Solvent-extraction and Langmuir-adsorption-based transport in chemically functionalized nanopore membranes

We have investigated the transport properties of nanopore alumina membranes that were rendered hydrophobic by functionalization with octadecyltrimethoxysilane (ODS). The pores in these ODS-modified membranes are so hydrophobic that they are not wetted by water. Nevertheless, nonionic molecules can be transported from an aqueous feed solution on one side of the membrane, through the dry nanopores, and into an aqueous receiver solution on the other side. The transport mechanism involves Langmuir-type adsorption of the permeating molecule onto the ODS layers lining the pore walls, followed by solid-state diffusion along these ODS layers; we have measured the diffusion coefficients associated with this transport process. We have also investigated the transport properties of membranes prepared by filling the ODS-modified pores with the water-immiscible (hydrophobic) liquid mineral oil. In this case the transport mechanism involves solvent extraction of the permeating molecule into the mineral oil subphase confined with the pores, followed by solution-based diffusion through this liquid subphase. Because of this different transport mechanism, the supported-liquid membranes show substantially better transport selectivity than the ODS-modified membranes that contain no liquid subphase.     

Hybrid liquid membrane (HLM) system in separation technologies

A novel liquid membrane system, denoted hybrid liquid membrane (HLM), was developed for the separation of solutes (metal ions, acids, etc.). It utilizes a solution of an extracting reagent (carrier solution), flowing between membranes. The membranes, which separate the carrier solution from feed and receiving (strip) solutions, enable the transport of solutes, but block the transfer of the carrier to the feed or to the strip. Blocking the carrier is achieved through membranes hydrophilic/hydrophobic or ion exchange properties, or through their rentention abilities, due to pore size.     

The effect of the ion exchanger site-counterion complex formation on the selectivities of ISEs

Using the model of ideally associated solution, the effect of ion association of the ion exchanger sites with main and foreign counterions on the selectivity of ISEs based on liquid ion exchangers has been considered. Equations which describe the potentiometric selectivity coefficient as a function of ion association constants in the membrane phase and of standard free energies of transfer of the determined and foreign ions from water to the membrane are obtained for the following main cases: (a) the determined and foreign ions are single-charged; (b) the determined ion is double-charged and the foreign ion is single-charged. It is shown that in the case of single-charged main and foreign ions, the ratio of the ion association constants has a great effect on the potentiometric selectivity of membranes, only if the ion exchanger sites produce less strong associates with the determined counterion as compared with the foreign one. Otherwise, this effect is insignificant. The selectivity for double-charged ions should increase, other things being equal, as the first constant of association of these ions with the ion exchanger sites increases. The effect of producing ion triplets of the type I(2)R((+/-)) on the selectivity of ISEs is also considered. Experimental data are presented which illustrate the effect of the nature of the ion exchanger on the potentiometric selectivity. Some procedures employing the factor of ion association for increasing the potentiometric selectivity of liquid ion exchange membranes are considered.     

Transport properties of highly ordered heterogeneous ion-exchange membranes

Model "ordered" heterogeneous ion exchange membranes are made with ion exchange particles heaving ion exchange capacity in the range 3 to 2.5 meq/gr (dry basis) and diameters ranging from 37 to 7 microm and 2 component room-temperature vulcanizing silicon rubber as a polymeric matrix, by applying an electric field normal to the membrane surface during preparation. These membranes were shown to have an improved ionic conductivity compared with "nonordered" membranes based on the same ion exchange content (for instance, at 10% resin content "nonordered" membranes show <10(-5) mS/cm while "ordered" membranes have conductivity of 1 mS/cm). The transport properties of ordered membranes were compared with those of nonordered membranes, through the current-voltage characteristics. Limiting currents measured for the ordered membranes were significantly higher than those of the nonordered membranes with the same resin concentration. In addition, higher limiting currents were observed in ordered membranes as the resin particles became smaller. Energy dispersion spectrometry analyses revealed that the concentration of cation exchange groups on the membrane surface was higher for ordered membrane as compared to that of nonordered membranes. This implies that the local current density for the conducting domains at the surface of the nonordered membranes is higher, leading to higher concentration polarization and, eventually, to lower average limiting current densities. The effect of ordering the particles on the membrane conductivity and transport properties was studied, and the advantages of the ordered membranes are discussed.     

Transport properties and electroanalytical response characteristics of drotaverine ion-selective sensors

The construction and electroanalytical response characteristics of poly(vinyl chloride) matrix ion-selective sensors (ISSs) for drotaverine hydrochloride are described. The membranes incorporate ion-association complexes of drotaverine with tetraphenylborate, picrate, tetraiodomercurate, tetraiodobismuthate, Reinecke salt, and heteropolycompounds of Keggin structure—molybdophosphoric acid, tungstophosphoric acid, molybdosiliconic acid and tungstosiliconic acid as electroactive materials for ionometric sensor controls. These ISSs have a linear response to drotaverine hydrochloride over the range 8×10^–6 to 5×10^–2 mol L^–1 with cationic slopes from 51 to 58 mV per concentration decade. These ISSs have a fast response time (up to 1 min), a low determination limit (down to 4.3×10^–6 mol L^–1), good stability (3–5 weeks), and reasonable selectivity. Permeabilities and ion fluxes through a membrane were calculated for major and interfering ions. Dependences of the transport properties of the membranes on the concentrations of the ion exchanger and near-membrane solution and their electrochemical characteristics are presented. The ISSs were used for direct potentiometry and potentiometric titration (sodium tetraphenylborate) of drotaverine hydrochloride. Results with mean accuracy of 99.1±1.0% of nominal were obtained which corresponded well to data obtained by use of high-performance liquid chromatography.     

Potentiometric determination of coextraction constants of potassium salts in ion-selective electrodes utilizing a nitrobenzene liquid membrane phase

A theoretical treatment of potentiometric data is applied to calculate coextraction constants (K_IA) for three potassium salts from water into a liquid nitrobenzene phase. The experiment involves treating nitrobenzene as a membrane and contacting it with two aqueous solutions of different ion activities. In the presence of either a cation or anion exchanger, the ratio of activities of ions in the two aqueous phases gives rise to a potential difference across the membrane that depends upon the nature and charge of the counter ion of the ion-exchanger in excess. Here, the cation exchanger was chosen to be potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and the anion exchanger was tetradodecylammonium chloride (TDDACl). TDDACl was incrementally added to the nitrobenzene phase containing a fixed concentration of KTpClPB, and the corresponding emf was recorded as a function of concentration of TDDACl. The membrane changes from one with cation exchanger properties (excess KTpClPB) to one with anion exchanger properties (excess TDDACl). The potential difference and shape of the titration curve can be predicted by theory based on the phase boundary potential model. Log(K_IA) values calculated for KCl, KNO₃ and KClO₄ in nitrobenzene were found as: −10.53 (± 0.09), −8.16 (± 0.05) and −5.63 (± 0.03) respectively, in accordance with the Hofmeister series of lipophilicity, and similar to those observed in PVC membranes containing other plasticizers. The method presented here offers the advantage over other methods to calculate K_IA, in that it is relatively experimentally simple without compromising the accuracy of the calculated coextraction constants. The ability to titrate directly into the liquid membrane phase affords a higher precision compared to the preparation of a series of PVC/plasticizer membranes with different compositions.     

Selective Recognition of Calcium Ion through Liquid Membrane

The mole transport rate of alkaline earth metal ions through a bulk liquid membrane and a supported liquid membrane using a series of proton diionizable acyclic polyethers was measured. Among alkaline earth metal ions, the calcium ion was observed to be selectively transported in both single and competitive transport experiments. Potentiometric titration and solution calorimetric titration also gave calcium selectivity over other alkaline earth metal ions. Acyclic polyether bearing a diethylene glycol unit andn-tetradecyl lipophilic chain at the α position of carboxylic acid affords the best selectivity for the calcium ion in bulk and supported liquid membranes.     

Cation-Response Mechanism of Neutral Carrier Based Ion-Selective Electrode Membranes

Results of voltammetric, potentiometric, chronoamperometric, ion transport, and extraction studies on neutral carrier based, plasticized poly(vinyl chloride) membranes are summarized. They unambiguously confirm that such bulk membranes dispose of immobile anionic sites. These fixed sites lead to a Donnan exclusion of other anions from the membrane and thus to a permselectivity for cations. The results are in perfect agreement with the predictions of earlier membrane models. A rigorous Poisson-Boltzmann analysis of macroscopic liquid membranes clearly indicates that space-charge at the membrane/solution interfaces does not influence the electrochemical properties and the ion-selectivity behavior at steady state.     

Transport of ionic species through functionalized poly(vinylbenzyl chloride) membranes

Solid polymeric membranes of poly(vinylbenzyl chloride) (VBC), lightly crosslinked with divinyl benzene, were incompletely reacted such that a fraction of the benzyl chlorines in different membranes was replaced with either dimethyl phosphonate esters (MPE) or triethyl ammonium chloride groups (QA). This work was conducted in an effort to investigate ionic transport through charged and uncharged membranes and to develop fixed site carrier membranes to facilitate the transport of selected metal ions from an aqueous feed stream to a concentrated acid receiving stream. Bulk solution flow does not occur through these membranes. Instead, solute diffusion occurs through the membrane matrix. The effects of hydrogen ion gradient, metal ion identity and charge, reactive site type, acid type, and ionic strength on metal ion transport were investigated. Results are also presented on the effect of membrane orientation and pretreatment (swelling) on metal ion transport. Facilitated transport was investigated through the testing of membranes with varying MPE percent functionalization. The results presented compare the metal ion transport rate to the functionalization of the membranes.     

Lipophilic ionic additive for controlling the selectivity of ion-selective electrodes reversible to cations of nitrogen-containing organic bases

The effect of a lipophilic ionic additive, a tetradecylammonium salt of a liquid ion exchanger, on the selectivity of ion-selective electrodes (ISEs) for cations of nitrogen-containing organic bases was studied. Additive-containing ISEs exhibited a higher selectivity for cations of primary to tertiary amines as compared to that for quaternary ammonium cations. A maximum change in selectivity (up to more than two orders of magnitude) due to the introduction of tetradecylammonium was observed for membranes containing dinonyladipate as a plasticizer and tris(nonyloxy)benzene sulfonic acid as an ion exchanger. In this case, the introduction of lipophilic ionic additive may lead to the reversal of the selectivity series. The effect of the lipophilic ionic additive on the selectivity of ISEs with membranes plasticized with o-nitrophenyl octyl ether decreased approximately by an order of magnitude. The selectivity of ISEs with the membranes containing tetrakis(4-chlorophenyl) borate as a cation exchanger was virtually independent of the presence of lipophilic ionic additives. The results obtained were explained by the peculiarities of ion-pair formation in the membrane.     

Anion influence on extraction and transport of amino acid methyl esters by functionalised calix[4]arene

The liquid–liquid extraction of a series of amino acid methyl esters has been carried out with functionalised calix[4]arene (5,11,17,23-tetrakis(N-methylpiperazino)-25,26,27,28-tetrahydroxycalix[4]arene) from an aqueous phase into a chloroform phase as ion pairs in the presence of picrate ion or tropaeolin 00 as counter ion in order to study the molecular recognition properties of this receptor. The active transport assisted by pH gradient of amino acids as ion pairs through liquid membrane employing the functionalised calix[4]arene as carrier has been investigated. The results showed that the receptor exhibits good extractability towards amino acids and it can also act as carrier through liquid membrane aiming to the separation of amino acids. It was highlighted that the anion nature used as counter ion, the structure of calix[4]arene, and the structure of amino acids are responsible for the experimental results obtained. High yields in both amino acids extraction and transport were obtained for picrate ion used as counter ion.     

Enhanced transport properties and thermal stability of agro-based RO-membrane for desalination of brackish water

This present work focused on preparation of economic and high performance reverse osmosis membranes, characterized by high transport properties (salt rejection and flux) towards desalination of brackish water. In this respect cellulose acetate from sugar-cane bagasse (BCA) and polymethyl methacrylate (PMMA) wastes were used as the substrates of membrane. The function of PMMA for enhancing the performance of bagasse-based cellulose acetate RO-membranes was investigated at operating pressure 35.85 bar and feed temperature 25 °C. The effects of casting solution, percentage of polymer and treatment of polymer by alkali (HPMMA) on the performance of RO-membrane were discussed. The preferable composition (wt.%) of the 90% BCA and 10% HPMMA was achieved salt rejection 92.18% and flux 325.9 l h⁻¹ m⁻². High water purity was obtained by pre-passing the salted water through membrane made from dissolved bagasse (methylol cellulose) together with PMMA, instead of ion exchanger, followed by passing the accepted water through BCA–HPMMA membrane, whereas the salt rejection increased to 98%. Also, by this approach we obtained high thermal stability membrane compared to CA-RO-membrane. This data gives highlight on possibility of application such type of membrane with high temperature operation conditions.     

Synthesis of novel mono-and bisaminophosphoryl compounds and their membrane transport properties for acidic substrates

Some novel aminophosphoryl compounds were synthesized by the Kabachnik-Fields reaction. Their membrane transport properties for mono-and polyfunctional carboxylic acids with different number of functional groups were studied to establish that the transport rate of acidic substrates through liquid impregnated membranes increases in going from mono-to diphosphoryl carriers. Additional hydrophilic groups in the substrate molecule, too, affect transport efficiency.     

Crystal Channel Engineering for Rapid Ion Transport: From Nature to Batteries

Ion transport behaviours through cell membranes are commonly identified in biological systems, which are crucial for sustaining life for organisms. Similarly, ion transport is significant for electrochemical ion storage in rechargeable batteries, which has attracted much attention in recent years. Rapid ion transport can be well achieved by crystal channels engineering, such as creating pores or tailoring interlayer spacing down to the nanometre or even sub-nanometre scale. Furthermore, some functional channels, such as ion selective channels and stimulus-responsive channels, are developed for smart ion storage applications. In this review, the typical ion transport phenomena in the biological systems, including ion channels and pumps, are first introduced, and then ion transport mechanisms in solid and liquid crystals are comprehensively reviewed, particularly for the widely studied porous inorganic/organic hybrid crystals and ultrathin inorganic materials. Subsequently, recent progress on the ion transport properties in electrodes and electrolytes is reviewed for rechargeable batteries. Finally, current challenges in the ion transport behaviours in rechargeable batteries are analysed and some potential research approaches, such as bioinspired ultrafast ion transport structures and membranes, are proposed for future studies. It is expected that this review can give a comprehensive understanding on the ion transport mechanisms within crystals and provide some novel design concepts on promoting electrochemical ion storage capability in rechargeable batteries.     

Facilitated and reverse transport of electrolytes through an asymmetric membrane

It is well known that the asymmetry of a membrane structure is closely related to its functions. Transport of ions is also affected by the asymmetry of the membrane structure. In this paper, ion transport through an asymmetric membrane is discussed theoretically. Equations are derived for the partition coefficient and the fixed charge density of a membrane with different surfaces. It is concluded that facilitated transport as well as reverse transport takes place both in membranes which are asymmetric with respect to the partition coefficient and in membranes with asymmetric charge distribution. In addition, the following two kinds of asymmetric membranes were prepared: one is a cellulose acetate—collodion membrane, which is asymmetric with respect to the partition coefficient, and the other is an NaOH-treated collodion—collodion membrane, which is asymmetric with respect to the membrane charge density. Ion transport through these membranes was investigated in order to verify the validity of the theory; the experimental results are in agreement with the theory.     

Electrochemical Properties of Membranes Based on Associates of Beta-Lactam Antibiotics with Tetradecilammonium

The electrode and transport properties of liquid and plasticized membranes based on associates of beta-lactam antibiotics with tetradecilammonium are studied. Rates of transport, penetrability, and ion flux of antibiotics are evaluated in conditions of self-diffusion and applied potential. Apparent dissociation constants are calculated for organic ion exchangers from steady-state resistances of membranes.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 981–986.Original Russian Text Copyright © 2005 by E. Kulapina, Baraguzina, O. Kulapina, Chernov.     

2D Nanosheets and Their Composite Membranes for Water,Gas, and Ion Separation

Two‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.     

2D Nanosheets and Their Composite Membranes for Water,Gas, and Ion Separation

Two‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.     

大环分子载体液膜传输--一种新型的分离技术

大环主体分子能选择地与客体分子如金属离子,中性分子结合,这一特性使其可作为液膜分离的高选择性载体。评述了大环超分子载体的液膜传输的数学模型以及在金属阳离子,中性离子,中性分子,氨基酸的传输,协同传输中的应用。