Electroconductive Membrane Research Articles

Electro‐Conductive Ti3C2 MXene Multilayered Membranes: Dye Removal and Antifouling Performance

AbstractThis work describes the fabrication of a novel electroconductive membrane made of Ti3C2Tx (MXene) nanosheet coating through a one‐step pressure‐assisted technique. Ti3C2‐MXene is firmly attached over a polyamide–imide (PAI) microfilter by employing a binder composed of carboxymethyl cellulose (CMC)/glutaraldehyde (GA). Through coating a proper amount of multilayer Ti3C2‐MXene, the electrical conductivity of 174 ± 0.16 S m−1 is achieved. The rejection rates of reactive red 120 (RR120), reactive black (RB), and methyl orange (MO) by the pristine PAI membrane are 45.2%, 40.81%, and 33.65%, respectively. However, rejection rates significantly improve with the Ti3C2 MXene coating to over 99.71%, 97.95%, and 68.91% for RR120, RB, and MO. Applying a 4 V cathodic potential resulted in a flux recovery ratio (FRR) of 99.83% and a flux decline rate (FDR) of less than 1% during humic acid (HA) filtration. Without applying voltage, the MXene‐coated membrane shows an FRR and FDR of 92.51% and 45.56%, respectively. Surface energy analysis reveals strong repulsive interactions between foulants and the membrane surface. Moreover, the surface free energy indicates that foulants such as sodium alginate (SA) and bovine serum albumin (BSA) exhibit stronger adhesion to the membrane than HA, consistent with the fouling experiment results.

Mechanism of mitigating organic fouling on an electro-conductive membrane under anaerobic conditions and cathodic operation

Anaerobic electroconductive membrane (ECM) bioreactors are promising wastewater treatment technology, yet their organic antifouling mechanism remains unclear. This research investigated the impact of reactive oxygen species (ROS) oxidation, pH alteration, and electrostatic repulsion on carbon nanotube-based ECM organic fouling. Using a decoupled anode–cathode filtration system ensured unbiased results from the anode while studying distinct conditions near the cathodic ECM surface. The results demonstrated a 50 % reduction in transmembrane pressure (TMP) onset applying potential due to electroosmosis, emphasizing its importance in fouling studies. Fouling experiments using alginate in synthetic wastewater solution showed substantial organic fouling at open circuit potential, −1 and −1.5 V, as the TMP increased by about 2.5 times than the initial value. Fouling decreased significantly at −2.5 V (vs. Ag/AgCl), as indicated by the stable TMP. Analysis of ROS effects and fouling experiments at pH 7–––12 found no influence on organic fouling. Simplified force balance analysis and filtration tests suggested electrostatic repulsion as the antifouling mechanism. At potentials below −2.5 V, electrostatic repulsion maximizes closer to the ECM surface, causing fouling from short-range attractive forces. Electrochemical quartz crystal microbalance analysis at 0.1 V (vs. Ag/AgCl) proposed that a smooth ECM surface can reduce organic fouling at lower potentials.

Persulfate enhanced ciprofloxacin removal from water by laser-induced graphene-based electroconductive ultrafiltration membrane

The ineffective removal of emerging pollutants by conventional treatment plants has necessitated the use of advanced treatment techniques such as electroconductive membranes.

Fabrication of polyether sulfone-laser induced graphene composite electroconductive membrane and its application in biofouling control and chromium removal

Polymeric membranes used in water purification face challenges due to high-pressure requirements, fouling propensity, and permeability-selectivity trade-offs. Electroconductive membranes (ECMs) can deal with these challenges and have the potential to improve the performance and lifetime of membranes using a low electric potential. In the present work, robust ultrafiltration (UF) ECMs were fabricated using polyether sulfone (PES) and laser-induced graphene (LIG) through the phase inversion process. LIG is a conductive material with electrochemical and catalytic activity fabricated directly on a polymeric substrate with a CO2 laser in a chemical-free single-step process. The fabricated ECMs were optimized with PES concentration and membrane thickness, can perform reduction, precipitation, and filtration simultaneously. These ECMs have a permeability ranging from 450 to 200 LMH bar−1 with BSA rejection of ∼60 % and FRR up to ∼90 %. The electrochemically enhanced Cr(VI) removal reached ∼94 % by applying a low electrical potential. Furthermore, in the biofouling experiments, the attached live biomass was reduced by ∼67 % for fabricated ECMs compared to the pristine membrane. The results showed the anti-biofouling potential of fabricated ECMs, which can be further enhanced using their electrochemical activity. These new-generation ECMs have immense potential for dealing with permeability-selectivity trade-offs, enhancing pollutant removal, and antifouling applications with low applied potential.

Using an anti-fouling electro- (stainless-steel/ PVC) membrane reactor in electrocoagulation process for arsenic removal: Experimental study and mechanism development in multiphase media using CFD

The electrocoagulation (EC) method is an effective way to remove arsenic (As) from water. However, to obtain high-quality floc-free water, it needs further purification, and membrane processes can be used to achieve this goal, but fouling is their main problem. In this study, a PVC/stainless steel electro-conductive membrane was used as a cathode electrode, and the effects of voltage, current, and time on the reduction of membrane fouling and arsenic removal were investigated. By increasing the applied voltage, due to the increase of the repulsive force between the membrane and negatively charged arsenic particles, the percentage of arsenic removal increased. While increasing the current density, more coagulant materials were produced from the anode, and the rejection rate of arsenic also became higher. The optimal conditions for removing arsenic at 22 V, 0.2 A, and 50 min were obtained according to the box-Behnken design in deionized water. After the second one-hour cycle, the concentration of arsenic in the model water decreased by 99.6% and fell below the maximum permissible level. Additionally, increasing voltage and current reduces membrane fouling due to an increase in the repulsive force and formation of bubbles on the membrane surface, respectively. Also, the process modeling results, considering the adsorption mechanism and repulsive force, showed that at 0.2 and 0.32 amperages, the model follows the Freundlich and Langmuir isotherms better, respectively, and showed an accurate prediction of experimental outcomes. Furthermore, 3D process modeling results indicated the distribution of velocity, current, voltage, and concentration inside the reactor.

Low-biofouling anaerobic electro-conductive membrane bioreactor: The role of pH changes in bacterial inactivation and biofouling mitigation

Membrane biofouling presents a great challenge to the adoption of anaerobic membrane bioreactors (AnMBRs) for wastewater treatment. A promising method for mitigating biofouling is applying an external charge to carbon-based electroconductive membranes (ECMs). This research investigated biofouling mitigation in an AnMBR mimicking system equipped with an ECM (EC-AnMBR), where the ECM serves as a cathode and a platinum plate as the counter electrode. A cation exchange membrane separated the anode and cathode to decouple the reactions on each electrode. Bacterial inactivation was estimated under varying cathodic potentials (0 to −2.5 V vs. Ag/AgCl), and reactive oxygen species formation and changes in pH were monitored. Bacterial inactivation was also evaluated in solutions with pH values similar to those recorded in the applied potentials experiments. Biofouling formation under the different applied potentials was then assessed during 48 h of filtration, and the biofilm formed on the ECM after 48 h was analyzed. Our results show that the EC-AnMBR had very low biofouling, attributed to bacterial inactivation and biofilm mitigation from extreme local pH conditions developed by hydrogen evolution at the cathode. This work addresses biofouling mechanisms on externally charged ECMs, which could be potentially applicable to AnMBRs for advanced wastewater treatment.

Novel metallic stainless-steel mesh-supported conductive membrane and its performance in the electro-filtration process

In this study, we demonstrate the fabrication of a thoroughly metallic electro-conductive membrane by using simple filtration to uniformly coat AgNWs dispersion through stainless steel (SUS)-mesh, which functions both as filter and a flexible conductive substrate. The as-prepared AgNWs networks layer on the SUS-mesh was further strengthened by electroplating Ag layers (P-SUS membrane); exhibiting an overall electrical conductivity of 9.2 × 104 S/m, which is up to 42 times greater than the conductivity of pristine SUS-mesh. The P-SUS membrane exhibited adequate physical durability against chemical and mechanical stresses under prolonged filtration, and high pure water flux of 534 ± 54 LMH/bar. This electro-membrane displayed the anticipated flux recovery in harvesting microalgae (Chlorella sp. HS-2) when filtration was done with the membrane used as a cathode: micro-sized bubbles, generated from the cathodic membrane, functioned to detach the foulants and recover the relative flux to a significant level. The P-SUS membrane indeed possesses necessary traits that the polymer-support membrane lacks, in terms of not only electrical conductivity and mechanical strength but also filtration performance with anti-fouling capability, all of which are of necessity to be considered workable electroconductive membrane.

Dielectrophoresis-Based Universal Membrane Antifouling Strategy toward Colloidal Foulants

Membrane fouling compromises the benefits of membrane technology, leading to its performance deterioration and incremental cost. Coupling with an electric field has been attractive but is limited by the electrical dependence of the electrophoresis (EP) mechanism and undesired faradic reactions. This study reports a universal dielectrophoresis-based (DEP) membrane antifouling strategy for electronegative, electropositive, and neutral colloidal foulants, which depends on the particle polarizability rather than its charge. The porous Ni@PVDF model electroconductive membrane was fabricated to construct a nonuniform electric field inducing DEP, while applying a low voltage avoided side electrochemical reactions. For electronegative SiO2(-) and electropositive Al2O3(+) particles with a lower relative permittivity than the medium water (78), the membrane permeability all remarkably increased by 90.1% under AC/DC (±1.0 V) fields. By contrast, serious membrane fouling occurred for the BaTiO3 colloids with a higher relative permittivity (∼2000). Notably, the permittivity of nearly all colloids in wastewater treatment is much less than that of water, which makes the dielectrophoresis-based antifouling strategy universal. The theoretical simulation systematically analyzed the forces on particles including DEP, EP, and others, indicating that the formed protected area on the membrane pore wall by DEP forces prevented the irreversible membrane blockage of colloids and facilitated loose cake layer formation for alleviating membrane fouling. In brief, this work reported a hopeful concept for dielectrophoresis-based membrane antifouling and verified its antifouling mechanism.

Prospects for the Use of Electrooxidation and Electrocoagulation Techniques for Membrane Filtration of Irrigation Water

The problem of water insufficiency within the agriculture sector creates the need to create new strategies to optimize the use of this resource to the maximum. The purpose of this study was to evaluate if the use of membrane technology and the application of electrochemical techniques can be a viable strategy to create a system to achieve the continuous reuse of irrigation water in closed agricultural production systems. From an extensive review carried out, it was determined that the conventional treatment methods used in closed agricultural systems have considerable limitations since they cannot produce high purity water, which is a mandatory requirement for such systems. Because of this, membrane technology was selected as the basis for our proposal in this study, since it is widely used to generate potable water and to treat wastewater. Membrane fouling by natural organic matter (NOM) was identified as the main limitation of this technology. On this basis, the most effective technologies to solve this problem were sought and evaluated. The application of electrochemical techniques like electrooxidation, electrocoagulation, and the use of electroconductive membranes modified by nanomaterials, were found to be the most feasible means. From the analysis of the mechanisms of action of these technologies, we deduce that the application of electrocoagulation techniques adapted to electroconductive membranes which can carry out electrooxidation processes, could achieve a significant decrease in NOM. This would reduce the fouling problem considerably, optimizing irrigation water treatment systems to allow the reuse of water.

Graphene-based electro-conductive anti-fouling membranes for the treatment of oil sands produced water

In this study, a thin layer of polyaniline (PANI)-reduced graphene oxide (rGO) was laminated on polyethersulfone (PES) support by pressure-assisted technique. Organic fouling on the resulting robust and electro-conductive membranes reduced significantly by applying an external electric field. The electrical conductivity of pristine PANI film was 0.46 S/m while it was increased up to 84.53 S/m by adding appropriate amount of rGO. Both anodic and cathodic potentials in a wide range were applied to the prepared membranes using synthetic sodium alginate and real oil sands boiler feed water (BFW) waste of Alberta, Canada. Filtration tests showed that fouling resistance of electro-oxidative membranes towards sodium alginate improved, and 31.9% flux decline recovered when 2 V anodic cell potential was applied. By increasing the applied voltage from 3 V to 9 V, the antifouling property of membrane, as well as flux recovery ratio (FRR), improved dramatically and reached to 97.47% in the anodic setting. Such a significant improvement was attributed to electrostatic repulsive force between foulant and membrane surface, massive gas bubble generation, and electro-oxidation reactions. The cathodic electro-reduction configuration was also tested for BFW, where water flux decline and rejection performance were both improved by elevating electric potential.

Antifouling electrically conductive membrane for forward osmosis prepared by polyaniline/graphene nanocomposite

Forward Osmosis (FO) has been listed as one of the best strategies to combat growing worldwide water scarcity. Not only FO, but all membrane-based technologies are still suffering from unpleasant fouling propensity, hindering their continuous performance in a long-term application. Using polyaniline (PANI) and graphene, herein, we fabricated a novel electro-conductive membrane (graphene/PANI laminated membrane, GPANILM) through laminating by facile pressure-assisted technique onto polyamide-imide (PAI) support layer. To improve the mechanical stability of the fabricated film via crosslinking of PANI with graphene nanosheetsthe membrane was thermal treated in 140 °C for 3 h (GPANILM-140). Both nanocomposite membranes (GPANILM and GPANILM-140) demonstrated excellent mechanical stability and their performances in terms of water permeation (JW) and reverse salt flux (Js) were verified using a regular FO desalination system. Our results showed that the selectivity ratios (Js/Jw) of GPANILM and GPANILM-140 membranes are 0.79 and 0.69 g/L in FO mode (top active layer of nanocomposite was facing to feed solution (FS)) and 0.67 and 0.58 g/L in PRO mode (PAI support layer was facing to FS), respectively. The anti-fouling behaviors of the electro-conductive membranes were investigated by a FS containing alginate as a model organic foulant. By applying 2 V anodic potential, both flux recovery rate (FRR) and fouling resistance were substantially improved in both membranes.

A novel method for the fabrication of silver nanowires-based highly electro-conductive membrane with antifouling property for efficient microalgae harvesting

In this study, a new method of fabricating highly electro-conductive membranes, namely electroplating, was developed and its product performance was examined via microalgae harvesting. In this method, a layer of silver nanowires (AgNWs) was first vacuum-deposited on a poly(ether sulfone) support, followed by electroplating of silver layer. The electroplated membrane (C-AgNWs) found to exhibit surpassingly enhanced electrical conductivity (3.9 × 104 S/cm) and a satisfactory level of mechanical stability under prolonged filtration. When microalgae, Chlorella sp. HS-2, was harvested via electro-filtration, the membrane exhibited the intended effect of fouling mitigation, both in continuous and intermittent electric fields. This was attributed to the enhanced electrostatic repulsive forces between foulants and membrane along with in-situ electro-bubble generation from the membrane, reducing the overall blockage of the membrane surface. The intermittent mode was able to effectively mitigate fouling and recover flux to its initial level, with the effect compromised in successive steps. The continuous mode, however, did not display such performance degradation over time, but an increase of 480% in permeate flux at 20 V/mm. All this supported that the electroplating can serve as a promising route for the sake of fabricating the workable electro-membranes, conductive membranes that have boundless application potentials.

Electro-Conductive Membranes for Permeation Enhancement and Fouling Mitigation: A Short Review.

The research on electro-conductive membranes has expanded in recent years. These membranes have strong prospective as key components in next generation water treatment plants because they are engineered in order to enhance their performance in terms of separation, flux, fouling potential, and permselectivity. The present review summarizes recent developments in the preparation of electro-conductive membranes and the mechanisms of their response to external electric voltages in order to obtain an improvement in permeation and mitigation in the fouling growth. In particular, this paper deals with the properties of electro-conductive polymers and the preparation of electro-conductive polymer membranes with a focus on responsive membranes based on polyaniline, polypyrrole and carbon nanotubes. Then, some examples of electro-conductive membranes for permeation enhancement and fouling mitigation by electrostatic repulsion, hydrogen peroxide generation and electrochemical oxidation will be presented.

Formation of nanoparticle added functional polymer network membrane via micro-phase separation process

Electro-conductive membranes formed by carbon nanoparticle network array were fabricated via micro-phase separation process in the polymer system of cellulose acetate/acetone/water ternary solution. Micro-phase separation technique is the most common method for preparation and production of polymeric membrane. With the formation of polymer network, added nanoparticles became network by the drive of non-solvent owing to thermodynamic and compatible properties between particles and ternary solution. Meanwhile, the nanoparticle surface properties affected the binding force of neighbor particles for the continuous nanoparticle network structure. Heat treatment on the membrane aims at removing polymer from. Thus, electro-conductive nanoparticle network membrane can be facilely prepared.

A simple and highly stable free-flow electrophoresis device with thermoelectric cooling system

Complex assembly, inconvenient operations, poor control of Joule heating and leakage of solution are still fundamental issues greatly hindering application of free-flow electrophoresis (FFE) for preparative purpose in bio-separation. To address these issues, a novel FFE device was developed based on our previous work. Firstly, a new mechanical structure was designed for compact assembly of separation chamber, fast removal of air bubble, and good anti-leakage performance. Secondly, a highly efficient thermoelectric cooling system was used for dispersing Joule heating for the first time. The systemic experiments revealed the three merits: (i) 3min assembly without any liquid leakage, 80 times faster than pervious FFE device designed by us or commercial device (4h); (ii) 5s removing of air bubble in chamber, 1000-fold faster than a normal one (2h or more) and (iii) good control of Joule heating by the cooling system. These merits endowed the device high stable thermo- and hydro-dynamic flow for long-term separation even under high electric field of 63V/cm. Finally, the developed device was used for up to 8h continuous separation of 5mg/mL fuchsin acid and purification of three model proteins of phycocyanin, myoglobin and cytochrome C, demonstrating the applicability of FFE. The developed FFE device has evident significance to the studies on stem cell, cell or organelle proteomics, and protein complex as well as micro- or nano-particles.

Synthesis of an electroconductive membrane using poly(hydroxymethyl-3,4-ethylenedioxythiophene-co-tetramethylene-N-hydroxyethyl adipamide)

Synthesis of a novel electroconductive membrane (ECM) was studied with the aim of producing an electroconductive membrane (ECM) with low electrical resistance and appropriate mechanical properties. The method was based on copolymerization of a highly electroconductive monomer (hydroxymethyl-3,4-ethylenedioxythiophene) with highly mechanical resistant hydrophilized polyamide 46 (polytetramethylene-N-hydroxyethyl adipamide). Due to the lack of hydroxyl groups, polyamide 46 does not have the tendency to take part in any chemical reactions, therefore prior to copolymerization, PA 46 was hydrophilized with acetaldehyde to create reactive sites, which allowed copolymerization to occur. At the final stage, a very thin layer, 566 nm conductive poly(hydroxymethyl-3,4-ethylenedioxythiophene) homopolymer was localised using in situ plasma polymerization in order to improve the electrical conductivity of the obtained copolymer. The result was an adherent, highly conductive, semi-hydrophilic and flexible ECM. The presence of hydroxyl groups in the final product led to improved hydrophilicity of the conductive membrane with a surface tension of 41 mJ m−2. The electrical resistance of PA 46 was dramatically reduced after copolymerization, to 202 in dry and 54 kΩ cm−2 in wet conditions; furthermore, after plasma treatment, this reduction continued to 105 in dry and 2 kΩ cm−2 in wet conditions. Other parameters such as flux flow, roughness, pore size, pore distribution, contact angle, surface energy and thermal stability of the ECM were also investigated.

Improvement of Porous Electro-conductive Membrane Preparation and Its Application in Sample Injection Pre-concentration in the Capillary Electrophoresis of Proteins

The success rate of porous conductive joint preparation on fused silica capillary was greatly improved by voltage bias control and electroosmosis effect. The column was filled with basic media and a dc voltage was applied between the capillary inlet and the etching reservoir during the etching. The etching was automatically stopped owing to electroosmosis effect when electro-conductivity of the joint occurred, and over etching was thus avoided. The joint was successfully used in on-line electro injection pre-concentration and capillary electrophoresis separation of a model protein mixture of lysozyme and bovine serum albumin in 0.05 M pH 2.50 Tris-H 3PO 4 with 2%-4% dextran, and a concentration factor up to 300 was obtained as estimated by the peak height. The difference of concentration factor for basic and acidic proteins is discussed. The detection limit for the model proteins was decreased to 10 −11 M with a routinely used UV photometric detector (214 nm) by electro-injection pre-concentration for 30 min.

Effects of co-ions on transport of iodide ions through a non-conventional anion exchange paper membrane

To study the effects of co-ions on iodide ion transport through a novel anion exchange paper membrane containing trimethylhydroxypropylammonium groups with approximately 0.30 meq. g −1 dry-membrane ion exchange capacity, transmembrane potential, membrane conductance and ionic fluxes were measured in the concentration-cell system for seven kinds of iodine salts (1:1-electrolytes) at 10 −3 to 10 −1 mol dm −3. For analysis of ion transport, the electroconductive membrane permeability, representing the solution/membrane ion distribution due to electrostatic effects, and the diffusional membrane permeability, representing the migration speed of ions within the membrane phase, concerning ion pair diffusion, and increasing with co-ion penetration and diffusion, were introduced in terms of linear phenomenological equations. Electroconductive membrane permeabilities of iodide ions were found to increase linearly with increasing hydrated co-ion radii; r 2=0.855, while diffusional membrane permeabilities of iodide ions increased linearly with increasing crystal co-ion radii; r 2=0.899. These results for a paper membrane differ from those of synthetic amphoteric membrane and nanoporus membranes in which ions of both charges penetrate equally, in which membrane permeabilities decreased with increasing co-ion radii. This suggests that iodide ion transport may be partially controlled by co-ion transport dependent on surface cationic charge density rather than ion radii in the anion exchange paper membrane, as the pores are large enough for ions to freely permeate within membrane matrix.

Removal of sodium ion from bile acid solution using diffusional dialysis with cation exchange membrane

The behavior of sodium ions passing through a CM1 cation exchange membrane was studied with electroconductive and diffusional membrane permeabilities based on nonequilibrium thermodynamics to remove sodium ion from bile acid solution. These membrane permeabilities of sodium ion in order of amplitude showed sodium chloride>sodiumtaurocholate>sodium cholate systems in all cases. In the sodium cholate and sodium taurocholate systems, the curves relating the electroconductive membrane permeability with concentration showed distinct changes in gradient at around the concentration of primary micelle formation of each bile acid solution. This was attributable to an increase in membrane/solution distribution of bile acid anion on basis of the micelle formation. Using diffusional dialysis, 7.3% of sodium ion was removed from rat serum. Sodium ion was significantly reduced with increasing total bile acid concentration in rat serum (P<0.05; correlation coefficient=−0.606).

Radioactive iodine and chloride transport across a paper membrane bearing trimethylhydroxypropylammonium anion exchange groups

The separation performance of radioactive iodine from radioactive waste is examined using the paper membrane made of long length pulp fiber bearing trimethylhydroxypropylammonium anion exchange group. Prepared paper membrane is sturdy and high of ion-exchange capacity as the introduction of ion exchange group into the paper membrane with high density and well-bonding between pulp fibers are achieved. Ion transport across the paper membrane is evaluated with electroconductive membrane permeability derived from transmembrane potential and membrane conductance data, and diffusional membrane permeability derived from transmembrane potential and ionic flux in Na 125 I or Na 36 Cl single electrolyte concentration-cell system. The ratio of electroconductive membrane permeability of 125 I to that of 36 Cl reaches 6.2, while the ratio of diffusional membrane permeability of 125 I to that of 36 Cl is almost unity. The novel prepared paper membrane exhibits the 125 I permselectivity by solution/membrane distribution process due to electrostatic effect.