Preparation of nanostructure silver powders by mechanical decomposing and mechanochemical reduction of silver oxide

The mechanical decomposing and mechanochemical reductions of silver oxide for preparation of nanocrystalline silver powders by high planetary ball mill was investigated. XRD and HRSEM techniques were used to characterize the structural evolution and morphological changes of products. The results show that the nanostructured silver with an average crystallite size of 14 nm and internal strain of 0.75% is synthesized by mechanical decomposing of Ag2O after 95 h milling. While, the product of mechanochemical reduction of silver oxide using graphite after 22 h milling is nanostructured silver with an average crystallite size of 28 nm and internal strain of 0.44%.

Thermodynamic approach to synthesis of silver nanocrystalline by mechanical milling silver oxide

Thermodynamic analysis of the possibility of silver nanocrystalline preparation by high energy milling silver oxide was investigated. The molar Gibbs free energy function of mechanically activated samples was calculated from the structural defects such as amorphization, dislocation and surface energy. According to the molar Gibbs free energy function, the equilibrium temperature of mechanical reduction of silver oxide milled for 21 h was estimated at about 304 K. Consequently, at this temperature silver oxide cannot be stable and will transform to silver during the milling.

Studies on the Preparation of Bioactive Oligomerstilbene by Oxidative Coupling Reaction(Ⅰ)-Preparation of Shegansu B using Silver Oxide as Oxidant

篢he oxidative coupling reaction of isorhapontigenin using sliver oxide as oxidant afforded a major product, named shegansu B（2）， which was isolated from the roots of Belamcanda chinensis (L．)DC. Both the natural and synthetic Shegansu B have the same potent antagonism activities of leukotriene B4，D4 receptor．

Evolution of the structural and optical properties of silver oxide films with different stoichiometries deposited by direct-current magnetron reactive sputtering

Nitrogen doping of silver oxide （AgxO） film is necessary for its application in transparent conductive film and diodes because intrinsic AgxO film is a p-type semiconductor with poor conductivity. In this work, a series of AgxO films is deposited on glass substrates by direct-current magnetron reactive sputtering at different flow ratios （FRs） of nitrogen to 02. Evolutions of the structure, the refiectivity, and the transmissivity of the film are studied by X-ray diffractometry and sphectrophotometry, respectively. The specular transmissivity and the specular refiectivity of the film decreasing with FR increasing can be attributed to the evolution of the phase structure of the film. The nitrogen does not play the role of an acceptor dopant in the film deposition.

Catalytic performance of Ag/Co-Ce composite oxides during soot combustion in O_2 and NO_x:Insights into the effects of silver

The composite oxides xAg/Co_（0.93）Ce_（0.07）（x=Ag/（Co＋Ce） molar ratio）,intended for use as high performance catalytic materials,were successfully prepared via citric acid complexation.The effects of silver on the performance of these substances during soot combustion were subsequently investigated.Under O_2,the 0.3Ag/Co_（0.93）Ce_（0.07） catalyst resulted in the lowest ignition temperature,T_（10）,of197 ℃,while the minimum light-off temperature was obtained from both 0.2Ag/Co_（0.93）Ce_（0.07） and0.3Ag/Co_（0.93）Ce_（0.07） in the NO_x atmosphere.These materials were also characterized by various techniques,including H_2,soot and NO_x temperature programmed reduction,X-ray diffraction,and electron paramagnetic resonance,Raman,X-ray photoelectron,and Fourier transform infrared spectroscopic analyses.The results demonstrated that silver significantly alters the catalytic behavior under both O_2 and NO_x,even though the lattice structure of the mixed oxide is not affected.Surface silver oxides generated under the O_2 atmosphere favor soot combustion by participating in the redox cycles between soot and the silver oxide,whereas the AgNO_3 that forms in a NO_x-rich atmosphere facilitates soot abatement at a lower temperature.The inferior activity of AgNO_3 relative to that of Ag_2O results in the different catalytic performance in the presence of NO_x or O_2.

Preparation of silver tin oxide powders by hydrothermal reduction and crystallization

Silver tin oxide composite powders were synthesized by the hydrothermal method with a silver ammine solution and a Na2SnO3 solution as raw materials. H2C2O4 was used as the co-precipitator of silver ions and tin ions. The co-precipitation conditions were investigated. The results show that the co-precipitate of Ag2C2O4 and Sn（OH）4 is available when the pH value of the solution is 4.27-8.36. Using the obtained precipitate as precursor,the reduction of Ag＋ and the crystallization of tin oxide were carried out simultaneously by the hydrothermal method and silver tin oxide composite powders were obtained. The composite powders were characterized by X-ray diffraction （XRD） analysis,scanning electron microscope （SEM）,and energy spectrum analysis. The results show that the silver tin oxide composite powders are small with a diameter of about 2 μm and with homogeneous distribution of tin.

Silver(I) Oxide Mediated Regioselective Monoacylation of 2,4-Dihydroxyls in L-Rhamnopyranosides

A series of acyls （Ac, Bz and Ts） were introduced regioselectively to the 2-hydroxyl in methyl and ally 3-O-benzyl-α-L-rhamnopyranosides mediated by silver（I） oxide in the presence of a catalytic amount of potassium iodide in 56-78% yields.

Silver Nanoparticles Synthesized by Laser Ablation in Acetone： Influence of Ablation Time and Their Reactivity with Oxygen in the Air

In this work, a method is proposed to control silver nanoparticle dimensions produced by laser ablation varying the ablation time and introducing a sonication phase between ablation and the successive deposition on the substrate. The absorption spectra during laser ablation show a main band, which identifies the dimensions of main particles. The appearance of secondary bands indicates the beginning of an aggregation process with the formation of a small concentration of particles which are spheroid in shape. SEM （secondary electron microscope） images of particle produced with different ablation times confirm the results of absorption measurements. X-ray photoelectron spectroscopy and cathodo-luminescence spectroscopy indicate a high reactivity of the nanoparticles deposited on a substrate. They react with oxygen in the air forming an oxide layer which reveals a luminescence in the blue region.

Solvothermal Synthesis and Electrochemical Properties of Octahedral Cobalt Oxide Decorated with Ag_2O

Octahedral CoO with nanostructures decorated with Ag nanoparticles was prepared via a facile solvothermal approach. After being annealed at 500 ℃ for 1 h, an electrochemical capacitor material of Co3O4 decorated with Ag2O was obtained. The cyclic voltammetry and galvanostatic charge-discharge were used to evaluate the electrochemical properties of the as-prepared products. The results indicated that the as-prepared samples exhibited fine pseudo-capacitive performance, and the surface modifications of Ag2O can significantly increase the capacitance of the Co3O4 material. The specific capacitance of Ag2O/Co3O4 composite electrode was up to 217.6 F·g^-1, which was 3.35 times as high as that of pure Co3O4. Moreover, Ag2O/Co3O4 composite showed an excellent cycle performance, and 65.3% of specific capacitance was maintained after 200 cycles.

Green synthesis of iron oxide(Fe_3O_4)nanoparticles using two selected brown seaweeds:Characterization and application for lead bioremediation

The exploitation of different plant materials for the biosynthesis of nanoparticles is considered a green technology because it does not involve any harmful chemicals. In this study, iron oxide nanoparticles（Fe3O4-NPs） were synthesized using a completely green biosynthetic method by reduction of ferric chloride solution using brown seaweed water extracts. The two seaweeds Padina pavonica（Linnaeus） Thivy and Sargassum acinarium（Linnaeus） Setchell 1933 were used in this study. The algae extract was used as a reductant of Fe Cl3 resulting in the phytosynthesis of Fe3O4-NPs. The phytogenic Fe3O4-NPs were characterized by surface plasmon band observed close to 402 nm and 415 nm; the obtained Fe3O4-NPs are in the particle sizes ranged from 10 to 19.5 nm and 21.6 to 27.4 nm for P. pavonica and S. acinarium, respectively. The strong signals of iron were reported in their corresponding EDX spectra. FTIR analyses revealed that sulphated polysaccharides are the main biomolecules in the algae extracts that do dual function of reducing the Fe Cl3 and stabilizing the phytogenic Fe3O4-NPs. The biosynthesized Fe3O4-NPs were entrapped in calcium alginates beads and used in Pb adsorption experiments. The biosynthesized Fe3O4-NPs alginate beads via P. pavonica（Linnaeus） Thivy had high capacity for bioremoval of Pb（91%） while that of S. acinarium（Linnaeus） Setchell 1933 had a capacity of（78%） after 75 min.The values of the process parameters for the maximum Pb removal efficiency by Fe3O4-NPs alginate beads synthesized via P. pavonica（Linnaeus） Thivy were also estimated.

Facile synthesis of Ag_2O-TiO_2/sepiolite composites with enhanced visible-light photocatalytic properties

Ag2O-TiO 2/sepiolite heterostructure composites were synthesized by a simple two-step method at low temperatures（100–450 °C）. Acid red G aqueous solution and gaseous formaldehyde were chosen as model organic pollutants to evaluate the photocatalytic performance of the as-prepared composites. The results showed that the Ag2O-TiO 2/sepiolite exhibited enhanced photocatalytic activity over pure Ag2O-TiO 2,TiO 2/sepiolite,and Ag2O/sepiolite under visible-light irradiation（λ 420 nm）. The excellent photocatalytic efficiency of these composites can be ascribed to the synergistic effect between the heterojunction and the porous structure of the clay layers,which induced high adsorption and efficient charge separation. In addition,the active species involved in the degradation reaction have been investigated by photoluminescence spectroscopy and quenching experiments. A possible photocatalytic degradation mechanism of acid red G dye by the Ag2O-TiO 2/sepiolite composite is also discussed.

Photochemical oxidation mechanism of microcystin-RR by p-n heterojunction Ag/Ag_2O-BiVO_4

Microcystin-RR（MC-RR）,a form of microcystin with two arginine moieties,is a cyanobacterial toxin that has been detected across a wide geographic range.It is a great concern globally because of its potential liver toxicity.Herein,the abilities of BiVO4,Ag-BiVO4,Ag2O-BiVO4 and Ag/Ag2O-BiVO4 to photocatalytically degrade MC-RR under visible-light irradiation（λ≥420 nm） were investigated and compared.The possible degradation pathways were explored through analysis of the reaction intermediates by high-performance liquid chromatography-mass spectrometry.The results showed that the presence of Ag^0 enhanced the photocatalytic efficiency of Ag/Ag2O-BiVO4 via a synergetic effect between Ag2O and Ag^0 at the p-n heterojunction.Moreover,the presence of Ag^0 also greatly promoted the adsorption of MC-RR on the photocatalyst surface.Toxicological experiments on mice showed that the toxicity of MC-RR was significantly reduced after photocatalytic degradation.

Surface-sulfurized Ag_2O nanoparticles with stable full-solar-spectrum photocatalytic activity

Ag2O has attracted much recent attention,because of its high photocatalytic activity in the ultraviolet(UV)‐visible region.However,there have been few reports on the near‐infrared(NIR)photocatalytic activity of Ag2O.This paper reports the high NIR photocatalytic activity of Ag2O nanoparticles.Ag2O is unsuitable for application in full‐solar‐spectrum photocatalysis,because it is unstable under UV irradiation.A surface sulfurization process was carried out to address this issue.Specifically,a layer of Ag2S2O7nanoparticles was grown on the surface of the Ag2O nanoparticles,to improve the stability of the Ag2O photocatalyst and enhance its photocatalytic activity in the UV,visible and NIR regions.The Ag2O/Ag2S2O7heterostructure is a stable and efficient full‐solar‐spectrum photocatalyst.It has potential application in the photodegradation of organic pollutants,and more generally in environmental engineering where full utilization of the solar spectrum is required.

Arrhenius parameters determination in non-isothermal conditions for mechanically activated Ag_2O-graphite mixture

The non-isothermal kinetics of mechanochemical reduction of Ag2O with graphite was studied by DSC and TGA with a model of fitting Malek approach and a model-free advanced isoconversional method of Vyazovkin. To evaluate the kinetics parameters, Ag2O–graphite mixture of as-received and milled for 2 and 4 h samples were selected. Based on the results obtained by Vyazovkin method calculation, however, the difference between the maximum and minimum values of activation energy is less than 20%-30%of the average activation energy （（99.38±2.36） kJ/mol） and thermal decomposition of mechanically activated Ag2O for 2 h is a multi-step process. Moreover, the thermal decomposition of mechanically activated Ag2O–graphite powder activated for 4 h is a single-step process （the average activation energy=（93.68±2.26） kJ/mol）. The kinetics modeling shows that the complexity of thermal decomposition of as-received Ag2O–graphite mixture is higher than that of the others. While, the autocatalytic tendency of as-received Ag2O–graphite mixture is lower than that of the others.

Synthesis and Excellent Antibacterial Activity of Ag_(2)O-Loaded Carboxymethyl Starch Nanocomposites

Carboxymethyl starch/silver oxide nanocomposites(CMS-Ag_(2)O NCs)were successfully fabricated by modifying carboxymethyl starch(CMS)with Ag_(2)O obtained from an aqueous AgNO_(3)solution as silver source.Ag_(2)O nanoparticles(NPs)formed on the surface of CMS by ion exchange.Based on SEM images,the diameters of Ag_(2)O NPs were determined to be between 50 and 100 nm.From the XRD spectra of CMS-Ag_(2)O NCs,the new diffraction peaks appeared at 33.88°and 38.08°,which were attributed to the Ag_(2)O NPs.According to the XPS analysis,Ag 3d_(5/2)and Ag 3d_(3/2)peaks in CMS-Ag_(2)O NCs were fitted into two main peaks centered at 367.6 eV and 373.6 eV,which were attributed to Ag^(+).The antibacterial efficiencies of CMS-Ag_(2)O NCs against Escherichia coli,Staphylococcus aureus,Pseudoalteromonas tetraodonis,Micrococcus luteus,and Shewanella putrefaciens were determined to be 99.6%,99.7%,99.4%,99.5%,and 99.6%,respectively.The antibacterial efficiencies of CMS-Ag_(2)O NCs against the bacterial species were all greater than 99%.Therefore,these results indicated that CMS-Ag_(2)O NCs was highly effective as a bactericidal agent against multiple bacterial species.CMS-Ag_(2)O NCs can be further applied to antifouling coating.

Reinvestigate the C^2Π-X^2Π(0,0)Band of AgO

The C^2Π-X^2Π(0,0)band of AgO has been reinvestigated by laser induced fluorescence spectroscopy with a spectral resolution of ~0.02 cm^−1.The AgO molecules are produced by discharging a gas mixture of O2/Ar with silver needle electrodes in a supersonic jet expansion.By employing a home-made narrowband single longitude mode optical parametric oscillator(SLM-OPO)as the laser source,high-resolution spectra of the C^2Π-X^2Π(0,0)band have been recorded for both 107Ag16O and 109Ag16O isotopologues.The spectroscopic constants of the C^2Π state are consequently determined,with the 109Ag16O one being reported for the first time.The nature of the spin-orbit coupling effect in the C^2Π state is proposed to be due to state mixing with the nearby repulsive 4Σ− and 4Π states.

A New AgMeO Contact Material

A new silver rare earth oxide contact material, Ag/La2O3(12), was produced by powder metallurgy method. Its performances are as follows: the density is 9.71 similar to 9.96 g.cm(-3); the hardness (HB) is 760 similar to 970 MPa and the resistivity is 2.25 similar to 2.38 mu Omega . cm. The microstructure of Ag/La2O3(12) mas analyzed by SEM and EDS. Rare earth oxide La2O3 shows two shapes, which are uniformly distributed in the form of sphere and abnormality in Ag matrix. La2O3 shows fine spherical shape in the melted area of Ag after laser acting which is used to simulate electric are. The results are contributed to the less splash erosion of Ag. Compared with the main physical and mechanical properties of Ag/SnO2(12) and Ag/CdO(12), the properties of three contact materials are similar, and hence Ag/La2O3(12) may become a potential contact material to be used as the substitute of Ag/CdO(12).

Facile Synthesis of 7-epi-Taxane and Its Derivatives and Preliminary Evaluation of Anticancer Activity

7-epi-Taxane has been achieved efficiently in gram scale from natural taxane via inversion of the 7-hydroxyl group simply using Ag20 as catalyst and DMF as solvent. The catalyst could he quantitatively recovered by filtra- tion without loss of catalytic activity. This condition is also applicable to the direct epimerization of taxane derivatives （e.g., docetaxel and paclitaxel） to 7-epi-taxane derivatives （e.g., 7-epi-docetaxel and 7-epi-paclitaxel）. Furthermore, 33 ester derivatives of 7-epi-taxane with different amino acid moieties at the position of C-13 were successfully synthesized via esterification without protecting C-7-OH. Bioassay results revealed that compounds 13 and 18 have good selectivity against prostatic cancer cell line DU145, with ICs0 value as low as 15.9 nmol/L for 18.

Oxidation State as a Descriptor in Oxygen Reduction Electrocatalysis

Electrocatalysts for the oxygen reduction reaction(ORR)are critically important in the development of fuel cells and metal-air batteries.Intensive research interests have been devoted to improving the electrocatalytic performance by tuning the morphology and defect-active sites.Herein,we demonstrate that the oxidation state can also serve as an effective strategy for designingORR electrocatalysts.Valencemodels of silver with gradient chemical valence from zero valence to trivalence were successfully built.Their oxidation states were evaluated by cryo-X-ray photoelectron spectroscopy,X-ray absorptionfinestructure,and electron paramagnetic resonance spectroscopy.For the first time,our results demonstrated that the electrocatalytic activities of silver species can be improved by increasing their valence,conforming the orderofAg<Ag_(2)O<Ag_(2)O_(2)<Ag_(3)O_(4)<Ag_(2)O_(3).Computational studies reveal that higher valence Ag species possess a higher proportion of d band holes andmore electrons closer to the Fermi level.Therefore,the oxygen adsorption and activation energy on the Ag sites can be regulated to a near-optimal level and the ORR catalytic efficiency increases.This work clearly presents that oxidation state is another degree of freedom in designing efficient ORR electrocatalysts.