Electrochemical formation and reduction of silver oxides in alkaline media

The anodic oxidation of silver electrodes in NaOH solution and the reduction of the silver oxides formed were studied by potential step chronoamperometry. Oxidation of Ag to Ag₂O is a diffusion-controlled reaction, the diffusion control being established in the solid phase. Oxidation of Ag₂O to AgO proceeds via a nucleation and growth-controlled process. The amount of AgO decreased with increasing step height. The current—time curves for this reaction have been analysed with the Kolmogoroff—Avrami equation. Reduction of AgO to Ag₂O occurs initially on the outside of the electrode, and the rate of the reaction is limited by diffusion of ions across the thickening layer of Ag₂O. Reduction of Ag₂O to Ag proceeds via a nucleation and growth reaction.     

Electronic Structure of Silver Oxides Investigated by AgL XANES Spectroscopy

The chemistry of binary and multinary silver oxides spans from subvalent species (with a mean oxidation number for Ag smaller than + 1) to compounds with Ag in high oxidation states as + 2 and + 3. We have investigated a range of silver oxides, including the binary compounds Ag₂O, AgO, Ag₃O₄ and Ag₂O₃ as well as subvalent ternary oxides, by AgL₃ and AgL₁ XANES spectroscopy. The different valence states of silver are clearly reflected in AgL₃ and AgL₁ XANES spectra. The method thus allows the determination of average oxidation numbers. In addition, the degree of electronic interaction (localized or delocalized electronic states) in silver‐oxygen compounds can be estimated on the basis of AgL₃ XANES spectra.     

氧化银纳米线在官能化二氧化硅颗粒表面的自组装合成

在碱性水醇溶液中, 硝酸银与用3-(2-氨乙基氨丙基)三甲氧基硅烷[N-(2-aminoethyl)-3-aminopropyl-trimethoxy- silane, AMPTS]表面修饰后的二氧化硅胶体颗粒相互作用, 发现所生成的氧化银纳米颗粒可以在二氧化硅颗粒表面自组装为氧化银纳米线. 通过调变反应物中Ag/Si摩尔比, 可对氧化银纳米线的形貌进行调控. 在较小的Ag/Si摩尔比下, 可以得到结构均匀、直径约为50 nm、长度几十微米的氧化银纳米线. 随Ag/Si摩尔比增大, 得到的氧化银纳米线逐渐变短变粗, 且结构变得不均匀. 高分辨透射电镜(HRTEM)显示, 所有的氧化银纳米线均由直径10～20 nm的氧化银颗粒定向堆积而得. 利用透射电镜(TEM)对氧化银纳米线的形成过程进行了观察, 并对氧化银颗粒形成及组装机理进行了探讨.     

火焰辅助热解方法制备Ag_2O/TiO_2及其光催化制氢性能

以钛酸丁酯和硝酸银为前驱体,采用一步火焰辅助热解法制备了Ag_2O/TiO_2光催化剂并研究了样品在紫外-可见光照射下的光催化制氢性能。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)和紫外-可见漫反射吸收光谱(UV-Vis DRS)对样品进行了表征。XRD结果表明TiO_2均为锐钛矿晶型,Ag的引入对XRD结果无明显影响。SEM图显示未修饰的TiO_2是微球形貌,随着引入Ag含量的增加,微球减少直至消失。通过XPS分析和化学沉淀法表明样品中Ag的存在形式为Ag_2O。UV-Vis DRS测试发现引入Ag后提高了样品的光吸收。前驱体中Ag的量影响样品的光催化活性,最高的光催化制氢的活性可以达到相同条件下的P25的15倍。对光催化反应后的样品进行分析,认为在光催化过程中部分Ag_2O通过光生电子转化为Ag形成Ag/TiO_2,进一步提高光催化制氢活性。     

火焰辅助热解方法制备Ag2O/TiO2及其光催化制氢性能

以钛酸丁酯和硝酸银为前驱体,采用一步火焰辅助热解法制备了Ag₂O/TiO₂光催化剂并研究了样品在紫外-可见光照射下的光催化制氢性能。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、X射线光电子能谱（XPS）和紫外-可见漫反射吸收光谱（UV-Vis DRS）对样品进行了表征。XRD结果表明TiO₂均为锐钛矿晶型,Ag的引入对XRD结果无明显影响。SEM图显示未修饰的TiO₂是微球形貌,随着引入Ag含量的增加,微球减少直至消失。通过XPS分析和化学沉淀法表明样品中Ag的存在形式为Ag₂O。UV-Vis DRS测试发现引入Ag后提高了样品的光吸收。前驱体中Ag的量影响样品的光催化活性,最高的光催化制氢的活性可以达到相同条件下的P25的15倍。对光催化反应后的样品进行分析,认为在光催化过程中部分Ag₂O通过光生电子转化为Ag形成Ag/TiO₂,进一步提高光催化制氢活性。     

Microstructure and optical properties of Ag-doped ZrO2 thin films prepared by sol gel method

Ag doped ZrO₂ thin films were deposited on quartz substrates by sol–gel dip coating technique. The effect of Ag doping on tetragonal to monoclinic phase transformation of ZrO₂ at a lower temperature (500 °C) was investigated by X-ray diffraction. It is found that the Ag doping promotes the phase transformation. The phase transformation can be attributed to the increase in the tetragonal grain size and concentration of oxygen vacancies in the presence of the Ag dopant. Accumulation of the Ag atoms at the film surface and surface morphology changes in the films were observed by AFM as a function of varying Ag concentration. X-ray photoelectron spectroscopy gave Ag 3d and O 1s spectra on Ag doped thin film. The chemical states of Ag have been identified as the monovalent state of Ag⁺ ions in ZrO₂. The Ag doped ZrO₂ thin films demonstrated the tailoring of band gap values. It is also found that the intensity of room temperature photoluminescence spectra is suppressed with Ag doping.     

Anodic silver (II) oxides investigated by combined electrochemistry,ex situ XPS and in situ X‐ray absorption spectroscopy

Silver (II) oxide layers (AgO) were prepared by anodic oxidation of pre‐oxidized, Ag₂O‐covered silver electrodes in 1 M NaOH (pH 13.8). The oxidized electrodes were investigated using a combination of electrochemical techniques, ex situ X‐ray photoelectron spectroscopy (XPS) and in situ surface‐sensitive grazing incidence X‐ray absorption spectroscopy (EXAFS) under full potential control. The application of these different techniques leads to a detailed, consistent picture of the anodic silver (II) oxide layer formation. The experiments have shown that the chemical composition of the AgO layer varies significantly with oxidation potential, revealing a decreasing oxygen deficiency with increasing anodization potential and oxidation time. XPS as well as EXAFS experiments support the interpretation of the oxide as a mixed valence Ag ⁺ Ag^{3 +} O₂ with different contributions of Ag ⁺ and Ag^{3 +} species, depending on potential and anodization time. Copyright © 2009 John Wiley & Sons, Ltd.     

A solid composite electrode for the determination of the electrochemical oxygen demand of aqueous samples

A composite electrode containing graphite, paraffin, AgO and CuO is described for the determination of the electrochemical oxygen demand (EOD) of waste waters. The oxidation of dissolved organic compounds at the electrode is based on a heterogeneous chemical reaction of AgO/CuO with the organic constituents of the waste water. This chemical reaction can be followed by a solid state electrochemical oxidation of the formed Ag₂O/Cu₂O. The method has been tested with various organic compounds and applied to real samples of sewage water. The EOD values correlate well to BOD and COD values.     

Studies on Indian Ocean Manganese Nodules: XI. Physicochemical Characterization and Catalytic Activity of Silver Oxide Mixed Manganese Nodules

The promoting effect of Ag₂O on the physicochemical properties and catalytic activity of manganese nodules has been investigated. The surface area and surface oxygen increased with addition of Ag₂O, reaching a maximum at 1 mol% of Ag, and then decreased with further addition of Ag₂O. The catalytic activity of manganese nodules substantially increased with addition of Ag₂O over a wide range (0.25–25 mol% Ag). Addition of only 0.25 mol% of Ag to the nodule decreased the temperature of complete CO oxidation from 350°C to as low as 100°C. This enhanced activity was explained by the concerted action of Ag and Mn, where CO was preferentially adsorbed on Ag₂O and oxidized. The reduced Ag was then reoxidized rapidly by oxygen transferred from Mn. The promoting effect of Ag₂O on H₂O₂decomposition and ketonization of acetic acid, however, was less pronounced.     

Formation mechanism of nanostructured Ag films from Ag2O particles using a sonoprocess

Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag₂O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag₂O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag⁺ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag⁺ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag⁺, Ag ₄ ²⁺ and Ag_n (n?≈?3). The Ag_n clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag₂O particles with ethanol under ultrasonication. The reactions of Ag⁺ ions in ethanol to form Ag nanomaterials (through the formation of Ag ₄ ²⁺ clusters) were also accelerated by ultrasonication.     

Synthesis of Ag2O and Ag co-modified flower-like SnS2 composites with enhanced photocatalytic activity under solar light irradiation

Three-dimensional Ag₂O and Ag co-modified flower-like SnS₂ composites have been synthesized through a facile hydrothermal and photoreduction process. The physical and chemical properties of Ag₂O and Ag co-modified flower-like SnS₂ composites were carefully studied by using XRD, SEM, TEM, UV–vis diffuse reflectance spectra (DRS) and XPS. The photocatalytic activity of the as-prepared products was evaluated by photocatalytic decolorization of Rhodamine B (Rh B) aqueous solution at ambient temperature under solar light irradiation. The photocatalytic result shows that Ag₂O and Ag co-modified flower-like SnS₂ composites exhibit enhanced photocatalytic activity compared with that of pure SnS₂. Three of the Ag₂O and Ag co-modified flower-like SnS₂ composites form the Z-scheme systems, because of their unique charge-carrier transfer process, the oxidation/reduction ability of photogenerated holes and electrons could be enhanced. Therefore, the new Ag₂O and Ag co-modified flower-like SnS₂ composites possess a favorable photocatalytic activity, and it can be a promising candidate for the solar energy conversion process.     

Impedance study on the capacitance of silver electrode oxidised in alkaline electrolyte

Electrochemical properties of oxide-covered polycrystalline Ag electrodes were studied in a 0.1 M KOH aqueous electrolyte. The oxide layers formed by a constant potential oxidation at 420 mV vs. Hg|HgO are composed of oxygen-deficient Ag₂O as follows from the XPS and Auger experiments. Steady-state conditions required for collection of valid impedance spectra were obtained at a potential range of 345–365 mV. The components of the equivalent circuit used for the impedance spectra analysis are analysed as a function of the Ag₂O layer thickness. The value of the coefficient of the constant phase element (CPE) attributed to the oxide layer is Ag₂O thickness dependent. On the other hand, the components of the CPE describing the double-layer capacitance of the oxide-covered Ag electrode are independent on the oxide thickness and their values are comparable to those obtained for the oxide-free metal. This indicates that the double-layer capacitances of oxide-covered and oxide-free Ag electrodes are similar.

     

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.     

Synthesis,Structures, and Properties of Two Novel Supramolecular Architectures Constructed from [2,3‐f]Pyrazino[1,10]phenanthroline‐2,3‐dicarboxylic Acid

Two new compounds, [Ag(Hppdb)]_n ( 1 ) and {[Ag₂(Hppdb)₂(bpe)] · 5.5H₂O}_n( 2 ) [H₂ppdb = [2,3‐f]pyrazino[1,10]phenanthroline‐2,3‐dicarboxylic acid, bpe = trans‐1,2‐bis(4‐pyridyl)ethylene], were synthesized and characterized. In 1 , Hppdb^– ions link Ag^I cations to form an infinite 1D [–Ag–(Hppdb)–Ag–]_n chain, furthermore, the dimensionality is extended to 2D layers through synergistic π–π stacking, hydrogen‐bonding and weak Ag ··· O interactions. Correspondingly, the dimeric [(Ag)(Hppdb)]₂ subunits in 2 are connected by bpe ligands to generate a loop‐link‐shaped 1D chain motif, which is further joined through a R₂²(18)C–H ··· O hydrogen‐bonding ring to afford interesting diagonal/diagonal inclined catenation 2D + 2D → 3D supramolecular architectures. In addition, solid‐state properties such as photoluminescence and thermal stability of the two compounds were studied.     

Spectral,magnetic and thermal studies on homometallic and heterometallic complexes of piperanol thiosemicarbazone

Piperanol thiosemicarbazone (HL) has been interacted with Ag⁺, Co(II), Ni(II) or Cu(II) binary to produce [Ag(HL)]EtOH · NO₃, [Ag₂(L)(H₂O)₂]NO₃, [Co(L)₃], [Cu(L)(H₂O)₃(OAc)]H₂O or [Ni(L)₂] and template with Ag⁺ to form [Cu₂Ag₂(L)₂(OH)₂(H₂O)₄]NO₃ and [NiAg(L)₂(H₂O)₂]NO₃. The prepared complexes are characterized by microanalysis, thermal, magnetic and spectral (IR, ¹H NMR, ESR and electronic) studies. Ag⁺ plays an important role in the complex formation. The variation in coordination may be due to the presence of two different metal ions and the preparation conditions. The outside nitrate is investigated by IR spectra. The outer sphere solvents are detected by IR and thermal analysis. Ni(II) complexes are found diamagnetic having a square-planar geometry. Cu(II) is reduced by the ligand to Cu(I). The cobalt complex is found diamagnetic confirming an air oxidation of Co(II) to Co(III) having a low spin octahedral geometry. The ligand and its metal complexes are found reducing agents which decolorized KMnO₄ solution in 2N H₂SO₄. CoNS and NiNS are the residual parts in the thermal decomposition of [Co(L)₃] and [Ni(L)₂].     

Photocatalytic degradation of acid blue 74 in water using Ag–Ag2O–Zno nanostuctures anchored on graphene oxide

Water pollution due to industrial effluents from industries which utilize dyes in the manufacturing of their products has serious implications on aquatic lives and the general environment. Thus, there is need for the removal of dyes from wastewater before being discharged into the environment. In this study, a nanocomposite consisting of silver, silver oxide (Ag₂O), zinc oxide (ZnO) and graphene oxide (GO) was synthesized, characterized and photocatalytically applied in the degradation (and possibly mineralization) of organic pollutants in water treatment process. The Ag–Ag₂O–ZnO nanostructure was synthesized by a co-precipitation method and calcined at 400 °C. It was functionalized using 3-aminopropyl triethoxysilane and further anchored on carboxylated graphene oxide via the formation of an amide bond to give the Ag–Ag₂O–ZnO/GO nanocomposite. The prepared nanocomposite was characterized by UV–Vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electronic microscopy (SEM), energy dispersive X-ray spectrometry (EDX), Fourier transformed infrared spectroscopy (FTIR), and Raman spectroscopy. The applicability of Ag–Ag₂O–ZnO/GO nanocomposite as a photocatalyst was investigated in the photocatalytic degradation of acid blue 74 dye under visible light irradiation in synthetic wastewater containing the dye. The results indicated that Ag–Ag₂O–ZnO/GO nanocomposite has a higher photocatalytic activity (90% removal) compared to Ag–Ag₂O–ZnO (85% removal) and ZnO (75% removal) respectively and thus lends itself to application in water treatment, where the removal of organics is very important.     

A novel three‐dimensional AgI coordination polymer based on mixed naphthalene‐1,5‐disulfonate and aminoacetate ligands

The three‐dimensional coordination polymer poly[[bis(μ₃‐2‐aminoacetato)di‐μ‐aqua‐μ₃‐(naphthalene‐1,5‐disulfonato)‐hexasilver(I)] dihydrate], {[Ag₆(C₁₀H₆O₆S₂)(C₂H₄NO₂)₄(H₂O)₂]·2H₂O}_n, based on mixed naphthalene‐1,5‐disulfonate (L1) and 2‐aminoacetate (L2) ligands, contains two Ag^I centres (Ag1 and Ag4) in general positions, and another two (Ag2 and Ag3) on inversion centres. Ag1 is five‐coordinated by three O atoms from one L1 anion, one L2 anion and one water molecule, one N atom from one L2 anion and one Ag^I cation in a distorted trigonal–bipyramidal coordination geometry. Ag2 is surrounded by four O atoms from two L2 anions and two water molecules, and two Ag^I cations in a slightly octahedral coordination geometry. Ag3 is four‐coordinated by two O atoms from two L2 anions and two Ag^I cations in a slightly distorted square geometry, while Ag4 is also four‐coordinated by two O atoms from one L1 and one L2 ligand, one N atom from another L2 anion, and one Ag^I cation, exhibiting a distorted tetrahedral coordination geometry. In the crystal structure, there are two one‐dimensional chains nearly perpendicular to one another (interchain angle = 87.0°). The chains are connected by water molecules to give a two‐dimensional layer, and the layers are further bridged by L1 anions to generate a novel three‐dimensional framework. Moreover, hydrogen‐bonding interactions consolidate the network.     

Temperature‐programmed reduction of silver(I) oxide using a titania‐supported silver catalyst under a H2 atmosphere

Reduction kinetics of silver(I) oxide using a titania‐supported silver catalyst was analyzed using temperature‐programmed reduction (TPR) with hydrogen as a reducing gas. Ag₂O reduction to Ag was observed in all samples as a single reduction step occurring at two reduction peaks. Observation of these reduction peaks indicates the existence of different lattice oxygen species, that is, surface and bulk, which are, respectively, attributed to surficial and pore‐deposited Ag₂O aggregates. The powdered samples exhibited high reducibility with average final oxidation states ranging from 0 to +0.18. The apparent activation energies for Ag₂O reduction to Ag metal were 73.35 and 81.71 kJ/mol for surficial and pore‐deposited Ag₂O aggregates, respectively. In this study, a unimolecular decay model was reported to accurately describe the reduction mechanism of Ag/TiO₂ catalysts. Hence, this would also infer that the catalyst reduction is rate‐limited by the nucleation of Ag metal instead of the topochemical reaction and the diffusion of hydrogen and oxygen molecules.     

Synthesis,Characterization and Thermal Behavior of Two 4d‐4f Coordination Polymers Based on N and O Donor Ligands

Two new 4d‐4f coordination polymers, [Ag₂Nd(nic)₄(H₂O)₄·(ClO₄)·H₂O] ( 1 ) and [Ag₈Yb₄(inic)₈(ox)₆]· [Ag₂(inic)₂] ( 2 ) [nic = nicotinate, inic = isonicotinate and ox = oxalate] have been synthesized and characterized by element analysis, IR spectroscopy and thermal analysis, as well as single crystal X‐ray diffraction. Complex 1 exhibits a wavelike layer that is assembled from neodymium‐carboxylate subunits, silver centres and perchlorate ions. Complex 2 represents a extended heterometallic sandwich‐like layered network that is constructed from ytterbium‐oxalate layers and Ag(inic) chains.     

Syntheses and Structural Characterization of Four New Silver(I) Complexes with the N,N′(O)‐bidentate Bridging Ligands

Four new bridged silver(I) complexes, namely [Ag₂(μ₂‐teda)(μ₂‐fbc)₂] ( 1 ), [Ag₂(μ₂‐1,6‐dah)₂](bpdc) · 4H₂O ( 2 ), [Ag₂(μ₂‐2‐ap)(2‐ap)(bnb)] · 0.34H₂O ( 3 ), [Ag₂(μ₂‐pyc)₂(2‐apy)₂] · 0.5H₂O ( 4 ), have been synthesized and characterized by elemental analysis and crystallographic methods [fbc = 4‐fluorobenzoate, teda = triethylenediamine ( 1 ); bpdc = biphenyl‐4,4′‐dicarboxylate, 1,6‐dah = 1,6‐diaminohexane ( 2 ); bnb = 3,5‐binitrobenzoate, 2‐ap = 2‐aminopyrimidine ( 3 ); pyc = 3‐pyridinecarboxylate acid, 2‐apy = 2‐aminopyridine ( 4 )]. Complex 1 contains a 1D linear chain paralleling to the c‐axis, whereas in complex 2 silver(I) atoms were bridged by the 1,6‐dah ligand into a zigzag chain, further giving a 1D ribbon by weak Ag ··· Ag interactions. Complex 3 consists of a dinuclear silver(I) [Ag₂(μ₂‐2‐ap)(2‐ap)(bnb)] moiety and a lattice water molecule, forming a 3D network via a number of hydrogen‐bonding interactions such as N–H ··· O, N–H ··· N and C–H ··· O hydrogen bond and other weak interactions such Ag ··· Ag, Ag ··· N, N ··· O as well as O ··· O interaction. Similar to 3 , the asymmetric unit of 4 consists of one dinuclear silver(I) [Ag₂(μ₂‐pyc)₂(2‐apy)₂] moiety and half lattice water molecule, further generating a tetranuclear silver(I) {[Ag₂(μ₂‐pyc)₂(2‐apy)₂]₂ · H₂O} moiety. These moieties construct a 3D supramolecular network structure of 4 through N–H ··· O, O–H ··· O and C–H ··· O hydrogen bonds as well as other weak interactions such as Ag ··· O and N ··· O interactions.