Improvement of Selectivity of RALEX-CM Membranes via Modification by Ceria with a Functionalized Surface

Ion exchange membranes are widely used for water treatment and ion separation by electrodialysis. One of the ways to increase the efficiency of industrial membranes is their modification with various dopants. To improve the membrane permselectivity, a simple strategy of the membrane surface modification was proposed. Heterogeneous RALEX-CM membranes were surface-modified by ceria with a phosphate-functionalized surface. Despite a decrease in ionic conductivity of the prepared composite membranes, their cation transport numbers slightly increase. Moreover, the modified membranes show a threefold increase in Ca²⁺/Na⁺ permselectivity (from 2.1 to 6.1) at low current densities.

Novel polyaniline-polyethersulfone nanofiltration membranes: effect of in situ polymerization time on structure and desalination performance

In this research, novel polyaniline-layered nanofiltration membranes were prepared by phase inversion of base polyethersulfone (PES) membranes and subsequent in situ solution-phase deposition of polyaniline as a thin surface layer. In these composite membranes, the impact of the polyaniline deposition time on steric hindrance and electrostatic interactions during permeation was elucidated. The chemical structure, thermal stability, and mechanical properties of the PES and PANI-PES membranes were investigated using Fourier-transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA), respectively. The membranes' porosity and pore size decreased as PANI deposition time increased. As PANI deposition time increased, PANI layered nanofiltration membranes exhibited improved thermal stability but deteriorated mechanical characteristics due to free radical destruction from prolonged exposure to the oxidant. These PANI-PES membranes showed 43% rejection (NaCl) at 1.7 bar coupled with a flux of 11.59 L h^-1 m² that is quite promising when comparing with similar Nanofilteration (NF) membranes in the literature and commercial NF membranes, as well. As the deposited layer, PANI is partially doped; hence, permeation results have been interpreted in terms of steric hindrance and electrostatic repulsion by electrochemical PANI layering.

Preparation and comparative evaluation of PVC/PbO and PVC/PbO/graphite based conductive nanocomposites

Two series, A and B, of PVC based nanocomposite polymer membranes (nCPMs) were prepared using PbO only and PbO/graphite mixture as a filler by solution casting method. Seven samples with varying compositions (5–35%) of filler particles were prepared for each series and were compared by thickness measurements, porosity, water uptake, swelling degree, ionic conductivity, ion exchange capacity (IEC), membrane potential and transport number. The maximum values for these characteristics were observed as 0.402 mm, 0.77, 141.3%, 0.11, 0.0033 Scm−1, 8.6 milli-eq.g−1, 0.19 V and 0.01391 for series-A composites whereas that of 0.367 mm, 0.83, 63.4%, 0.019, 0.00981 Scm−1, 5.21 milli-eq.g−1, 0.13 V and 0.0108 for series-B nCPMs respectively. The SEM images of membranes showed greater voids produced in the series-B compared to series-A composites. The maximum Ionic conductivity, IEC, membrane potential and transport number were observed for membrane with 25% PbO/graphite, 20% PbO and 35% PbO particles respectively.

Fabrication of a lead ion selective membrane based on a polycarbazole Sn(iv) arsenotungstate nanocomposite and its ion exchange membrane (IEM) kinetic studies

A polycarbazole-Sn(iv) arsenotungstate (Pcz-SnAT) nanocomposite cation exchanger membrane (CEM) was prepared via the casting solution technique utilizing polycarbazole-Sn(iv) arsenotungstate and PVC (polyvinyl chloride) as a binder. The synthesis of the Pcz-SnAT membrane was confirmed via various characterization methods such as EDX, SEM, TGA, XRD, and FTIR spectroscopy. This membrane having a 4.5 : 1 composition ratio of composite by PVC exhibited the most effective outcomes for swelling, thickness, porosity, and water content. Our research indicates that the present ion selective membrane electrode is selective towards Pb(ii) ions, with the detection limit ranging from 1 × 10-7 mol L-1 to 1 × 10-1 mol L-1 where 20 s is the response time and 3-7 is the working value pH. The mechanism of the Pcz SnAT ion exchange membrane was obtained by kinetic studies by utilizing the equation given by Nernst Planck at 40-80 °C. As a result, activation energy and thermodynamic studies were done. The analytical utility of this electrode is conventional by utilizing it as an electrode indicator within the potentiometric titration.

Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement

Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.

Heterogeneous ion exchange membranes based on thermoplastic polyurethane (TPU): effect of PSS/DVB resin on morphology and electrodialysis

In this research, novel heterogeneous cation exchange membranes based on thermoplastic polyurethane (TPU) have been prepared by the solution casting technique. The effects of incorporation level of sulfonated polystyrene divinyl-benzene (PSS/DVB) resin on water uptake, ion exchange capacity, membrane potential and salt extraction have been elucidated. Morphological and water uptake studies suggested a two-phase heterogeneous membrane morphology owing to the presence of hard and soft segments in the TPU backbone and swelling of PSS/DVB particles. This morphology was shifted to a semi-gelled morphology throughout the membrane bulk when resin loading exceeded 50 wt%. The physically cross-linked hard segments in the TPU backbone ensured a compact membrane morphology and prevented the formation of water channels. The membrane potential showed that increasing the resin content increased the membrane transport number (max. 0.95) up to 50 wt% resin loading and beyond this, the transport number started decreasing showing a pronounced effect of voids and water flow channels developing on excessive swelling. The permselectivity reached a maximum (up to 0.92) and salt extraction values also increased (by varying voltage) up to 50 wt% loading and started decreasing beyond this optimum content. This study shows successful development of low-cost heterogeneous cation exchange membranes based on TPU with acceptable electrochemical properties.