Self-assembly of inner skin hollow fiber polyelectrolyte multilayer membranes by a dynamic negative pressure layer-by-layer technique

Efficient Pervaporation for Ethanol Dehydration: Ultrasonic Spraying Preparation of Polyvinyl Alcohol (PVA)/Ti3C2Tx Nanosheet Mixed Matrix Membranes

Polyvinyl alcohol (PVA) pervaporation (PV) membranes have been extensively studied in the field of ethanol dehydration. The incorporation of two-dimensional (2D) nanomaterials into the PVA matrix can greatly improve the hydrophilicity of the PVA polymer matrix, thereby enhancing its PV performance. In this work, self-made MXene (Ti₃C₂T_x-based) nanosheets were dispersed in the PVA polymer matrix, and the composite membranes were fabricated by homemade ultrasonic spraying equipment with poly(tetrafluoroethylene) (PTFE) electrospun nanofibrous membrane as support. Due to the gentle coating of ultrasonic spraying and following continuous steps of drying and thermal crosslinking, a thin (~1.5 μm), homogenous and defect-free PVA-based separation layer was fabricated on the PTFE support. The prepared rolls of the PVA composite membranes were investigated systematically. The PV performance of the membrane was significantly improved by increasing the solubility and diffusion rate of the membranes to the water molecules through the hydrophilic channels constructed by the MXene nanosheets in the membrane matrix. The water flux and separation factor of the PVA/MXene mixed matrix membrane (MMM) were dramatically increased to 1.21 kg·m^-2·h^-1 and 1126.8, respectively. With high mechanical strength and structural stability, the prepared PGM-0 membrane suffered 300 h of the PV test without any performance degradation. Considering the promising results, it is likely that the membrane would improve the efficiency of the PV process and reduce energy consumption in the ethanol dehydration.

Modification of Polysulfone Ultrafiltration Membranes via Addition of Anionic Polyelectrolyte Based on Acrylamide and Sodium Acrylate to the Coagulation Bath to Improve Antifouling Performance in Water Treatment

Surface modification of polysulfone ultrafiltration membranes was performed via addition of an anionic polymer flocculant based on acrylamide and sodium acrylate (PASA) to the coagulation bath upon membrane preparation by non-solvent induced phase separation (NIPS). The effect of PASA concentration in the coagulant at different coagulation bath temperatures on membrane formation time, membrane structure, surface roughness, hydrophilic-hydrophobic balance of the skin layer, surface charge, as well as separation and antifouling performance was studied. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, contact angle and zeta potential measurements were utilized for membrane characterization. Membrane barrier and antifouling properties were evaluated in ultrafiltration of model solutions containing human serum albumin and humic acids as well as with real surface water. PASA addition was found to affect the kinetics of phase separation leading to delayed demixing mechanism of phase separation due to the substantial increase of coagulant viscosity, which is proved by a large increase of membrane formation time. Denser and thicker skin layer is formed and formation of macrovoids in membrane matrix is suppressed. FTIR analysis confirms the immobilization of PASA macromolecules into the membrane skin layer, which yields improvement of hydrophilicity and change of zeta potential. Modified membrane demonstrated better separation and antifouling performance in the ultrafiltration of humic acid solution and surface water compared to the reference membrane.

Pre-deposited dynamic membrane filtration - A review

A dynamic membrane (DM) is a layer of particles deposited via permeation drag onto a conventional membrane, such that the deposited particles act as a secondary membrane that minimizes fouling of the primary membrane to lower transmembrane pressures (TMP) and enable higher permeate fluxes. Since the first DM was created in 1966 at the Oak Ridge National Laboratory, numerous studies have reported synthesis of DMs using various materials and explored their abilities to perform reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF). DMs are classified into two categories, namely, (i) self-formed, whereby the feed constituents form the DM; and (ii) pre-deposited, whereby the DM is formed by a layer of particles other than the feed prior to introduction of the feed. This paper endeavors to present a comprehensive review of the state-of-the-art on the latter. Key materials used as DMs, their formation and various factors influencing it, regeneration of DMs and modifications to DM systems for performance enhancement are discussed. The role of DMs in preventing fouling in the primary membrane (PM) is explained. The applications of DMs in four major areas, namely, salt and organic solute rejection, treatment of industrial effluents, treatment of water and wastewater, and oily-wastewater treatment are reviewed. Furthermore, technical and economic advantages of DMs over conventional processes are considered, and challenges in current DM research are discussed. Finally, directions for future research are suggested.

Effects of different plasticizers on highly crosslinked NaAlg/PSSAMA membranes for pervaporative dehydration of tert-butanol

Polystyrene sulfonic acid-co-maleic acid (PSSAMA) crosslinked sodium alginate (NaAlg) membranes were developed by incorporating diethyl phthalate (DEP), dibutyl phthalate (DBP) and dioctyl phthalate (DOP).

Membranes for dehydration of alcohols via pervaporation

Alcohols are the essential chemicals used in a variety of pharmaceutical and chemical industries. The extreme purity of alcohols in many of such industrial applications is essential. Though distillation is one of the methods used conventionally to purify alcohols, the method consumes more energy and requires carcinogenic entertainers, making the process environmentally toxic. Alternatively, efforts have been made to focus research efforts on alcohol dehydration by the pervaporation (PV) separation technique using polymeric membranes. The present review is focused on alcohol dehydration using PV separation technique, which is the most efficient and benign method of purifying alcohols that are required in fine chemicals synthesis and developing pharmaceutical formulations. This review will discuss about the latest developments in the area of PV technique used in alcohol dehydration using a variety of novel membranes.

Covalent organic framework membranes through a mixed-dimensional assembly for molecular separations

Covalent organic frameworks (COFs) hold great promise in molecular separations owing to their robust, ordered and tunable porous network structures. Currently, the pore size of COFs is usually much larger than most small molecules. Meanwhile, the weak interlamellar interaction between COF nanosheets impedes the preparation of defect-free membranes. Herein, we report a series of COF membranes through a mixed-dimensional assembly of 2D COF nanosheets and 1D cellulose nanofibers (CNFs). The pore size of 0.45-1.0 nm is acquired from the sheltering effect of CNFs, rendering membranes precise molecular sieving ability, besides the multiple interactions between COFs and CNFs elevate membrane stability. Accordingly, the membranes exhibit a flux of 8.53 kg m-2 h-1 with a separation factor of 3876 for n-butanol dehydration, and high permeance of 42.8 L m-2 h-1 bar-1 with a rejection of 96.8% for Na2SO4 removal. Our mixed-dimensional design may inspire the fabrication and application of COF membranes.

Top-Down Strategy of Implantable Biosensor Using Adaptable, Porous Hollow Fibrous Membrane

Fabrication of an outer membrane is crucial for an implantable biosensor to enhance the long-term stability and accuracy of sensors. Herein, an adaptable, controllable, porous outer membrane for an implantable biosensor was fabricated using a "top-down" method, allowing maximum retention of enzyme activity and fine control over membrane microstructure. Polysulfone hollow fibrous membranes with different pore sizes and porosities were used as a base membrane. Chitosan (CH) and sodium alginate (SA) were self-assembled on the inner surface of PSfHM to construct a biocompatible and conductive interface between PSfHM and the electrode. In vitro and in vivo experiments were used to evaluate the performance of implantable glucose biosensors with PSfHM and CH/SA modified PSfHM (PSfHM-CH/SA). The glucose biosensor with PSfHM-CH/SA exhibited a more stable output current than bare sensors and a quick response time (<50 s). The glucose biosensor with PSfHM-CH/SA linear sensing range was between 0 and 22 mM ( R² = 0.9905), and relative sensitivity remained at >87% within 7 days and >76% within 15 days. Furthermore, response currents recorded by implanted sensors closely followed the blood glucose trend from the tail vein blood during in vivo experiments.

Rapid spray-crosslinked assembly of a stable high-performance polyelectrolyte bipolar membrane

Rapid spray assembly coupled with chemical cross linking was used to prepare a stable high-performance polyelectrolyte bipolar membrane.

Constructing a novel zwitterionic surface of PVDF membrane through the assembled chitosan and sodium alginate

A novel zwitterionic surface of PVDF membrane with significantly improved antifouling properties was prepared though pressure-assisted layer by layer self-assembly method based on the electrostatic interactions of chitosan (CS), sodium alginate (SA) and polyfunctional lysine. For the modified C-S-C-S-L membrane, the contact angle decreased to 35°, the bovine serum albumin (BSA) adsorption mass of static fouling on the membrane surface decreased to 10μg/cm(2), and the secondary water flux recovery rate (FRR) of dynamic fouling of BSA and humic acid (HA) pollutants increased to 98% and 99%, respectively, exhibiting excellent antifouling performance. The results demonstrated that using charged bio-macromolecules and amino acids to build zwitterionic surface was effective and convenient to change the interface properties of the separation membrane through the pressure-assisted self-assembly modification method, and provided a new way for the industrial scale hydrophilic modification of hydrophobic porous membrane materials.

Development of thin-film composite forward osmosis hollow fiber membranes using direct sulfonated polyphenylenesulfone (sPPSU) as membrane substrates

This study investigates a new approach to fabricate thin-film composite (TFC) hollow fiber membranes via interfacial polymerization for forward osmosis (FO) applications. Different degrees of sulfonation of polyphenylenesulfone (PPSU) were adopted as membrane substrates to investigate their impact on water flux. It has been established that the degree of sulfonation plays a role in both creating a macrovoid-free structure and inducing hydrophilicity to bring about higher water fluxes. The fabricated membranes exhibit extremely high water fluxes of 30.6 and 82.0 LMH against a pure water feed using 2.0 M NaCl as the draw solution tested under FO and pressure retarded osmosis (PRO) modes, respectively, while maintaining low salt reverse fluxes below 12.7 gMH. The structural parameter (S) displays remarkable decreases of up to 4.5 times as the membrane substrate is switched from a nonsulfonated to sulfonated one. In addition, the newly developed TFC-FO membranes containing 1.5 mol % sPPSU in the substrate achieves a water flux of 22 LMH in seawater desalination using a 3.5 wt % NaCl model solution and 2.0 M NaCl as the draw solution under the PRO mode. To the best of our knowledge, this value is the highest ever reported for seawater desalination using flat and hollow fiber FO membranes. The use of sulfonated materials in the FO process opens up a frontier for sustainable and efficient production of potable water.

Construction of metal-ligand-coordinated multilayers and their selective separation behavior

In this article, a layer-by-layer (LbL)-assembled coordination multilayer on planar and 3D substrates was explored by the alternate deposition of a transition-metal-containing polyelectrolyte and a ligand-containing polymer via the formation of complexes. The metal-ligand coordination between the building blocks of Co(2+)-exchanged poly(styrene sulfonate) (PSS) and poly(4-vinyl pyridine) (P4 VP) has been demonstrated using UV-vis, FTIR, and XPS. The film thickness, structure, and morphology as well as the wettability as a function of bilayer number have been systematically investigated by profilometry, SEM, AFM, and contact angle analyzers. For the purpose of separation applications, the metal-ligand-coordinated multilayer was assembled on both flat sheet and hollow fiber polymeric porous substrates using a dynamic pressure-driven LbL technique. It was demonstrated that the LbL-assembled PSS(Co)(1/2)/P4 VP multilayer membrane had high dehydration performance with respect to different solvent-water mixtures; it also had aromatic compound permselectivity from aromatic-aliphatic hydrocarbons and water-softening capacity. Meanwhile, the successful assembly of multilayers on hollow fibers indicates that the dynamic pressure-driven LbL technique is a unique approach to the construction of multilayers on porous 3-D substrates. Therefore, the metal-ligand-coordinated self-assembly could emerge as a powerful technique for the preparation of a range of separation membranes in different types of modules.