Formation Of Composite Membranes Research Articles

Heat diffusion during thin-film composite membrane formation

Thin-film composite (TFC) membranes, the backbone of modern reverse osmosis and nanofiltration, combine the high separation performance of a thin selective layer with the robust mechanical support. Previous studies have shown that heat released during interfacial polymerization (IP) can have a significant impact on the physical and chemical structure of the selective layer. In this study, we develop a multilayer transient heat conduction model to analyze how the thermal properties of the materials used in TFC fabrication impact interfacial temperature, focusing on support-free (SFIP), conventional (CIP), and interlayer-modulated IP (IMIP). Using a combination of analytic solutions and computational models, we demonstrate that the thermal effusivities of fluid and material layers can have a significant effect on the temporal evolution of interfacial temperature during IP. In CIP, we show that the presence of a polymeric support adjacent to the reaction interface yields a 20% to 60% increase in interfacial temperature rise, lasting for ∼0.1s. Furthermore, we demonstrate that inorganic or metallic interlayers, which have high thermal effusivities, can lead to short-lived order-of-magnitude reductions in interfacial temperature rise. Finally, we provide analytical approximations for transient heat conduction through multilayered systems, enabling rapid evaluation of the thermal impact of novel membrane support and interlayer materials and structures on interfacial temperature during TFC fabrication. Quantifying how the thermal properties of solvents, support layers, and interlayers affect interfacial temperature during IP is critical for the rational design of new TFC membranes.

Композиционные мембраны для обессоливания воды

Methods of coatings forming on the surface of a poly(ethylene terephthalate) track-etched membrane by magnetron and electron-beam sputter deposition of polytetrafluoroethylene in vacuum are considered. It is established that the involve of these modification methods leads to the formation of composite membranes consisting of two layers, one of which is the original track-etched membrane, characterized by an average level of hydrophilicity. The second layer has a hydrophobic nature. The contact angle of wettability by water of this layer varies depending on its thickness and the modification method used. It is shown that deposition of coatings by magnetron sputtering of polytetrafluoroethylene leads to smoothing of structural inhomogeneities of the surface of the initial membrane. Deposition of coatings by electron-beam dispersion of polymer, on the contrary, causes an increase in surface roughness. The observed differences in the morphology of the composite membranes surface layer are related to the size of the deposited polymer nanostructures. Nanostructures formed on the surface of track-etched membranes, when polytetrafluoroethylene is dispersed under the action of electron beam, have greatly large sizes. A significant increase in roughness due to the increase in the size of nanostructures makes it possible to obtain coatings with high- and superhydrophobic properties. It is shown that composite membranes consisting of a hydrophilic base with a hydrophobic coating deposited on the surface provide higher separation selectivity during desalination of an aqueous solution of sodium chloride by membrane distillation compared with the initial poly(ethylene terephthalate) track-etched membrane. In addition, the performance of two-layer composite membranes in the process of membrane distillation due to low resistance to mass transfer is higher in comparison with a track-etched membrane made of polypropylene.

Photocatalytic degradation of pollutants by PbBiO2Cl/TiO2/CS membrane with UV–Vis light irradiation

The PbBiO2Cl/TiO2/CS composite membrane material was prepared by solvent thermal method and casting. The structure, morphology and optical properties of the PbBiO2Cl/TiO2/CS membranes were characterized by FTIR, XRD, XPS, SEM and DRS. It was shown that the PbBiO2Cl/TiO2/CS-2(PTC-2) exhibited excellent photodegradation with 97.4 % of tetracycline (TC) and 96.3 % of methyl orange (MO) in 120 min. The main reason for the favourable performance was the formation of composite membranes of PbBiO2Cl/TiO2/CS, which reduced electron-hole recombination and improved the improved light absorption properties. Meanwhile, it was found that light-generated free radicals (⋅O2–, ⋅OH and h+) play a key crucial role during photocatalysis. This study presents a simple strategy to construct photocatalyst membranes to activity enhancement for organic pollutants.

Fabrication of Cellulose Acetate-Based Proton Exchange Membrane with Sulfonated SiO2 and Plasticizers for Microbial Fuel Cell Applications.

Developing a hybrid composite polymer membrane with desired functional and intrinsic properties has gained significant consideration in the fabrication of proton exchange membranes for microbial fuel cell applications. Among the different polymers, a naturally derived cellulose biopolymer has excellent benefits over synthetic polymers derived from petrochemical byproducts. However, the inferior physicochemical, thermal, and mechanical properties of biopolymers limit their benefits. In this study, we developed a new hybrid polymer composite of a semi-synthetic cellulose acetate (CA) polymer derivate incorporated with inorganic silica (SiO2) nanoparticles, with or without a sulfonation (-SO3H) functional group (sSiO2). The excellent composite membrane formation was further improved by adding a plasticizer (glycerol (G)) and optimized by varying the SiO2 concentration in the polymer membrane matrix. The composite membrane's effectively improved physicochemical properties (water uptake, swelling ratio, proton conductivity, and ion exchange capacity) were identified because of the intramolecular bonding between the cellulose acetate, SiO2, and plasticizer. The proton (H+) transfer properties were exhibited in the composite membrane by incorporating sSiO2. The composite CAG-2% sSiO2 membrane exhibited a higher proton conductivity (6.4 mS/cm) than the pristine CA membrane. The homogeneous incorporation of SiO2 inorganic additives in the polymer matrix provided excellent mechanical properties. Due to the enhancement of the physicochemical, thermal, and mechanical properties, CAG-sSiO2 can effectively be considered an eco-friendly, low-cost, and efficient proton exchange membrane for enhancing MFC performance.

Tailoring the dual role of styrene-maleic anhydride copolymer in the fabrication of polysulfone ultrafiltration membranes: Acting as a pore former and amphiphilic surface modifier

• The ring opening of SMA(anh) in NaOH solution enhanced the interaction with PSF. • The transformation of SMA(anh) into SMA enhanced the pore-forming ability. • Long finger-like pores were created on the cross section of PSF/SMA-4 h membrane. • Membrane performances were optimized by the cumulative effects of SMA and PEG. To enhance the membrane performances, amphiphilic copolymers are extensively used to modify polymeric membranes by the surface segregation. Notably, they also act as a pore former in the membrane fabrication by the nonsolvent induced phase separation (NIPS). However, it is rarely reported to systematically adjust the pore-forming ability. Herein, a simple method is proposed to simultaneously adjust the surface segregation and pore-forming ability of styrene-maleic anhydride copolymer (SMA (anh)) in the PSF composite membrane formation by its ring opening reaction in the alkaline environment. The surface segregation and pore-forming ability were obviously enhanced accompanying with the miscibility improvement of dope solutions. Subsequently, the membrane microstructure was further optimized by selecting polyethylene glycol (PEG) as the second additive. Significantly, high-molecular-weight PEG was anchored on the membrane surface via strong hydrogen bonding and chain entanglement with sodium styrene-maleic anhydride copolymer (SMA). Compared with the PSF/SMA (anh) membrane, water contact angle (WCA) was obviously reduced due to the cumulative effects of SMA and PEG. Moreover, the resultant membranes displayed the pure water flux of 415.8 L/m 2 ·h·bar, BSA rejection of 98.3 % and flux recovery ratio (FRR) of 95.15 %, which remarkably excelled those reported values for other similar PSF composite membranes.

Computational analysis of atomic binding energy for organosilicon‐ low‐density polyethylene‐coated silica embedded in polyvinylidene fluoride composite membrane for membrane gas absorption

In an effort to enhance the wetting resistance and chemical stability of membrane contactors, silica nanoparticles (SiNP) have been incorporated into polyvinylidene fluoride (PVDF) membrane. These SiNP have been hydrophobically functionalized with three separate organosilicons (hexamethyldisilane, dimethyldichlorosilane, and polydimethylsiloxane) to produce TS-530, TS-610, and TS-720 SiNP. Then, they were coated with low-density polyethylene (LDPE) before adding them to the membrane casting dope. Using HyperChem, the molecular interaction between SiNP, organosilicons, and LDPE, as well as their aggregation tendency, was predicted using a semi-empirical computational approach (PM3). Both theoretical predictions and experimental results show that TS-610 and TS-720 SiNP have a high propensity to agglomerate, leading to the formation of composite membranes with large macrovoids. The HyperChem analysis, however, also indicates that LDPE/f-SiNP can resist chemical corrosion, and all composite membranes show positive binding energy interactions with amines. This enables the LDPE/f-SiNP membranes to perform better than the neat PVDF membrane with an adequate amine solution, and it remains hydrophobic after prolonged exposure.

Fabrication of Composite Ultrafiltration Membrane by Coating Urea Formaldehyde Resin on Filter Paper

Urea-formaldehyde resin (UFR), a thermosetting resin, is used to prepare ultrafiltration membranes because of its excellent mechanical properties and filtration performance. Herein, a porous ultrafiltration membrane is prepared by coating a mixture of UFR and carboxymethylcellulose (CMC) on the surface of filter paper via a facile acid-curing treatment method. CMC is used as a thickening agent, and hydrochloric acid is used as a curing agent to accelerate composite membrane formation. The mesoporous UFR is embedded in the large pores of the paper matrix by coating treatment, and the presence of CMC can decrease the flowability of the resin. The effects of UFR concentration, CMC dosage, and hydrochloric acid concentration on the performance of the composite ultrafiltration membrane are studied. The ultrafiltration membrane demonstrates a rejection rate of 85% and a pure water flux of 850 L/(m2·h) with the optimized resin concentration, CMC dosage, hydrochloric acid concentration, and coating amount at 30%, 20% (resin dry), 12%, and 250 g/m2, respectively.

Investigation on carbon nanotube oxide for anhydrous proton exchange membranes application

ABSTRACTThe widespread participation of polymers in the membrane preparation has been considering to be critical for the development of proton exchange membranes (PEMs). For the polymers without functional groups to conduct protons, the introduction of proton conduction carriers with the formation of composite membranes is an effective strategy to prepare PEMs with the outstanding proton conductivity. However, there remains a potential risk of the components leaking from composite membranes due to the lack of the interaction force. Here, the composite of carbon nanotube oxide (OCNT) assembling with cadmium telluride (CdTe) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate (bmimPF6) was introduced into the system of phosphoric acid (PA) doping poly(vinylidene fluoride) (PVDF) with the formation of PVDF/OCNT‐CdTe‐bmimPF6/85%PA membranes. PA molecules are anchored by the inorganics of OCNT‐CdTe‐bmimPF6 and are stabilized in membranes. The high and stable proton conductivity values at the elevated temperature are obtained comparing the reported PVDF/bmimPF6/PA membranes. Specifically, the proton conductivity value reached 1.28 × 10−1 S/cm at 160 °C and the value is stable 1.70 × 10−2 S/cm at 120 °C lasting for 350 h. The fine stability in components could make the membranes extricate from the predicament of proton conductivity decline exceeding 120 °C under anhydrous conditions in PVDF/bmimPF6/PA membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48833.

Supercritical CO2 assisted formation of composite membranes containing an amphiphilic fructose-based polymer

With the aim of increasing the mechanical and biological properties of different materials, a supercritical CO2 (SC-CO2) assisted technique was used to include a polymer with a natural origin (levan) in membranes of cellulose acetate (CA) and polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP). CA-levan membranes were characterized by interconnected pores ranging from 9 to 13 μm; due to levan addition, composite membranes increased their mechanical resistance and cells adhesion (from 8% to 30%). In the second system, the processing of a PVDF-HFP-DMSO-levan colloidal suspension system caused a morphological modification and the generation of a foam-like structure; a decrease of the mechanical resistance and an increase of cells adhesion (from 8% to 35%) were observed. Stress-strain responses for both systems were fitted using two different hyperelastic equations, Yeoh and Ogden; deviations from experimental data lower than 15% were obtained.In conclusion, SC-CO2 assisted process was able to generate composite structures with levan, accessible to the cells; i.e., transforming polymers like CA and PVDF-HFP in potentially useful materials for biological applications.

Mesoporous silica based composite membrane formation by in-situ cross-linking of phenol and formaldehyde at room temperature for enhanced CO2 separation

In the present report, composite membranes (CM) were prepared from a resin, derived from phenol and formaldehyde as matrix and mesoporous silica SBA-15 as filler on the clay-alumina tubular support. Membrane matrix was formed by in-situ cross-linking of phenol (P) and formaldehyde (F) at room temperature. The structural changes of membrane matrix with curing time influence the final properties of the membranes. The surface morphology and the filler-polymer interaction i.e. surface silanol group of SBA-15 and –CH2OH/–OH group of P–F resin of composite membrane were established by FESEM and Fourier transformation of infrared spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS) respectively. Thermal stability of the membranes was characterized by Thermogravimetric analysis (TGA) and Differential Thermal Analysis (DTA). Finally, the permeability and the separation efficiencies of the developed composite membranes were studied in details with varying curing time of resin at room temperature, feed pressure and different gas compositions for CO2/H2 and CO2/CH4 mixture gases. For CO2/H2 ‘reverse selectivity’ was observed with the membrane. The highest separation factor of CO2/H2 and CO2/CH4 were achieved upto 16.6 and 62.4 for 67:33 (CO2/H2) and 45:55 (CO2/CH4) feed composition respectively. The room temperature cross-linking of P–F resin modified the interfacial defect of membrane and its effect on the CO2 separation efficiencies is the unique observation of the present work. The obtained permeability and selectivity values of different gases were surpassing the 2008 Robeson upper bound line.

Composite Membrane Formation by Combination of Reaction‐Induced and Nonsolvent‐Induced Phase Separation

A novel method of preparing skinned asymmetric membranes with two distinctive layers is described: a top layer composed of chemically cross‐linked polymer chains (dense layer) and a bottom layer of non‐cross‐linked polymer chains (porous substructure). The method consists of two simple steps that are compatible with industrial membrane fabrication facilities. Unlike conventional processes to prepare asymmetric membranes, with this approach it is possible to finely control the structure and functionalities of the final membrane. The thickness of the dense layer can be easily controlled over several orders of magnitude and targeted functional groups can be readily incorporated in it. image

Composite electrodes for current sources based on graphene-like films in porous silicon

In this work, the results of formation of composite membranes with a thickness of about 200 μm with a high electric conduction based on porous silicon and graphene-like films have been presented. A method of CVD film synthesis that makes it possible to form a graphene-like coating on the inner surface of gradient-porous silicon with variable pore morphology across the thickness has been proposed. The pore sizes vary gradually from units of nanometers on the upper surface to several micrometers deep in silicon.

Formation of composite membranes containing hydrophobic polymer layers by electron-beam sputter deposition

The chemical structure and the contact and morphological properties of composite membranes prepared by electron-beam sputter deposition of a polytetrafluoroethylene layer on the surface of track-etched polypropylene membrane have been studied. It has been found that the application of such layers results in bilayer composite membranes with both the layers having hydrophobic properties. It has been shown that an increase in the thickness of the deposited polytetrafluoroethylene layer leads to development of its roughness, resulting in the formation of a polymer with superhydrophobic properties on the surface of the initial membrane.

Novel composite membrane coated with a poly(diallyldimethylammonium chloride)/urushi semi-interpenetrating polymer network for non-aqueous redox flow battery application

Abstract Novel composite membranes of a semi-interpenetrating network (semi-IPN) coated on the surfaces of a porous Celgard 2400 support are prepared and investigate for application in a non-aqueous redox flow battery (RFB). A natural polymer, urushi, is used for the matrix because of its high mechanical robustness, and poly(diallyldimethylammonium chloride) (PDDA) provides anionic exchange sites. The PDDA/urushi (P/U) semi-IPN film is prepared by the photo polymerization of urushiol in the presence of PDDA. The thin layer composed of the P/U semi-IPN on the porous support provides selectivity while maintaining the ion conductivity. The coulombic and energy efficiencies increase with increasing amounts of PDDA in the P/U semi-IPN layer, and the values reach 69.5% and 42.5%, respectively, for the one containing 40 wt% of PDDA. These values are substantially higher than those of the Neosepta AHA membrane and the Celgard membrane, indicating that the selective layer reduces the crossover of the redox active species through the membrane. This result implies that the formation of composite membranes using semi-IPN selective layers on the dimensionally stable porous membrane enable the successful use of a non-aqueous RFB for future energy storage systems.

A Facile Method to Prepare Double-Layer Isoporous Hollow Fiber Membrane by In Situ Hydrogen Bond Formation in the Spinning Line.

A double-layer hollow fiber is fabricated where an isoporous surface of polystyrene-block-poly(4-vinylpyridine) is fixed on a support layer by co-extrusion. Due to the sulfonation of the support layer material, delamination of the two layers is suppressed without increasing the number of subsequent processing steps for isoporous composite membrane formation. Electron microscope-energy-dispersive X-ray spectroscopy images unveil the existence of a high sulfur concentration in the interfacial region by which in-process H-bond formation between the layers is evidenced. For the very first time, our study reports a facile method to fabricate a sturdy isoporous double-layer hollow fiber.

Diffuse-In/Condense-Out Behavior of Glycerol Induces Formation of Composite Membranes with Uniform Pores

In this paper, an interesting glycerol behavior which can lead to the formation of composite polymer membranes with uniform pores in their surface layers is reported. Specifically, when cellulose acetate (CA) solution is spin-cast on a porous substrate filled with glycerol, with the evaporation of the volatile solvent of CA, the nonvolatile glycerol in the substrate firstly diffuses up into the CA solution layer and then condenses out and arranges into uniform droplets on the coated layer. These glycerol droplets act as template for the precipitation of the CA molecules and thus result in the formation of the uniform pores in the CA layer.

Ion-Responsive Channels of Zwitterion-Carbon Nanotube Membrane for Rapid Water Permeation and Ultrahigh Mono-/Multivalent Ion Selectivity

The rational combination of polymer matrix and nanostructured building blocks leads to the formation of composite membranes with unexpected capability of selectivity of monovalent electrolytes and water, which affords the feasibility to effeciently remove harmful ions and neutral molecules from the environment of concentrated salines. However, the multivalent ion rejection in salined water of routine nanocomposite membranes was less than 98% when ion strength is high, resulting in a poor ion selectivity far below the acceptable value. In this contribution, the ion-responsive membrane with zwitterion-carbon nanotube (ZCNT) entrances at the surface and nanochannels inside membrane has been proposed to obtain ultrahigh multivalent ion rejection. The mean effective pore diameter of ZCNT membrane was dedicated tuned from 1.24 to 0.54 nm with the rise in Na2SO4 concentration from 0 to 70 mol m(-3) as contrary to the conventional rejection drop in carbon nanotube (CNT) membrane. The ultrahigh selective permeabilities of monovalent anions against divalent anions of 93 and against glucose of 5.5 were obtained on ZCNT membrane, while such selectivities were only 20 and 1.6 for the pristine CNT membrane, respectively. The ZCNT membranes have potential applications in treatment of salined water with general NaCl concentration from 100 to 600 mol m(-3), which are widely applicable in desalination, food, and biological separation processes.

Main laws of the formation of composite membranes made of palladium alloys on a carrier made of corrosion-resistant steel with directional porosity

The main stages of formation of thin-film membranes with a functional layer of palladium-ruthenium alloy on a foil carrier made of corrosion-resistant steel with directed pores are studied. Selective etching agents and etching modes are determined, and a project of a technological route for the production of such composite hydrogen-permeable membranes is developed.

Effect of cellulose fi bers on morphology and pure water permeation of PSf membranes

Chemical and physical changes are necessary to improve the transport properties of polymeric membranes. Cellulose fiber pulp from Pinus taeda was processed in knives and balls mills in order to reduce the dimensions of the fibers for later application in polysulfone (PSf) membranes. By adding cellulosic fibers in PSf membranes, a composite membrane with improved morphological properties, permeate flux and good resistance to pressure was obtained. The fibers as well as the PSf and PSf/cellulose fibers membranes were morphologically characterized by scanning electron microscopy. Tests of pure water permeate flux were performed with pressure up to 20 bar. The addition of 0.2% (wt) of cellulose fibers in the formation of composite membranes resulted in the elimination of macrovoids, causing an increase in pure water flux (50% ±10) when pressure was risen.

Poly(vinyl trimethylsilane) and block copolymers of vinyl trimethylsilane with isoprene: Anionic polymerization, morphology and gas transport properties

Poly(vinyl trimethylsilane) (PVTMS) and block copolymers of vinyl trimethylsilane with isoprene were synthesized by anionic polymerization and characterized. The synthesized pure PVTMS has properties similar to a reference material produced about two decades ago and can be used for thin film composite membrane formation. Even at low isoprene content the block copolymers have improved film forming properties compared to the pure PVTMS. However, the presence of the isoprene units in the block copolymers leads to a decrease of the gas permeability but does not affect the selectivity of the membranes (α(O2/N2)=3.9).