Sensor–actuator system for dynamic chloride ion determination

Chloride is a crucial anion for various analytical applications from biological to environmental applications. In order to measure the chloride ion concentration, a measurement system is needed which can detect this concentration for prolonged times reliably. Chronopotentiometry is a technique which does not need a long term stable reference electrode and is therefore very suitable for prolonged ion concentration measurements. As the used electrode might be fouled by reaction products, this work focuses on a chronopotentiometric approach with a separated sensing electrode (sensor) and actuating electrode (actuator). Both actuation and sensor electrode are made of Ag/AgCl. A constant current is applied to the actuator and will start the reaction between Ag and Clˉ, while the resulting Clˉ ion concentration change is observed through the sensor, which is placed close to the actuator. The time it takes to locally deplete the Clˉ ions is called transition time. Experiments were performed to verify the feasibility of this approach. The performed experiments show that the sensor detects the local concentration changes resulting from the current applied to the actuator. A linear relation between the Clˉ ion concentration and the square root of the transition time was observed, just as was predicted by theory. The calibration curves for different chips showed that both a larger sensor and a larger distance between sensor and actuator resulted in a larger time delay between the transition time detected at the actuator and the sensor.     

Properties of Ag/AgCl electrodes fabricated with IC-compatible technologies

The purpose of this work is to fabricate and characterize Ag/AgCl electrodes made on a silicon chip at the wafer level with integrated circuit-compatible fabrication techniques. Such electrodes are useful as reference electrodes in several kinds of chemical sensors. Two types of electrode were investigated. The first type uses an evaporated AgCl layer that is patterned with lift-off photolithography. The second type is formed by exposing a selected part of the silver substrate to a KCrO₃Cl solution. Both types of electrode give the thermodynamically expected potential response to variations of Cl⁻ ion concentration. The potential generated by the KCrO₃Cl-formed electrodes was more stable, however. Auger electron spectroscopy depth profiles indicate that immersion in a KCrO₃Cl solution produces a thin layer of AgCl on top of a layer of AgO. The low electronic resistance of AgO then reduces the measured series resistance of the KCrO₃Cl-formed electrodes. Impedance plane plots and the impedance as a function of frequency were measured for both types of electrode, and the impedance of the evaporated AgCl electrodes was indeed considerably higher. The impedance measurements could be successfully modelled by assuming a Randles equivalent circuit for the AgCl/electrolyte interface. For the KCrO₃Cl-formed electrodes, the impedance was modified by the porosity these electrodes manifested.     

银离子与聚酰胺-胺型树形高分子配位作用的研究

The complexation between poly(amidoamine) (PAMAM) dendrimers and silver ion was studied in this paper. The results showed that generations and surface groups of dendrimers， reaction time， pH value， mole ratio of Ag⁺/PAMAM dendrimers， as well as reaction temperature strongly influence complexation between Ag⁺ and PAMAM dendrimers. The maximum complexing number of Ag⁺ that amino-， hydroxyl- and carboxylate- terminated PAMAM dendrimers could bind has been obtained. It has been found that the measured value of amino- and hydroxyl- ter-minated PAMAM is almost similar to the theory value， but to carboxylate- terminated PAMAM， there is a dis-crepancy between the measured value and theory value because of the electrostatic interaction between the silver ion and carboxyl group.     

薄层循环伏安法研究硝基苯/水界面上离子诱导的电子转移反应

应用薄层循环伏安法研究了硝基苯/水两相界面间,且有共同离子四丁基铵TBA+存在于两相中,在有机相中的四氰化二甲基苯醌(TCNQ)与水相中的K4Fe(CN)6之间发生的反向电子转移反应。在直径为0.64cm的裂解石墨电极上用2μL硝基苯溶液使之自然扩散在电极表面形成薄层的有机相,并以此作为工作电极。对电极为铂丝(0.5mm),参比电极为Ag/AgCl电极,均置于总体积为2mL的水相中。由于共同离子TBA+的诱导,在硝基苯/水界面间,在已氧化的TCNQ+阳离子(在有机相中)与[Fe(CN)6]4-阴离子(在水相中)之间发生了反向电子转移反应。试验证明:在一定条件下,通过改变两相中共同离子的浓度,可使一些不能发生的两相界面的电子转移反应得以发生;这类电子转移反应系受界面电位差所控制。此外,还测得了在恒定的共同离子浓度比值的条件下,此两相界面电子转移反应的表观速率常数(k)为0.135cm.s-1.mol-1。     

银纳米线的制备及电催化还原氧性能研究

分别以聚乙烯基吡咯烷酮(PVP),乙二醇作为软模板和还原剂,采用不同晶种(AgCl、Ag)快速合成了银纳米线.通过SEM和TEM表征,证明合成银纳米线材料形貌均一,颗粒含量很少.并且发现以AgCl为晶种合成的银纳米线长径比为200左右(SNWH),而以Ag为晶种合成的长径比为30左右(SNWL).以银纳米线作为电催化氧...     

氧化铝模板中直流电沉积镍纳米线

氧化铝模板中直流电沉积镍纳米线;多孔阳极氧化铝模板;镍纳米线;电沉积     

Catalytic resonance scattering spectral method for the determination of trace amounts of Se

A new catalytic kinetic method has been proposed for the determination of Se from 8.0x10(-9) to 8.0x10(-8) M, using the fact that Se(IV) can catalyze the slow reaction between KClO(3) and phenylhydrazine sulfate (PH) in 0.1 M H(2)SO(4) solution at 100 degrees C. The reduction product of ClO(3)(-), Cl(-), reacts with Ag(+) to form (AgCl)(n) nanoparticles. The nanoparticles exhibit a maximum resonance scattering spectral peak at 470 nm. The intensity of resonance scattering light at 470 nm is linear with respect to the Se concentration, using the fixed-reaction time procedure. The factors influencing the determination of Se were examined. This catalytic resonance scattering spectral method has been applied to the analysis of Se in real samples, with satisfactory results.     

Transport of ions through the oil phase of W(1)/O/W(2) double emulsions

Using a capillary video microscopy technique, the ion transport at liquid-liquid interfaces and through a surfactant-containing emulsion liquid membrane was visually studied by preparing a double emulsion globule within the confined space of a thin-walled, transparent, cylindrical microtube. NaCl and AgNO(3) were selected as the model reactants and were prepared to form a NaCl/AgNO(3) pair across the oil film. By observing and measuring the formed AgCl deposition, it was found that both Cl(-) and Ag(+) could transport through a thick oil film and Ag(+) was transported faster than Cl(-). Interestingly, the ion transport was significantly retarded when the oil film became extremely thin (<1 microm). The results suggested that the transport of ions mainly depends on the "reverse micelle transport" mechanism, in which reverse micelles with entrapped ions and water molecules can be formed in a thick oil film and their construction will get impeded if the oil film becomes extremely thin, leading to different ion transport rates in these two cases. The direction of ion transport depends on the direction of the osmotic pressure gradient across the oil film and the ion transport is independent of the oil film thickness in the investigated thick range. Ions with smaller Pauling radii are more easily entrapped into the formed reverse micelles and therefore will be transported faster through the oil film than bigger ions. Oil-soluble surfactants facilitate ion transport; however, too much surfactant in the oil film will slow down the ion migration. In addition, this study showed no support for the "molecular diffusion" mechanism of ion transport through oils.     

Ag/AgCl/铁-海泡石异相可见光Fenton催化降解双酚A

光-Fenton技术是高级氧化技术中的一种,常用于难降解废水处理,由于其反应速度快、毒性低、反应条件温和而受到广泛关注.然而,传统的光-Fenton体系具有可见光利用率低、回收困难等缺点.为了解决这些问题,本文采用廉价易得、无污染、吸附能力强的天然矿物海泡石作为催化剂载体,并利用Ag/AgCl能够吸收可见光的表面等离子响应这一光学性质,合成了一种有潜力的非均相等离子体光催化剂Ag/AgCl/铁-海泡石催化剂(Ag/AgCl/Fe-S),并对该催化剂的形貌结构、性能和机理等进行了系统研究.通过XRD,SEM,XPS,BET,UV-vis等表征手段对催化剂形貌、结构和可见光性能进行了分析.其中,XRD和SEM结果显示,Ag/AgCl粒子已经成功负载在Fe-海泡石上;XPS结果显示,铁氧化物的组成主要为FeOOH和Fe2O3;UV-vis结果显示,催化剂有较好的可见光吸收性能.以双酚A为目标污染物,分别考察了Ag/AgCl/Fe-S,Ag/AgCl和Fe-海泡石的光-Fenton催化性能.结果显示,Ag/AgCl/Fe-S降解双酚A的效果明显优于另外两种催化剂,在H2O2浓度为6mmol/L,pH为4,光照强度500W,Ag/AgCl/Fe-S催化剂量为1.0 g/L,双酚A初始浓度为10 mg/L的条件下,1 h时,双酚A基本被完全降解,且3 h时,其矿化率达到61.2%;而Ag/AgCl和Fe-海泡石催化剂在同样的条件下完全降解双酚A至少要3 h,且其矿化率分别只有46.61%和28.85%.另外,还分别探讨了H2O2浓度、pH值、光照强度和催化剂剂量对双酚A降解的影响.最后,通过活性物种捕获、ESR、电化学和PL实验对该体系的反应机理进行了探讨.活性物种捕获实验和ESR实验结果表明,羟基自由基(?OH)和空穴(h+)是该体系中的主要活性物种,且Ag/AgCl/Fe-S+H2O2+vis体系产生的?OH明显多于Fe-S+H2O2+vis体系.为了探讨?OH增多的原因,我们进行了电化学实验和PL实验.电化学实验结果显示,Ag/AgCl/Fe-S催化剂具有更低的阻抗,因此有利于电子-空穴分离.PL结果显示,Ag/AgCl/Fe-S催化剂的电子-空穴复合率更低.结合以上实验,我们提出了Ag/AgCl/Fe-S+H2O2+vis体系对双酚A的降解机理,即一方面催化剂能够发生Fenton反应而产生?OH,另一方面,催化剂中的Ag/AgCl在可见光下由于表面等离子响应而产生电子-空穴,空穴本身可作为活性物种降解双酚A.同时,产生的电子被体系中的Fe3+捕获生成Fe2+,从而促进了铁循环,有利于体系中产生更多的?OH.最后,空穴和羟基自由基发生协同作用共同促进污染物降解.     

Sonochemical synthesis of Ag/AgCl nanocubes and their efficient visible-light-driven photocatalytic performance

A novel one-step sonochemical approach to synthesize a plasmonic photocatalyst of AgCl nanocubes (ca. 115 nm in edge length) with a small amount of Ag metal species is presented. The nanoscale Ag/AgCl hybrid photocatalysts with cubic morphology are readily formed under ambient ultrasonic conditions and neither external heat treatment nor reducing agents are required. The size of the Ag/AgCl photocatalysts could be controlled by changing the concentrations of Ag(+) ions and polyvinylpyrrolidone molecules in precursor solutions. The compositions, microstructures, influencing factors, and possible growth mechanism of the Ag/AgCl hybrid nanocubes were systematically investigated. The Ag/AgCl photocatalysts show excellent photocatalytic performance for degradation of various dye molecules under visible light.     

A general route to synthesize water-dispersive noble metal-iron oxide bifunctional hybrid nanoparticles

This communication describes a simple, general route for preparing bifunctional hybrid nanoparticles based on direct adsorption and spontaneous reduction of Ag(+) and Pd(2+) onto the surface of carbon-encapsulated superparamagnetic colloidal nanoclusters. Because of the existence of carbon coating and surface hydrophilic carboxyl, the bifunctional hybrid nanoparticles show excellent water-dispersity. In addition, the size (35 nm-86 nm) and number of Ag nanocrystals can be tuned by changing the molar ratios and reaction concentration between Ag(+) and nanoclusters.     

Heterogeneous Au-Pt nanostructures with enhanced catalytic activity toward oxygen reduction

Heterogeneous Au-Pt nanostructures have been synthesized using a sacrificial template-based approach. Typically, monodispersed Au nanoparticles are prepared first, followed by Ag coating to form core-shell Au-Ag nanoparticles. Next, the galvanic replacement reaction between Ag shells and an aqueous H(2)PtCl(6) solution, whose chemical reaction can be described as 4Ag + PtCl(6)(2-)→ Pt + 4AgCl + 2Cl(-), is carried out at room temperature. Pure Ag shell is transformed into a shell made of Ag/Pt alloy by galvanic replacement. The AgCl formed simultaneously roughens the surface of alloy Ag-Pt shells, which can be manipulated to create a porous Pt surface for oxygen reduction reaction. Finally, Ag and AgCl are removed from core-shell Au-Ag/Pt nanoparticles using bis(p-sulfonatophenyl)phenylphosphane dihydrate dipotassium salt to produce heterogeneous Au-Pt nanostructures. The heterogeneous Au-Pt nanostructures have displayed superior catalytic activity towards oxygen reduction in direct methanol fuel cells because of the electronic coupling effect between the inner-placed Au core and the Pt shell.     

Synthesis of confined Ag nanowires within mesoporous silica via double solvent technique and their catalytic properties

Ag nanowires within the channels of mesoporous silica have been successfully synthesized via a double solvent technique, in which n-hexane is used as a hydrophobic solvent to disperse mesoporous silica and an AgNO(3) aqueous solution is used as a hydrophilic solvent to fill mesochannels. The morphology of the obtained Ag (nanowires, nanoparticles or nanorods) can be controlled by adjusting the concentration of AgNO(3) solution and the template pore size. HRTEM images demonstrate extensive Ag nanowires with several to tens of hundreds nanometers in length are deposited along the long axis of mesochannels when the atomic AgNO(3)/Si ratio is 0.090. When the atomic AgNO(3)/Si ratio is 0.068 or 0.11, there is a combination of Ag nanoparticles and nanowires; nanoparticles are mainly formed when the atomic AgNO(3)/Si ratio is higher than 0.14. Further, the catalytic results of the oxidation of styrene show that styrene oxide and benzaldehyde are the main products of the reaction, and the morphology and diversity of Ag in Ag/mesoporous silica composites have an effect on the conversion of styrene and selectivity of styrene oxide.     

Preparation and photocatalytic activity of carbon dot/Ag/AgCl

CD (carbon dot)/Ag/AgCl compound photocatalysts with different compounding degrees were prepared via a precipitation method, and their physiochemical properties were characterized by X‐ray diffraction, FE‐SEM, UV–vis and the like. Through the degradation experiment of methyl orange (MO), the effects of different compounding amount and methyl orange concentration on photocatalytic degradation were investigated to find the best ratio. It was found the photocatalytic activity of CD/Ag/AgCl was significantly higher than Ag/AgCl, and the best compounding dosage was 6 mg/l carbon dot. The degradation rate of CD/Ag/AgCl was lower when the initial MO concentration was higher. Five repeated experiments were conducted to test the stability of the catalysts, and showed the MO degradation rates were all above 85%, indicating the CD/Ag/AgCl compound photocatalysts all showed high stability and repeatability. The reaction mechanism of CD/Ag/AgCl photocatalyst was studied by electrochemical experiments and ESR experiments. The results show that the doping of CD effectively improves the photocatalytic degradation ability of MO.     

Control of Interfacial Potentials and Redox Reactions on Bipolar Electrodes Using Ag/AgCl

The interfacial potential difference on the surface of bipolar electrodes was controlled by placing Ag/AgCl on part of the electrode. Oxygen reduction on the cathodic pole was coupled with an electrochemiluminescence (ECL) reaction on the anodic pole. In an open bipolar system, the ECL intensity depended on the location of Ag/AgCl and the concentration of Cl⁻ ions. A current flowed through Ag/AgCl and the ratio of currents generated at the anodic and cathodic poles was affected by the position of Ag/AgCl. Further, the effect of Ag/AgCl placement was also demonstrated in a closed bipolar system using hydrogen peroxide (H₂O₂) and glucose as analytes. Ag/AgCl was also effective in adjusting the sensitivity to these analytes to achieve the best performance. This method of interfacial potential control is expected to contribute toward the development of reliable sensing devices and applications such as redox cycling, which require precise potential control.     

The fabrication and performance of an Ag/AgCl reference electrode in human serum

A simple set of electric circuits was used to assemble a pulse generator. With pulse potentials and under galvanostatical control, a clean silver wire was anodized electrochemically for 0.2–0.5 min in 1.0 mol l⁻¹ HCl with a pulse current density of 20 mA cm⁻², and the pulse wave parameters of t_a/t_c = 1 and a cycle of 4 s forming an Ag/AgCl reference electrode. Even though the AgCl layer was consumed during the working period when the Ag/AgCl electrode was used as a cathode, the AgCl layer could be in situ recovered electrochemically in serum used when a reversed potential was applied to the electrode system immediately after the measuring program was finished. The current response curve of the anode indicated that an AgCl layer in high density was basically accomplished during the first 6 pulse cycles in human serum. In order to keep a stable and uniform AgCl layer on the reference electrode after each measuring cycle, the ratio of the recovery time (t_r) to the working time (t_w) was measured and the smallest value was obtained at 0.03. The open-circuit potential of the Ag/AgCl electrode with respect to a SCE in 0.1 mol l⁻¹ KCl was monitored over a period of 14 days and the mean value was 40.09 mV vs SCE with a standard deviation of 2.55 mV. The potential of the Ag/AgCl reference electrode did remain constant when the measurements were repeated more than 600 times in undiluted human serum with a standard deviation of 1.89 mV. This study indicated that the Ag/AgCl reference electrode could been rapidly fabricated with a pulse potential and could be used as a reference electrode with long-term stable properties in human serum samples.     

F127反相微乳液的组成对AgCl纳米粒子形成及AgCl/F127-PMMA杂化膜结构和性能的影响

以F127为表面活性剂构成的反相微乳液制备AgCl纳米粒子和AgCl/F127-PMMA杂化膜,通过紫外可见光谱(UV-visible)、透射电镜(TEM)研究了微乳液的增容水量(ω)和盐浓度(Csalt)对AgCl粒子形成与形貌的影响;结合表面ζ电位测定、扫描电镜(SEM)分析和溶胀实验等考察了AgCl/F127-PMMA杂化膜的结构和性能。研究结果表明,低ω下盐浓度增加,胶束中AgCl反应速率增大,导致大量小粒径AgCl粒子的形成;高ω下盐浓度增加,将加快AgCl粒子的生长,从而导致胶束中的AgCl粒子粒径增大;各种ω下盐浓度的增加,都会引起胶束中单质Ag的形成。杂化膜的SEM分析显示,AgCl粒子粒径越小,在杂化膜中的分散性越好,膜表面的ζ电位也越高,膜在苯中的溶胀性能也越高;单质Ag的出现和AgCl粒子数目的增多,杂化膜中将显现明显的粒子团聚现象,这极大地影响了杂化膜在苯中的溶胀性能;而杂化膜在环己烷中的溶胀性能较低,且随ω和盐浓度的变化极小。     

Reactivity of ammonia ligands of the antitumor agent cisplatin: a unique dodecanuclear Pt4,Pd4,Ag4 platform for four cytosine model nucleobases

The reaction of a potential mono(nucleobase) model adduct of cisplatin, cis-[Pt(NH(3))(2)(1-MeC-N3)(H(2)O)](2+) (6; 1-MeC: 1-methylcytosine), with the electrophile [Pd(en)(H(2)O)(2)](2+) (en: ethylenediamine) at pH approximately 6 yields a kinetic product X which is likely to be a dinuclear Pt,Pd complex containing 1-MeC(-)-N3,N4 and OH bridges, namely cis-[Pt(NH(3))(2)(1-MeC(-)-N3,N4)(OH)Pd(en)](2+). Upon addition of excess Ag(+) ions, conversion takes place to form a thermodynamic product, which, according to (1)H NMR spectroscopy and X-ray crystallography, is dominated by a mu-NH(2) bridge between the Pt(II) and Pd(II) centers. X-ray crystallography reveals that the compound crystallizes out of solution as a dodecanuclear complex containing four Pt(II), four Pd(II), and four Ag(+) entities: [{Pt(2)(1-MeC(-)-N3,N4)(2)(NH(3))(2)(NH(2))(2)(OH)Pd(2)(en)(2)Ag}(2){Ag(H(2)O)}(2)](NO(3))(10) 6 H(2)O (10) is composed of a roughly planar array of the 12 metal ions, in which the metal ions are interconnected by mu-NH(2) groups (between Pt and Pd centers), mu-OH groups (between pairs of Pt atoms), and metal-metal donor bonds (Pt-->Ag, Pd-->Ag). The four 1-methylcytosinato ligands, which are stacked pairwise, as well as the four NH(3) ligands and parts of the en rings, are approximately perpendicular to the metal plane. Two of the four Ag ions (Ag2, Ag2') of 10 are labile in solution and show the expected behavior of Ag(+) ions in water, that is, they are readily precipitated as AgCl by Cl(-) ions. The resulting pentanuclear complex [Pt(2)Pd(2)Ag(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(4)7 H(2)O (11) largely maintains the structural features of one half of 10. The other two Ag(+) ions (Ag1, Ag1') of 10 are remarkably unreactive toward excess NaCl. In fact, the pentanuclear complex [Pt(2)Pd(2)AgCl(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(3)4.5 H(2)O (12), obtained from 10 with excess NaCl, displays a Cl(-) anion bound to the Ag center (2.459(3) A) and is thus a rare case of a crystallized "AgCl molecule".     

Molecular dynamics simulation of glycine zwitterion in aqueous solution

A classical molecular dynamics method was used to study the modifications of the solution structure and the properties of glycine zwitterion in aqueous solution due to the increase of glycine zwitterion concentration and the incorporation of Na(+) and Cl(-) ions to the solution. The glycine zwitterion had fundamentally a hydrophilic behavior at infinite dilution, establishing around six hydrogen bonds with the water molecules that surrounded it, which formed a strong hydration layer. Because of the increase of glycine zwitterion concentration, the hydration structure became more compact and the quantity of water molecules bound to this molecule decreased. The Na(+) ion bound to the CO(2) group of glycine, while the Cl(-) ion bound mainly to the NH(3) group of this molecule. The integration of the ions to the hydration layer of the glycine zwitterion produced modifications in the orientational correlation between atoms of glycine zwitterion and water that surrounded them and an increase of the approaches between the glycine zwitterion molecules. The incorporation of ions to the solution also produced changes in the water-water orientational correlation. Decreases of the water-water hydrogen bonds and diffusion coefficient of all molecules were observed when the glycine zwitterion concentration increased and when the ions were incorporated to the solution.     

Dielectrophoretic growth of platinum nanowires: concentration and temperature dependence of the growth velocity

The growth velocity of platinum nanowires in an aqueous solution of K(2)PtCl(4) is investigated as a function of the metal complex concentration and temperature. The solution is specially prepared to provide mainly the neutral complex cis-[PtCl(2)(H(2)O)(2)] for growing nanowires by dielectrophoresis. The measured growth velocities indicate diffusion-limited nanowire growth at low concentration and high temperature in qualitative agreement with a theoretical analysis that includes the diffusion of metal complexes and the dielectrophoretic force on the complexes. At concentrations greater than 100 μM and low temperature, different behavior is observed, suggesting the growth rate to be limited by the deposition reaction of platinum at the nanowire tip. The enhancement of the K(+) concentration is found to support nanowire growth. Possible reasons for a rate limitation and for the difference between observed and calculated nanowire growth velocities are discussed.