Ab Initio Study on Structures and Vibrational Spectra of M+(H2O)Ar2 (M = Cu,Au)

Previous investigations have shown that it is difficult to acquire the infrared (IR) spectra of M⁺(H₂O) (M?=?Cu, Au) using a single IR photon by attaching an Ar atom to M⁺(H₂O). To explore whether the IR spectra can be obtained using the two Ar atoms tagging method, the geometrical structures, IR spectra and interaction energies are investigated in detail by ab initio electronic structure calculations for M⁺(H₂O)Ar₂ (M?=?Cu, Au) complexes. Two conceivable isomeric structures are found, which result from different binding sites for two Ar atoms. CCSD(T) calculations predict that two Ar atoms are most likely to attach to Cu⁺ for the Cu⁺(H₂O)Ar₂ complex, while the Au⁺(H₂O)Ar₂ complex prefers the isomer in which one Ar atom attaches to an H atom of the H₂O molecule and the other one is bound to Au⁺. Moreover, the calculated binding energies of the second Ar atom are smaller than the IR photon energy, and so it is possible to obtain the IR spectra for both Cu and Au species. The changes in the spectra caused by the attachment of Ar atoms to M⁺(H₂O) are discussed.     

Verteilungskoeffizienten von Ag,In, Re,Au, Hg,Tl, Pb und Bi in Salpetersäure-Methanol-Gemischen

Der Anionenaustausch unter Verwendung von Salpetersäure-Methanol-Gemischen ist in den letzten Jahren von einer Anzahl von Autoren untersucht worden [1, 2, 3, 4]. In einer früheren Arbeit hatten wir bereits auf seine praktisehc Anwendbarkeit für die Trennung der SK hingewiescn [5]. In der vorliegenden Arbeit werden von uns die Verteilungs-koeffizienten von Ag, In, Re, Au, Hg, Tl, Pb und Bi angegeben und Beispiele für mögliche Trennungen angeführt.     

Investigation on shape variation of Au nanocrystals

A variety of shapes, such as rod, tripod, -shape and cube, of Au nanocrystals were synthesized by employing different reaction conditions. The nanocrystals and their shape variation were characterized by transmission electron microscopy and UV–vis spectrophotometry. The evolution of shape was accomplished by controlling the parameters used in their synthesis, the concentration of reducing agent and surface capping agent. The effect of synthetic parameters on shape was explored, to determine suitable conditions for producing each shape of nanocrystals. Nanocrystals with different shapes have different plasmon bands in the visible region of the spectrum, which is a valuable property for sensor applications.     

A novel rhodamine-based turn-on probe for fluorescent detection of Au3+ and colorimetric detection of Cu2+

In this work, we design and synthesize the novel probe RC through introduction the 1-aza-4,13-dithia-15-crown-5 ring into the structure of rhodamine 6G hydrazide, where the N atom of crown ring is responsible for quenching of rhodamine fluorescence. The compound obtained behaves as multifunctional cation sensor providing selective fluorescent response to Au³⁺ and selective colorimetric response to Cu²⁺ ions in aqueous acetonitrile (1/1, v/v) at pH 7.0. The use of 10^?5?M RC solution allowed reliable determination of target cations in the presence of a wide range of environmentally relevant ions with detection limits of 2?×?10^?6?M and 5?×?10^?7?M for gold and copper, respectively.     

Highly Robust but Surface‐Active: An N‐Heterocyclic Carbene‐Stabilized Au25 Nanocluster

Surface organic ligands play a critical role in stabilizing atomically precise metal nanoclusters in solutions. However, it is still challenging to prepare highly robust ligated metal nanoclusters that are surface‐active for liquid‐phase catalysis without any pre‐treatment. Now, an N‐heterocyclic carbene‐stabilized Au₂₅ nanocluster with high thermal and air stabilities is presented as a homogenous catalyst for cycloisomerization of alkynyl amines to indoles. The nanocluster, characterized as [Au₂₅(ⁱPr₂‐bimy)₁₀Br₇]²⁺ (ⁱPr₂‐bimy=1,3‐diisopropylbenzimidazolin‐2‐ylidene) ( 1 ), was synthesized by direct reduction of AuSMe₂Cl and ⁱPr₂‐bimyAuBr with NaBH₄ in one pot. X‐ray crystallization analysis revealed that the cluster comprises two centered Au₁₃ icosahedra sharing a vertex. Cluster 1 is highly stable and can survive in solution at 80 °C for 12 h, which is superior to Au₂₅ nanoclusters passivated with phosphines or thiols. DFT computations reveal the origins of both electronic and thermal stability of 1 and point to the probable catalytic sites. This work provides new insights into the bonding capability of N‐heterocyclic carbene to Au in a cluster, and offers an opportunity to probe the catalytic mechanism at the atomic level.     

Facile Synthesis of ZnO-Au Nanopetals and Their Application for Biomolecule Determinations

Using dextran as both reductant and stabilizing agent, nanopetals(ZnO-Au NPs) were easily synthesized and possessed a petal-like morphology. The feature structure and size of such ZnO-Au NPs were adjustable by regulating the amount of chloroauric acid(HAuCl4). Moreover, the electrochemical property of the obtained NPs was evaluated by being immobilized on the glassy carbon electrode(GCE), which performed both high sensitivity and stability in dopamine(DA) determinations. Furthermore, the as-prepared ZnO-Au NPs could also detect DA and uric acid(UA) simultaneously in the mixture without interference, indicating good selectivity and showing promising potential in biosensing.     

In situ Deposition of ‘Naked’ Gold Nanoparticles Supported on Silica Spheres as Recyclable Catalysts in Styrene Epoxidation

Tlie rational designs of particle size, morphology and surface states of the Au nanoparticles(AuNPs) are crucial for Au nanocatalyst. We herein report a method to synthesize the silica microspheres supported AuNPs(ca.1 nm) and their application in controlling the reaction conversion and selectivity in styrene epoxidation. Surfactant-ftee AuNPs deposited on silica microspheres were in situ fabricated with aid of the Ag nanoparticles (AgNPs) as sacrificial template by galvanic replacement reaction, leading to AuNPs/SiO2 catalyst directly without any post-treatment to expose crystal facets.A high conversion of 46.7% and selectivity of 91.7% to styrene oxide was achieved with H2O2 as oxidant in ethanol. The solid catalyst could be reused at least 10 reaction cycles without significant decrease in activity and selectivity. This study not only supplies an active, recoverable catalyst for styrene oxidation with green oxidant and solvent, but also demonstrates that the silica microspheres functionalized with thiol groups have a superior ability in stabilizing noble metal nanoparticles even without any surfactant.     

Negative Charging of Au Nanoparticles during Methanol Synthesis from CO2/H2 on a Au/ZnO Catalyst: Insights from Operando IR and Near‐Ambient‐Pressure XPS and XAS Measurements

The electronic and structural properties of Au/ZnO under industrial and idealized methanol synthesis conditions have been investigated. This was achieved by kinetic measurements in combination with time‐resolved operando infrared (DRIFTS) as well as in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS) and X‐ray absorption near‐edge spectroscopy (XANES) measurements at the O K‐edge together with high‐resolution electron microscopy. The adsorption of CO during the reaction revealed the presence of negatively charged Au nanoparticles/Au sites during the initial phase of the reaction. Near‐ambient‐pressure XPS and XANES demonstrate the build‐up of O vacancies during the reaction, which goes along with a substantial increase in the rate of methanol formation. The results are discussed in comparison with previous findings for Cu/ZnO and Au/ZnO catalysts.