A galvanic solid-state sensor for monitoring ozone and nitrogen dioxide

The sensor is based on silver and platinum electrodes with an intervening silver iodide disk as a solid electrolyte. The small disk (13 mm diameter) is easily made by pressing (7000 kg cm^-2) silver powder, silver iodide and a platinum gauze in layers in a die. The detector cell containing the disk is thermostated at 120 ± 0.1°C. When sample gas at 30 ml min^-1 impinges on the platinum cathode, the current flowing in the external circuit is linearly related to the concentration of ozone and/or nitrogen dioxide up to 0.5 ppm from the detection limit of 0.5 ppb for ozone or 1 ppb for nitrogen dioxide.     

The fluorimetric determination of phosphate with thiamine

A method for the microdetermination of sulphur in organic compounds by means of combustion in a flow of oxygen is described. The oxides of sulphur are absorbed and stored on a small silver layer. After completion of the combustion, the oxygen is replaced first by nitrogen and secondly by hydrogen which liberates the sulphur as sulphur dioxide and regenerates the silver layer. The sulphur dioxide can be easily absorbed by dilute hydrogen peroxide and determined by any convenient method.     

Apatite-forming ability of titanium compound nanotube thin films formed on a titanium metal plate in a simulated body fluid

We compared the apatite-forming ability of a sodium titanate nanotube thin film, an anatase-type titanium dioxide nanotube thin film, and a silver nanoparticle/silver titanate nanotube nanocomposite thin film, in simulated body fluid. The ability of the silver nanoparticle/silver titanate nanotube nanocomposite thin film is slightly higher than that of the anatase-type titanium dioxide nanotube thin film and significantly higher than that of the sodium titanate nanotube thin film. The high ability of the silver nanoparticle/silver titanate nanotube nanocomposite thin film is a newly observed phenomenon, which is probably due to the crystal structure of silver titanate – specifically, to the surface atomic arrangement, the large amount of Ti–OH formed on the nanotube surface, or both. The anatase-type titanium dioxide nanotube thin film and the silver nanoparticle/silver titanate nanotube nanocomposite thin film may have bright prospects for future use in implant materials such as artificial joints. The silver nanoparticle/silver titanate nanotube nanocomposite thin film is particularly promising for its antibacterial properties.     

鱼明胶介质中AgBr/I纳米粒子的生长与感光性能

本文以鱼明胶为分散介质,采用双注法制备AgBr/I纳米粒子乳剂,控制银盐与卤溶液的注入速率(R),以TEM观测了粒子的生长,据此探讨了该乳剂中AgBr/I纳米粒子平均粒径(d)及分布(±σ)与反应条件的关系.发现在R为1.3 mmol/min^-8 mmol/min范围内,随R增大,d减小,R-d间呈良好的线性关系.除个别外,±σ值变化不明显.对于该纳米粒子乳剂采用二氧化硫脲进行化学敏化,结果表明:适当增加二氧化硫脲的加入量和延长敏化时间,均可有效提高乳剂的感光度,并有助于改善其低照度互易律失效,此外还揭示了曝光光源色温对该乳剂感光性能的影响.     

光析出二氧化钛负载银膜的制备及其光催化特性

以二氧化钛膜为载体,配制一定浓度的AgNO₃溶液,利用光析出方式在氧化钛膜表面还原析出Ag,控制光析出时间来控制氧化钛膜表面上的银析出量,制备银负载氧化钛膜,研究膜的抗菌特性和光催化特性.结果表明:由于银在氧化钛膜上的负载,使膜的抗菌性能得到很大的提高,在保持氧化钛膜的光催化能力基本维持不变的前提下,由于在氧化钛膜的表面负载银,对E.coli和青霉菌的杀菌能力分别提高了10⁴和10²,光催化降解甲基橙的能力与氧化钛膜相比,能够提高10%左右,显示了良好的光化学特性.     

Accurate determination of sulfur at trace levels by isotope dilution mass spectrometry

Sulfur is recovered as silver sulfide which is converted to sulfur dioxide by combustion with pure oxygen at low pressure in 1 min. Isotopic analysis of as little as 40 μg of sulfur is possible with a precision better than 0.2%. The technique is applicable to materials such as Cu, Fe, Sn, ti, Zr, zircaloys and standard rocks.     

Synthesis and steric stabilization of silver nanoparticles in neat carbon dioxide solvent using fluorine-free compounds

The adjustable solvent properties, vanishingly low surface tensions, and environmentally green characteristics of supercritical carbon dioxide present certain advantages in nanoparticles synthesis and processing. Unfortunately, most current techniques employed to synthesize and disperse nanoparticles in carbon dioxide use environmentally persistent fluorinated compounds as metal precursors and/or stabilizing ligands. This paper illustrates a one-step process for synthesis and stabilization of silver nanoparticles in carbon dioxide using only fluorine-free compounds. Isostearic acid coated silver nanoaparticles were formed and stably dispersed through arrested precipitation. Silver bis(3,5,5-trimethyl-1-hexyl)sulfosuccinate (Ag-AOT-TMH) was reduced in the presence of isostearic acid as a capping ligand in carbon dioxide solvent to form silver nanoparticles. The addition of cyclohexane as cosolvent or an increase in carbon dioxide solvent density enhances the dispersibility of the particles due to an increase in solvent strength. The dispersibility of the isostearic acid capped silver nanoparticles diminished with time until a stable dispersion was achieved due to the precipitation of a fraction of particle sizes too large to be stabilized by the solvent medium, thereby leaving a smaller size fraction of nanoparticles stably dispersed in the CO2 mixtures. This paper presents the one-step synthesis and stabilization of metallic nanoparticles in neat carbon dioxide without the aid of any fluorinated compounds.     

Thermal decomposition of silver carbonate

Conflicting results have been reported by different workers on the thermal decomposition of silver carbonate, Ag₂CO₃. In the present study, the decomposition mechanism was elucidated by various analytical methods; gas analysis (differential thermal gas analyses) in helium, carbon dioxide and oxygen flows with and without a P₂O₅ trap or a KOH trap, DTA-TG in a carbon dioxide flow and high-temperature X-ray diffraction analysis in a carbon dioxide flow. The gas evolution at ca. 200?C consisted of carbon dioxide. A simultaneous evolution of carbon dioxide and oxygen occurred at ca. 400?C. Two endothermic peaks (ca. 189 and 197?C) without weight change during the heating in a carbon dioxide atmosphere were due to the phase transition of silver carbonate from the normal viaΒ toα phase. The reverse transition occurred during the cooling.     

Stable dispersions of silver nanoparticles in carbon dioxide with fluorine-free ligands

Iso-stearic acid, a short, stubby compound with branched, methylated tails has been shown to have high solubility in carbon dioxide. Tail solvation by carbon dioxide makes iso-stearic acid a good choice for use as a ligand to sterically stabilize metallic nanoparticles. Iso-stearic acid coated silver nanoparticles have been stably dispersed in carbon dioxide with hexane cosolvent. Neat carbon dioxide has successfully dispersed iso-stearic acid coated silver nanoparticles that had been deposited on either quartz or polystyrene surfaces. These results are the first reports of sterically stabilized nanoparticles in carbon dioxide without the use of any fluorinated compounds.     

Raman spectroscopic investigation of silver electrodes

Raman spectroscopy has been applied to the study of the reduction of carbon dioxide and of formate and carbonate ions at a silver electrode. Raman spectra of adsorbed intermediate species, which are as yet only partially identified, have been detected and show marked variations with electrode potential. These spectral variations are clearly correlated with the voltammetric features for carbonate solutions and suggest that these reduction products complicate most measurements on silver electrodes in the cathodic region. The interpretation of the previously reported spectra due to adsorbed pyridine at silver electrodes has been reconsidered; interactions with surface carboxy species may be significant.     

A galvanic gas sensor using poly (ethylene oxide) complex of silver trifluoromethane sulphonate electrolyte

Summary A galvanic sensor for monitoring nitrogen dioxide was developed by using a poly(ethylene oxide) complex of silver trifluoromethanesulphonate electrolyte. The sensor, which is expressed as Au/P(EO)_4.5 AgCF₃SO₃/Ag, is a small disk (i.d. 13 mm). The polymeric electrolyte film was made by casting the mixture of acetonitrile solutions of both P(EO) (MW 6×10⁵) and AgCF₃SO₃. The working electrode was made by sputtering of gold in argon. The thicknesses of the desposited gold, polymeric electrolyte film and silver are 25 nm, 30 m and 1 mm, respectively. When the sample gas containing nitrogen dioxide impinges at 20 ml min^–1 on the gold cathode, the current flowing in the external circuit was linearly related to the concentration of nitrogen dioxide from 20 ppb to about 10 ppm. The current efficiency of the cell was 0.051%. The cell's response time was about 2 min for 0.5 ppm of nitrogen dioxide.     

Computer-assisted study of silver absorption by porous silicon dioxide nanoparticles

The absorption of silver atoms by porous silicon dioxide particles is studied by the molecular dynamics method. Upon the absorption of silver atoms, (SiO₂)₅₀ nanoparticles do not increase their volume. A particle is divided into two unequal parts by an island shell formed from SiO₂ structural units, which causes anisotropy in the electrical and thermal conductivity of the nanocomposite. IR absorption and emission spectra, Raman spectra, as well as the number of electrons active with respect to IR radiation are calculated. The calculated absorption spectra show the mode corresponding to the stretching vibrations of Si-O surface groups. The addition of silver atoms to nanoparticles can enhance significantly the power of heat radiation emission.     

Determination of trace chlorine dioxide based on the plasmon resonance scattering of silver nanoparticles

A plasmon resonance scattering (PRS) method for chlorine dioxide is reported based on the oxidization of silver nanoparticles (NPs) by it, in pH 9.1 ammonia-ammonium nitrate buffer solutions. Silver NPs exhibit strong PRS signals at 470nm, and can be oxidized by ClO(2), which results in PRS quenching at 470nm. It was found that the PRS quenching intensity is proportional to the concentration of chlorine dioxide over the range of 0.0011-0.185microg/mL, with a detection limit (3sigma) of 0.00050microg/mL and the correlation coefficient of 0.9995. The method is simple, rapid and cost effective. It was applied to the determination of chlorine dioxide in drinking water, with satisfactory results.     

Determination of Amino Acids at a Silver Oxide/Silver Phosphate Electrode and the Analysis of Structure‐Response Relationships

When a silver electrode is conditioned in a solution of 0.5 M sodium hydroxide with added sodium phosphate and using a dual pulse (500 mV/750 mV vs. Ag/AgCl), a stable silver(I)/silver(II) oxide surface is formed. It has been previously shown that various moieties react with the silver(II) oxide in a chemical oxidation at the outer surface of the oxide layer. This is then followed by re‐oxidation of the silver with the generation of current at approximately 500 mV relative to the silver/silver chloride electrode. Previously we found the need to remove carbon dioxide from the base and condition the electrode in a solution containing phosphate ion in order to provide mechanical stability to the oxide layer. We have previously shown this electrode to be applicable to the detection of a variety of carbohydrates. The applicability of the silver oxide/silver phosphate electrode to the post‐chromatographic amperometric detection of amino acids was investigated. Calibration studies of amino acids representative of the various classes demonstrated good sensitivity and linearity in the 1–100 μM range. Responses of amino acids were measured using glucose as an external standard, in order to correct for variability of the oxide layer. Relative responses of the amino acids ranged from 3 down to 0.1. Correlation with structure suggested the importance of absorption in determining the rate of oxidation. Comparison of arginine with n‐benzoyl‐L ‐arginine ethyl ester indicated that side chains as well as the backbone amino group can be oxidized. A Levitch plot of alanine was shown to be linear from approximately 30 to 300 radians per second spin rate at a scan rate of 50 mV per second. Application to post‐chromatographic detection was demonstrated.     

Determination of oxygen-18 in inorganic compounds

A relatively simple and rapid method has been developed for the analysis of the oxygen-18 content of many inorganic compounds including water. The samples are heated with silver cyanide at 500 degrees and the carbon dioxide formed is separated from the other products by means of a methylcyclohexane slush at -130 degrees and analysed mass spectrometrically.     

Thermal decomposition process of silver behenate

The thermal decomposition processes of silver behenate have been studied by infrared spectroscopy (IR), X-ray diffraction (XRD), combined thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS), transmission electron microscopy (TEM) and UV-vis spectroscopy. The TG-DTA and the higher temperature IR and XRD measurements indicated that complicated structural changes took place while heating silver behenate, but there were two distinct thermal transitions. During the first transition at 138 °C, the alkyl chains of silver behenate were transformed from an ordered into a disordered state. During the second transition at about 231 °C, a structural change took place for silver behenate, which was the decomposition of silver behenate. The major products of the thermal decomposition of silver behenate were metallic silver and behenic acid. Upon heating up to 500 °C, the final product of the thermal decomposition was metallic silver. The combined TG-MS analysis showed that the gas products of the thermal decomposition of silver behenate were carbon dioxide, water, hydrogen, acetylene and some small molecule alkenes. TEM and UV-vis spectroscopy were used to investigate the process of the formation and growth of metallic silver nanoparticles.     

Comparative study of the bond energy of oxygen at the surface of supported silver catalysts and of the activity of these catalysis for ethylene epoxidation

A heat-flow microcalorimeter equipped with a pulsed flow reactor has been used to study the reaction of oxygen, at 473 K, with a series of silica-supported silver catalysts. Combustion of impurities with the production of carbon dioxide and water was detected and allowed to correct the calorimetric data. At 473 K, adsorption of oxygen at the surface of silver is a fast process; incorporation of oxygen into deeper metal layers, though present, is a slow process. The differential heats of interaction decrease with increasing amounts of consumed oxygen but always exceed the heat of formation of bulk silver oxides. The average heat of formation of an oxygen monolayer varies from sample to sample and is correlated with the intrinsic activity of the catalysts for ethylene oxidation: surface oxygen species are apparently more catalytically active when they are less energetically bonded at the silver surface.     

Simultaneous microdetermination of carbon, hydrogen, chlorine, bromine, sulfur, and metals in organometallic compounds

A method for the simultaneous microdetermination of carbon, hydrogen, chlorine, bromine, sulfur, and metals which combines features of the known intermediate storage technique in organic microanalysis and formation of the metal-oxine complex, is described. Carbon and hydrogen are determined gravimetrically as usual. Sulfur and halogens are absorbed and stored on electrolytic silver. After completion of the combustion, the oxygen is replaced first by nitrogen and secondly by hydrogen which liberates the sulfur as sulfur dioxide and halogens as hydrogen halides and regenerates the silver layer. The liberated gases can be easily absorbed by dilute hydrogen peroxide and determined titrimetrically. The metal oxide, remaining in the platinum boat, is dissolved in a mixture of nitric-perchloric acids in a test tube and the metal content is determined gravimetrically and titrimetrically using 8-hydroxyquinoline.     

Ion exchange of some transition metal cations on hydrated titanium dioxide in aqueous ammonia solutions

The adsorption of transition metal cations on hydrated titanium dioxide in complexing ammonia and amine solutions has been studied as a function of ammonia (amine) concentration. The relationships between the distribution coefficients and ammonia concentration as well as the effects of various amines on sorption of transition metals indicate that a coordinate bond is formed between the metal ions and the hydroxy groups of the sorbent. The distribution coefficients of silver(I) and cobalt(III), which form strong ammonia complexes in aqueous solutions, decrease with increasing concentration of ammonia already at concentrations exceeding 10^–3. mol·dm^–3. Cations of zinc, manganese and mercury which form much weakerammonia complexes do not exhibit any effect of ammonia concentration in the whole range investigated. In the case of sorption of macroamounts of ammonia or amine complexes of silver, the molecular sieve effect plays an important role. The differences in the affinity of hydrated titanium dioxide for ammonia solvates of various transition metal ions can serve as a tool for effective separation of these ions in ammonia solutions.     

Novel one pot synthesis of silver nanoparticle-polymer composites by supercritical CO2 polymerisation in the presence of a RAFT agent

We report the one pot synthesis of a silver-polymer nanocomposite in supercritical carbon dioxide (scCO(2)) whereby an organometallic silver complex is thermally decomposed in the presence of a reversible addition fragmentation chain transfer (RAFT) agent during a polymerisation reaction in which the RAFT agent simultaneously stabilises the growing polymer microparticles and the formation of surface located silver nanoparticles.