Oxidation‐induced nanostructures on Cu{100}, Cu(Ag) and Ag/Cu{100} studied by photoelectron spectroscopy

Initial surface oxidation and nanoscale morphology on Cu{100}, Cu(Ag) and Ag/Cu{100} have been investigated in situ by X‐ray photoelectron spectroscopy (XPS), X‐ray induced Auger electron spectroscopy (XAES) and the inelastic electron background analysis as a function of oxygen exposure at 3.7 × 10^?2 and 213 mbar pressures at a surface temperature of 373 K. Relative Cu₂O concentrations have been quantified by analysis of the peak shape of the XAES Cu LMM transition. The surface morphology of Cu₂O islands and the Ag layer has been characterized by inelastic electron background analysis of XAES O KLL and Ag 3d transitions. Oxygen‐induced segregation of Cu, as well as the subsequent Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces, has been investigated quantitatively. Our results indicate that Ag has a clear inhibitive effect on the initial oxidation and Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces. The Cu₂O islands are also observed to remain highly strained on Ag/Cu{100} even at higher O₂ exposures. The results suggest that strained Cu₂O islands eventually penetrate through the buried Ag layer, and in conjunction with segregating Cu atoms enable the oxidation to proceed at a similar rate to or even faster than on the unalloyed Cu surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Chemisorption of O and O2 on Ag(110): An LCGTO-LSD cluster study

As part of a study aimed at better understanding of molecular and dissociative chemisorption of oxygen on Ag(110), linear combinations of Gaussian type orbitals-local spin density (LCGTO -LSD ) calculations have been performed for O, O^?, O₂, O^?₂, O^2?₂ and a variety of silver clusters interacting with O or O₂. For atomic O adsorption a very small cluster, Ag₄, chosen to model the long-bridge site already affords very good agreement with both recent EXAFS experiments and recent ab initio calculations. We calculate O to be 0.25 Å above the surface (exp. 0.2 Å). The Ag₄? O vibrational frequency is estimated to be 400 cm^?1, in reasonable accord with the experimental EELS value of 325 cm^?1. Determination of the geometry for O₂ (ads.) and, ultimately, of the dissociation path are far more difficult tasks. An extensive search for local minima in the vicinity of the LB site is being carried out. Results to date for small, Ag₂ and Ag₄, clusters have furnished insight into the factors influencing the structure. Overlap between the π* orbital of the O₂ moiety and Ag s functions is a key factor; that is, there is an important covalent component of the binding. For geometries with O₂ parallel to the surface, this is achieved by twisting the O₂ fragment with respect to the [11¯0] grooves (geometries either parallel or perpendicular to the grooves yield zero π‖*?s overlap by symmetry). The structure with O₂ perpendicular to the surface also achieves reasonable overlap and lies close in energy to the most stable ‘parallel’ geometry.     

Density functional study of ethylene oxidation on an Ag(111) surface

The mechanism of ethylene epoxidation on Ag surfaces has been investigated using the density functional method and Ag _n clusters (n = 3 to 10) modeling the Ag(111) surface. The adsorption energy of O₂ to the Ag clusters was strongly dependent on the HOMO level of the cluster, and the clusters with higher HOMO levels afforded larger O₂ adsorption energies. The energetics was investigated for both the molecular and atomic oxygen epoxidation mechanisms. For the atomic oxygen mechanism, epoxidation was found to proceed without an activation energy, whereas a small amount of activation energy (about 5 kcal/mol) was calculated for the molecular oxygen mechanism. Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

X-Ray absorption spectroscopy: sensitive characterization of (model-) catalysts with the electron yield technique

Small chromium oxide particles (Cr₂O₃, CrO₂) supported on titanium dioxide and oxidized Ag(111) single crystals were investigated by X-ray absorption spectroscopy at the oxygen K-edge. The spectra were collected in the electron yield mode in order to increase the surface sensitivity. The shape of the sharp split White line (WL) in the O K-edges spectra depended strongly on the oxidation state of the chromium ions in the probed samples suggesting that the WL can be used as an indicator of different environments in the supported chromium oxide films. On the other hand, the O K-edges of the oxidized Ag(111) crystal indicated that the formation of the distinct oxygen species at the surface and in the near-surface region was accompanied by a different silver-to-oxygen covalent interaction. Received: 15 July 1997 / Revised: 22 December 1997 / Accepted: 29 December 1997     

A New 3D 4d‐4f La–Ag Coordination Polymer Constructed by Interesting [Ag2]n and Flat [La2(IN)6(CH3COO)]n Layers

One new 3D La‐Ag coordination compound formulated as [La₂Ag₃(IN)₆(OAC)(H₂O)₃][NO₃]₂ · 2H₂O ( 1 ) (HIN = isonicotinic acid; HOAC = acetic acid) was synthesized. The structure represents an interesting 3D open framework that is built upon 2D lanthanide layers and [Ag(IN)₂]⁺ linkers. The triple helical [La(IN)₂(H₂O)]_n chain and zigzag [LaIN(OAC)]_n chain are found in the 2D La‐IN layers. Channels are also found in the framework of 1 , owing to shape‐controlled synthesis templated by the free NO₃^– ions and water molecules.     

Ein neuer Aluminium/Nickel/Oxo‐Cluster: [Ni(acac)OAl(OtBu)2]4

A New Aluminum/Nickel/Oxo‐Cluster: [Ni(acac)OAl(OtBu)₂]₄ When bis(tert‐butoxy)alane (tBu‐O)₂AlH is allowed to react with nickeldiacetylacetonate at elevated temperature a new nickel/aluminum/oxo cluster [Ni(acac)OAl(OtBu)₂]₄ is formed together with aluminum acetylacetonate Al(acac)₃ and some other products. The metal/oxo cluster is isolated by crystallization and structurally fully characterized by X‐ray diffraction analysis. The molecule [Ni(acac)OAl(OtBu)₂]₄ contains an eight membered Al₄O₄ cycle, to which eight mutually edge sharing NiO₂Al cycles are fused. The overall point symmetry of the metal/oxo cluster is almost S₄. While the aluminum atoms are tetrahedrally surrounded by oxygen ligands (mean distances Al‐O in‐between 1, 730(6) and 1, 789(6) Å)), the nickel atoms are in a square pyramidal coordination sphere of oxygen atoms (Ni‐O_axial = 1.938(6) Å, Ni‐O_basal = 2.056(9) Å; all polyhedra are distorted). The nickel atoms have a d⁸ high spin electron configuration (μ_eff = 3.32 B.M.).     

An EELS study of CO2 and CO3 adsorbed on oxygen covered Ag(110)

The vibrational spectra of CO₂ and CO₃ adsorbed on Ag(110) was studied with high-resolution electron energy-loss spectroscopy (EELS). CO₂ does not adsorb on the clean surface at 100 K. EELS results show that preadsorbed atomic oxygen can induce adsorption and reaction with CO₂ to form a stable surface carbonate as well as a molecular CO₂ binding state at 100 K. The latter desorbs at 130 K while CO₃ decomposes to CO_2(g) and O_(a) at 480 K as shown by both EELS and thermal desorption. The vibrational spectrum of CO_2(a) bears remarkable similarities with CO₂ gas; both the strong asymmetric stretch at 2350 cm^? and the Fermi resonance are seen. EELS measurements performed as a function of annealing temperature indicate that the carbonate species binds with one oxygen down and the other two up with respect to the surface. Additionally, an irreversible conversion between this form and that with two oxygens down does not occur.     

Counter‐anion role in the formation of two supramolecular complexes: [Ag2(DPP)2](ClO4)2·CH3CN and [Ag2(DPP)2(NO3)2] {DPP is N‐[(diphenylphosphanyl)methyl]pyridin‐4‐amine}

The title compounds, bis{μ‐N‐[(diphenylphosphanyl)methyl]pyridin‐4‐amine‐κ²N¹:P}disilver bis(perchlorate) acetonitrile monosolvate, [Ag₂(C₁₈H₁₇N₂P)₂](ClO₄)₂·CH₃CN, (1), and bis{μ‐N‐[(diphenylphosphanyl)methyl]pyridin‐4‐amine‐κ²N¹:P}bis[(nitrato‐κ²O,O)silver], [Ag₂(C₁₈H₁₇N₂P)₂(NO₃)₂], (2), each contain disilver macrocyclic [Ag₂(C₁₈H₁₇N₂P)₂]²⁺ cations lying about inversion centres. The cations are constructed by two N‐[(diphenylphosphanyl)methyl]pyridin‐4‐amine (DPP) ligands linking two Ag⁺ cations in a head‐to‐tail fashion. In (1), the unique Ag⁺ cation has a near‐linear coordination geometry consisting of one pyridine N atom and one P atom from two different DPP ligands. Two ClO₄⁻ anions doubly bridge two metallomacrocycles through Ag...O and N—H...O weak interactions to form a chain extending in the c direction. The half‐occupancy acetonitrile molecule lies with its methyl C atom on a twofold axis and makes a weak N...Ag contact. In (2), there are two independent [Ag(C₁₈H₁₇N₂P)]⁺ cations. The nitrate anions weakly chelate to each Ag⁺ cation, leading to each Ag⁺ cation having a distorted tetrahedral coordination geometry consisting of one pyridine N atom and one P atom from two different DPP ligands, and two chelating nitrate O atoms. Each dinuclear [Ag₂(C₁₈H₁₇N₂P)₂(NO₃)₂] molecule acts as a four‐node to bridge four adjacent equivalent molecules through N—H...O interactions, forming a two‐dimensional sheet parallel to the bc plane. Each sheet contains dinuclear molecules involving just Ag1 or Ag2 and these two types of sheet are stacked in an alternating fashion. The sheets containing Ag1 all lie near x = , , etc, while those containing Ag2 all lie near x = 0, 1, 2 etc. Thus, the two independent sheets are arranged in an alternating sequence at x = 0, , 1, etc. These two different supramolecular structures result from the different geometric conformations of the templating anions which direct the self‐assembly of the cations and anions.     

A Novel 3‐D Heterobimetallic Cyano‐bridged Coordination Polymer Incorporating Ag···Ag Interaction: [Cu(dien)Ag(CN)2]2[Ag2(CN)3][Ag(CN)2]

A three‐dimensional cyano‐bridged copper(II) complex, [Cu(dien)Ag(CN)₂]₂[Ag₂(CN)₃][Ag(CN)₂] ( 1 ) (dien = diethylenetriamine), has been prepared and characterized by X‐ray crystallography. Complex 1 crystallized in the monoclinic space group P2₁/n with a = 6.988(2), b = 17.615(6), c = 12.564(4) Å, β = 90.790(5)°. The crystal consists of cis‐[Cu(dien)]²⁺ units bridged by [Ag(CN)₂]^— to form a zig‐zag chain. The Ag atoms of the free and bridging [Ag(CN)₂]^— link together to form additional infinite zig‐zag chains with short Ag···Ag distances. The presence of Ag···Ag interactions effectively increases the dimensionality from a 1‐D chain to a 3‐D coordination polymer.     

Ab initio study of molecular oxygen adsorption on Pu (111) surface

Using the generalized gradient approximation to density functional theory (DFT), molecular and dissociative oxygen adsorptions on a Pu (111) surface has been studied in detail. Dissociative adsorption with a layer‐by‐layer alternate spin arrangement of the plutonium layer is found to be energetically more favorable, and adsorption of oxygen does not change this feature. Hor1 (O₂ is parallel to the surface and lattice vectors) approach on the center2 (center of the unit cell, where there is a Pu atom directly below on the third layer) site, both without and with spin polarization, was found to be the preferred chemisorbed site among all cases studied with chemisorption energies of 8.365 and 7.897 eV, respectively. The second‐highest chemisorption energy occurs at the Ver (O₂ is vertical to the surface) approach of the bridge site with chemisorption energies of 8.294 eV (non‐spin‐polarized) and 7.859 eV (spin‐polarized), respectively. We find that 5f electrons are more localized in the spin‐polarized case than the non‐spin‐polarized counterparts. Localization of the 5f electrons is higher in the oxygen‐adsorbed plutonium layers compared with the bare layers. The ionic part of O? Pu bonding plays a significant role in the chemisorption process, along with Pu 5f? O 2p hybridization. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Synthesis,crystal structure and studies on the interaction with albumin of a new silver(I) complex based on 2‐(4‐nitrobenzenesulfonamido)benzoic acid

In the present work, the two‐dimensional (2D) polymer poly[[μ₄‐2‐(4‐nitrobenzenesulfonamido)benzoato‐κ⁴O¹:O¹:O^1′:N⁶]silver(I)] (AgL), [Ag(C₁₃H₉N₂O₆S)]_n, was obtained from 2‐(4‐nitrobenzenesulfonamido)benzoic acid (HL), C₁₃H₁₀N₂O₆S. FT–IR, ¹H and ¹³C{¹H} NMR spectroscopic analyses were used to characterize both compounds. The crystal structures of HL and AgL were determined by single‐crystal X‐ray diffraction. In the structure of HL, O—H…O hydrogen bonds between neighbouring molecules result in the formation of dimers, while the silver(I) complex shows polymerization associated with the O atoms of three distinct deprotonated ligands (L^?). Thus, the structure of the Ag complex can be considered as a coordination polymer consisting of a one‐dimensional linear chain, constructed by carboxylate bridging groups, running parallel to the b axis. Neighbouring polymeric chains are further bridged by Ag—C monohapto contacts, resulting in a 2D framework. Fingerprint analysis of the Hirshfeld surfaces show that O…H/H…O hydrogen bonds are responsible for the most significant contacts in the crystal packing of HL and AgL, followed by the H…H and O…C/C…O interactions. The Ag…Ag, Ag…O/O…Ag and Ag…C/C…Ag interactions in the Hirshfeld surface represent 12.1% of the total interactions in the crystal packing. Studies of the interactions of the compounds with human serum albumin (HSA) indicated that both HL and AgL interact with HSA.     

Disinfection of Escherichia Coli Gram Negative Bacteria Using Surface Modified TiO2: Optimization of Ag Metallization and Depiction of Charge Transfer Mechanism

The antibacterial activity of silver deposited TiO₂ (Ag‐TiO₂) against Gram negative Escherichia coli bacteria was investigated by varying the Ag metal content from 0.10 to 0.50% on the surface of TiO₂. Ag depositions by the photoreduction method were found to be stable. Surface silver metallization was confirmed by EDAX and XPS studies. Photoluminescence studies show that the charge carrier recombination is less for 0.1% Ag‐TiO₂ and this catalyst shows superior bactericidal activity under solar light irradiation compared to Sol gel TiO₂ (SG‐TiO₂) due to the surface plasmon effect. The energy levels of deposited Ag are dependent on the Ag content and it varies from ?4.64 eV to ?1.30 eV with respect to the vacuum energy level based on atomic silver to bulk silver deposits. The ability of electron transfer from Ag deposit to O₂ depends on the position of the energy levels. The 0.25% and 0.50% Ag depositions showed detrimental effect on bactericidal activity due to the mismatch of energy levels. The effect of the EROS (External generation of the Reactive Oxygen Species by 0.1% Ag‐TiO₂) and IROS (Interior generation of Reactive Oxygen Species within the bacteria) on the bactericidal inactivation is discussed in detail.     

Ag(I), Cu(II), and Cd(II) sulfacetamide complexes: Synthesis,spectral, thermal study,and antimicrobial activity assessment

Sulfacetamide complexes of Ag(I), Cu(II), and Cd(II) were synthesized and characterized by the elemental analyses and IR and ¹H NMR spectra. Structural assessment revealed two modes of coordination in the sulfacetamide complexes, showing that sulfacetamide reacts as a bidentate ligand and coordinates to Ag(I) and Cd(II) through the amido and sulfonyl oxygens and to Cu(II) through the NH₂ nitrogen. Molar conductance measurements in DMSO showed that both the complexes are nonelectrolytes in nature, which allowed they to be assigned the formulas [Ag(SAM-Na)(NO₃)H₂O)]·3H₂O, [Cu(SAM-Na)₂(Cl)₂], and [Cd(SAM-Na)(Cl)₂]·10H₂O. The kinetic and thermodynamic parameters of the thermal decomposition reactions of the complexes were estimated from the TG/DTG curves by the Coats–Redfern and Horowitz–Metzeger methods. The surface morphology of sulfacetamide complexes was scanned using X-ray powder diffraction (XRD) and scanning electron microscope (SEM) analyses.     

Density functional study of O2 adsorption on (100) surface of γ‐uranium

Chemisorption of the oxygen molecule on the (100) surface of γ‐uranium was investigated using the generalized gradient approximation to Density Functional Theory. Dissociative adsorptions of O₂ are found to be significantly favored compared to molecular adsorptions. Interstitial adsorptions of molecular oxygen are less probable, as no bound states are found in this case. Only after dissociation of O₂ is atomic oxygen diffusion through the surface possible. The O 2p orbitals are found to hybridize with U 5f bands, and some of the U 5f electrons become more localized. A significant charge transfer from the first layer of the uranium surface to the oxygen atoms is found to occur, making the bonding partly ionic. For the most favored site, the dissociative chemisorption energy is ～9.5 eV, which indicates a strong reaction of uranium surface with oxygen. Spin polarization does not have a significant effect on the chemisorption process. For most of the sites and approaches, chemisorption configurations are almost same for both spin‐polarized and non‐spin‐polarized cases. For the most favored chemisorption sites of oxygen on uranium, paramagnetic adsorption is slightly stronger, by 0.304 eV, compared to magnetic adsorption. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

The investigation of Ag decorated double‐wall hollow TiO2 spheres as photocatalyst

In this paper, a novel TiO₂ nanosheets assembled double‐wall hollow sphere (DHS)has been prepared successfully via hydrothermal treatment of SiO₂@TiO₂ with the assistant of CTAB.The prepared samples are characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron spin resonance (ESR), X‐ray diffraction (XRD) and X‐ray photoelectron spectra (XPS), etc.Results show that redeposited silica species play a key role in the formation of the double‐wall structure. The as‐synthesized DHS nanostructure exhibits a large surface area (417.6 m² g^‐1) and excellent mechanical strength. Furthermore, after decoration of Ag and calcination treatment, the double‐shelled TiO₂/Ag heterostructures show an enhanced photocatalytic performance in the degradation of RhB under UV or visible light irradiations for the following reasons: the surface plasmon resonance effect of Ag, strong interaction between Ag and TiO₂ nanosheets, large surface area, excellent adsorption capacityand unique double‐wall structure. On the basis of the experimental results, a possible mechanism for pollutantdegradation under visual light irradiation has been proposed.     

A Novel Octahedral Hexasilver（I） Cluster： Ag[SSCN（n—C4H9）2]6

The first crystal structural report of a AgDTC complex (DTC-dialkyldithiocarbamate,R=n-butyl)presented in this paper shows that it is a hexanuclear species.The structural arrangement for the DDP(dialkyldithiophosphate)ligands is different from that of Cu6(DDP)6,but is the same as that of Ag6-[SSP(O-i-Pr)2]6.     

A highly reactive and magnetic recyclable catalyst based on silver nanoparticles supported on ferrite for N‐monoalkylation of amines with alcohols

Fe₃O₄@SiO₂‐Ag catalyst was found to be highly active and selective in the N ‐alkylation of amines with a variety of aromatic and linear alcohols. The heterogeneous nature of the Fe₃O₄@SiO₂‐Ag catalyst allows easy recovery and regeneration by applying an external magnet for six subsequent reaction cycles. The prepared catalyst was characterized using electron microscopy techniques, X‐ray diffraction, vibrating sample magnetometry and atomic absorption spectroscopy.     

A candidate for a single‐chain magnet: [Mn3(OAc)6(py)2(H2O)2]n (OAc is acetate and py is pyridine)

The title complex, catena‐poly[di‐μ₃‐acetato‐κ⁶O:O:O′‐tetra‐μ₂‐acetato‐κ⁴O:O;κ⁴O:O′‐diaquabis(pyridine‐κN)trimanganese(II)], [Mn₃(CH₃COO)₆(C₆H₅N)₂(H₂O)₂]_n, is a true one‐dimensional coordination polymer, in which the Mn^II centres form a zigzag chain along [010]. The asymmetric unit contains two metal centres, one of which (Mn1) lies on an inversion centre, while the other (Mn2) is placed close to an inversion centre on a general position. Since all the acetates behave as bridging ligands, although with different μ₂‐ and μ₃‐coordination modes, a one‐dimensional polymeric structure is formed, based on trinuclear repeat units (Mn1...Mn2...Mn2′), in which the Mn2 and Mn2′ sites are related by an inversion centre. Within this monomeric block, the metal–metal separations are Mn1...Mn2 = 3.36180 (18) Å and Mn2...Mn2′ = 4.4804 (3) Å. Cation Mn1, located on an inversion centre, displays an [MnO₆] coordination sphere, while Mn2, on a general position, has a slightly stronger [MnO₅N] ligand field, as the sixth coordination site is occupied by a pyridine molecule. Both centres approximate an octahedral ligand field. The chains are parallel in the crystal structure and interact via hydrogen bonds involving coordinated water molecules. However, the shortest metal–metal separation between two chains [5.3752 (3) Å] is large compared with the intrachain interactions. These structural features are compatible with a single‐chain magnet behaviour, as confirmed by preliminary magnetic studies.     

Gallium and Indium Alkoxides with Hydride,Cyclopentadienediide and Copper(I) tert‐Butoxide as further Components

Gallium hydride stabilized by the base quinonuclidine reacts with acetone under addition of the Ga‐H function to the carbon–oxygen double bond yielding (HGa)₅(OiPr)₈O ( 1 ) as isolable compound. (HGa)₅(OiPr)₈O may be formally split in to four entities of HGa(OiPr)₂ and one entity HGaO. The inner atomic skeleton of 1 is a novel Ga₅O₉ heterocluster with gallium atoms occupying the corners of a distorted trigonal bi‐pyramid, an oxygen atom in the center and the remaining alcoholate oxygen atoms bridging eight of the nine edges of the bi‐pyramid (X‐ray diffraction analysis). Potassium indium alkoxide KIn(OtBu)₄ has been used to synthesize several new compounds like In₄(OtBu)₈(C₅H₄)₂ ( 2 ), (py)₂CuIn(OtBu)₄ ( 3 ), and [CuIn(OtBu)₄]₂ ( 4 ) by reaction with TiCl₂cp₂ ( 2 ) and CuCl ( 3 , 4 ). All compounds were characterized by spectroscopic means and by X‐ray structure analyses revealing novel polycyclic structures.     

Improved Photocatalytic Activity and Stability of Nano‐sized Ag/Ag2CO3 Plasmonic Photocatalyst by Surface Modification of Fe(III) Nanocluster

The surface modification of Ag/Ag₂CO₃ with Fe(III) ions has been achieved through simply photoreduction‐impregnation method. The obtained products were characterized by means of X‐ray diffraction (XRD), scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and UV‐vis absorption spectroscopy. Under visible‐light irradiation (γ>420 nm), the Fe(III)/Ag/Ag₂CO₃ sample displays a higher photocatalytic activity and stability than pure Ag₂CO₃ and Ag/Ag₂CO₃ samples for the degradation of methyl orange (MO). The improved photocatalytic activity and stability of this ternary system could be ascribed to the synergetic effect between Ag nanoparticles and Fe(III) nanocluster. The metallic Ag nanoparticles cause an obviously enhanced visible‐light absorption to produce more photogenerated charges, while the Fe(III) works as an active site for the following oxygen reduction to reduce the recombination rate of photogenerated electrons and holes.