crystalline counterparts, the growth of nanoparticles that contain twin defects can be difficult to control because multiple competitive growth pathways can yield such structures. We used spherical, cubic, and octahedral single-crystalline gold nanoparticles as dual electron microscopy labels and plasmonic seeds to track the growth of multiply twinned silver nanostructures. As the bimetallic nanostructures grew, they successively developed twin planes to ultimately form multiply twinned nanoparticles from single-crystalline seeds. Collectively, these data demonstrate how a series of nanoparticles of different shapes and internal crystal structures are interrelated and develop from one another. 相似文献
15.
Knowing the thermodynamic stability of transition metal oxide nanoparticles is important for understanding and controlling their role in a variety of industrial and environmental systems. Using calorimetric data on surface energies for cobalt, iron, manganese, and nickel oxide systems, we show that surface energy strongly influences their redox equilibria and phase stability. Spinels (M(3)O(4)) commonly have lower surface energies than metals (M), rocksalt oxides (MO), and trivalent oxides (M(2)O(3)) of the same metal; thus, the contraction of the stability field of the divalent oxide and expansion of the spinel field appear to be general phenomena. Using tabulated thermodynamic data for bulk phases to calculate redox phase equilibria at the nanoscale can lead to errors of several orders of magnitude in oxygen fugacity and of 100 to 200 kelvin in temperature. 相似文献
16.
磁性纳米结构是近年来化学、材料及生物领域交叉性研究热点,在催化、生物技术、磁共振成像、数据存储和环境修复等方面应用非常广泛。随着合成、检测技术的发展,对磁性纳米粒子的尺寸和形貌控制日趋完善。在设计带有特定活性点、配体、酶、手性催化剂、药物以及其它复杂客体的多功能磁性纳米体系及其组装结构的基础上,通过合成、包裹和功能化新技术的发展和完善,磁性粒子在各个领域的大规模、经济的应用已经实现。对磁性纳米结构的合成技术和方法进行了讨论,并对其在不同领域内的应用进行了阐述。 相似文献
17.
Although solution self-assembly of block copolymers (BCPs) represents one of the most promising approaches to the creation of nanoparticles from soft matter, the formation of non-centrosymmetric nanostructures with shape anisotropy remains a major challenge. Through a combination of crystallization-driven self-assembly of crystalline-coil BCPs in solution and selective micelle corona cross-linking, we have created short (about 130 nanometers), monodisperse cylindrical seed micelles that grow unidirectionally. These nanostructures grow to form long, non-centrosymmetric cylindrical A-B and A-B-C block co-micelles upon the addition of further BCPs. We also illustrate the formation of amphiphilic cylindrical A-B-C block co-micelles, which spontaneously self-assemble into hierarchical star-shaped supermicelle architectures with a diameter of about 3 micrometers. The method described enables the rational creation of non-centrosymmetric, high aspect ratio, colloidally stable core-shell nanoparticles in a manner that until now has been restricted to the biological domain. 相似文献
18.
Maya blue paint was often used in Mesoamerica. The origin of its color and its resistance to acids and biocorrosion have not been fully understood. High-resolution transmission electron microscopy, electron energy loss spectroscopy, and x-ray microanalysis studies of authentic samples show that palygorskite crystals in the paint form a superlattice that probably occurs as a result of mixing with indigo molecules. An amorphous silicate substrate contains inclusions of metal nanoparticles encapsulated in the substrate and oxide nanoparticles on the surface. The beautiful tone of the color is obtained only when both the particles and the superlattice are present. 相似文献
19.
以硝酸锌、硫脲、乙二醇以及氨基乙酸等为原料,运用溶胶凝胶自燃烧法合成了尺寸和形貌均一性较好的ZnS多晶纳米颗粒.经X射线衍射仪、扫描电子显微镜、紫外-可见分光光度计等表征发现合成的ZnS纳米颗粒具有闪锌矿结构,其平均粒径为160nm且每个纳米颗粒均由约10nm的晶粒组成,且样品具有良好的光吸收性能,其能带带隙为3.46eV.还详细研究了前驱物中组分比例对ZnS纳米颗粒粒径分布的具体影响.研究表明前驱物中n(乙二醇)/n(氨基乙酸)是影响ZnS纳米颗粒粒径分布的主要因素.这一研究结果提供了一种基于自燃烧法的可靠的ZnS纳米颗粒合成工艺,并且实现了利用n(乙二醇)/n(氨基乙酸)独立优化纳米颗粒粒径均一性,有利于基于此工艺的功能材料设计和光电性能优化. 相似文献
20.
[目的]研究黄鲫蛋白抗菌肽-纳米氧化锌络合物对肠黏膜氧化作用的影响。[方法]以小鼠为动物模型,透射电镜分析显示,黄鲫蛋白抗菌肽-纳米氧化锌络合物微观为形状不规则的聚合物,将该聚合物注射到小鼠空肠中吸收30 min,分别测定肠黏膜的髓过氧化物酶(MPO)和谷胱甘肽过氧化物酶(GPx)活性,脂质过氧化物(LPO)和丙二醛(MDA)含量变化。[结果]试验表明,黄鲫蛋白抗菌肽-纳米氧化锌络合物显著提高了MPO活性,但是GPx活性则显著地降低;同样,在脂质氧化程度上,LPO含量显著地降低,而MDA含量则是显著地增加。[结论]该研究说明,黄鲫蛋白抗菌肽-纳米氧化锌络合物能改变小肠黏膜关键酶MPO和GPx活性,但是不同酶对其敏感性不同,MPO活性增强可能与LPO含量降低有关,而GPx活性降低则导致了MDA含量增加。 相似文献