Performance Of Hybrid Membranes Research Articles

Enhancing Separation and Mechanical Performance of Hybrid Membranes through Nanoparticle Surface Modification.

Membranes with selective gas transport properties and good mechanical integrity are increasingly desired to replace current energy intensive approaches to gas separation. Here, we report on the dual enhancement of transport and mechanical properties of hybrid cross-linked poly(ethylene glycol) membranes with aminopropyl-modified silica nanoparticles. CO2 permeability in hybrid membranes exceeds what can be predicted by Maxwell's equation and surpasses values of the pure polymer. Furthermore, dynamic mechanical and thermogravimetric analyses reveal increases in both the storage modulus and thermal stability in hybrid membranes, with respect to silica nanoparticle loading.

Tuning the performance of anion exchange membranes by embedding multifunctional nanotubes into a polymer matrix

Herein, a series of quaternized halloysite nanotubes (QHNTs) bearing different imidazoliums groups are prepared via distillation–precipitation polymerization and quaternarization, and then embedded into chitosan (CS) matrix to fabricate hybrid membranes. Systematic characterizations and measurements are performed to explore the relationships between the ligand of ammonium and the performance of hybrid membrane. It is found that QHNTs are well-dispersed within CS matrix, and the chain mobility of CS is promoted driven by repulsive interactions from QHNTs, in turn affording the increments of water uptake and area swelling. Together with the promoted chain mobility, low-barrier conduction pathways are formed along the QHNTs surface and then confer a significant enhancement in hydroxyl conductivity to hybrid membranes. For QHNTs, hydrophilic ligand could adsorb more water molecules and short ligand is more favorable for contacting with hydroxyl, both of which are beneficial for high hydroxyl conductivity. Particularly, incorporating 7.5% QHNTs with ester-type QA ligand endows the hybrid membrane with an 89% increase in conductivity from 0.009 to 0.017Scm−1 at 90°C and 100% RH. Yet under anhydrous conditions, the positive charge dispersity of QA and stereo-hindrance effect of the ligand are the predominant factors for hydroxyl ion hopping.

Improved Methanol Barrier Property of Nafion Hybrid Membrane by Incorporating Nanofibrous Interlayer Self-Immobilized with High Level of Phosphotungstic Acid.

High level of phosphotungstic acid (PWA) was self-immobilized on electrospun nylon nanofiberous sheet to fabricate highly selective methanol barrier layer for sandwich structured proton conducting membranes. Simple tuning for the assembly conditions of central layer and thickness of outer Nafion layers allowed obtaining different composite membranes with superior methanol barrier properties (namely, P=3.59×10(-8) cm2 s(-1)) coupled with proton conductivities reaching 58.6 mS cm(-1) at 30 °C. Comparable activation energy for proton transport and more than 20 times higher selectivity than Nafion 115 confirm the effectiveness of the central layer and resulting membranes for application in direct methanol fuel cells (DMFCs). When tested in DMFC single cell, the performance of hybrid membrane was far better than Nafion 115 especially at higher methanol concentrations.

Fabrication of Poly(MMA-co-ST) Hybrid Membranes Containing AgCl Nanoparticles by in Situ Ionic Liquid Microemulsion Polymerization and Enhancement of Their Separation Performance

To obtain high-performance membranes for the separation of aromatic/aliphatic hydrocarbons, AgCl nanoparticles were synthesized in a water-in-oil microemulsion using the ionic liquid 1-dodecyl-3-methyl imidazoium chloride (C12mimCl) as surfactant and methyl methacrylate-styrene (MMA-St) mixture as oil phase. Then, AgCl/poly(MMA-co-St) hybrid membranes were prepared by microemulsion by in situ polymerization. UV–visible spectrophotometry and transmission electron microscopy (TEM) were used to explore the influence of the St-to-MMA ratio in the oil phase on the morphology of AgCl nanoparticles in the microemulsion. The change in morphology of AgCl in membranes after polymerization was characterized by scanning electron microscopy and TEM. The separation performance of different hybrid membranes was evaluated by swelling–sorption experiments and pervaporation experiments. Results showed that adding a low amount of St slightly influenced the size and distribution of AgCl particles. Given the improvement in benzene separation, the performance of hybrid membranes after adding St was higher than that of AgCl/PMMA membranes. The maximum separation factor of hybrid membranes using MMA and St as the oil phase reached about 27 and exceeded twice that of AgCl/PMMA membranes. When the ratio of MMA and St was less than 2, the strong π combination between St and AgCl caused a large aggregation of AgCl particles both in the microemulsion and in the membranes, which evidently reduced the separation performance of the membranes. Increased AgNO3 concentration led to the formation of more AgCl particles in the microemulsion, which enhanced the separation performance of hybrid membranes. At high AgNO3 concentration, more particles with short distances more easily aggregated, thereby obviously reducing the separation performance of the membranes.

Cr(VI) Removal from Aqueous Solution by Chitosan/Carboxylmethyl Cellulose/Silica Hybrid Membrane

In the present study, chitosan/carboxymethyl cellulose/silica hybrid membrane (CS/CMC/Silica) was prepared by using chitosan and carboxymethyl cellulose in the presence of 3-glycidoxypro- pyltrimethoxysilane (GPTMS) as the crosslinking agent and used to remove Cr(VI) iron in effluent. The structure of CS/CMC/Silica hybrid membrane was characterized by FT-IR spectroscopy and scanning electron microscopy (SEM). The influence of Cr(VI) concentration, solution temperature, and pH, adsorption time on adsorption performance of hybrid membrane was investigated. Adsorption capacity increased with the increase of Cr(VI) concentration and absorbing time, and decreased with the increase of sorbent dosage and temperature. The adsorption equilibrium of Cr(VI) ion was attained within 60min of contact. The pseudo-second-order model fitted the kinetic data well.

Preparation, performances of PVDF/ZnO hybrid membranes and their applications in the removal of copper ions

ZnO hybridized Polyvinylidenefluoride (PVDF/ZnO) membranes were successfully prepared by two different methods. One method was immersing the pretreated PVDF films in the ZnO suspensions (method A), and the other was blending ZnO nanoparticles with PVDF solution and then casting films (method B). The structure of these PVDF/ZnO hybrid membranes were characterized by SEM, XRD and ATR-IR, and the performances of hybrid membranes were determined through the measurements of contact angle, pure water flux and static adsorption toward BSA. The results showed that the ZnO nanoparticles were incorporated into the pores and onto the surface of PVDF, and more uniform hybrid structure was obtained by method B. The ATR-IR spectra revealed that the weak physical interaction played role in the construction of hybrid membranes. Compared with the pristine PVDF films, the hydrophilicity, permeability and antifouling performance of hybrid membranes were improved. And more notably, the hybrid membranes also showed better adsorption and desorption properties for copper ions, which was rarely reported.

Improvement in the permeation performance of hybrid membranes by the incorporation of functional multi-walled carbon nanotubes

The morphology and swelling performance of poly(methyl methacrylate) (PMMA) and polyurethane (PU) membranes containing pristine multi-walled carbon nanotubes (P-MWCNTs) was investigated. Next, amino (NH2) groups were introduced into the MWCNTs by chemical modification for improving their affinity to the membranes, thereby resulting in a better distribution of the MWCNTs in the membranes. The performance of the hybrid membranes was evaluated by swelling and pervaporation experiments. The Fourier transform infrared and transmission electron microscopy analyses showed that the addition of both the pristine and functionalized MWCNTs to the membranes improved their permeation performance. The dispersion of the P-MWCNTs and MWCNTs-NH2 in the PU hybrid membranes was better than that in the corresponding PMMA hybrid membranes because of the rapid polymerization rate of the monomers and the elasticity of the membranes. Thus, the P-MWCNTs/PU and MWCNTs-NH2/PU hybrid membranes performed better than the corresponding P-MWCNTs/PMMA and MWCNTS-NH2/PMMA hybrid membranes. The surface functionalization promoted the affinity of the MWCNTs to the monomer solution and the polymer membranes. Compared to the P-MWCNTs, the MWCNTs-NH2 showed an improved distribution in the PU and PMMA hybrid membranes, and the membranes containing the MWCNTs-NH2 performed better than those containing the P-MWCNTs.

Enhanced proton conductivity of proton exchange membranes by incorporating sulfonated metal-organic frameworks

In this study, octahedral crystal MIL101(Cr) with a uniform size of ∼400 nm is synthesized via hydrothermal reaction. It is then functionalized with sulfonic acid groups by concentrated sulfuric acid and trifluoromethanesulfonic anhydride in nitromethane. The sulfonated MIL101(Cr) are homogeneously incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare hybrid membranes. The performances of hybrid membranes are evaluated by proton conductivity, methanol permeability, water uptake and swelling property, and thermal stability. The methanol permeability increased slightly from 6.12 × 10−7 to 7.39 × 10−7 cm2 s−1 with the filler contents increasing from 0 to 10 wt. %. However, the proton conductivity of the hybrid membranes increased significantly. The proton conductivity is increased up to 0.306 S cm−1 at 75 °C and 100% RH, which is 96.2% higher than that of pristine membranes (0.156 S cm−1). The increment of proton conductivity is attributed to the following multiple functionalities of the sulfonated MIL101(Cr) in hybrid membranes: i) providing sulfonic acid groups as facile proton hopping sites; ii) forming additional proton-transport pathways at the interfaces of polymer and MOFs; iii) constructing hydrogen-bonded networks for proton conduction via –OH provided by the hydrolysis of coordinatively unsaturated metal sites.

Influence of modification of MWCNTs on the structure and performance of MWCNT-Poly(MMA-AM) hybrid membranes

Hybrid membranes containing multi-walled carbon nanotubes (MWCNTs) were initially prepared to separate benzene/cyclohexane mixtures. Subsequently, MWCNT surfaces were chemically modified using two methods to change the surface polarity of the MWCNTs and improve the distribution thereof in Poly(methylmethacrylate) (PMMA). This change consequently enhanced the separation performance of hybrid membranes with MWCNTs. Raman spectroscopy was used to characterize the structure of the pristine MWCNTs and the modified MWCNTs. The morphology and distribution of the MWCNTs in PMMA were investigated by transmission electron microscopy. The results showed that the addition of MWCNTs clearly improved the separation performance of the hybrid membranes. Surface modification introduced polar groups onto the MWCNT surface, which significantly improved the distribution of MWCNTs in the PMMA membranes and the performance of hybrid membranes. MWCNTs with higher surface polarity also increased the amount of MWCNTs distributed homogeneously in PMMA. Aminated MWCNTs (MWCNT-NH2) showed the highest surface polarity. Thus, the content of MWCNT-NH2 well distributed in PMMA was the highest among the three types of MWCNTs. The highest separation factor for the hybrid membranes with 1.0 wt% MWCNT-NH2 was about seven times that of membranes containing pristine MWCNTs. Copyright © 2013 John Wiley & Sons, Ltd.

Preparation of Multi-Walled Carbon Nanotubes (MWNTs)/Polymethyl Methacrylate (PMMA) Hybrid Membranes and their Sorption Performance of Benzene/Cyclohexane

Novel organic-inorganic hybrid membranes of polymethyl methacrylate (PMMA) containing multi-walled carbon nanotubes (MWNTs) were successfully prepared. Then, the swelling adsorption experiments of benzene/cyclohexane mixtures were employed to evaluate the performance of these membranes. Via transmission electron microscopy (TEM), Fourier transform infrared spectrophotometry (FTIR), the effect of surface modification on the morphology and properties of carbon nanotubes and hybrid membranes were studied. The results indicated that the separation performance for benzene/cyclohexane of the hybrid membranes depended on both the polarity of carbon nanotubes and the distribution of MWNTs in PMMA. Because the dispersion of MWNTs were obviously improved after acidification and ammonization modification, the hybrid membranes including modified MWNTs showed higher performance than membranes with un-modified MWNTs. In addition, a large number of polar group were introduced in the MWNTs during modification of acidification and ammonization, which depressed obviously the physical adsorption of cyclohexane by MWNTs. Therefore, these two changes in the properties of MWNTs both improved the separation performance of hybrid membranes.

Enhanced pervaporation dehydration performance of ultrathin hybrid membrane by incorporating bioinspired multifunctional modifier and TiCl4 into chitosan

3-(3,4-Dihydroxyphenyl)propionic acid (DHPPA) was introduced as a bioinspired multifunctional modifier to mediate the in situ sol–gel reaction of TiCl4 within chitosan (CS) matrix through metal–organic coordination. Ultrathin, robust chitosan–titania hybrid membranes were obtained in a facile way. The morphology, chemical and physical structures, as well as the hydrophilicity and thermal stability of hybrid membranes were extensively characterized. An ethanol/water mixture was chosen as a model system to evaluate the swelling resistance property and pervaporation dehydration performance of the hybrid membranes. The simultaneous enhancement of hydrophilicity and swelling resistance was achieved due to the presence of numerous carboxyl groups and the stable hybrid structure. The multiple interfacial interactions between polymeric and inorganic phases, as well as the steric effect of the bioinspired modifier, led to significant pervaporation performance enhancement of CS membrane. When the mass ratio of TiCl4 to CS was 14wt%, the hybrid membrane exhibited the optimal pervaporation performance with a permeation flux of 1403g/(m2h) and a separation factor of 730 for 90wt% ethanol aqueous solution at 350K. The operation stability was also testified in long-term pervaporation separation test.

Preparation of PVDF/Al2O3 hybrid membrane via the sol–gel process and characterization of the hybrid membrane

In this study we present a new method to prepare organic–inorganic hybrid polyvinylidene fluoride (PVDF)/Al2O3 membranes via in situ polymerization of aluminum isopropoxide (AIP) using the sol–gel process. FTIR analysis showed the existence of Al in hybrid membrane when AIP was added to the casting solution. The effects of AIP on the performances of hybrid membranes were investigated. The results showed that the pure water flux and the bovine serum albumin (BSA) rejection increased firstly and then decreased with increasing AIP content. When AIP content was 12 wt.%, compared with PVDF membrane without the addition of AIP, the pure water flux of hybrid membrane was increased by 83.4% and the BSA rejection was improved from 88.3 to 96.6%. In addition, other performances of the hybrid membrane such as hydrophilicity, mechanical properties, and antipollution were also improved.

Silane‐modified NaA zeolite/PAAS hybrid pervaporation membranes for the dehydration of ethanol

AbstractTo improve the pervaporation selectivity of poly(acrylic acid) sodium (PAAS) membranes incorporated with NaA zeolite, the interface compatibility between zeolite nanocrystals and the polymer matrix was improved by modifying NaA zeolite using 3‐aminopropyltriethoxysilane (APTES). Both X‐ray photoelectron spectra and FTIR confirmed the chemical modification, while the results of zeolite particle size analysis and scanning electron microscopy revealed the improved dispersion of the modified zeolite. Transmission electron microscopy images of these hybrid membranes indicated that the interface between the polymer and modified zeolite phases had improved. The effects of loaded NaA zeolite on the pervaporation performance of hybrid membranes were investigated. The selectivity of hybrid membranes made from APTES‐modified zeolite was higher than that using the original zeolite under the same conditions, because fewer voids resulted from the incompatibility between the zeolite and PAAS and the structure was more homogenous. Based on the Arrhenius plots, the activation energies of water and the ethanol ratio were lower for modified zeolite hybrid membranes, because water molecules experienced less restrictive passage through the membranes compared with the original zeolite‐based hybrid membrane. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Sulfonated poly(arylene ether sulfone)/Laponite-SO 3H composite membrane for direct methanol fuel cell

Polymer nanocomposite membranes based on sulfonated poly(arylene ether sulfonate) (SPAES) containing a flake filler (Laponite) with varying degrees of sulfonation, were prepared and characterized for application in direct methanol fuel cells (DMFCs). Unlike most other clays, Laponite crystals are very small in size with a very low aspect ratio (diameter to thickness ratio) of 25–30. They improve the mechanical, thermal properties and decreased the fuel permeability. However, polymer composite membranes containing non-proton conducting inorganic particles tend to show low proton conductivity, as compared with pristine polymer membranes. To resolve this problem, prior to the preparation of the composite membranes, Laponite-Na+(NLa) was sulfonated with various amounts of organo silanes (3-Mercaptopropyl trimethoxysilane (SH-silane)) via an ion exchange method. Functionalized Laponite with the organic silane compound showed higher ion exchange capacity and ion conductivity, respectively. In order to minimize the loss of proton conductivity while reducing the methanol permeability, various amounts (0.5–2.0 wt%) of the organically sulfonated Laponite (SLa) were introduced into the SPAES matrices. The performances of hybrid membranes for DMFCs in terms of mechanical properties, behavior of water in membranes, proton conductivity and methanol permeability were investigated.

Intensifying esterification reaction between lactic acid and ethanol by pervaporation dehydration using chitosan–TEOS hybrid membranes

Esterification assisted by pervaporation separation can enhance the yield of ester for thermodynamically or kinetically limited reaction via selective removal of water from the reaction mixture. In the present study, organic–inorganic hybrid membranes were prepared by in situ hydrolysis and condensation of tetraethoxysilane (TEOS) within chitosan (CS) aqueous solution for pervaporation-assisted esterification of lactic acid with ethanol, catalyzed by Amberlyst 15 ion-exchange resin. The composition and structural properties of CS–TEOS hybrid membranes were investigated by FT-IR, XRD, TGA and contact angle. The dehydration performances of hybrid membranes were evaluated by pervaporation of aqueous ethanol solution. Comparing with CS pristine membrane, CS–TEOS hybrid membranes exhibited remarkably enhancing pervaporation property. Pervaporation-assisted esterification results suggested that the incorporation of pervaporation process to preferentially remove water from the reaction mixture substantially enhanced the yield of ethyl lactate from 66 wt.% to 80 wt.%. The effects of membrane casting solution recipe, reaction temperature, initial molar ratio of ethanol to lactic acid and catalyst loading amount on the process performance have been examined in detail.

In situ fabrication of cross-linked PEO/silica reverse-selective membranes for hydrogen purification

Abstract Targeting at hydrogen purification, cross-linked organic–inorganic reverse-selective membranes containing poly(ethylene oxide) (PEO) are fabricated in situ by using functional oligomers (O,O′-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol: Jeffamine® ED-2003) with a high content of PEO and epoxy-functional silanes (3-glycidyloxypropyltrimethoxysilane: GOTMS). Changes in physicochemical properties due to varying silica content have been characterized; including a great decline in melting temperature; an improvement in glassy and degradation temperature, and the suppression of PEO crystallinity. The strong affinity between quadrupolar CO2 and polar ethylene oxide (EO) groups enhances the CO2/H2 separation performance of hybrid membranes, which can be further tuned by controlling the organic/inorganic ratio. The organic–inorganic hybrid membrane with 90 wt% of ED-2003 demonstrates an appealing CO2 permeability of 367 Barrer with an attractive CO2/H2 selectivity of 8.95 at 3.5 atm and 35 °C. The transport performance trend with composition variations is explained by analyzing the calculated solubility and diffusivity based on the solution-diffusion mechanism. Moreover, CO2 permeability increases with applied pressure in pure gas tests because of CO2 plasticization phenomena, which is beneficial for CO2/H2 separation. Attributing to CO2 plasticization and CO2 dominant sorption, the mixed gas test results of the membrane containing only 25 wt% ED-2003 show greatly improved CO2/H2 selectivity of 13.2 with CO2 permeability of 148 Barrer at 35 °C compared to pure gas results. Interestingly, at a stipulated CO2 pressure, the inherent tension in cross-linked networks maintains the CO2 permeability stable with the time. The cross-linked organic–inorganic membranes with enhancements in mechanical and thermal properties are promising for industrial-scale hydrogen purification.

Sulfonated poly(ether ether ketone)/clay-SO 3H hybrid proton exchange membranes for direct methanol fuel cells

A new type of sulfonated clay (clay-SO 3H) was prepared by the ion exchange method with the sulfanilic acid as the surfactant agent. The grafted amount of sulfanilic acid in clay-SO 3H was 51.8 mequiv. (100 g) −1, which was measured by thermogravimetric analysis (TGA). Sulfonated poly(ether ether ketone) (SPEEK)/clay-SO 3H hybrid membranes which composed of SPEEK and different weight contents of clay-SO 3H, were prepared by a solution casting and evaporation method. For comparison, the SPEEK/clay hybrid membranes were produced with the same method. The performances of hybrid membranes for direct methanol fuel cells (DMFCs) in terms of mechanical and thermal properties, water uptake, water retention, methanol permeability and proton conductivity were investigated. The mechanical and thermal properties of the SPEEK membranes had been improved by introduction of clay and clay-SO 3H, obviously. The water desorption coefficients of the SPEEK and hybrid membranes were studied at 80 °C. The results showed that the addition of the inorganic part into SPEEK membrane enhanced the water retention of the membrane. Both methanol permeability and proton conductivity of the hybrid membranes decreased in comparison to the pristine SPEEK membrane. However, it was worth noting that higher selectivity defined as ratio of proton conductivity to methanol permeability of the SPEEK/clay-SO 3H-1 hybrid membrane with 1 wt.% clay-SO 3H was obtained than that of the pristine SPEEK membrane. These results showed that the SPEEK/clay-SO 3H hybrid membrane with 1 wt.% clay-SO 3H had potential usage of a proton exchange membrane (PEM) for DMFCs.

A new method to prepare organic–inorganic hybrid membranes

In this paper we present a new method to prepare organic–inorganic hybrid PVDF/Si membranes by adding tetraethyl orthosilicate (TEOS) into the polyvinylidene fluoride (PVDF) casting solution. During the membrane coagulation in acid bath (pH = 1), the TEOS was hydrolyzed and polymerized, and silicon–oxygen polymers were formed. The silicon–oxygen polymers may entangle or interpenetrate with PVDF chains, which is beneficial to the mechanical performances of hybrid membranes. Element analysis showed Si existed on the surface and bottom of hybrid membrane when TEOS was added to the casting solution. The effects of TEOS on the performances of hybrid membranes were investigated. The results showed that the pure water flux increased firstly and then decreased and the BSA retention decreased with TEOS content increasing. When TEOS content was about 12 wt.%, the pure water flux of hybrid membrane was similar to that of PVDF membrane without TEOS addition, but the tensile strength and elastic modulus of hybrid membrane was almost twice.

Study on the influence of the free volume of hybrid membrane on pervaporation performance by positron annihilation spectroscopy

To improve the pervaporation separation performance, an organic–inorganic hybrid membranes were prepared by adding zeolite 13X into the polyimide (BAPP–BODA), which was synthesized using one-step polycondensation polymerization of 2,2-bis(4-(4-aminophenoxy)phenyl)propane (BAPP) with bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BODA). The influence of the zeolite 13X content on the free volume and pervaporation performance of hybrid membranes were systematically analyzed by positron annihilation spectroscopy (PAS). The trend of ortho-positronium ( o-Ps) lifetime and free volume holes changes consistently well with the permeation rate variation of aqueous isopropanol mixtures dehydration. The BAPP–BODA/13X hybrid membrane morphology was characterized by AFM and SEM. Compared with the BAPP–BODA membrane, the BAPP–BODA/13X hybrid membrane had good pervaporation performance for aqueous alcohol solution dehydration. The sorption selectivity dominates the behavior of pervaporation while adding zeolite 13X into the polyimide matrix.

Filler-polymer combination: a route to modify gas transport properties of a polymeric membrane

Polydimethylsiloxane (PDMS) has been used as host matrix to prepare hybrid membranes, by a dry phase inversion process, where fillers with different surface and molecular sieving properties have been dispersed. The hybrid membranes have been characterised morphologically by scanning electron microscopy (SEM) and their gas transport properties have been measured at different temperatures.The influence of the temperature and different fillers on the gas separation performance of hybrid membranes has been analysed. These membranes showed higher selectivity values for some gas pairs combined to lower permeabilities with respect to pure PDMS films, as consequence of the contribution of the filler to the transport. A proper filler choice could be used to meet some specific requirements in industrial gas separations.