PVC Membrane Selective Electrode for Determination of Cadmium(Ⅱ) Ion in Chocolate Samples

Benzil bis(carbohydrazone)(BBC) is prepared and explored as new N N Schiff's base, which plays the role of an excellent ion carrier in the construction of a Cd(II) ion membrane sensor. The tris(2-ethylhexyl) phosphate best performance corresponds to a membrane composition of 30% poly(vinyl chloride), 65%(TEHP), 3.5% BBC and 1.5% tetradodecyl-ammoniumtetrakis(4-chlorophenyl) borate(ETH 500). This sensor shows very good selectivity and sensitivity towards cadmium ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition, selectivity, pH and influence of additive on the response properties of electrode were investigated. The response mechanism was discussed in the view of UV-spectroscopy. The electrode exhibits a Nernstian behavior(with slope of 29.7 mV per decade) over a very wide concentration range from 1.0×10?1 to 1.0×10?8 mol·L?1 with a detection limit of 3.2×10?8 mol·L?1. It shows rela-tively fast response time in whole concentration range(<8 s) and can be used for at least 10 weeks in the pH range of 2.0-9.0. The proposed sensor is successfully used for the determination of cadmium in different chocolate sam-ples and as indicator electrode in titration with ethylene diamine tetraacetate(EDTA).

Enrichment of Cd^(2＋) from water with a calcium alginate hydrogel filtration membrane

A new method was developed for effective enrichment of Cd2+ ions from water with a calcium alginate(CaAlg) hydrogel filtration membrane. First, the CaAlg hydrogel filtration membrane was prepared without a pore-forming agent. This membrane was used to remove Cd^(2+) via ion exchange with Ca^(2+), and the Cd^(2+) was preserved in the CaAlg hydrogel. Then, the CaAlg hydrogel containing Cd^(2+) was soaked in a sodium citrate solution, and the hydrogel was fully dissolved. The removal rate of the CaAlg filtration membrane reached almost 100% within 120 min when the Cd^(2+) concentration was under 1 mg/L. Factors affecting the removal rate were investigated, such as NaAlg concentration, operating pressure, operating time and the initial concentration of Cd^(2+). The effects of initial Cd^(2+) concentration, pressure and filtration time on the enrichment factor were also investigated. The results show that the enrichment factor reached 87.3 when the pressure was 0.18 MPa and the filtration time was 240 min. Different enrichment factors could be achieved by adjusting the operating pressure and filtration time.

Monovalent cation perm-selective membranes(MCPMs)"New developments and perspectives

As one of the most typical and promising membrane processes, electrodialysis(ED) technique plays a more and more significant role in industrial separation. Especially, the separation of monovalent cations and multivalent cations is currently a hot topic, which is not only desirable for many industries but also challenging for academic explorations. The main aim of the present contribution is to view the advances of a wide variety of monovalent cation perm-selective membranes(MCPMs) and their preparation technologies including(1) covalent crosslinking,(2) surface modification,(3) polymer blending,(4) electrospinning,(5) nanofiltration alike membrane,and(6) organic–inorganic hybrid. The relevant advantages and disadvantages with respect to some specific cases have been discussed and compared in detail. Furthermore, we elaborately discuss the opportunities and challenges of MCPMs, the fabricating strategies to take and the future perspectives.

The control and optimization of macro/micro-structure of ion conductive membranes for energy conversion and storage

Ion conductive membranes(ICMs)are frequently used as separators for energy conversion and storage technologies of fuel cells,flow battery,and hydrogen pump,because of their good ion-selective conduction and low electronic conductivity.Firstly,this feature article reviews the recent studies on the development of new nonfluorinated ICMs with low cost and their macro/micro-structure control.In general,these new nonfluorinated ICMs have lower conductivity than commercial perfluorinated ones,due to their poor ion transport channels.Increasing ion exchange capacity(IEC)would create more continuous hydrophilic channels,thus enhancing the conductivity.However,high IEC also expands the overall hydrophilic domains,weakens the interaction between polymer chains,enhances the mobility of polymer chains,and eventually induces larger swelling.The micro-scale expansion and macro-scale swelling of the ICMs with high IEC could be controlled by limiting the mobility of polymer chains.Based on this strategy,some ef ficient techniques have been developed,including covalent crosslinking,semi-interpenatrating polymer network,and blending.Secondly,this review introduces the optimization of macro/microstructure of both perfluorinated and nonfluorinated ICMs to improve the performance.Macro-scale multilayer composite is an ef ficient way to enhance the mechanical strength and the dimensional stability of the ICMs,and could also decrease the content of per fluorosulfonic acid resin in the membrane,thereby reducing the cost of the perfluorinated ICMs.Long side chain,multiple functionalization,small molecule inducing micro-phase separation,electrospun nano fiber,and organic–inorganic hybrid could construct more ef ficient ion transport channels,improving the ion conductivity of ICMs.

Study on the permselectivity of ion exchange membrane

Ion exchange membranes with high permselectivity (the character of separatingcations from anions or anions from cations) and high selectivity (the character of separatingcations or anions of different valencies) are important for electrodialysis process. The Donnanequilibrium theory, based on the equilibrium of ions and no electric field, can not exactly explainthe permselectivity of ion exchange membrane for ED process, since it is impossible to set up a ionexchange equilibrium between membrane and solution and to neglect the influence of electricaldriving force on ions during ED process. A novel model named 'anti-electric potential' isestablished to interpret the permselectivity of ion exchange membrane, according to thedetermination of electric potential between membranes and the variation of elements content insolutions and membranes. The results of experiment prove that the 'anti-electric potential' reallyexists within membranes. As for the selectivity, the results reveal that electric potential andhydration energy have great influence on the concentration and mobility of ions in membranes.

Structure and resistance of concentration polar layer on cation exchange membrane-solution interface

Membrane/solution interface consists of a neutral concentration polai layer(CPL) and a charge layer(CL) under external electrical field, and the neutral CPL can be neglected under high frequency AC electrical field. The relationship of CL thickness e with electrolyte concentration C and fixed ion exchange sites density σ in membrane surface layer can be expressed as e

Extended adsorption transport models for permeation of copper ions through nanocomposite chitosan/polyvinyl alcohol thin affinity membranes

Transport of copper ions through nanocomposite chitosan/polyvinyl alcohol thin adsorptive membranes has been mathematically investigated in the current study. Unsteady-state diffusive transport model was coupled with the Freundlich isotherm to predict the concentration of the ions in dialysis permeation operation. Pristine model was not successful in predicting the experimental data based upon its low coefficients of determination（0.1

PREPARATION AND CHARACTERIZATION OF ION EXCHANGE MEMBRANES BASED ON POLYVINYLIDENE FLUORIDE

A new ion exchange membrane based on polyvinylidene fluoride (PVDF) and sulfonated poly(styrene-divinylbenzene) was prepared by in-situ polymerization. The incorporation of sulfonic groups into the polyvinylidene fluoride composite membrane was confirmed by infrared spectroscopy (IR), ion exchange capacity (IEC) and energy dispersive X-ray analysis (EDAX). Area resistance, IEC and water uptake of the treated membrane were evaluated. When 20% of the crosslinked membrane was sulfonated at 80degreesC for 22 h, the PVDF ion exchange membrane can attain 0.8 Omega . cm(2) area resistance in NaCl aqueous solution at 25degreesC, IEC is as high as 2.43 millimoles per grain of the wet membrane. The hydrophilicity of PVDF membrane is also significantly improved after treatment. When 60% of crosslinked membrane was sulfonated at 80degreesC for 6 h, water uptake of the treated membrane can attain 64.7%.

SPES/PVDF Binary Membrane as an Alternative Proton Exchange Membrane in Vanadium Redox Flow Battery Application

SPES/PVDF blends were employed to prepare the ion exchange membranes for vanadium redox flow battery(VRB) application for the first time. The addition of the highly crystalline and hydrophobic PVDF effectively limited the swelling behavior of SPES. The vanadium ion permeability of SPES/PVDF membranes was one order of magnitude lower than that of Nafion 117 membrane and pristine SPES membrane. Single cells with SPES/PVDF composite membranes showed significantly lower capacity loss, higher coulombic efficiency and higher energy efficiency than that with Nafion117 and pristine SPES membranes. The blend membrane with 40 wt% of PVDF(denoted as S_(0.6) P_(0.4)) showed energy efficiency of 83.2% at 30 mA?cm^(-2), which was superior to that of the Nafion117 and SPES membranes. In the self-discharge test, S_(0.6) P_(0.4) membrane showed twice longer duration in open circuit decay than that with Nafion 117 membrane. With all the good properties and low cost, the SPES/PVDF membranes are expected to have excellent commercial prospects as ion exchange membranes for VRB system.

STUDY ON THE ELECTROCHEMICAL BEHAVIOR OF ION EXCHANGE MEMBRANE IN PREPARING POTASSIUM CARBONATE

This investigation describes the one step preparation of potassium carbonate by electrolysis of potas-sium chloride solution in electrolyzers with various Nation membranes.Potassium bicarbonate solution wasfed to the cathode compartment,where it was converted into carbonate by reaction with the hydroxideformed at cathode.Because of the low OH^- concentration in the cathode compartment,the back migrationof OH^- through the membrane was almost negligible,resulting in a higher current efficiency,say 90% or more.In this study,electroconductivity,mass transfer,current efficiency and cell voltage were measured.Thefeasibility of the process was discussed and the optimal conditions examined.

THE STUDY ON THE MASS TRANSFER MECHANISM OF EUROPIUM ION THROUGH LIQUID SURFACTANT MEMBRANES

The transfer of trivalent europium ion in a liquid surfactant membrane system is investigated in order toclarify the characteristics of liquid membrane separation process and the availability of this technique forrecovering trivalent lanthanides and actinides.A layered structure model for the emulsion globule is sug-gested.The equations describing the relationship among the effective membrane thickness,the time andother factors are derived and verified experimentally.Results show that under certain conditions the decreas-ing concentration of europium ion in the external phase is proportional to the square root of the time,the acidity of the internal phase and the carrier concentration in the membrane phase.The membrane phase consists of kerosene（solvent）,Span-80（surfactant）and di-（2-ethylhexyl） phosphoricacid（HDEHP,carrier）.The internal phase is dilute nitric acid and the external phase is aqueous solu-tion containing Eu（NO3）3.The mass transfer rate of europium in this system is high and the recovery ofeuropium may be more than 99%.

Comparison of Nine Membrane Pairs for Electrodialytic Removal of Nitrate Ions

Electrodialysis (ED) of NaNO3 solutions was performed to stress the role of the membrane pair as a unit i.e. the behavior as a whole of Anion Exchange Membrane (AEM) and Cation Exchange Membrane (CEM), in the process at room temperature. The membrane pair was also tested in the reclamation of nitric acid and sodium hydroxide. It was found that the membrane pair ranking in Limiting Current Density does not agree with that of ions leakage and both rankings are not the same as for Current Efficiency or Specific Power Consumption, each parameter for a specific membrane pair depends on the associated membrane and at a lesser degree on the flow rate. Results show that one cannot select a membrane or a membrane pair only by its limiting current density i.e. it is necessary to evaluate several parameters of the process by characterizing the whole membrane pair and to decide the parameter of interest, i.e. denitrification speed, ions leakage, proton back migration, current efficiency or specific power consumption.

ELECTRODIALYTIC PRODUCTION OF HYPOPHOSPHOROUS ACID

Disclosed is a method of preparing hypophosphorous acid comprising contacting an insoluble anode with an aqueous solution of hypophosphite anions and applying a direct current through the insoluble anode to a cathode in electrical contact with the aqueous solution to generate H+ ions in the aqueous solution thereby forming a hypophosphorous acid solution. The process is simple, low cost and high efficient, which can be tied into an existing process for producing sodium hypophosphite wherein the product of sodium hypophosphite process is used as a starting material in the hypophosphorous acid process.

Advances and challenges of electrolyzers for large-scale CO_(2) electroreduction

CO_(2) electroreduction(CO_(2) ER)to high value-added chemicals is considered as a promising technology to achieve sustainable carbon neutralization.By virtue of the progressive research in recent years aiming at design and understanding of catalytic materials and electrolyte systems,the CO_(2) ER performance(such as current density,selectivity,stability,CO_(2) conversion,etc.)has been continually increased.Unfortunately,there has been relatively little attention paid to the large-scale CO 2 electrolyzers,which stand just as one obstacle,alongside series-parallel integration,challenging the practical application of this infant technology.In this review,the latest progress on the structures of low-temperature CO_(2) electrolyzers and scale-up studies was systematically overviewed.The influence of the CO_(2) electrolyzer configurations,such as the flow channel design,gas diffusion electrode(GDE)and ion exchange membrane(IEM),on the CO_(2) ER performance was further discussed.The review could provide inspiration for the design of large-scale CO_(2) electrolyzers so as to accelerate the industrial application of CO_(2) ER technology.

Highly Conductive Proton Selectivity Membrane Enabled by Hollow Carbon Sieving Nanospheres for Energy Storage Devices

Ion conductive membranes(ICMs)with highly conductive proton selectivity are of significant importance and greatly desired for energy storage devices.However,it is extremely challenging to construct fast proton-selective transport channels in ICMs.Herein,a membrane with highly conductive proton selectivity was fabricated by incorporating porous carbon sieving nanospheres with a hollow structure(HCSNs)in a polymer matrix.Due to the precise ion sieving ability of the microporous carbon shells and the fast proton transport through their accessible internal cavities,this advanced membrane presented a proton conductivity(0.084 S·cm^(-1))superior to those of a commercial Nation 212(N212)membrane(0.033S·cm^(-1))and a pure polymer membrane(0.049 S·cm^(-1)).The corresponding proton selectivity of the membrane(6.68×10^(5) S·min·cm^(-3))was found to be enhanced by about 5.9-fold and 4.3-fold,respectively,compared with those of the N212 membrane(1.13×10^(5) S·min·cm^(-3))and the pure membrane(1.56×10^(5) S·min·cm^(-3)).Low-field nuclear magnetic resonance(LF-NMR)clearly revealed the fast protonselective transport channels enabled by the HCSNs in the polymeric membrane.The proposed membrane exhibited an outstanding energy efficiency(EE)of 84%and long-term stability over 1400 cycles with a0.065%capacity decay per cycle at 120 mA·cm^(-2) in a typical vanadium flow battery(VFB)system.

Ion exchange membranes from poly(2,6-dimethyl-1,4-phenylene oxide) and related applications

Ion exchange membranes(IEMs) play a significant role in fields of energy and environment, for instance fuel cells, diffusion dialysis, electrodialysis, etc. The limited choice of commercially available IEMs has produced a strong demand of fabricating IEMs with improved properties via facile synthetic strategies over the past two decades. Poly(phenylene oxide)(PPO) is considered as a promising polymeric material for constructing practical IEMs, due to its advantages of good physicochemical properties, low manufacturing cost and easy post functionalization. In this review, we present the accumulated efforts in synthetic strategies towards diverse types of PPO-based IEMs. Relation between polymer structures and the resulted features is discussed in detail. Besides, applying IEMs from PPO and its derivatives in fuel cell, diffusion dialysis and electrodialysis is summarized and commented.

San copolymer membranes with ion exchangers for Cu(Ⅱ)removal from synthetic wastewater by electrodialysis

Heterogeneous membranes were obtained by using styrene-acrylonitrile copolymer（SAN）blends with low content of ion-exchanger particles（5 wt.%）. The membranes obtained by phase inversion were used for the removal of copper ions from synthetic wastewater solutions by electrodialytic separation. The electrodialysis was conducted in a three cell unit, without electrolyte recirculation. The process, under potentiostatic or galvanostatic control, was followed by p H and conductivity measurements in the solution. The electrodialytic performance,evaluated in terms of extraction removal degree（rd） of copper ions, was better under potentiostatic control then by the galvanostatic one and the highest（over 70%） was attained at8 V. The membrane efficiency at small ion-exchanger load was explained by the migration of resin particles toward the pores surface during the phase inversion. The prepared membranes were characterized by various techniques i.e. optical microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis and differential thermal analysis and contact angle measurements.

Ion sieving in graphene oxide membranes via cationic control of interlayer spacing

With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Prof.Fang Haiping(方海平)from Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Prof.Wu Minghong(吴明红)from Shanghai Applied Radiation Institute。

Highly stable side-chain-type cardo poly(aryl ether ketone)s membranes for vanadium flow battery

Vanadium flow batteries(VFBs)have drawn considerable attention as an emerging technology for largescale energy storage systems(ESSs).One of the pivotal challenges is the availability of eligible ion exchange membranes(ICMs)that provide high ion selectivity,proton conductivity,and stability under rigorous condition.Herein,a‘side-chain-type’strategy has been employed to fabricate highly stable phenolphthalein-based cardo poly(arylene ether ketone)s(PAEKs)membrane with low area resistance(0.058Ωcm^(2)),in which flexible alkyl spacers effectively alleviated inductive withdrawing effect from terminal ion exchange groups thus enabling a stable backbone.The assembled VFBs based on PAEKs bearing pendent alkyl chain terminated with quaternary ammonium(Q-PPhEK)demonstrated an energy efficiency above 80%over 700 cycles at 160 mA/cm^(2).Such a remarkable results revealed that the side-chain-type strategy contributed to enhancing the ICMs stability in strong oxidizing environment,meanwhile,more interesting backbones would be woken with this design engaging in stable ICMs for VFBs.

‘‘Soggy sand'' polymer composite nanofber membrane electrolytes for lithium ion batteries

A kind of octanol-modifded silica nanoparticle was fabricated and employed as a framework to form‘‘soggy sand’’electrolyte along with 1-butyl-3-methylimidazolium tetrafluoroborate.‘‘Soggy sand’’and poly（vinylidene fluoride-hexafluoropropylene）composite electrolyte membranes were electrospun for the frst time.The properties of this membrane electrolyte have been evaluated by the mechanical test and electrochemical test.The Young’s modulus increased by 275%from 6.8 MPa to 25.5 MPa and the electrical conductivity increased to 7.6 10à5S/cm at 290.15 K when compared to pristine P（VdF-HFP）membrane electrolyte.The conductivity is 3.1 10à4S/cm at 323.15 K.