Amphoteric Charged Membranes Research Articles

Amphoteric Charged Membranes

Amphoteric Charged Membranes

Arsenate removal using a combination treatment of precipitation and nanofiltration

A combination treatment of Ca-precipitation and nanofiltration membrane was studied to remove arsenate from water. The selected nanofiltration membrane was an amphoteric charged membrane, proved by the results of ATR-FTIR spectra and zeta potential. The arsenate and calcium removal efficiencies had the lowest values at the isoelectric point of the nanofiltration membrane, attributed to the loosest steric hindrance and the weakest electrostatic repulsion. Above the isoelectric point, arsenate precipitated with calcium ion to form the low solubility compound calcium arsenate, while steric hindrance was the main mechanism of arsenate removal. In contrast, below the isoelectric point, the nanofiltration membrane with positive charges rejected calcium ion by electrostatic repulsion. The high electrostatic shielding of calcium ion prevented arsenate from coming close to the NF membrane. Either high feed arsenate concentration or high calcium oxide dose improved the removal amount of arsenate during the nanofiltration membrane separation process. In addition, the arsenate removal efficiency approached the highest value at 200 μg/L of feed arsenate concentration. The optimal transmembrane pressure was in a range of 0.5-0.7 MPa to restrict the formation of fouling cake on the nanofiltration membrane surface.

Studies of Protein Absorption and Fouling Behavior on Amphoteric Charged Polypropylene Microfiltration Membrane

To improve the antifouling property of PP membrane, a series of amphoteric charged membranes was prepared by the introduction of cysteine on polypropylene membrane. The modified membrane presents higher water flux than original membrane due to the improved hydrophilicity. It was proved by zeta potential that modified membrane inherited the amphoteric characteristic from cysteine. The isoelectric point of modified membranes are at pH 7.2 and 6.5 for 7.6% and 16.1% grafted membranes respectively. Due to the amphoteric characteristic of both modified membrane and BSA, electrical repulsion exsists among grafting chains and BSA in acid and alkaline solution. As a result, modified membranes have much lower adsorption amount of BSA than original PP membrane. Moreover, modified membranes show obvious antifouling property to BSA, due to the improved hydrophilicity of membrane and the electrical repulsion between BSA and membrane. Therefore, the amphoteric charged membranes modified by cysteine show great potential to resist protein fouling in a wide range of pH.

Characterization of Insulin Adsorption Behavior on Amphoteric Charged Membranes

With view to develop an amphoteric charged membrane for drug delivery, we have studied the adsorption of insulin on it. In the present study, the amphoteric charged membranes were prepared by pore-surface modification of porous poly(acrylonitrile) (PAN) membranes by grafting with acrylic acid (AAc) and/or N,N-(dimethylamino)propyl acrylamide (DMAPAA). Their surface charge properties and the insulin adsorption behaviors were investigated by zeta potential measurement and UV spectrophotoscopy, respectively, at different pHs. The equilibrium adsorbed amount of insulin correlates well with the charge properties of the membranes and insulin, which indicates that electrostatic interaction played an important role in the insulin adsorption. In addition, adsorption kinetics changed from a Fickian mode to a non-Fickian one when adsorbed amount increased to very high values.

Interfacial Properties of Amphoteric Charged Membranes

Interfacial Properties of Amphoteric Charged Membranes

荷電膜の性質 荷電膜表面の電気化学的性質

Surface electrochemical property, which is represented as ζ-potential or surface charge density, is a key parameter in membrane science. Charge on membrane surface plays an important role in the separation performance and fouling tendency. Electrokinetic measurements are a straightforward and powerful method to provide information about charge characteristics at the membrane-solution interface. This method also has higher sensitivity than the spectroscopic surface analysis methods (e.g., SEM, EDX, and FT-IR). Therefore, the electrokinetic characterization can be widely used for not only separation membrane surfaces and biocompatible interfaces, but also nano-engineered surfaces. Here, we presented general remarks on electrokinetic characterization of charged membranes based on streaming potential measurements, focusing on amphoteric charged membranes.

Pore-surface characterization of amphoteric charged membranes by means of zeta potential measurements

Abstract Weak amphoteric charged membranes were prepared by the radiation-induced graft copolymerization of the poly(ethylene glycol) (PEG) derivatives with pendant ionizable groups onto polyethylene (PE) porous membranes. In this study, two types of amphoteric charged membranes, which are the amphoteric ion-pair side chain (ASC) type and the mixed grafted chain (MGC) type, were prepared and then characterized by means of zeta (ζ)-potential measurements. The ζ-potential measurements were performed using streaming potential method over the pH range of 2–12. The ζ-potential/pH profiles for the amphoteric charged membranes showed their characteristic behavior. The pH dependence of the apparent surface charge density derived from the ζ-potential was compared with the calculated result from the theoretical model, site dissociation model (SDM), which was based on the dissociation of ionizable groups on the pore surface. Our analysis indicated that the interfacial charge of the ASC-type membrane was ascribed to the dipolar ion structure of cysteine residues. On the other hand, not only the charge groups but also the conformation of grafted polyelectrolyte chain affected the electrokinetic pore-surface charge of the MGC-type membrane.

Interaction of proteins with weak amphoteric charged membrane surfaces: effect of pH

Weak amphoteric charged membranes were prepared by the graft copolymerization of poly(ethylene glycol) (PEG) derivatives with pendant ionizable groups onto polyethylene (PE) porous membranes. Two types of weak amphoteric charged membranes and two types of weak single charged membranes were prepared. The pH dependence of the protein (fluorescein isothiocyanate-labeled bovine serum albumin, FITC-BSA) adsorption onto the membranes was investigated by fluorescence spectroscopy. The interfacial charge properties of the membranes and protein were also characterized at different pH values by streaming potential and electrophoretic light scattering (ELS) measurements, respectively. The adsorbed amount onto each ionic PEG chain grafted membrane showed a uniform maximum value near the isoelectric point (IEP) of the protein (pH 4.1). On both sides of the IEP (pHs 3.3 and 7.2), the adsorption experiments and zeta ( ζ) potential measurements were well correlated: the contribution of electrostatic interaction was dominant for the protein adsorption behavior. In the alkaline condition (pH 10.2), the adsorption experiments contradict the ζ potential measurements. It suggested that the conformational change of protein molecule influenced the adsorption behavior. Finally, these results indicated the potential of controlling the protein–ionic PEG chain interaction on the membrane surfaces by the pH adjustment of the outer solution.

Interaction of Organic Molecules with Weak Amphoteric Charged Membrane Surfaces: Effect of Interfacial Charge Structure

Weak amphoteric charged membranes were prepared by graft copolymerization of poly(ethylene glycol) (PEG) derivatives with pendant ionizable groups onto porous polyethylene (PE) membranes. Two types of weak amphoteric charged membranes and two types of weak single charged membranes were prepared and then characterized by zeta (ζ) potential and dynamic contact angle measurements. To identify the characteristics of interactions between organic molecules and membrane surfaces, we used four kinds of model organic molecules: pyrene (highly hydrophobic), 1-pyrenesulfonic acid (having an anionic group), 1-pyrenemethylamine (having a cationic group), and 1-aminopyrene (having a polar group). The time dependence of the adsorbed amount on the membrane was investigated with fluorescence spectroscopy. The results demonstrated that ionic PEG chains on the membrane surfaces reduced the adsorption of hydrophobic adsorbents and interacted with polar groups by hydrogen bonding. On the other hand, for ionic adsorbents, ele...

Effect of Proton Concentration on Membrane Potential across a Weak Amphoteric Polymer Membrane

An amphoteric membrane consists of both positively and negatively fixed charge groups chemically bound to the polymer chains. If the external solution is changed from alkali to acid, it is possible to obtain an experimental result in which the membrane potential changes from positive to negative through the isoelectric point. It was characterized by examining the relationship between membrane potential and proton concentration (pH) obtained from both experimental and theoretical considerations. The Nernst-Planck flux equation and the Donnan equilibrium theory were also solved for a four-component system combined with the dissociation constant, in order to discuss the pH dependence of membrane potential in a weak amphoteric membrane by comparing the experimental results with the calculated results. It was proven that the calculated results substantially deviated from the theoretical results despite a similar tendency. Such a deviation was caused by the fact that the original theory disregarded the activity coefficient and the ionic mobility, which were dependent on the fixed charge concentration in a membrane. The original theoretical model was modified by adding the effect of a fixed charge group to the activity coefficient and ionic mobility. The calculated results using the modified model explained well the experimental results if the parameter called charge effectiveness, φ, was introduced into the equations. Introduction of φ into the prediction of membrane potential was already done by Kobatake et al. in a system of a strong polyelectrolyte monopolar membrane/salt aqueous solution. In this study, it was proved that φ can also be introduced into a weak amphoteric polymer membrane/salt aqueous solution system. Finally it was also concluded that the Donnan equilibrium and the Nernst-Planck flux equation were still applicable for examining the transport phenomena for the system of a weak amphoteric charged membrane and electrolyte solutions at various pH.

Preparation and Characterization of Novel Weak Amphoteric Charged Membrane Containing Cysteine Residues

Novel weak amphoteric charged membranes having cysteine residues were prepared. Cysteine (Cys) is one of the amino acids and has an amphoteric ion pair, which consists of an amino group and a carboxyl group. The poly(ethylene glycol) derivatives, with cysteine residues added to their side chains (PEG–Cys), were graft-polymerized onto a porous cellulose acetate (CA) membrane. The zeta potential was measured using a streaming potential method at various pH values ranging from 2.5 to 10 to investigate the behavior of the charge groups on the pore surface of these membranes. The zeta potential of this PEG–Cys-grafted membrane was pH-dependent, and the zeta potential/pH profile showed a plateau which was characteristic of an amphoteric ion pair in the range pH 4/9. The apparent surface charge density on these membranes was obtained from the zeta potential. The experimental results could be well explained by a calculated value using a site dissociation model including the contribution of not only the amphoteric ion pairs on the grafted polymer chains but also the negative charge groups originating from the base CA membrane.

Characterization of Novel Weak Amphoteric Charged Membranes Using ζ-Potential Measurements: Effect of Dipolar Ion Structure

Weak amphoteric charged membranes were prepared by the radiation-induced graft copolymerization of the weakly charged poly(ethylene glycol) derivatives onto high-density polyethylene porous membranes. In this study, two kinds of amphoteric charged membranes, which are the amphoteric ion-pair side chain type and the mixed grafted chain type, were prepared and then characterized using the ζ-potential measurements. For the amphoteric ion-pair type membrane, the ζ-potential/pH profile showed a plateau in the range of pH 6−11 which was characteristic of the dipolar ion structure of an amphoteric ion-pair. On the other hand, the ζ-potential for the mixed grafted chain type membrane showed an intermediate pH dependence between the separate positively charged chain- and negatively charged chain-grafted membranes. The apparent surface charge density on these membranes was obtained from the ζ-potential. For the amphoteric ion-pair side chain type membrane, the experimental results could be explained by the theoreti...