电容去离子脱盐技术：离子交换膜复合活性炭电极的性能

引言随着世界经济及工业的发展、人口的不断增长及环境污染的日益严重,淡水资源的需求量与日俱增。如何从占世界总储水量96%的海水中获得廉价的淡水在世界范围内日益受到关注。目前实现海     

The formation and properties of single nuclei

The formation and growth of single metallic nuclei of silver, mercury and copper have been studied at microscopically small electrodes of platinum and carbon. Once formed, metallic nuclei act as point sinks, growing under hemispherical mass-transfer control. The rate of growth at low overpotential is a function of the mean surface concentration as determined by the Nernst relation.The rate of formation of isolated nuclei has been determined as the inverse of the delay time attending their birth as indicated by the onset of the growth current. A distribution of delay times is observed in keeping with the statistical nature of the nucleation process.The nuclei or crystallites formed are spherical droplets in the case of mercury or microscopic single crystals in the case of solid metals, their size being accessible from the current—time integral of their growth. They are stable on open circuit and exhibit the residual overpotential of their excess surface free energy, ie their Gibbs—Kelvin potential. This potential is a linear function of their inverse equivalent spherical radius. The surface tensions calculated from the simplest application of the Gibbs—Kelvin equations appear to be higher than the known or estimated bulk values.The microscopic metallic crystallites have been used as reactive electrodes. The high mass-transfer flux to their surface enabled the exchange current to be determined by a simple, steady state small amplitude dc procedure.These studies confirm the considerable promise of microscopically small electrodes in electrochemistry.     

Graphite-epoxy composite as an alternative material to design mercury free working electrodes for stripping voltammetry

The use of graphite-epoxy composite electrodes (GECE) as an alternative to mercury or modified electrodes for stripping voltammetry is presented. The effect of preconcentration time on the peak current was studied. It is shown, unlike traditional mercury electrodes, that the accumulation of lead using GECE does not yield a saturation current even at high preconcentration times of 30 min. A preconcentration time of 1 min was chosen as a compromise between analysis time and sensitivity. The peak current was increased by decreasing pH, the pH range 1-2 being the most sensitive. Concentrations as low as 1 ppb for lead and copper and 10 ppb for cadmium in standard solutions have been detected. Both analytical results and SEM characterisation confirm the behaviour of GECE as a complex microelectrode array at a rough surface.     

Electrochemical behaviour of the Cr(II)/Cr(III) couple on silver,silver amalgam and silver-based mercury film electrodes

The electrocatalytic activity of silver, mercury, silver-based mercury films, and silver amalgam electrodes for the reduction of Cr(III) ions in acidic solutions is analysed. An enhancement in the activity of the last two electrodes is observed when they are pretreated with high cathodic current polarization or ultrasonic waves. These effects can be explained by the formation of an unstable highly reactive amalgam. The electrocatalytic enhancement is not observed when the same electrode pretreatments are applied to sitting-drop mercury or silver electrodes.     

Synthesis and Electrochemical Sensing Toward Heavy Metals of Bunch-like Bismuth Nanostructures

Large-scale bunch-like bismuth (Bi) nanostructures were the first time to be synthesized via two-step electrochemical deposition. The growth mechanism of the nanostructures was discussed. Such a designed bunch-like Bi electrode has high sensitivity to detect the heavy metal ions due to its unique three-dimensional structures and strong ability of adsorbing the heavy metal ions. The bunch-like Bi electrode’s detection of heavy metals was statically performed using anodic stripping voltammetry (ASV). The detection in the Pb(II) concentration range of 2.5–50 μg/l was also performed. Based on the experimental results, this bunch-like Bi electrode can be considered as an interesting alternative to common mercury electrodes and bismuth film electrodes for possible use in electrochemical studies and electroanalytical applications.     

燃煤电厂吸附剂喷射脱汞技术的研究进展

燃煤汞污染已引起广泛关注。燃煤电厂控制汞排放最成熟可行的技术是烟道活性炭喷射技术,但该技术在我国燃煤电厂的广泛应用还存在较多的科学问题,因为活性炭对烟气汞的脱除是包含吸附、扩散、传质及化学反应在内的多元化过程,因此,针对燃煤电厂吸附剂喷射脱汞技术的研究已成为当前的热点课题。本文从吸附剂喷射脱汞技术原理、脱汞吸附剂的评价方法、汞吸附机理研究以及吸附剂喷射脱汞数学模型方面评述了燃煤电厂吸附剂喷射脱汞技术近些年取得的研究进展,并在此基础上提出了开发廉价高效、可再生的脱汞吸附剂,全面深入研究吸附剂的脱汞机理以及开发简单、精确的吸附剂喷射脱汞数学模型等后续研究方向,可为我国燃煤电厂吸附剂喷射脱汞技术的开发提供一定指导。     

Nucleation truncation by time-dependent supersaturation: a unified model for homogeneous and heterogeneous nucleation

In this paper, a unified model for heterogeneous, as well as for homogeneous two-dimensional nucleation and growth processes for electrochemical phase transitions is derived. It accounts for three different mechanisms of the termination of nucleation and growth: the geometric mechanism by surface exhausting, the stoichiometric mechanism by the consumption of active surface sites and the systemic mechanism by the time dependence of the supersaturation of the initial phase as the thermodynamic driving force of the phase transition. The special role of time-dependent supersaturation in truncating the nucleation process is discussed by means of numerical simulations of the model equations. It could be shown that some—until now—poorly understood experimental findings concerning phase transition kinetics at electrodes, as for example, the occurrence of instantaneous homogeneous nucleation at the mercury electrode or of non-integer Avrami slopes for heterogeneous nucleation at single crystal electrodes, can be explained easily in the frame of the presented model.     

Electrochemical analysis of a photoelectrochemical chloralkali reactor

In the present study, the electrochemical model for a newly designed photo electrochemical hydrogen production reactor is discussed. The reactor integrates the photochemical hydrogen production with an electrochemical chloralkali process. To neutralize the hydroxyl ions into the chloralkali process, the ideal minimum required potential is 2.18 V. However, there are losses in the solution, membranes and electrodes. These losses should be calculated to find the exact voltage requirement of the photoelectrochemical hydrogen production reactor. An electrochemical model is developed to calculate these losses in the reactor. Effect of brine concentration, electrolyte concentration, distance between the electrodes, current density and temperature are evaluated. The results show that a minimum voltage is required when the distance between the electrodes becomes a minimum at the highest possible temperature, lowest current density and at highest concentrations of brine and electrolyte. Furthermore, they indicate that brine and electrolyte concentrations do not have significant effect on required voltage.     

Influence of geometric variables on the current distribution uniformity at the edge of parallel plate electrodes

In electrochemical processes, the reaction is controlled by electrodes relative placement; to many respects parallel plates seems close to the ideal configuration. However, edge effect represents a detrimental phenomenon that can compromise overall process efficiency. Cell's enclosing insulating walls can attenuate extreme current densities occurring at the electrode edge if appropriately designed to modify the current flow paths. Configurations comprising a limited counter electrode width, an enclosing normal insulating wall, an enclosing oblique insulating wall and a thin parallel mask have been studied. Potential distribution and electrical current lines of these configurations are obtained from algebra operations of complex variables owing to conformal mapping method. It was found that current distribution non-uniformity is conveniently expressed as the absolute deviation from the prescribed value. The dependence of this parameter on geometric variables can be mapped. The picture given by these maps solved the engineering problem of deducing the cell geometry complying with a given current distribution uniformity. Furthermore, optimal parameters providing the best possible performance of each configuration have been identified. Among the geometric variables, the gap between electrodes is the governing parameter of uniformity; it scales the magnitude of edge effect.     

Gas purification by removal of atomic mercury using electrochemical cells

Electrochemical cells are described, which allow the oxidative removal of gaseous atomic mercury from gas streams. The gas stream is fed into an electrochemical cell containing an electrolyte solution and a three-dimensional anode with a large surface. The results can be explained by assuming that the atomic mercury is first transferred from the gas to the electrolyte solution followed by oxidation to mercury(II) ions at the electrode surface. Once mercury(II) has reached a sufficient concentration, it reacts with the atomic mercury to form mercury(I). The dissolved mercury(I) is than oxidized to mercury(II) at the electrodes. Therefore the efficiency of mercury removal from the gas stream can be enhanced by adding mercury(II) to the electrolyte at the very beginning of the process.     

Synthesis of the Silver Nanofluid by ASNSS Process

Arc Spray Nanoparticle Synthesis System (ASNSS) has been used to prepare the silver nanofluids in this study. The metal electrodes under the electrical discharge will melt and evaporate rapidly and condense to form the nanoparticles in the dielectric fluid at lower temperature and produce the suspended nanoparticle fluid. Thus, the mechanism of the ASNSS process is superheating the electrodes by plasma to form metallic nuclei and supercooling these nuclei by dielectric liquid to produce nanofluid. This study considers the different controlling parameters such as discharge current,discharge voltage, pulse-duration time, electrode diameter, and the temperature of dielectric liquid. The optimally operated parameters can be obtained to produce the finer particle size in nanofluid. The results indicate the silver electrodes in alcohol fluid will produce the spherical nanosilver particles. The mean particle size of silver in different dielectric liquid temperatures of-40, -20, 0, and 10℃ is about13.4, 15.8, 17.5, and 21.6 nm, respectively. This indicates that the well suspended fluid can be obtained by controlling the lower dielectric fluid temperature.     

Oxygen reduction at the basal plane of stress-annealed pyrolytic graphite in acetonitrile solutions

The oxygen reduction process occurring at the basal plane of stress-annealed pyrolytic graphite (SAPG) in acetonitrile containing 0.2 M tetrapropylammonium tetrafluoroborate has been studied by cyclic voltammetry. The first step is reported to be outer-sphere electron transfer to form the superoxide radical anion. The second step is reported to be the reduction of products formed by a following chemical reaction involving the superoxide radical anion and the SAPG surface. Support for this mechanism is based on a comparative study using mercury electrodes.     

Direct mercury determination in natural waters by chronopotentiometric stripping analysis in macroelectrode process vessel

By using a specific electrochemical cell with a rotating glassy carbon process vessel as the working electrode, a significant enhancement of mercury determination comparing to commonly used disc electrodes of glassy carbon was achieved. Detection limit obtained for electrolysis time of 600 s was 0.1 ng dm^− 3 of Hg(II). The influence of the most important experimental factors of chronopotentiometric stripping analysis was investigated and the defined method was applied for mercury determination in different types of waters without any pretreatment. Methods accuracy was confirmed by analysing standard reference material. Obtained results showed that similar electrochemical systems can be proposed for continual or semicontinual monitoring of mercury content in different types of waters.     

Construction strategies of self-cleaning ceramic composite membranes for water treatment

Ceramic membranes have received much popularity due to their high mechanical strength, satisfactory acid/alkali resistance, and long-term stability. However, ceramic membranes are also inevitably fouled by contaminates during the membrane separation process. Therefore, construction strategies of anti-fouling ceramic membranes are a main topic in current research. In this work, we review a better anti-fouling ceramic membrane, which is named “self-cleaning” membrane and membrane process. Date to now, there are four main strategies to construct self-cleaning ceramic membranes: 1) porous piezoelectric ceramic membranes; 2) photo-catalytic ceramic membrane; 3) electrochemical ceramic membranes and 4) self-cleaning ceramic membrane surface. Self-cleaning ceramic membranes can in-situ remove and decompose the pollutants on the membrane surface and recover the water permeance that exhibits a great potential to treat industrial wastewater without backwashing or other methods. The detailed membrane fabrication period, mechanism and important case studies are reported in this review. Self-cleaning ceramic membrane is expected to be next-generation anti-fouling ceramic membrane material for continuous water treatment. It is a first review work that systematically concluded all the strategies for self-cleaning ceramic membranes that can be an important reference in ceramic or membrane fields.     

Halide-reversible electrodes in propylene carbonate

The halide-reversible amalgam electrodes of cadmium, lead and thallium and the calomel electrode have been evaluated as reference electrodes in propylene carbonate. The stability and magnitude of the bias potential and the response to micropolarization of each electrode were determined. Of the chloride-reversible electrodes, thallium is superior, lead is significantly poorer and cadmium and mercury are so poor as to be of limited use. The bromide-reversible electrodes of thallium, lead and cadmium are relatively stable, whereas the iodide-reversible electrodes of these three metals are very stable. The halides of cadmium, lead and thallium interact with propylene carbonate—alkali halide solutions, probably to yield either a solid solvate or a solid double salt, and this interaction has a substantial effect on the potentials of binary cells. The relative magnitude of the interaction, which is independent of the particular halide anion, is lead > thallium > cadmium. The interaction and its influence on the potentials of the electrodes indicate a need for caution in interpretation of potentiometric measurements made with these electrodes.     

Recent Advances in Light Energy Conversion with Biomimetic Vesicle Membranes

Lipid bilayer membranes are ubiquitous in natural chemical conversions. They enable self-assembly and compartmentalization of reaction partners and it becomes increasingly evident that a thorough fundamental understanding of these concepts is highly desirable for chemical reactions and solar energy conversion with artificial systems. This minireview focusses on selected case studies from recent years, most of which were inspired by either membrane-facilitated light harvesting or respective charge transfer. The main focus is on highly biomimetic liposomes with artificial chromophores, and some cases for polymer-membranes will be made. Furthermore, we categorized these studies into energy transfer and electron transfer, with phospholipid vesicles, and polymer membranes for light-driven reactions.     

金属硫化物吸附剂脱除烟气汞研究进展

工业烟气排放的汞严重危害人体健康及生态环境,金属硫化物是一种新型的高效汞吸附剂,受到广泛关注。本文总结了近年来金属硫化物应用于脱除烟气汞的研究进展。归纳了不同金属硫化物的吸附性能,并对影响吸附性能的常见因素进行了梳理,已有研究表明金属硫化物在复杂的反应条件下仍具有优异的脱汞性能;进一步归纳了金属硫化物的汞吸附机理;总结出活性位和比表面积的调控是当前强化金属硫化物汞吸附性能的常见方法;最后对金属硫化物的再生方法进行了介绍。基于当前研究进展,未来的研究应关注如何强化金属硫化物在高温下的脱汞性能,以及如何在低温条件下实现汞的脱附从而避免当前高温热脱附方法对金属硫化物结构的破坏。     

Electrochemical reduction of imazamethabenz methyl on mercury and carbon electrodes

This paper presents polarographic and voltammetric studies of the reduction of the herbicide imazamethabenz methyl (2/3-methyl-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-p-toluate), on mercury and carbon electrodes. The electrochemical studies were performed in strongly acidic media (0.1-2.7 M H₂SO₄) as well as in the pH range of 1-12. The overall reduction process involves the uptake of two electrons. The results obtained in polarography show that there is the reduction of two species, related via an acid-base equilibrium, and having very close reduction potentials. The voltammetric results obtained with a glassy carbon electrode were very similar to those observed on mercury electrodes. The reducible group in the molecule is the imidazolinone ring. In strongly acidic media (pH < pK_a), the reaction mechanism proposed is the reduction of the protonated herbicide by an electrochemical-chemical-electrochemical (ECE) process, being the r.d.s. the second electron transfer. At pH > pK_a the neutral form of the herbicide is reduced and the second electron transfer becomes reversible or quasi-reversible. In basic media, the species reduced is the deprotonated imazamethabenz methyl and the r.d.s. is the second electron transfer.     

On the mechanism of hydrogen evolution catalysis by proteins: A case study with bovine serum albumin

The catalysis of the hydrogen evolution reaction (HER) by proteins has been known for decades but was only recently found to be useful for electroanalytical purposes. The mechanism of the catalytic process is investigated at hanging mercury drop electrodes by cyclic voltammetry, with bovine serum albumin as a model system. It is shown that the catalyst is the protein in the adsorbed state. The influence of various parameters such as the accumulation time, scan rate or buffer concentration is studied, and interpreted in the framework of a surface catalytic mechanism. Under the experimental conditions used in the work, a “total catalysis” phenomenon takes place, the rate of HER being limited by the diffusion of the proton donor. The adequacy of the existing models is discussed, leading to a call for the development of more refined models.     

On the adsorption and kinetics of phase transients of adenosine at the different carbon electrodes modified with a mercury layer

Optical roughness of a pyrolytic graphite electrode with basal (PGEb) and edge orientation (PGEe), a glassy carbon electrode (GCE), and the same electrodes modified with mercury (MFE) was studied by an optical diffractive element (DOE) based sensor. Electrochemical characterisation of these electrodes used was performed by cyclic voltammetry (CV) and capacitance measurements (C-E curves and electrochemical impedance spectroscopy, EIS). The kinetics of phase transients of adenosine adsorbed on PGEb, and GCE modified with mercury layer of different thicknesses (thickness was changed from 0.02 to 2 μm) was studied by chronoamperometry (j-t curves) and capacitance measurements (C-E curves). In acidic (pH 5) solution adenosine forms two different two-dimensional (2D) physisorbed condensed layers on the MFE. The first of these (region I) is located at more positive potential; the centre of this adlayer is situated around −0.4 V. The second 2D physisorbed film (region III) is formed at more negative potentials; the centre of the region III is around −1.3 V. The 2D condensed films (adlayer I and III) of adenosine still exist on the PGEb substrate modified by 0.02 μm thick mercury layer. Adlayers III and I of adenosine exist on the GCE modified with mercury layer down to 0.02 and 0.2 μm, respectively. The kinetics of phase transients of the adenosine films taking place by a potential jump from dilute adsorption region (state II and IV) to the 2D physisorbed film (region I and III) at the PGEb and GCE substrates modified with mercury (Hg-PGEb and Hg-GCE) were studied, respectively. During both of the phase transients of IV→III and II→III of adenosine a polynucleation and growth process on both the Hg-PGEb and Hg-GCE was detected. The phase transients of II→I are characterised by an exponential decay of the current without the current maximum (the adsorption process took place only). It was observed that the phase transients of IV→III are the fastest at the HMDE and gradually slow down on 2 μm Hg-GCE and 2 μm Hg-PGEb, respectively.