Characterization Of Composite Membranes Research Articles

Chemical vapor deposition graphene transfer onto asymmetric PMMA support

AbstractGraphene is a promising material for membrane applications. However, the graphene production with large specific area and good structural quality is a challenge. Therefore, the production and characterization of composite membranes with graphene grown by chemical vapor deposition (CVD) over a porous polymethylmethacrylate (PMMA) substrate was investigated. The experimental strategy consisted in applying CVD‐graphene on a PMMA surface using PMMA‐assisted graphene wet transfer. The proposed methodology resulted in large‐area membranes with 2 cm diameter. The samples were characterized by Raman spectroscopy, indicating the presence of graphene in good quality and relative structural integrity. The analysis by scanning electron microscopy revealed the formation of a microporous support with an asymmetric structure. The gas permeation measurements of graphene/PMMA membranes showed a permeability reduction of 81.9% for CO2 and 83.7% for N2. The contribution of PMMA to flow resistance was 2% and 11% for CO2 and N2, respectively, and the contribution of graphene was 98% and 89% for CO2 and N2. Therefore, this research presents a potential advance in transferring graphene to porous support, and the impermeability process of membranes composed of graphene/PMMA, a fundamental step for the development of graphene membranes before the production of controlled‐sized pores.

Oxygen Barrier Composite Membrane for Li-Air Battery Using Cuboid LiAlTiPO4 in Orthogonal Array

The Li-Air batteries which convert the electrochemical reactions of lithium and O2 into electrical energy have high theoretical gravimetric capacity (3861 mAh/gLi) that is ten times higher than that of lithium ion batteries (372 mAh/gc). Its potential to generate high energy density makes it a promising candidate to replace the lithium ion in the electric vehicle applications. To meet the requirements of the electric vehicle applications, the technical barriers that limit the cycle life such as oxygen permeation, electrolyte and cathode instability and low rate capability need to be overcome. Especially the consumption/de-activation of Li metal is accelerated when oxygen in cathode side moves into Li metal side through the electrolyte, which is one of the most significant factors preventing long-term operation of the system. Ceramic solid state electrolyte (SSE) separator has a remarkable gas blocking capability, but it should be thick and heavy (~0.3 mm) to be used as a gas barrier of Li-Air battery due to fragile property. This leads to a sharp decrease in energy density. We fabricated composite membrane consisting of micron-sized SSE particles arrayed in matrix shape and polymer grid. Here SSE particles and polymer have functions of lithium ion conduction and gas blocking, respectively. Cuboid particles were synthesized using silicon wafer template with cuboid pattern on it in size of 50 ~ 200um. Interface energy between particle and polymer was controlled by bimodal surface modification for better mechanical strength of membrane. Compared to amorphous particles, composite membrane using cuboid LATP particle has many benefits in high ionic conductivity, uniform thickness, light weight and flexibility. In this presentation, how to fabricate cuboid SSE particles in matrix shape array and characterization of composite membrane using it will be discussed.

Synthesis and Characterization of Composite Membranes Based on Carbon Functionalized with Gold Nanoparticles

The purpose of this experimental laboratory work is to obtain composite membranes having carbon and gold nanoparticles in the matrix. Consideration was made of using graphene oxide, a material which, under certain conditions, can generate membranes by a self-assembly process under vacuum in an aqueous or organic medium. The cellulose acetate (CA) - graphene oxide (GO) composite membranes have been functionalized with gold nanoparticles (AuNP) by two technological processes: thermal evaporation and ultrasonic mixing of stable graphene oxide and gold suspensions. The stable suspensions containing gold nanoparticles were obtained by chemical reduction of aqueous solutions of Tetrachloroauric acid trihydrate (HAuCl4) precursors with sodium citrate under high temperature conditions. Dispersibility of carbon nanostructures and precious metal nanoparticles has been studied with a DLS granulometer - Malvern Instruments Zetasizer ZS90. It was determined the mean particle size and Zeta potential function of the suspensions pH. The graphite based membranes were further subjected to various characterizations techniques. It was found that both the surfaces and the cross-sections were functionalized with gold particles. The presence of Au particles was revealed both on the membrane surface and also inside its structure. Hydrophilic tests demonstrate that the membrane filters have potential to be used in various applications.

Preparation and characterization of composite membrane via layer by layer assembly for desalination

Cellulose acetate (CA) incorporated with sepiolite and Polyvinylpyrrolidone (PVP) multilayer composite on Polysulfone (PSf) substrate have been prepared by layer by layer (LbL) assembly method. Fourier TransformInfrared Spectroscopy (FTIR) results verified the hydrogen bonding among the components of composite membrane. Atomic force microscopy (AFM), scanning electron microscope (SEM) was carried out for the determination and elucidation of roughness and morphology of the fabricated membranes on PSf substrate. The AFM and SEM results showed the increased surface roughness with the porous and spongy structure. The performance results verified that the successful incorporation of sepiolite in membranes showed maximum MgSO4 rejection (98.9%) and flux of 38.7L/m2h. Whereas, in case of NaCl the rejection is 98.3% and flux is 34.9L/m2h. The modification was evidenced to be effective in increasing the surface hydrophilicity that led to increase in surface roughness. The chlorine resistivity is improved by dropping the active sites for chlorine attack and protecting the underlying PSf substrate.

Preparation and characterization of composite membranes with Brønsted acidic ionic liquid

Poly-(vinyl alcohol) (PVA) proton-conducting composite membranes were prepared using succinic acid (SA) as a cross-linking agent and Bronsted acidic ionic liquid (BAIL) as a proton source. The incorporated BAILs resulted in a relatively high proton conductivity compared with PVA/SA membrane without BAILs. The proton conductivities of PVA/SA/BAIL composite membranes increased versus the BAIL content. In addition, the optimal resultant proton conductivity of PVA/SA/BAIL composite membrane under dry condition could reach 0.4 mS/cm at 140 °C, which was higher than that of PVA/sulfosuccinic acid (SSA) composite membrane (0.032 mS/cm), PVA/SSA/5-aminotetrazole membrane (0.022 mS/cm at 130 °C), and PVA/chlorosulfonic acid/glutaraldehyde membrane (0.0585 mS/cm at 90 °C) measured at the same condition. It was notable that the PVA/SA/BAIL composite membranes could reach high thermal stability up to 150 °C, which was higher than that of traditional PVA membranes (below 80 °C).

Preparation and characterization of composite membranes with ionic liquid polymer-functionalized multiwalled carbon nanotubes for alkaline fuel cells

Multiwalled carbon nanotubes functionalized with an imidazolium-type ionic liquid polymer, PIL(BF4)–MWCNTs, have been successfully prepared via in situ free radical polymerization of 1-vinyl-3-methylimidazolium iodide ([VMIm][I]) and then blended with poly(2,6-dimethyl-1,4-phenylene oxide) containing imidazolium groups (PPO–MIm) in solution to fabricate composite membranes. The composite membranes were characterized by scanning electron microscopy (SEM) and the SEM images of the membranes show that the PIL(BF4)–MWCNTs can be homogeneously dispersed in the PPO–MIm matrix. The conductivity and mechanical properties of the composite membranes were examined. It was demonstrated that the incorporation of the PIL(BF4)–MWCNTs into the membranes of PPO–MIm can increase both conductivity and mechanical properties. The composite membrane containing 0.3 wt% of PIL(BF4)–MWCNTs (P(0.3)) exhibits a dramatic enhancement in ionic conductivity (95.3%) and tensile strength (82.9%) in comparison with the membrane without PIL(BF4)–MWCNTs. Therefore, this research demonstrates that the incorporation of functionalized carbon nanotubes is a facile and useful strategy for improving both ionic conductivity and mechanical properties of alkaline polymer electrolyte membranes.

Synthesis and Characterization of Composite Membranes Derived From Mono Sulfonated Poly (Ether Sulfone) and Silicotungstic Acid

A series of composite membranes based on mono sulfonated poly(ether sulfone) (SPES) embedded with silicotungstic acid (STA) was synthesized. SPES was synthesized by nucleophilic aromatic polymerization and solution blended with silicotungstic acid. Direct synthesis of sulfonated polymer controls the degree of sulfonation and this leads to higher thermal stability. The composite membranes were characterized for water uptake, swelling ratio, ion-exchange capacity, thermal stability and proton conductivity for evaluating the suitability of these membranes for fuel cells. The proton conductivity of the composite membranes was increased with increasing STA content. The conductivity of the composite membranes at 30°C was increased from 0.082 S/cm to 0.095 S/cm, whereas the parent membrane shows 0.078 S/cm. The composite membranes not only have good proton conductivity, but also showed excellent thermal stability. This study shows that the composite membranes based on SPES and STA can be viable candidates for electrolyte membranes.

Polyvinyl alcohol nanofiber reinforced Nafion membranes for fuel cell applications

This work has been focused on the preparation and characterization of composite membranes with thickness between 19 and 97 μm and containing Nafion ® infiltrated into a porous mat obtained by electrospinning of an aqueous solution of Poly vinyl alcohol (PVA). The mat was composed of PVA nanofibers with diameters between 200 and 300 nm, which were functionalized on their external surface with sulfonic acid groups in order to cooperate in the proton conductivity of Nafion ®. The proton conductivity of a composite membrane (47 μm thick) measured by impedance spectroscopy reached 0.022 S/cm at 70 °C and fully hydrated. This value is lower than the conductivity measured in the same conditions for a pristine Nafion ® cast membrane (46 μm), 0.032 S/cm. However, the performance of both membranes in Direct Methanol Fuel Cell tests was evaluated and showed comparable results. The proton conductivity of a series of cast Nafion ® membranes with thickness similar to those of the composite membranes was found to behave linearly thickness-dependent, while NAF/PVA composite membranes do not show such a linear behavior due to their heterogeneous composition. Nevertheless, the composite membrane presenting a thickness of 47 μm records the maximum peak conductivities at the whole temperature range. An intrinsic value for the activation energy of our cast Nafion ® membranes at fully hydrated conditions was estimated to be 7 kJ/mol.

Synthesis and characterization of composite membrane by deposition of acrylic acid plasma polymer onto pre-treated polyethersulfone support

The plasma techniques were explored to deposit a layer of hydrophilic polymer on asymmetric porous membranes used as support material. Microporous membranes were synthesized by the phase inversion technique from polyethersulfone (PES) and submitted to a surface treatment with RF-plasma of non-polymerizable gas. Carbon dioxide (CO2) was selected to generate this plasma and to increase the surface energy. Further plasma treatment proceeded with acrylic acid (AA) in vapor phase as source for the permanent surface hydrophilic functionalization. The infrared spectra with horizontal attenuated total reflectance (HATR) show that the deposited plasma polymer provides a high concentration of carbonyl and hydroxyl groups. The hydrophilic polymer layer was evenly deposited, with good adhesion to the support, as was observed by electronic microscopy (SEM). The surface free energy (γS) was increased through plasma treatments and confirmed by the decrease of contact angle (θ) measurements and increase of adhesion work (Wa). The nitrogen permeability decreased 650 times; after that a dense thin film was deposited by plasma treatment during 40 min (at 5 W and 8 Pa). Final composite membranes show stability, high surface hydrophilicity, and a surface chemical nature very stable with time.

Synthesis and Characterization of Composite Membrane with Three-Dimensionally Ordered Macroporous Polyimide Matrix for DMFC

A composite membrane consisting of three-dimensionally ordered macroporous (3DOM) polyimide matrix and a proton-conducting gel polymer was prepared for direct methanol fuel cells (DMFCs). The matrix effect on the physico-electrochemical properties of the composite membrane was investigated in order to compare 3DOM silica composite membrane containing the same proton-conducting polymer. From the comparison of 3DOM polyimide matrix with the 3DOM silica matrix reported in our previous paper, it was confirmed that the polyimide matrix has some structural advantages. In particular, the high uniformity of 3DOM structure provides fairly continuous proton-conducting pathways in the composite membrane, resulting in considerably high proton conductivity of at under 90% relative humidity, which is about three times greater than that obtained with the 3DOM silica composite membrane. Furthermore, high mechanical strength of 3DOM polyimide suppressed polymer swelling in the composite membrane, which resulted in low methanol permeability of in methanol solution. Consequently, was obtained as transfer selectivity of the composite membrane, which was about ten times larger than that of Nafion membrane.

Preparation and characterization of composite membranes using blends of SPEEK/PBI with boron phosphate

In this contribution composite membranes have been prepared from acid–base polymer blend and solid inorganic proton conductive boron phosphate (BPO 4). The blends are composed of sulfonated polyether-ether ketone (SPEEK) as the acidic component and polybenzimidazole (PBI) as the basic component. The contents of solid BPO 4 in the composite membrane varied from 10 to 40 wt%. The conductivity of the composite membranes was measured by impedance spectroscopy at room temperature. The conductivity of the composite membranes was found to increase with the incorporation of boron phosphate particles into blend membranes. The highest conductivity of 6 mS/cm was found for composite membrane at room temperature. The membranes were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and FTIR which showed acid–base interaction in the blend membranes and also confirmed the presence of solid BPO 4 into the composite membranes. These membranes show good perspective in the membrane fuel cell applications.

Characterization of Composite Membrane of Poly(vinyl alcohol) and Regenerated Silk Fibroin for Immobilization of Horseradish Peroxidase and an Amperometric Neckelocene-Mediated Sensor Sensitive to Hydrogen Peroxide

Horseradish peroxidase (HRP) was effectively entrapped in a novel composite membrane of poly(vinyl alcohol) and regenerated silk fibroin. IR spectroscopy was employed to characterize the structure of the composite membrane and scanning electron microscopy was used to visualize the morphology of the composite membrane. HRP was utilized to amplify the amperometric response of the sensor by catalyzing reduction of hydrogen peroxide via nickelocene, an electron transfer mediator between immobilized HRP and a glassy carbon electrode. The influence of various experimental parameters such as pH, temperature and applied potential were explored for optimum analytical performance. The sensor possessed a variety of characteristics including good sensitivity, rapid response time and a low detection of limit of 0.1 μmol dm -3 , which arose from the efficiency of electron transfer between immobilized HRP and the electrode via nickelocene.

Preparation of supported thin palladium-silver alloy membranes and their characteristics for hydrogen separation

Abstract Studies have been made on the characterization of composite membranes, consisting of a palladium-silver alloy film on the outer surface of an inorganic porous support, for hydrogen separation. The membranes were prepared in the manner of consecutive electroless-plating of palladium and silver, and then heat treatment in a stream of argon. As high temperatures above 1073 K were required to form a miscible palladium-silver alloy film, thermally durable porous alumina ceramic was selected as the support. The membranes thus prepared had a complete selectivity for hydrogen separation and they exhibited an extremely high rate of hydrogen permeation compared with commercial palladium-based membranes. For instance, permeation was about 30 times faster when 23 wt.% silver was melted to give a film thickness of 5.7 μm. The high rate of hydrogen permeation is a result of enhanced hydrogen solubility into the metal film as well as its reduced thickness.