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排序方式: 共有423条查询结果,搜索用时 15 毫秒
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Sergio R. Calvo 《Surface science》2007,601(1):165-171
We investigate the reactivity of various PtxPdy combinations (with x + y = 10 and various x:y ratios) towards the adsorption of specific intermediates of the oxygen reduction, using the B3PW91 hybrid density functional theory. The reactivity is shown to be not only sensitive to the composition of the cluster, but also to the atomic distribution. The calculations indicate that two different ensembles: one ordered and one randomly mixed, with overall composition Pt3Pd7 are thermodynamically more favorable than pure Pt10 for the oxygen reduction reaction. The reasons for this behavior are clearly explained in terms of the atomic and electronic distribution, which makes the Pd atoms to act as electron donors both to Pt atoms and to the adsorbates, thus the reactivity of the Pd atoms in such environment becomes intermediate between Pt and Pd. Moreover, it is found that in a mixed Pt3Pd7 state the electronic distribution makes the average atom more similar to Pt than to Pd, whereas in an ordered Pt3Pd7 cluster, the average atom is more similar to Pd than to Pt. 相似文献
43.
We present a study on dielectric response of Ag14 nanocluster dimer using first principles methods. The interaction energy, (hyper)polarizability of dimer are predicted under various separations of the two identical Ag14 nanoclusters. The appropriate separation makes the second-order hyperpolarizability of Ag14 dimer is about 70 times larger than the Ag14 monomer. The increase of polarizability and hyperpolarizability is ascribed to reconfiguration of molecular electronic state from Ag cluster monomer to dimer. Nonlinear response is more susceptible to the steady intermediate state compared to linear response. The crucial transitions contributed to hyperpolarizability are assigned to be from highest occupied molecular orbitals to the lowest unoccupied molecular orbital (HOMOs-LUMO) of nanocluster dimer. Binding character of LUMO plays an important role in determining nonlinear optical properties. 相似文献
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Dr. Concha Bosch‐Navarro Zachary P. L. Laker Helen R. Thomas Alexander J. Marsden Dr. Jeremy Sloan Dr. Neil R. Wilson Dr. Jonathan P. Rourke 《Angewandte Chemie (International ed. in English)》2015,54(33):9560-9563
Atomic‐resolution transmission electron microscopy was used to identify individual Au9 clusters on a sulfur‐functionalized graphene surface. The clusters were preformed in solution and covalently attached to the surface without any dispersion or aggregation. Comparison of the experimental images with simulations allowed the rotational motion, without lateral displacement, of individual clusters to be discerned, thereby demonstrating a robust covalent attachment of intact clusters to the graphene surface. 相似文献
46.
本文建立了一种快速灵敏检测水中硫离子的新方法。该方法利用聚胸腺嘧啶单链DNA保护的铜纳米簇为荧光探针。以聚胸腺嘧啶单链DNA为模板制备了具有荧光性质的铜纳米簇,当加入S2-后,铜纳米簇荧光显著猝灭。铜纳米簇荧光猝灭量与S2-浓度在0.125~8μmol/L范围内有良好的线性,检测限为22nmol/L。该方法对S2-有较好的选择性,实际样品检测结果显示回收率良好,说明该方法可以用于实际水样中S2-的检测。由于聚胸腺嘧啶单链DNA为模板制备的铜纳米簇制备过程简单快速,可在5min内完成,使得检测时间大大缩短。 相似文献
47.
《Macromolecular rapid communications》2017,38(17)
Easy access to discrete nanoclusters in metal‐folded single‐chain nanoparticles (metal‐SCNPs) and independent ultrafine sudomains in the assemblies via coordination‐driven self‐assembly of hydrophilic copolymer containing 9% imidazole groups is reported herein. 1H NMR, dynamic light scattering, and NMR diffusion‐ordered spectroscopy results demonstrate self‐assembly into metal‐SCNPs (>70% imidazole‐units folded) by neutralization in the presence of Cu(II) in water to pH 4.6. Further neutralization induces self‐assembly of metal‐SCNPs (pH 4.6–5.0) and shrinkage (pH 5.0–5.6), with concurrent restraining residual imidazole motifs and hydrophilic segment, which organized into constant nanoparticles over pH 5.6–7.5. Atomic force microscopy results evidence discrete 1.2 nm nanoclusters and sub‐5‐nm subdomains in metal‐SCNP and assembled nanoparticle. Reduction of metal center using sodium ascorbate induces structural rearrangement to one order lower than the precursor. Enzyme mimic catalysis required media‐tunable discrete ultrafine interiors in metal‐SCNPs and assemblies have hence been achieved. 相似文献
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Mojtaba Alipour 《International journal of quantum chemistry》2014,114(4):255-260
As an important lineage of metal oxides, alkaline earth oxides have attracted significant interest due to their unique properties and potential applications in material science and industry. In this article, we present the first ab initio (HF, MP2, and CCSD(T)) and density functional theory (TPSSh functional) investigation on the optical properties such as polarizabilities per atom (PPA), differential polarizability per unit (DPPU), and anisotropies of (BeO)n [n = 2–9] nanoclusters as an illustrative example of alkaline earth oxides nanostructures. Basis set augmentation effects on the studied properties of BeO nanoclusters have been explored by using basis sets of triple‐zeta quality starting from 6‐311G with increasing completeness of the diffuse and polarization functions to the 6‐311+G(3df) basis. Checking carefully the basis set effects, it is shown that the 6‐311+G(3d) basis set provides the best compromise between the accuracy and computational cost. We found a decreasing trend for PPA values of BeO nanoclusters using all considered methods, indicating the strong electron delocalization with increasing cluster size. Moreover, in accordance with the energetic analysis of stability of BeO nanoclusters, the values of PPA show that the (BeO)4 and (BeO)6 clusters are the most stable magic numbers compared to the neighbors, satisfying the minimum polarizability principle. The computed values of DPPU demonstrate a strong binding effect in BeO nanoclusters. Taking into account the electron correlation correction (ECC), it is observed that the variations of ECC on dipole polarizabilities are almost smooth for clusters under study. © 2013 Wiley Periodicals, Inc. 相似文献
49.
This Concept article provides an elementary discussion of a special class of large‐sized gold compounds, so‐called Au nanoclusters, which lies in between traditional organogold compounds (e.g., few‐atom complexes, <1 nm) and face‐centered cubic (fcc) crystalline Au nanoparticles (typically >2 nm). The discussion is focused on the relationship between them, including the evolution from the Au???Au aurophilic interaction in AuI complexes to the direct Au? Au bond in clusters, and the structural transformation from the fcc structure in nanocrystals to non‐fcc structures in nanoclusters. Thiolate‐protected Aun(SR)m nanoclusters are used as a paradigm system. Research on such nanoclusters has achieved considerable advances in recent years and is expected to flourish in the near future, which will bring about exciting progress in both fundamental scientific research and technological applications of nanoclusters of gold and other metals. 相似文献
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