Water dissociation phenomena in a bipolar membrane

The models were established for the theoretical current-voltage characteristics in water dissociation process on a bipolar membrane. Particular attention was given to the transport of the water ions and electrolyte ions as well as the membrane physical structure and configuration. The factors on the water splitting process were adequately analysed based on the derived theoretical current-voltage characteristics and several good suggestions were proposed for decreasing the work voltage in practical operations. In addition, the model can give a reasonable explanation for the catalytic effect of some chemicals, such as amphiprotic hydroxide compounds, weak polymeric acids and bases, etc. It is shown that the catalyst may be responsible for the increase in dissociation rate constant of water and therefore enhance the water dissociation. The guidelines for choosing a proper catalyst were also proposed. Project supported by the Youth Foundation of USTC[1999], the Foundation of the State Kay Lab. of Func. Poly. Materials for Adsor. & Sep., Nankai Univ. [1998], the Foundation of Post-doctoral of China (No. 1996(2)) and the National Natural Science Foundation of China (Grand No. 2997604).     

Fundamental studies on the intermediate layer of a bipolar membrane: Part III. Effect of starburst dendrimer PAMAM on water dissociation at the interface of a bipolar membrane

Starburst dendrimer polyamidoamine (PAMAM) with ellipsoidal or spheroidal shape is structure-regular and has much more amino groups than conventional polymers. This paper investigates the possibility of these amino groups on water dissociation in a bipolar membrane interface. To do this, a bipolar membrane is prepared by casting the solution of sulfonated poly(phenylene oxide) (SPPO) in dimethyl formamide (DMF) on a commercial anion exchange membrane that is immersed in PAMAM aqueous solution in advance. The existence of PAMAM adsorbed on the membrane is proved by X-ray photoelectron spectroscopy (XPS), and the adsorption amount is evaluated by weighting method. The junction thickness of the prepared bipolar membrane is determined by electrochemical impedance spectroscopy (EIS), and the performance is evaluated by current–voltage curves. The experiments show that both the generation and concentration of PAMAM would strongly affect the characteristics of the bipolar membranes. There exists a transitional concentration for various generations PAMAMs to catalyze effectively the water dissociation, and above or below the transitional concentration the performance of bipolar membranes is decreasing. The higher the generation, the lower the concentration. Moreover, at a fixed solution concentration, there is not the simple relation of monotone decreasing or increasing between the performance of bipolar membranes and the generations of PAMAMs. All these can be explained according to the characteristics of PAMAMs combined with available water dissociation theory.     

Irreversible dissociation of water molecules on the ion-exchange membrane-electrolyte solution interface in electrodialysis

The fluxes of hydrogen ions through the cation-exchange membrane and hydroxyl ions through the anion-exchange membrane in the electrodialysis were measured using the method of selective polarization. The experiments, which were conducted in a wide range of current densities, enabled us to obtain the results of ionic transport different from the literature data and to explain them on the basis of chemical reactions proceeding in the system. It is shown that a decrease in the hydration of ionogenic groups intensifies the ionic fluxes of the medium in the electrodialysis.     

Fabrication of cellulose triacetate/graphene oxide porous membrane

Cellulose triacetate (AC)/graphene oxide (GO) porous membranes were successfully fabricated by combining ultrasonication and phase inversion method. The structures and morphologies of the resultant composite membranes were investigated by X‐ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy, respectively. Microscopic and X‐ray diffraction measurements revealed that GO sheets were uniformly dispersed within the AC matrix. The pore size and structure were modulated by changing GO concentration from 0.25 to 1 wt%. Membrane thermal properties were also studied. Among all tested membranes, the most favorable GO amount was 1 wt%, giving Td_3% of 274°C, which represents a 22°C enhancement compared with AC. Conversely, the membranes showed improved barrier properties against water and ethanol. The decrease of both ethanol and water fluxes was assigned to the stabilization of composite membrane structure, as a result of GO progressive addition. Bovine serum albumin rejection assay indicated an increasing from 78% in the case of CA membrane to 99% in the case of CA/GO 1 wt% of the rejection degree after 90 min. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of the nature of membrane ionogenic groups on water dissociation and electrolyte ion transport: A rotating membrane disk study

Polarization properties of electromembrane systems (EMS) consisting of a heterogeneous membrane, either the MK-41 phosphonic acid membrane or the MK-40 sulfonic acid membrane, and dilute sodium chloride solutions are investigated with the rotating membrane disk method. For the MK-41/0.01 M NaCl and MK-41/0.001 M NaCl EMS, effective ion transport numbers and partial current-voltage curves (CVC) are measured for sodium and hydrogen ions, and limiting-current densities and the diffusion-layer thickness are calculated as functions of the rotation rate of the membrane disk. With the theory of the overlimiting state of EMS, internal parameters of the systems under investigation—the diffusion-layer thickness, the space-charge distribution, and electric-field strengths in the diffusion layer and in the membrane—are calculated from experimentally obtained CVC and the dependence of effective transport numbers on current density. The catalytic influence of ionogenic groups on the dissociation rate of water is analyzed quantitatively. Partial CVC for H⁺ ions are calculated for the space-charge region in MK-40 and MK-41 membranes. Analogous CVC for bipolar membranes containing sulfonic acid and phosphonic acid groups are compared. The dissociation mechanism of water is the same in all EMS and is independent of the membrane type and the nature of the functional groups.     

Three-compartment bipolar membrane electrodialysis for splitting of sodium formate into formic acid and sodium hydroxide: Role of diffusion of molecular acid

Bipolar membrane electrodialysis is used in a three-compartment configuration to regenerate formic acid and sodium hydroxide from sodium formate. A previous study showed that the diffusion of molecular formic acid induces the loss of acid current efficiency. The present study shows the following results: the diffusion of molecular formic acid through the bipolar membrane explains quantitatively the presence of sodium formate in the sodium hydroxide solution. The loss of acid current efficiency is only due to diffusion of molecular acid through both anion-exchange and bipolar membranes. The sodium hydroxide current efficiency is determined by acid diffusion through the bipolar membrane and OH⁻ leakage through the cation-exchange membrane. The flux of acid diffusion through the membranes is proportional to acid concentration and depends on sodium hydroxide concentration for bipolar membrane and on sodium formate concentration for anion-exchange membrane. The flux rates vary with temperature.     

Electrochemical Pseudocapacitors Based on Ternary Nanocomposite of Conductive Polymer/Graphene/Metal Oxide: An Introduction and Review to it in Recent Studies

This review gives an overview of the synthesis, surface and electrochemical investigations over ternary nanocomposite of conductive polymers in the development of new supercapacitors. They utilize both Faradaic and non‐Faradaic procedures to store charge, leading to higher specific capacitance and energy density, higher cell voltage, longer life cycle and moderated power density. Owing to a unique combination of features such as superb electrical conductivity, corrosion resistance in aqueous electrolytes, highly modifiable nanostructures, long cycle life and the large theoretical specific‐surface area, the use of ternary nanocomposites as a supercapacitor electrode material has become the focus of a significant amount of current scientific researches in the field of energy storage devices. In these nanocomposites, graphene not only can be utilized to provide a substrate for growing nanostructured polymers in a polymer‐carbon nanocomposite structure in order to overcome the insulating nature of conductive polymers at dedoped states, but also is capable of providing a platform for the decoration of metal oxide nanoparticles to avoid their agglomeration. In this regard, synthesis, characterization and performance of different ternary nanocomposites of conductive polymer/graphene/metal oxide are discussed in detail. These remarkable results demonstrate the exciting commercial potential for high performance, environmentally friendly and low‐cost electrical energy storage devices based on ternary nanocomposite of conductive polymer/graphene/metal oxide.     

Electrical interaction between two cylinders with an ion-penetrable charged membrane in an oil/water interface

The electrical interaction between two long, parallel cylinders each is covered by an ion-penetrable charged membrane immersed in an oil/water interface is investigated. The effects of contact angle, radius of cylinder, and membrane thickness on the electrical interaction force are examined. The results of numerical simulation reveal that the following conditions lead to a greater electrical interaction force: (i) a larger contact angle, i.e. a larger fraction of a cylinder in the oil phase; (ii) a larger cylinder radius; and (iii) a thinner membrane. For a fixed ionic strength, the electrical interaction force is insensible to the type of electrolytes in the water phase, in general. However, if two cylinders are close enough, then the higher the valence of counterions the greater the electrical interaction force.     

Ionic rectification properties of a bipolar interface consisting of a cationic surfactant and cation-exchange membrane

A novel bipolar interface that consists of cationic surfactant and cation-exchange membrane was successfully prepared in an aqueous electrolyte system. This bipolar interface shows a ionic rectification behavior similar to that observed in bipolar membranes. However, different from bipolar membranes, this system has a total rectification behavior, where we cannot observe the occurrence of a water-splitting phenomenon, which always occurs in the bipolar membrane process under reverse bias conditions.     

Fundamental studies on the intermediate layer of a bipolar membrane V. Effect of silver halide and its dope in gelatin on water dissociation at the interface of a bipolar membrane

The effect of silver ions on the water dissociation of bipolar membranes was first investigated in this paper. To do this, the bipolar membranes were prepared by immersing the anion exchange layers in an AgNO3 solution and then coating a solution of sulfonated polyphenylene oxide (SPPO) on the anion exchange layers. XPS and AES observations indicated that silver at the intermediate layer was in the form of AgCl. The experimental results proved that AgCl has an excellent catalytic function for water dissociation in terms of I-V curves, and the quantity of AgCl played an important role in the behavior of a bipolar membrane. The bipolar membranes with gelatin and the gelatin doped with silver as a catalytic layer were also prepared in the same way, and their I-V behavior and the water dissociation pilot tests were also investigated. The experimental results showed that in the case of gelatin alone, the voltage drop increased slightly at high gelatin concentrations, due mainly to the steric effect and electrostatic interaction, but decreased at low gelatin concentrations due to the hydrophilicity. However, when gelatin was doped with AgCl, the bipolar membranes have an appreciable improvement in both stability and catalytic function, in comparison with those prepared from silver or gelatin.     

Interaction of water with the regenerated cellulose membrane studied by DSC

One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation processes. A large amount of non-freezable strongly bounded water was also detected. Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected during the first, the second and the third heating. This revised version was published online in July 2006 with corrections to the Cover Date.     

Understanding dynamics of myoglobin in heterogeneous aqueous environments using coupled water fractions

This work presents an analysis of near environment of myoglobin (Mb) in different aqueous solutions (in the presence of NaCl, sucrose, trehalose, urea, and glycerol) using the coupled water fractions measured using a quartz crystal microbalance (QCM). The secondary structural features of the protein from circular dichroic (CD) spectroscopy and the coupled water fractions give important clues to the overall dynamics of the protein. Using time resolved fluorescence, these leads have been applied to understand the observed lifetime relaxations of Mb. Though the time scales of observation of coupled water and the lifetimes are very different, our study suggests that the trends in coupled water fraction seem to be good indicators for regulation of the relaxation dynamics of the protein. The relaxations generally show a triphasic distribution of time scales. The initial relaxation in the picoseconds time scale represents the local motions of coupled water followed by a slightly slower decay in hundreds of picoseconds attributable to coupled water-‘quasi free’ water interactions. The third nanosecond lifetime is due to changes in transitions in isomers of hydrated protein. The dynamics of coupled water in Mb with NaCl is the fastest (around 21 ps) and is slowest in glycerol (250 ps). The results strongly indicate that it is the resident times of water molecules that play a dominant role in the overall stability of protein in a particular hydrated isomer and not just always the number of such water molecules in the hydrated protein.     

Antibacterial ultrafiltration membrane with silver nanoparticle impregnation by interfacial polymerization for ballast water

Interfacial polymerization technology was employed to immobilize silver (Ag) nanoparticles on the surface of commercial polyethersulfone (PES) membrane to develop antibacterial and antifouling ultrafiltration membrane. Ag nanoparticles were prepared from the reduction of silver nitrate (AgNO₃) by sodium borohydride in the presence of polyethyleneimine (PEI) as the stabilizer. The encapsulated Ag nanoparticles in the PEI solution were embedded into the PEI membrane when trimesoyl chloride solution was used to crosslink the PEI solution with the PES membrane, forming Ag-polyamide (PA) networks through the interfacial polymerization reaction. Experimental results showed that the membrane prepared with 50 mmol/L of AgNO₃ and 20 mmol/L of PEI had the optimized antibacterial effect against Escherichia coli. Bacterial concentration and species were also investigated. Exiguobacterium aestuarii and Staphylococcus aureus which are gram-positive bacteria, needed significantly more time for the Ag-PA/PES membrane to kill the bacteria completely when compared to E.coli and Vibrio coralliilyticus which are gram-negative bacteria. This study showed that Ag nanoparticles impregnated in membrane surfaces were 100% effective in killing various types of marine bacteria and bacteria in the seawater collected off Sentosa Island in Singapore. These membranes exhibit excellent antibacterial and antifouling properties which can be used to kill bacteria in ballast water and seawater.     

Performance of a photocatalytic hybrid system coupled with a stainless steel membrane for removal of humic acid

The objective of this study was to evaluate the performance of a photocatalysis/H₂O₂/metal membrane hybrid system in the degradation of humic acid. A metal membrane of nominal pore size 0.5 μm was used in the experiment for separation of TiO₂ particles. Hydrogen peroxide was tested as an oxidant. The efficiency of removal of COD_Cr and color increased rapidly for initial hydrogen peroxide concentrations up to 50 mg L⁻¹. The efficiency of removal of COD_Cr and color by 50 mg L⁻¹ initial hydrogen peroxide concentration was approximately 95 and 98%, respectively. However, addition of hydrogen peroxide over 50 mg L⁻¹ inhibited the efficiency of the system. Addition of hydrogen peroxide to a UV/TiO₂ system enhanced efficiency of removal of COD_Cr and color compared with no addition of hydrogen peroxide. This may be ascribed to capture electrons ejected from TiO₂ and to the production of OH radicals. Application of the metal membrane in the UV/TiO₂/H₂O₂ system enhanced the efficiency of removal of COD_Cr and color because of adsorption by the metal membrane surface and the production of OH radicals. By application of a metal membrane with a nominal pore size of 0.5 μm, TiO₂ particles were effectively separated from the treated water by metal membrane rejection. The photocatalytic metal membrane had much less resistance than the humic acid, TiO₂, and humic acid/TiO₂ because of the degradation of humic acid by the photocatalytic reaction.     

High-performance liquid chromatographic determination of phenolic compounds in natural water coupled with on-line flow injection membrane extraction-preconcentration

A liquid chromatographic method for determination of trace phenolic compounds has been established, coupled with an on-line supported liquid membrane extraction-preconcentration flow-injection system. Tributyl-phosphate dissolved in kerosene was used as the carrier of the supported liquid membrane. Four phenolic compounds (phenol, catechol, resorcinol and hydroquinone) were chosen as the model compounds and the experiment conditions were optimized. Under the optimum conditions, calibrations were linear in the range of 1-500 microg/L, with good correlation coefficients (r > 0.999). The total analysis time of the system was 22 min, including the membrane extraction, liquid chromatographic separation and equilibration times.     

Formation of PdNiZn thin film at oil‐water interface: XPS study and application as Suzuki‐Miyaura catalyst

Nanosheet of PdNiZn and nanosphere of PdNiZn/reduced‐graphene oxide (RGO) with sub‐3 nm spheres have been successfully synthesized through a facile oil‐water interfacial strategy. The morphology and composition of the films were determined by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive analysis of X‐ray (EDAX) and elemental mapping. In the present study, we have developed a method to minimize the usage of precious Pd element. Due to the special structure and intermetallic synergies, the PdNiZn and PdNiZn/RGO nanoalloys exhibited enhanced catalytic activity and durability relative to Pd nanoparticles in Suzuki‐Miyaura C‐C cross‐coupling reaction. Compared to classical cross‐coupling reactions, this method has the advantages of a green solvent, short reaction times, low catalyst loading, high yields and reusability of the catalysts.     

水冷壁气流床气化炉灰渣结构分析

在管式电炉还原性气氛下,对煤灰进行1 300℃和1 400℃的高温热处理。同时,在小型膜式水冷壁气流床气化炉热模装置中进行煤气化实验。利用XRD、SEM和EDS等方法,考察了热处理后灰渣与煤气化所得炉渣的表面形态、内部微观结构、矿物组成等结构特性,并对管式电炉内进行灰渣热处理实验的可行性进行评估。结果表明,热处理温度和灰渣流动温度对灰渣的结构具有重大影响,热处理温度高于灰渣流动温度约10℃时,灰渣中含有大量矿物晶体且表面形态粗糙,内部微观结构凹凸不平,灰渣难于流动;热处理温度高于灰渣流动温度约100℃时,渣中大部分矿物晶体已变成无定形的玻璃体物质,灰渣表面及内部微观结构变得光滑均匀。采用管式电炉模拟气化炉内灰渣氛围,研究气化炉操作温度对灰渣结构的影响,具有一定的可行性。     

A self-assembly pipette tip graphene solid-phase extraction coupled with liquid chromatography for the determination of three sulfonamides in environmental water

A sensitive, economical, and miniaturized self-assembly pipette tip graphene solid-phase extraction (PT-G-SPE) coupled with liquid chromatography fluorescence detection (LC-FD) was developed for rapid extraction and determination of three sulfonamide antibiotics (SAs) in environmental water samples. The PT-G-SPE cartridge, assembled by packing 1.0 mg of graphene as sorbent into a 100 μL pipette tip, showed high adsorption capacity for the SAs owing to the large surface area and unique structure of graphene. The factors that affected the extraction efficiency of PT-G-SPE, including sample volume, pH, sorbent amount, washing solvent and eluent solvent were optimized. Good linearity for SAs was obtained in a range of 2–4000 pg mL⁻¹ with correlation coefficients (r²) ≥ 0.9993. The recoveries of the SAs at three spiked levels ranged from 90.4% to 108.2% with relative standard deviations (RSD) ≤ 6.3%. In comparison with other sorbents such as C₁₈, HLB, SCX, PCX, and multiwalled carbon nanotubes, one advantage of using graphene as sorbent of pipette tip solid-phase extraction (PT-SPE) was that PT-G-SPE could adsorb larger sample volume (10 mL) at a small amount of sorbent (1 mg) and low solvent consumption with good extraction efficiency, which not only increased the fraction of analytes to LC and the sensitivity of SAs determination, but also reduced the cost and pollution.