Conductive and stable polyphenylene/CNT composite membrane for electrically enhanced membrane fouling mitigation

Investigating the effect of various foulants on the performance of intrinsically superhydrophobic polyvinylidene fluoride membranes for direct contact membrane distillation

Superhydrophobic dual layer functionalized titanium dioxide/polyvinylidene fluoride-co-hexafluoropropylene (TiO2/PH) nanofibrous membrane for high flux membrane distillation

Superhydrophobic nanofiber membrane containing carbon nanotubes for high-performance direct contact membrane distillation

Understanding fouling dynamics on functionalized CNT-based membranes: Mechanisms and reversibility

The demand to fabricate membranes much cheaper than usual expensive methods creates an opportunity to find low‐cost and more available modifying agents for synthesising an appropriate membrane for membrane distillation (MD) process. In this work, reactive ethylene terpolymer was applied to modify a commercial polyvinylidene fluoride (PVDF) membrane for using in the desalination process. Elvaloy4170 with a hydrophobic structure containing three different functional groups was coated (different contents of 0.5, 1, 1.5 and 2 wt%) on the top surface of the microporous commercial PVDF membrane and the resultant membranes were analysed under air‐gap MD process. The fabricated membrane structures were determined by scanning electron microscopy and atomic force microscopy to investigate their elemental and topographical properties. After experiments, the membrane with 1.5 wt% of Elvaloy4170 showed water vapour flux of 1.93 kg/m2 h and salt rejection of >99.7 which confirmed its suitability to be used in the desalination process. Moreover, to assess the anti‐fouling properties of the membranes, real seawater was used as feed solution, and as a result the membrane with 1.5 wt% of Elvaloy4170 presented flux recovery of 87% indicating its enhanced anti‐fouling properties compared with the commercial PVDF membrane (flux recovery of 71%).

Polyvinylidene fluoride (PVDF) membranes are widely used in membrane industry, especially for membrane bioreactors (MBRs). Many PVDF membranes contain residual polyvinyl pyrrolidone (PVP) that acts as a pore-forming additive. The presence of residual PVP in some commercial PVDF membranes is often not specified and, therefore, its impact is mostly overlooked in the literature. In this study, we investigated the effect of PVP leaching on membrane structure and its implication on membrane fouling in a lab-scale MBR. PVP leaching can occur in two ways: (1) over the course of filtration from PVDF/PVP blend membranes or (2) prior filtration operation by treating the aforementioned membrane. We prepared PVDF, PVDF/PVP blend, and PVDF/PVP blend post-treated with sodium hypochlorite (NaClO), then assessed their performance. Leaching of PVP prior to the filtration operation significantly enlarged membrane pore size and thus reduced the membrane resistance. However, this advantage was dismissed during operation in MBR because PVP leaching also induced surface hydrophobicity that promoted membrane fouling, suggesting the detrimental effect of post-treatment. For PVDF/PVP blend sample, two counter-acting phenomena occurred: (1) slow leaching of PVP which gradually enlarged the membrane pores and rendered the membrane surface more hydrophobic and (2) adsorption of foulants that formed a secondary layer atop of membrane surface, restricted the pore mouth, and rendered the surface hydrophilic. The findings are significant since the change of membrane morphology over the course of filtration, as demonstrated in this study, is often overlooked when assessing membrane performance.

A new class of valves for membranes is based on the formation of nanobubbles at the pore entrances of carbon nanotube (CNT) membranes. Nanobubble stabilization is achieved by electrochemically etching CNTs into a polymer matrix to form a well that can be reversibly filled. Such valves have applications in flow battery systems where high-energy chemicals can be stored indefinitely. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Application and characterization of electroactive membranes based on carbon nanotubes and zerovalent iron nanoparticles

Electrospun nanofibrous membranes (ENM) which have a porous structure have a huge potential for various liquid filtration applications. In this paper, we explore the viability of using plasma-induced graft copolymerization to reduce the pore sizes of ENMs. Poly(vinylidene) fluoride (PVDF) was electrospun to produce a nonwoven membrane, comprised of nanofibers with diameters in the range of 200-600 nm. The surface of the ENM was exposed to argon plasma and subsequently graft-copolymerized with methacrylic acid. The effect of plasma exposure time on grafting was studied for both the ENM and a commercial hydrophobic PVDF (HVHP) membrane. The grafting density was quantitatively measured with toluidine blue-O. The degree of grafting increased steeply with an increase in plasma exposure time for the ENM, attaining a maximum of 180 nmol/mg after 120 s of plasma treatment. However, the increase in the grafting density on the surface of the HVHP membrane was not as drastic, reaching a plateau of 65 nmol/mg after 60 s. The liquid entry permeation of water dropped extensively for both membranes, indicating a change in surface properties. Field emission scanning electron microscopy micrographs revealed an alteration in the surface pore structure for both membranes after grafting. Bubble point measurements of the ENM reduced from 3.6 to 0.9 um after grafting. The pore-size distribution obtained using the capillary flow porometer for the grafted ENM revealed that it had a similar profile to that of a commercial hydrophilic commercial PVDF (HVLP) membrane. More significantly, water filtration studies revealed that the grafted ENM had a better flux throughput than the HVLP membrane. This suggests that ENMs can be successfully engineered through surface modification to achieve smaller pores while retaining their high flux performance.

ABSTRACTA NEMD simulation system is constructed to simulate at two-dimensional (2D) periodic boundary conditions (PBCs) and to create two different pressures on two sides of the carbon nanotube (CNT) membrane. The simulation results show that water permeation through the same CNT membrane driven by different pressure differences exhibit similar transport phenomenon including unusually fast water permeation and a periodic (non-parabolic) radial velocity distribution unlike the parabolic form characteristic of continuum flow in the CNT membrane. A three-dimensional (3D) PBC system is also constructed to simulate water permeation through the same CNT membrane at the same pressure differences, to show the effect of PBC and simulation methodologies on transport phenomenon. The two systems both show that the forward/backward water flux increases/decreases with increasing the pressure difference from 1.0 MPa to 8.0 MPa. However, the net flux is higher for the 3D PBC system, especially at higher pressure difference is high. In general, the NEMD simulation method using the 2D PBC system is shown to be a feasible and valuable tool for studying pressure-driven permeation processes such as nanofiltration through these studies with model CNT membrane.

We report the lowest autofluorescent nanoporous polyvinylidene fluoride (PVDF) membranes exhibit near infra‐red (NIR) emission properties for western blot detection of high and low molecular weight proteins. The design involves post modification of PVDF membranes by an alkali treatment that reduces the native of PVDF at 450–520 nm. The background fluorescence of these modified membranes is eight times lower than the commercial available PVDF membranes and displayed NIR emission at 750 nm. Imparted alkene conjugated double bonds in the polymeric backbone by alkali treatment causes the NIR emission in the modified PVDF membranes and this translates improvement in detection of, in particular, high molecular weight proteins (130 kDa) compared to traditional western blot. To validate the pore size effect, two different pores sized (∼100 nm and ∼0.8 μm) PVDF membranes were prepared, surface modified and subjected for protein profiling. High linearity was achieved in detection of high molecular weight proteins and significant protein binding was noticed for the alkali treated membranes of ∼∼100 nm size. The methodology permits the design of modified PVDF membranes with lesser pore size could be an alternative for existing membranes with minimal autofluorescence for efficient and quick detection of high molecular weight proteins.

Modification of PVDF hydrophobic microfiltration membrane with a layer of electrospun fibers of PVP-co-PMMA: Increased fouling resistance

Hierarchically-structured superhydrophobic POSS/PVDF composite membrane for anti-fouling and anti-wetting membrane distillation

Objectives The reversible electrical modulation of chemical delivery is crucial for various biomedical engineering applications, enabling a tailored drug delivery profile. Electroosmosis flow (EOF) represents a significant electrokinetic phenomenon where a bulk flow is induced through narrow channels including capillaries or microfluidic devices or porous medium, under the influence of an applied electric field (Fig. 1a). Since the velocity of EOF is directly proportional to the applied current density ( I ) and the EOF strength ( K eo ), a standardized indicator related to the zeta potential of the channel walls, it provides the possibility of controlling the direction and velocity of EOF by simply adjusting the surface zeta potential.[1] Herein, a novel concept of electrically modulated delivery utilizing EOF generated within the porous network of the carbon nanotube (CNT) membrane is reported. The charge sign and magnitude of the micropores inside the CNT membrane are altered by applying varying voltages, leading to corresponding changes in the direction and velocity of the EOF. Results and Discussion The multi-walled carbon nanotubes powered are first treated with ozone and dispersed in ethanol. Then, the suspension is formed into the random alignment and cohesive CNT membrane by vacuum-assisted filtration (Fig. 1b-c). The experimental setup consists of symmetrically positioned reservoirs at both ends and a CNT membrane placed between the two reservoirs filled with 0.1 M KCl solution. The electrically modulated system is comprised of two circuits: the main circuit that generates an axial electric field to drive the EOF and the sub-circuit that varies the sign and magnitude of charges on the CNT membrane. The controllability of the EOF direction and velocity is evaluated by observing the movement of the liquid column in the reservoirs (Fig. 1d -e). Based on the established experimental setup, the voltage at which EOF is unobserved is referred to as the neutral voltage (or bias voltage) and is used as the reference for electrical modulation. Significant differences in the direction and velocity of EOF can be observed and measured on the CNT membrane when a positive (or negative) voltage relative to the bias voltage is applied. The EOF under the main circuit of + 0.25 mA and the sub-circuit voltage of + 0.5 V and - 0.5 V relative to the bias voltage, indicating a mobility rate of - 0.781 μL/mm2·min and + 0.972 μL/mm2·min, respectively (Fig. 1f). The plus and minus means that opposite directions of EOF are generated with applied voltages. Next, to demonstrate the effect of applied voltages on the EOF rate, the sub-circuit voltage of + 0.5 V and + 0.25 V relative to the neutral voltage was applied (with the same main circuit of + 0.25 mA), generating a mobility rate of - 0.781 μL/mm2·min and - 0.431 μL/mm2·min. The difference in velocity is due to the differential surface zeta potential within the microchannels of the CNT membrane. Conclusion Here, this study introduces a novel concept of a chemical delivery system by focusing on the electrically modulated EOFs generated in the microchannels of the CNT membrane. According to the results of the experiments, it can be demonstrated that altering the direction and velocity of EOF through electrical modulation is achievable. Additionally, the electrical modulation on EOF is feasible under varying axial electric field strengths and concentration solution environments. Reference [1] Kusama, S., Sato, K., Matsui, Y., Kimura, N., Abe, H., Yoshida, S., & Nishizawa, M. (2021). Transdermal electroosmotic flow generated by a porous microneedle array patch. Nature communications , 12 (1), 658. Fig. 1 Experimental setup and electrical modulation performance. (a) The mechanism of EOF. (b) Optical and SEM images of CNT membrane. (c) Schematic illustration of EOF generated in the micropores of CNT membrane. (d) An experimental setup consisting of Franz Cells with insertion of CNT membrane and the EOF direction and velocity were analyzed by observing the liquid movement. (e) Electrical modulation. (f) The relationship between the applied voltages (relative to the neutral voltage) and flow rates. Figure 1

Nonequilibrium molecular dynamics (NEMD) simulations are presented to investigate the effect of water-membrane interactions on the transport properties of pressure-driven water flow passing through carbon nanotube (CNT) membranes. The CNT membrane is modified with different physical properties to alter the van der Waals interactions or the electrostatic interactions between water molecules and the CNT membranes. The unmodified and modified CNT membranes are models of simplified nanofiltration (NF) membranes at operating conditions consistent with real NF systems. All NEMD simulations are run with constant pressure difference (8.0 MPa) temperature (300 K), constant pore size (0.643 nm radius for CNT (12, 12)), and membrane thickness (6.0 nm). The water flow rate, density, and velocity (in flow direction) distributions are obtained by analyzing the NEMD simulation results to compare transport through the modified and unmodified CNT membranes. The pressure-driven water flow through CNT membranes is from 11 to 21 times faster than predicted by the Navier-Stokes equations. For water passing through the modified membrane with stronger van der Waals or electrostatic interactions, the fast flow is reduced giving lower flow rates and velocities. These investigations show the effect of water-CNT membrane interactions on water transport under NF operating conditions. This work can help provide and improve the understanding of how these membrane characteristics affect membrane performance for real NF processes.