Reaction-driven restructuring of Rh-Pd and Pt-Pd core-shell nanoparticles

Heterogeneous catalysts that contain bimetallic nanoparticles may undergo segregation of the metals, driven by oxidizing and reducing environments. The structure and composition of core-shell Rh(0.5)Pd(0.5) and Pt(0.5)Pd(0.5) nanoparticle catalysts were studied in situ, during oxidizing, reducing, and catalytic reactions involving NO, O2, CO, and H2 by x-ray photoelectron spectroscopy at near-ambient pressure. The Rh(0.5)Pd(0.5) nanoparticles underwent dramatic and reversible changes in composition and chemical state in response to oxidizing or reducing conditions. In contrast, no substantial segregation of Pd or Pt atoms was found in Pt(0.5)Pd(0.5) nanoparticles. The different behaviors in restructuring and chemical response of Rh(0.5)Pd(0.5) and Pt(0.5)Pd(0.5) nanoparticle catalysts under the same reaction conditions illustrates the flexibility and tunability of the structure of bimetallic nanoparticle catalysts during catalytic reactions.     

Ammonia synthesis from first-principles calculations

The rate of ammonia synthesis over a nanoparticle ruthenium catalyst can be calculated directly on the basis of a quantum chemical treatment of the problem using density functional theory. We compared the results to measured rates over a ruthenium catalyst supported on magnesium aluminum spinel. When the size distribution of ruthenium particles measured by transmission electron microscopy was used as the link between the catalyst material and the theoretical treatment, the calculated rate was within a factor of 3 to 20 of the experimental rate. This offers hope for computer-based methods in the search for catalysts.     

Visualizing gas molecules interacting with supported nanoparticulate catalysts at reaction conditions

Understanding how molecules can restructure the surfaces of heterogeneous catalysts under reaction conditions requires methods that can visualize atoms in real space and time. We applied a newly developed aberration-corrected environmental transmission electron microscopy to show that adsorbed carbon monoxide (CO) molecules caused the {100} facets of a gold nanoparticle to reconstruct during CO oxidation at room temperature. The CO molecules adsorbed at the on-top sites of gold atoms in the reconstructed surface, and the energetic favorability of this reconstructed structure was confirmed by ab initio calculations and image simulations. This atomic-scale visualizing method can be applied to help elucidate reaction mechanisms in heterogeneous catalysis.     

Real-time imaging of Pt3Fe nanorod growth in solution

The growth of colloidal nanocrystal architectures by nanoparticle attachment is frequently reported as an alternative to the conventional growth by monomer attachment. However, the mechanism whereby nanoparticle attachment proceeds microscopically remains unclear. We report real-time transmission electron microscopy (TEM) imaging of the solution growth of Pt(3)Fe nanorods from nanoparticle building blocks. Observations revealed growth of winding polycrystalline nanoparticle chains by shape-directed nanoparticle attachment followed by straightening and orientation and shape corrections to yield single-crystal nanorods. Tracking nanoparticle growth trajectories allowed us to distinguish the force fields exerted by single nanoparticles and nanoparticle chains. Such quantification of nanoparticle interaction and understanding the growth pathways are important for the design of hierarchical nanomaterials and controlling nanocrystal self-assembly for functional devices.     

Nanoparticle-based bio-bar codes for the ultrasensitive detection of proteins

An ultrasensitive method for detecting protein analytes has been developed. The system relies on magnetic microparticle probes with antibodies that specifically bind a target of interest [prostate-specific antigen (PSA) in this case] and nanoparticle probes that are encoded with DNA that is unique to the protein target of interest and antibodies that can sandwich the target captured by the microparticle probes. Magnetic separation of the complexed probes and target followed by dehybridization of the oligonucleotides on the nanoparticle probe surface allows the determination of the presence of the target protein by identifying the oligonucleotide sequence released from the nanoparticle probe. Because the nanoparticle probe carries with it a large number of oligonucleotides per protein binding event, there is substantial amplification and PSA can be detected at 30 attomolar concentration. Alternatively, a polymerase chain reaction on the oligonucleotide bar codes can boost the sensitivity to 3 attomolar. Comparable clinically accepted conventional assays for detecting the same target have sensitivity limits of approximately 3 picomdar, six orders of magnitude less sensitive than what is observed with this method.     

Porous semiconductor chalcogenide aerogels

Chalcogenide aerogels based entirely on semiconducting II-VI or IV-VI frameworks have been prepared from a general strategy that involves oxidative aggregation of metal chalcogenide nanoparticle building blocks followed by supercritical solvent removal. The resultant materials are mesoporous, exhibit high surface areas, can be prepared as monoliths, and demonstrate the characteristic quantum-confined optical properties of their nanoparticle components. These materials can be synthesized from a variety of building blocks by chemical or photochemical oxidation, and the properties can be further tuned by heat treatment. Aerogel formation represents a powerful yet facile method for metal chalcogenide nanoparticle assembly and the creation of mesoporous semiconductors.     

General strategies for nanoparticle dispersion

Traditionally the dispersion of particles in polymeric materials has proven difficult and frequently results in phase separation and agglomeration. We show that thermodynamically stable dispersion of nanoparticles into a polymeric liquid is enhanced for systems where the radius of gyration of the linear polymer is greater than the radius of the nanoparticle. Dispersed nanoparticles swell the linear polymer chains, resulting in a polymer radius of gyration that grows with the nanoparticle volume fraction. It is proposed that this entropically unfavorable process is offset by an enthalpy gain due to an increase in molecular contacts at dispersed nanoparticle surfaces as compared with the surfaces of phase-separated nanoparticles. Even when the dispersed state is thermodynamically stable, it may be inaccessible unless the correct processing strategy is adopted, which is particularly important for the case of fullerene dispersion into linear polymers.     

Comparative Proteomic Analysis Shows an Elevation of Mdh1 Associated with Hepatotoxicity Induced by Copper Nanoparticle in Rats

Copper nanoparticle is a new material widely used in biological medicine, animal husbandry and industrial areas, but its potential toxicity to human health and environment remains unclear. In order to study the hepatotoxic mechanisms of nanoparticles copper, two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI/TOF MS) of proteomics technology were used to isolate and identify the differentially expressed proteins from liver, which associated with hepatotoxicity induced by copper nanoparticle in rats. In this study, we have screened 15 kinds of proteins related with hepatotoxicity, of which spot8212 was identified as Malate dehydrogenase (Mdh1). The mRNA expression trend of Mdh1 was consistent with the result of 2-DE by RT-PCR validation. Bioinformatics analysis showed that Mdh1 was stable and no signal peptides, subcellular location was in endoplasmic reticulum; it contained many functional sites such as malate dehydrogenase activity signal sites 155LTRLDHNRAKSQI167; α helixes and random coils were the two main elements. Homologous analysis demonstrated high homologous of Mdh1 in rats with mouse and human, and the phylogenetic tree of Mdh1 was constructed. The result indicated that copper nanoparticle could regulate up the Mdh1 protein expression so as to compensate the energy deficit. Energy metabolic disturbance may be a pathway for copper nanoparticle particles to exert the hepatotoxic effects in rats.     

ZnO/Bi_(3.6)Eu_(0.4)Ti_3O_(12)纳米复合薄膜的光致发光性能

采用化学溶液沉积法在石英衬底上制备纳米颗粒ZnO/Bi3.6Eu0.4Ti3O12(BEu T)铁电复合薄膜.光致发光研究结果表明,通过引入ZnO纳米颗粒,BEuT薄膜中Eu3+的发光大大增强,其强度大约是单纯BEu T薄膜的35倍.这种发光强度的极大改善归因于从ZnO到Eu3+的能量传递效率高.     

Electrostatic self-assembly of binary nanoparticle crystals with a diamond-like lattice

Self-assembly of charged, equally sized metal nanoparticles of two types (gold and silver) leads to the formation of large, sphalerite (diamond-like) crystals, in which each nanoparticle has four oppositely charged neighbors. Formation of these non-close-packed structures is a consequence of electrostatic effects specific to the nanoscale, where the thickness of the screening layer is commensurate with the dimensions of the assembling objects. Because of electrostatic stabilization of larger crystallizing particles by smaller ones, better-quality crystals can be obtained from more polydisperse nanoparticle solutions.     

Thermographic selection of effective catalysts from an encoded polymer-bound library

A general method is introduced for the rapid and simultaneous evaluation of each member of large encoded catalyst libraries for the ability to catalyze a reaction in solution. The procedure was used to select active catalysts from a library of potential polymer-bound multifunctional catalysts. From approximately 7000 beads screened (3150 distinct catalysts), 23 beads were selected for catalysis of an acylation reaction. Kinetic experiments indicate that the most strongly selected beads are also the most efficient catalysts.     

Heterogeneous catalysts

Proven catalysts exist in many different forms and with many different kinds of composition. An understanding of how catalysts function is beginning to emerge in a few areas, and some superior catalysts have been developed as a result of this knowledge. Applications of new techniques and disciplines should lead to impressive advances in the years ahead.     

Scanometric DNA array detection with nanoparticle probes

A method for analyzing combinatorial DNA arrays using oligonucleotide-modified gold nanoparticle probes and a conventional flatbed scanner is described here. Labeling oligonucleotide targets with nanoparticle rather than fluorophore probes substantially alters the melting profiles of the targets from an array substrate. This difference permits the discrimination of an oligonucleotide sequence from targets with single nucleotide mismatches with a selectivity that is over three times that observed for fluorophore-labeled targets. In addition, when coupled with a signal amplification method based on nanoparticle-promoted reduction of silver(I), the sensitivity of this scanometric array detection system exceeds that of the analogous fluorophore system by two orders of magnitude.     

查尔酮及其衍生物合成中均相催化剂的研究进展(Ⅰ)

综述了查尔酮及其衍生物均相合成的催化剂研究。同时,把催化剂分为碱性均相催化剂、酸性均相催化剂和有机金属化合物均相催化剂。     

Polyolefin spheres from metallocenes supported on noninteracting polystyrene

To obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of alpha-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40 degreesC affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time.     

纳米技术在畜牧业中的应用前景

纳米技术是20世纪80年代末诞生的一项新型科学技术。由于纳米微粒具有小尺寸效应、表面效应、量子尺寸效应和宏观量子隧道等效应,从而使其具有特殊的吸收、吸附、控释和缓释性能,因此在畜牧兽医领域具有重大的研究价值和广阔的应用前景。文章综述了纳米微粒的吸收、吸附、控释和缓释作用及其在饲料、兽药、疫苗、遗传育种、畜禽产品质量及环境保护等方面的应用,并展望了其前景。     

Nanoparticles with Raman spectroscopic fingerprints for DNA and RNA detection

Multiplexed detection of oligonucleotide targets has been performed with gold nanoparticle probes labeled with oligonucleotides and Raman-active dyes. The gold nanoparticles facilitate the formation of a silver coating that acts as a surface-enhanced Raman scattering promoter for the dye-labeled particles that have been captured by target molecules and an underlying chip in microarray format. The strategy provides the high-sensitivity and high-selectivity attributes of gray-scale scanometric detection but adds multiplexing and ratioing capabilities because a very large number of probes can be designed based on the concept of using a Raman tag as a narrow-band spectroscopic fingerprint. Six dissimilar DNA targets with six Raman-labeled nanoparticle probes were distinguished, as well as two RNA targets with single nucleotide polymorphisms. The current unoptimized detection limit of this method is 20 femtomolar.     

用于制备生物柴油的固体催化剂研究进展

生物柴油作为可再生的替代能源,已引起世界范围内的广泛关注。研制用于催化酯交换反应制备生物柴油的固体催化剂是目前的一大研究热点。综述了目前国内外研制的固体酸性和碱性催化剂的催化性能和研究现状,比较了各种固体催化剂的优劣和不足,提出了生物柴油用固体催化剂的研究和发展趋势。     

Heterogeneous catalysis: some recent developments

In recent years major progress has been made in the area of heterogeneous catalysis by metals. Much has been learned about the nature of metal catalysts and of catalytic phenomena on metals. Characteristic patterns of catalytic behavior among the metallic elements have been established for certain classes of reactions, and these patterns provide a first step toward a more comprehensive understanding of catalytic specificity. Studies on metal alloys and related bimetallic catalysts have revived interest in a geometric factor in surface catalysis to complement the traditional electronic factor. Closely related to this geometric factor is the discovery that selectivity, rather than activity alone, is a major factor in reactions on bimetallic catalysts. Concurrent with progress in understanding how catalysts work, advances are also being made in the development of new catalyst systems, examples of which are the bimetallic (or polymetallic) cluster catalysts. Research in this area provides an example of how advances in catalyst technology can be realized within a framework of fundamental research on catalytic phenomena (38).     

制备生物柴油固体催化剂的研究现状及前景展望

介绍了均相法制备生物柴油的方法,指出均相催化剂在应用中存在的不足,探讨了固体酸催化剂和固体碱催化剂在制备生物柴油中的应用现状,指出了固体催化剂的研究热点及应用前景。