Ion-exchange Particles Research Articles

Design of new zwitterionic microparticles with intrinsic antibacterial activity

AbstractThe crosslinked porous microparticles based on glycidyl methacrylate, N‐vinylimidazole, and triethylene glycol dimethacrylate (molar ratio between monomers 40:30:30) obtained in the presence of three porogenic agents (toluene, n‐butyl acetate, and toluene:n‐butyl acetate mixture, 1:1, v/v) are used as precursors in the polymer analogous reactions with some betainizing agents (sodium monochloroacetate, acrylic acid, methacrylic acid and 1,3–propane sultone) in order to introduce the carboxybetaine/sulfobetaine groups to the tertiary nitrogen atom from the imidazole ring. ATR–FTIR spectroscopy is used to highlight the presence of carboxybetaine/sulfobetaine groups on the structure of the microparticles, but also to calculate the degree of betainization (55.91%–90.2%) The zwitterionic microparticles are characterized by scanning electron and atomic force microscopies, equilibrium swelling ratio as a function of pH values, swelling kinetics, ion exchange capacities and particle size distribution. Also, the parameters of porous structure (pore diameter, pore volume, porosity, and specific surface area) are determined by mercury porosimetry. The antibacterial properties of Gram‐positive (Enterococcus faecalis and Staphylococcus aureus) and Gram‐negative (Escherichia coli and Klebsiella pneumoniae) bacteria are evaluated. It is found that the zwitterionic structures containing a shorter length alkyl chain between ionic groups exhibit excellent antibacterial activity of about 80%–92%.

Advanced degradation of refractory organic compounds in electroplating wastewater by an in-situ electro-catalytic biological coupling reactor: Removal performance, microbial community and possible mechanism

A high-efficiency treatment system for advanced degradation of refractory organic compounds such as saccharin sodium (SS) and polyethylene glycol 6000 (PEG 6000) in electroplating wastewater was proposed, which coupled ion exchange, electrocatalysis, and microbial interactions through ion exchange particle electrode (IEPE) in a reactor, named in-situ electro-catalytic biological coupling reactor (i-SECBCR). A small-scale experimental test system was established and a feasibility investigation was conducted under the condition of 1.248 L/h continuous flow. The results revealed that (1) the i-SECBCR showed higher average removal rates of SS, PEG 6000, COD and NH4+-N, i.e. 88.48 %, 41.26 %, 66.81 % and 51.61 %,which meant an increase by 5.04 %, 12.05 %, 0.46 %, and 34.50 %, respectively, compared with BAF; (2) the optimal current intensity (CI) of i-SECBCR for simultaneous removal of SS, PEG 6000, COD and NH4+-N was 0.40 mA cm−2; (3) Rhodobacter, Defluviimonas, unclassified_f__Microscillaceae, Pseudoxanthomonas, Novosphingobium, and unclassified_f__Xanthobacteraccae accounted for the main bacterial community in i-SECBCR; (4) the possible degradation mechanism was attributed mainly to the synergistic effect of ion exchange, electrocatalytic oxidation and biology. Therefore, the i-SECBCR was suitable to simultaneously advanced remove SS, PEG 6000, COD and NH4+-N in electroplating wastewater.

Use of electrochemical impedance spectroscopy to assess the stability of the anion exchange membrane MA-41, modified by poly-N,N-diallylmorpholine bromide in overlimiting current modes

The paper presents the results of studying the electrochemical characteristics and long-term stability of MA-41 membranes on the surface of which poly-N,N-diallylmorpholinium bromide was applied. The deposition of a polyelectrolyte on the membrane surface leads to an increase in the limiting current from 0.8 to 1.1 mA/cm2. The comparison of the experimental and theoretically calculated values of the limiting current density allows us to conclude that the modification of the membrane surface by poly-N,N-diallylmorpholinium bromide does not lead to the formation of a continuous polyelectrolyte film on the surface, but its fixation occurs due to the sorption of macromolecules on the surface of the ion-exchanger particles. To quantify the rate of the water dissociation reaction at the membrane/solution interface, the method of electrochemical impedance was used, which makes it possible to compare the rate constants of the water dissociation reaction for different membranes, assuming that the reaction is described by the Gericher impedance. It is shown that modification of the MA-41 membrane surface leads to a decrease in the rate of the water dissociation reaction in the current range i = 1.5–4ilim by a factor of 2–6. The reduction in water dissociation reaction rate is attributed to the substitution of catalytically active secondary and tertiary amino groups in the surface layer of the pristine membrane by stable heterocyclic ammonium bases of poly-N,N-diallylmorpholinium. The study of the long-term stability of the resulting membrane showed that when the membrane is polarized with a current equal to twice the limiting current, the desorption of the modifier occurs within 25 h, and the properties of the membrane become close to those of the unmodified MA-41 membrane. It was shown that the electrochemical impedance method can be used as a very sensitive method for studying the long-term stability of ion-exchange membranes.

Study of the Thermochemical Effect on the Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes by Combining the Cell Model and the Fine-Porous Membrane Model.

For the first time, based on the joint application of the fine-porous and cell models, a theoretical analysis of the changing transport and structural characteristics of heterogeneous polymeric ion-exchange membranes (IEMs) MK-40, MA-40, and MA-41 after exposure to elevated temperatures in water and aggressive media (H2SO4 and NaOH solutions), as well as after long-term processing in electrodialyzers of various types, was carried out. The studied membranes are composites of ion-exchange polymers with polyethylene and nylon reinforcing mesh. The external influences provoke the aging of IEMs and the deterioration of their characteristics. The transport properties of IEMs are quantitatively described using five physicochemical parameters: counterion diffusion and equilibrium distribution coefficients in the membrane, characteristic exchange capacity, which depends on the microporosity of ion-exchanger particles, and macroscopic porosity at a known exchange capacity of IEMs. Calculations of the physicochemical parameters of the membranes were performed according to a specially developed fitting technique using the experimental concentration dependences of integral diffusion permeability and specific electrical conductivity, and their model analogs. This made it possible to identify and evaluate changes in the membrane micro- and macrostructure and examine the process of artificial aging of the IEM polymer material due to the abovementioned external impacts.

Synthesis and Characterization of Ion Exchange Particles for Application of Anion Exchange Membrane

Synthesis and Characterization of Ion Exchange Particles for Application of Anion Exchange Membrane

Patterns of protein adsorption in ion-exchange particles and columns: Evolution of protein concentration profiles during load, hold, and wash steps predicted for pore and solid diffusion mechanisms

Elucidation of protein transport mechanism in ion exchanges is essential to model separation performance. In this work we simulate intraparticle adsorption profiles during batch adsorption assuming typical process conditions for pore, solid and parallel diffusion. Artificial confocal laser scanning microscopy images are created to identify apparent differences between the different transport mechanisms. Typical sharp fronts for pore diffusion are characteristic for Langmuir equilibrium constants of KL ≥1. Only at KL = 0.1 and lower, the profiles are smooth and practically indistinguishable from a solid diffusion mechanism. During hold and wash steps, at which the interstitial buffer is removed or exchanged, continuation of diffusion of protein molecules is significant for solid diffusion due to the adsorbed phase concentration driving force. For pore diffusion, protein mobility is considerable at low and moderate binding strength. Only when pore diffusion if completely dominant, and the binding strength is very high, protein mobility is low enough to restrict diffusion out of the particles. Simulation of column operation reveals substantial protein loss when operating conditions are not adjusted appropriately.

Electrochemical Performance Evaluation of Bipolar Membrane Using Poly(phenylene oxide) for Water Treatment System.

This study describes the use of poly(phenylene oxide) polymer-based ion-exchange polymers, polystyrene-based ion-exchange particles and a porous support for fabricating bipolar membranes and the results of an assessment of the applicability of these materials to water splitting. In order to achieve good mechanical as well as good ion-exchange properties, bipolar membranes were prepared by laminating poly(phenylene oxide) and polystyrene based ion-exchange membranes with a sulfonated polystyrene-block-(ethylene-ran-butylene)-block-polystyrene) (S-SEBS) modified interface. PE pore-supported ion-exchange membranes were also used as bipolar membranes. The tensile strength was 13.21 MPa for the bipolar membrane which utilized only a cation/anion-exchange membrane. When ion-exchange nanoparticles were introduced for high efficiency, a reduction in the tensile strength to 6.81 MPa was observed. At the same time, bipolar membrane in the form of a composite membrane using PE support exhibited the best tensile strength of 32.41 MPa. To confirm the water-splitting performance, an important factor for a bipolar membrane, pH changes over a period of 20 min were also studied. During water slitting using CA-P-PE-BPM, the pH at the CEM part and the AEM part changed from 5.4 to 4.18 and from 5.4 to 5.63, respectively.

Molten Lithium-Brass/Zinc Chloride System as High-Performance and Low-Cost Battery

Summary Batteries with high safety, low cost, and reasonable energy density are essential for grid-scale energy storage and still remain elusive. Here, we report a solid electrolyte-based liquid lithium-brass/zinc chloride (SELL-brass/ZnCl2) battery using garnet-type lithium-ion solid electrolyte, lithium anode, and brass/ZnCl2 cathode. The chemistry of the cell reaction and the ability of being assembled in discharged state ensures a high safety. The use of low-cost ZnCl2 cathode can realize a low cell material cost of $16 kWh−1. The adoption of lithium anode guarantees a high theoretical energy density of 750 Wh kg−1 and 2,250 Wh L−1. Moreover, by using brass powder as a Zn source in the cathode, the Zn particle growth issue is successfully solved, and a good cycling stability of the battery can be obtained. As full cell performance and scalability are also verified, our SELL-brass/ZnCl2 battery shows a high potential for practical use in grid energy storage.

MEMBRANES MODIFIED BY NANOCOMPOSITES OF HYDRATED ZIRCONIUM DIOXIDE AND OXIDIZED GRAPHENE

Organo-inorganic membranes were obtained by impregnating ultrafiltration membranes with a composite modifier - zirconium (IV) hydroxide, containing oxidized graphene (0.5 wt.%). The modifier was precipitated in the active layer of the membrane, thus forming a "secondary active layer". The layer thickness calculated according to the Kozeny-Carman equation is 0.66-1.38 μm. A thinner layer is formed in the membrane with smaller pore size. The diffusion coefficients of Li+ and Na+ ions were found. The effect of the modifier on the retention ability relative to hardness ions (10-14%) and to protein compounds (95-98%) during filtration is determined. Mathematical modeling of the dependence of the permeate flux via time showed that the presence of ion exchanger particles in the polymer active layer prevents the accumulation of organic substances in the pores. Therefore, only the outer surface of the membrane is contaminated, and the precipitate can be easily removed mechanically. It was shown that insertion of a carbon component into pores of the membranes, in addition to the inorganic ion-exchangers, is advisable only in the case of a finely porous active layer. In particular, the performance of the initial polymer membrane (20 dm3/m3.h)) and the selectivity to the calibration substance with a molecular weight of 40 kDa (99%) serve as expediency criteria. In comparison with a membrane modified only with inorganic ion exchanger, selectivity is increased, the rate of filtration of protein solutions is higher, and resistance to contamination by organic substances is achieved. The results are discussed from the view of the hydrophobic-hydrophilic properties of oxidized graphene.

Study of Ion Exchangers in Electric Fields Using Resistometric Measurement. Part 2. Methods and Equipment

The experimental technique and equipment used to study the kinetics of ion exchange in weak electric fields in the ion–exchange resins using a computer resistometric measurement method are described. In the course of ion exchange in the NaCl + NaOH model solution–ion exchanger system the chemical composition dynamics of a solution measuring the solution resistance with the help of a resistometer is measured with a flowing sensor; its signal is computer processed. The pattern of interaction between electrical and diffusion ion fields in the solid phase of the ion exchanger is discussed. It is shown that when a weak directional electric field is applied on the spherical ion exchanger particle, the spherical symmetry of the ion displacement rate is distorted, and the balance of the ion flows is changed. Thus, the exchange process is accelerated in the direction of the electric field vector. The test unit for the study of the ion exchange dynamics, which includes a convective reactor, a built-in column with a portion of the exchanger, a temperature control system, a flowing sensor of the electrical resistance of the solution, an electronic resistometer, and a potentiostat–galvanostat, is described. Three experimental methods are described: a nonstationary method with the ion exchange suspension in the enclosed volume, the nonstationary method with filtration through the ion exchanger in the column, and the method of open filtration through the column. It is shown that the speed of the ion flux in the solid phase is constant and does not depend on the saturation value of the exchanger in the suspension mode of exchange in the basic interval time of the process. This effect is caused by the operation of the electroneutrality law on two ion fluxes with the charges of the same sign but with the opposite concentration gradients.

Спектральные свойства флуктуаций концентрационного поля в электромембранных системах с сульфокатионообменными мембранами с разной дисперсностью ионообменника

Методом Фурье-анализа определен спектральный состав флуктуаций концентрационного поля в стратифицированных системах с экспериментальными гетерогенными сульфокатионообменными мембранами Ralex CM Pes («MEGA» a.s., Чехия), содержащими ионообменник различной дисперсности. С увеличением времени измельчения ионообменных частиц, соответственно степени их дисперсности, выявлено уменьшение размеров проводящих участков и расстояния между ними на поверхности мембран. Высокая шумовая составляющая колебаний концентрационного поля в растворе вследствие развития электроконвективных вихрей установлена на границе с мембраной, характеризующейся более однородной поверхностью.

Effect of Dispersity of a Sulfonated Cation-Exchanger on the Current–Voltage Characteristics of Heterogeneous Membranes Ralex CM Pes

The influence of the electrical and geometrical heterogeneity of the surface of heterogeneous sulfonated cation-exchange membranes on their current–voltage characteristic (CVC) has been experimentally studied. The objects of the study have been experimental samples of Ralex CM Pes membranes manufactured by MEGA a.s. (Czech Republic). A series of experimental membranes Ralex has been produced by hot rolling using an ion-exchanger with different particle sizes. The particle size of the ion-exchanger was controlled by its milling time from 5 to 80 min. It has been found that in the swollen state of the membranes, the ratio of conducting (ion-exchanger particles) and inert (polyethylene) areas on the membrane surface remains constant regardless of the milling time of the sulfonated cation-exchanger. At the same time, the dimensions of the conductive areas and the distance between them decreased and the surface microrelief became smoother. The influence of changes in the membrane surface properties on the CVC parameters has been revealed. With an increase in the ion-exchanger milling time corresponding to a decrease in the spacing of electrical heterogeneity of the surface, a reduction in the length of limiting-current plateau and a decrease in the resistance of the second and third regions on the current–voltage curve were observed. It has been assumed that the main cause of changes in the current–voltage characteristics is an increase in the intensity of heteroelectroconvection.

Dynamics of Binary Active Clusters Driven by Ion-Exchange Particles.

We present a framework to quantitatively predict the linear and rotational directed motion of synthetic modular microswimmers. To this end, we study binary dimers and characterize their approach motion as effective interactions within a minimal model. We apply this framework to the assembly of small aggregates composed of a cationic ion-exchange particle with up to five passive particles or anionic ion-exchange particles at dilute conditions. Particles sediment and move close to a substrate, above which the ion-exchange particles generate flow. This flow mediates long-range attractions leading to a slow collapse during which long-lived clusters of a few particles assemble. The effective interactions between unlike particles break Newton's third law. Depending on their symmetry, assemblies thus can become linear or circle swimmers, or remain inert (no directed motion).

Heterogeneity of heterogeneous ion-exchange membranes investigated by chronopotentiometry and X-ray computed microtomography

Chronopotentiometry is a powerful experimental technique for characterization of ion-exchange membranes, especially phenomena associated with ion transport and the occurrence of overlimiting current. One also uses this technique to estimate heterogeneity of ion-exchange membranes, or more precisely the fractions of conductive and nonconductive regions in the membrane, by measuring so called transition times and their substitution into Sand equation. Here, we test this approach on small pieces of heterogeneous cation- and anion-exchange membranes by combining two experimental techniques, namely chronopotentiometry and X-ray computed microtomography. While chronopotentiometry provides data for the theoretical analysis based on Sand equation, microtomography provides a detailed analysis of the membrane structure both on its surface and in its volume. Such a structural analysis allows for evaluation of volumetric and surface fractions of ion-exchange resin and also quantification of the surface area of the active ion-exchange material on the depletion side of the membrane. We compare the experimental data from both techniques to see how they correlate and discuss the obtained results. We conduct the same experimental investigation on single ion-exchange resin particles which are a component of the aforementioned heterogeneous membranes. The ion-exchange particles can be viewed as homogeneous ion-exchange systems. Our structural analysis by means of the newly developed technique based on micro-computed tomography showed that the volume and the surface compositions of the heterogeneous membranes differ. The surface fraction of the ion-exchange resin is two to three times smaller than the corresponding volumetric fraction. The experimental transition times showed very good agreement with the predictions of the Sand equation in case of the ion-exchange particles. Unlike that the transition times were not well predicted by the Sand equation in case of the heterogeneous ion-exchange membranes. This fact along with observed differences in the structure of these membranes on their surface and in their volume limit the use of the Sand equation to estimate the content of the ion-exchange resin in these membranes.

Membrane based direct pH parametric pumping

Membrane adsorbers have emerged as a promising alternative for classical chromatography since they have lower pressure drops and shorter diffusion paths. They are usually used in frontal flow-through configurations. Such membranes are regenerated using elution steps having the disadvantage of large dead volumes and extensive prior purification. Parametric pumping is an alternative process and is used in a variety of configurations. It uses a driving force perpendicular to fluid velocity for the adsorptive separation of mixtures utilizing a fixed adsorber bed. Here, we report a combination of a new mixed matrix hollow fiber membrane and its simultaneous use as a membrane contactor and membrane adsorber. The hollow fiber contains protein adsorbing ion exchange particles in the fiber wall. The fiber contacts the lumen-side protein containing solution with a pH-shifting gas (CO2 or NH3) on the shell side which in fact controls the pH inside the membrane wall. A silicone coating on the outside prevents a gas breakthrough from the outside. Switching between the two gasses and pH allows adsorption and desorption of proteins, enabling parametric pumping and protein recovery. As the feed flows on the inside of the hollow fiber adsorber, the dead volume can be minimized. Potentially, the solution would not even require prefiltration, as the adsorption particles are hidden and protected by the porous fiber wall.

Preparation and characterization of polysulfone/PEG heterogeneous ion exchange membrane for reverse electrodialysis (RED)

Heterogeneous cation-exchange membrane is synthesized using solution casting method. The casting solution is prepared by dispersing finely ground cation-exchange resin particles in N,N-dimethylacetamide (DMAc) solutions of polysulfone (PSf) while polyethylene glycol (PEG400) is used as a modifier. The results show that the PEG400 can increase water uptake, conductivity, and ion-exchange capacity (IEC) of the heterogeneous cation-exchange membrane due to the hydrophilic nature of PEG400. The more hydrophilic membrane results in higher water uptake and wider access for functional sites. However, when the concentration of PEG400 is increased further, the IEC and conductivity tend to decrease. This tendency is more pronounced when the ion-exchange resin particle is increased from 50 to 60%-wt. It could be attributed to the washed out of some ion-exchange particle during membrane immersion due to lower bonding between membrane matrix and the particles.

Effect of homogenization and hydrophobization of a cation-exchange membrane surface on its scaling in the presence of calcium and magnesium chlorides during electrodialysis

In this paper, two cation-exchange membranes, i.e. MK-40 and MK-40MOD, were studied by chronopotentiometry and voltammetry, MK-40MOD being obtained by covering the heterogeneous surface of a commercial MK-40 membrane with a homogeneous 20µm thick Nafion® film. Electrodialysis process was realized in an electrodialysis flow-through laboratory cell, in which the cation-exchange membrane under study formed a desalination chamber with an auxiliary anion-exchange (Neosepta AMX-SB) membrane. 0.02M and 0.04M solutions of CaCl2, MgCl2 and NaCl were used. The current densities were changed in the range from 0.25 ilimth to 2.5 ilimth, where the theoretical limiting current density, ilimth, was calculated using the Leveque equation. The potential drop over the modified MK-40MOD membrane and the water splitting at this membrane turned out to be lower in all studied cases. Formation of scaling was observed only in the case of the MK-40/0.04M MgCl2 system at current densities in the range from 1.1 ilimth to 1.4 ilimth. For these current densities, the (quasi)steady state value of potential drop slowly increased with time and the crystals of Mg(OH)2 were found on the ion-exchange particles embedded onto the MK-40 membrane surface facing the desalination chamber. At higher currents, stronger electroconvection at this membrane and higher water splitting at the AMX-SB membrane (the latter providing lower pH in the desalination chamber) prevented scaling. No scaling was found on the modified membrane at any current. It is due to the Nafion® film, which is relatively more hydrophobic than pristine MK-40 and which provides a “better” distribution of current lines near the surface, thus enhancing electroconvection and decreasing water splitting.

Assembly and Speed in Ion-Exchange-Based Modular Phoretic Microswimmers.

We report an experimental study on ion-exchange-based modular microswimmers in low-salt water. Cationic ion-exchange particles and passive cargo particles assemble into self-propelling complexes, showing self-propulsion at speeds of several micrometers per second over extended distances and times. We quantify the assembly and speed of the complexes for different combinations of ion-exchange particles and cargo particles, substrate types, salt types and concentrations, and cell geometries. Irrespective of the experimental boundary conditions, we observe a regular development of the assembly shape with increasing number of cargo. Moreover, the swimming speed increases stepwise upon increasing the number of cargo and then saturates at a maximum speed, indicating the active role of cargo in modular swimming. We propose a geometric model of self-assembly to describe the experimental observations in a qualitative way. Our study also provides some constraints for future theoretical modeling and simulation.

A microfluidic device with ion-exchange preconcentration column and photometric detection with Schlieren effect correction

This work describes the construction and evaluation of a microflow analyzer containing a Dowex® 1X8 packed column and LED-based photometric detection with Schlieren effect correction. Flow structures, including a reservoir for the preconcentration column with dimensions 25.0×2.0×1.0mm (l×w×h), were manufactured in a urethane–acrylate resin, and the ion-exchange particles (50–100mesh) were manually packed before sealing the device. Photometric measurements were performed using an integrated flow cell with a 5.0mm optical path by using optical fibers to guide the radiation from a 3.0W RGB LED to the microfluidic device and from the microdevice to a photodiode (OPT-101). It was demonstrated that the Schlieren effect is appropriately corrected by subtracting the signals for two diodes of the RGB LED and, by setting the intensity of light sources before measurements, the discordant response to the effect at different wavelengths is compensated. The preconcentration column was easily and successfully integrated into the microfluidic device without any clogging or leaking of the working solutions, and swelling of the packing particles caused no damage to the sealed structures because of the elastomeric nature of the microfluidic substrate. The application of the proposed device to the determination of nitrite in fresh water provides a linear response (R2=0.99) from 0.05 to 0.20mg NO2−L−1 and an approximate increase in concentration by four fold was estimated when 3.80mL of the sample/standard solutions is percolated through the column, providing recoveries from 96% to 101% for tested samples.

Controlled assembly of single colloidal crystals using electro-osmotic micro-pumps.

We assemble charged colloidal spheres at deliberately chosen locations on a charged unstructured glass substrate utilizing ion exchange based electro-osmotic micro-pumps. Using microscopy, a simple scaling theory and Brownian dynamics computer simulations, we systematically explore the control parameters of crystal assembly and the mechanisms through which they depend on the experimental boundary conditions. We demonstrate that crystal quality depends crucially on the assembly distance of the colloids. This is understood as resulting from the competition between inward transport by the electro-osmotic pump flow and the electro-phoretic outward motion of the colloids. Optimized conditions include substrates of low and colloids of large electro-kinetic mobility. Then a sorting of colloids by size is observed in binary mixtures with larger particles assembling closer to the ion exchanger beads. Moreover, mono-sized colloids form defect free single domain crystals which grow outside a colloid-free void with facetted inner crystal boundaries centered on the ion exchange particle. This works remarkably well, even with irregularly formed ion exchange resin splinters.