Organic-inorganic Membranes Research Articles

Palladium-Silica Organic-Inorganic Membrane Materials via a Sol-Gel Process: Preparation and Properties Calcined under H<sub>2</sub> Atmosphere

Pd-doped SiO2 organic-inorganic membrane materials were prepared via a sol-gel process. The sol stability is characterized by sol particle size and zeta potential analysis. And the properties of the Pd-doped SiO2 organic-inorganic membrane materials are investigated by X-ray diffraction (XRD), fourier transform infrared (FTIR), energy dispersive spectrum (EDS) analysis and N2 absorption-adsorption measurement. The results showed that the sol particle size distributions are relatively narrow. With the increase of Pd content, the sol particle sizes slightly increase and the zeta potentials decreases until the palladium/tetraethylorthosilicate molar ratio closes to the isoelectric point. After calcined at 350 °C under H2 atmosphere, the added PdCl2 is reduced to metallic Pd0 completely, and the hydrophobic Si−CH3 groups exist in the SiO2 network. The Pd atoms have a lower concentration on the surface and more Pd atoms embedded in the SiO2 matrix. The Pd-doped SiO2 membrane materials calcined at 350 °C with a palladium/tetraethylorthosilicate molar ratio of 0.15 exhibit large BET surface area (up to 683.36 m2/g) and total pore volume (up to 0.386 cm3/g), as well as a mean pore diameter of about 2.26 nm.

Fouling of polymer and organic-inorganic membranes during filtration of corn distillery

Fouling of polymer and organic-inorganic membranes during filtration of corn distillery

Structure and Properties of New sPEEK/Zirconia/Protic Ionic Liquid Membranes for Fuel Cell Application

Hybrid organic–inorganic membranes based on sulfonated poly(ether ether ketone) (sPEEK), zirconium oxide, and the protic ionic liquid (PIL) diethylmethylamine triflate ([dema][TfOH]) have been synthesized. Their structure has been investigated by X‐ray diffraction and small‐angle X‐ray scattering and correlated to their electrical and thermomechanical properties. The membranes present good mechanical and chemical stabilities, as well as thermal stability over 300 °C. Zirconia contents up to 5 wt% (10 wt% PIL) lead to the formation of isolated zirconia‐rich aggregates dispersed in the polymer matrix, constituted of spatially correlated zirconia nanoparticles. This segregation of zirconia species in nanodomains, interacting with sulfonic groups of sPEEK, inhibits conductivity. Differently, zirconia content of 6 wt% (10 wt% PIL) induces a conductivity much higher than pristine sPEEK, due to the formation of an extended fractal structure in the whole sample, constituted of connected zirconia‐rich aggregates. Interaction of PIL molecules with the zirconia aggregates along this extended structure shall form new conducting channels for ion transport, favoring conductivity. image

Formation of the organic-inorganic proton exchange membrane

Formation of the organic-inorganic proton exchange membrane

Homogeneous polyethersulfone hybrid membranes prepared with in-suit synthesized magnesium hydroxide nanoparticles by phase inversion method

Mg(OH)2/PES (magnesium hydroxide/polyethersulfone) hybrid membranes were prepared by in-suit synthesized phase inversion method. The highlight of this method is that it affords uniform distribution of Mg2+ on an atomic level in the casting solution, reacted with OH− in the coagulation bath during the formation of membrane via phase inversion process, and nano-sized Mg(OH)2 was in-suit formed and distributed uniformly in PES matrix. SEM, XPS and BET analysis were performed to characterize the membranes, and ultrafiltration properties were investigated and compared. The results indicated that all the tested performance of the PES membranes was generally improved by the existence of Mg(OH)2. Additionally, with the increase of MgCl2·6H2O, the surface hydrophilicity, porosity, and permeation flux improved proportionally, while EA retention rate and antifouling property increased firstly and then decreased. It is suggested that this research will provide a new line for the preparation of homogeneous organic-inorganic membranes.

Charge Transport through Organic Molecular Wires Embedded in Ultrathin Insulating Inorganic Membrane

A hybrid organic-inorganic membrane for facilitating artificial photosynthesis is made by embedding surface bound molecular wires in an inorganic ~2 nm thick silica layer by low temperature atomic layer deposition. This membrane is meant to facilitate electron and proton transport between water oxidation and carbon dioxide reaction sites while blocking products and intermediate reactions by compartmentalizing the reaction microenvironments. Here the membrane is studied in a flat form as an intermediate step towards a working artificial photosynthesis system. The membrane is characterized using FT-IR, XPS and EDS-STEM, confirming the wires are intact and embedded in silica. Charge transport through the wires is confirmed by directly measuring the short circuit photocurrent generated by hole injection from a Ru based dye solution while at the same time blocking charge transport from Sn based dye solution which does not have the proper energy level alignment to inject charges to the wires. The incorporation of a molecular wire in an inorganic matrix may facilitate the incorporation of other molecular electronic building block and enable their use in other applications and fields of study.

Organic-inorganic membranes for filtration of corn distillery

Organic-inorganic membranes were obtained by modification of polymer microfiltration membrane with inorganic ion-exchangers, which form secondary porosity inside macroporous substrate (zirconium hydrophosphate) or simultaneously in the macroporous substrate and active layer, depending of the particle size (from ?50 nm up to several microns). Precipitation of the inorganic constituent is considered from the point of view of Ostwald-Freundlich equation. Such processes as pressing test in deionized water and filtration of corn distillery at 1-6 bar were investigated. Theoretical model allowing to establish fouling mechanism, was applied. It was found that the particles both in the substrate and active layer prevent fouling of the membrane with organics and provide rejection of colloidal particles.

Demonstration of Multiscale Proton Transport in Hybrid Organic-Inorganic Membrane

Summary: Hybrid membranes containing a continuous functionalized silica network were synthesized by combining electrospinning and the sol-gel chemistry. The in-plane proton conductivity was evaluated at 80°C under 80% relative humidity and values of 100 mS/cm have been measured. We investigated the proton transport in these multiscale membranes through different techniques including electrochemical impedance spectroscopy, FG-NMR and QENS. We demonstrated that hydrated protons interact with silica network, but connected pathways for hydrated proton exist in the all membranes that facilitate in fine the proton transport. Introduction Improvements need to be performed before Polymer Electrolyte Membrane Fuel cells will be commercialized for transport application. One of the challenges is to replace Nafion, the state of the art by membranes that are efficient at high temperature (³ 100°C) and low humidity (50% RH). Up to date, the development on polymer electrolyte membranes capable of working at higher temperatures with dry gases is still under consideration. Among the different approaches, the addition of inorganic materials capable of retaining water to perfluorosulfonated ionomers has been developed [1]. But, the results are often poor mechanical properties of the membrane, inorganic particle leaching out of the membrane when the fuel cell is running. Only few examples point out the benefit of these particles and how their size, distribution, functionalization can result in unexpected activity. [2, 3] We propose here to develop hybrid organic-inorganic membranes, exempt of Nafion. These membranes consist of two intermingled networks of PVDF-HFP and functionnalized silica network.[3] To avoid the phase separation between these two components, we synthesized the hybrid membrane by combining electrospinning and the sol-gel process. To achieve satisfactory proton conduction, a comprehensive study was performed on the proton transport in these multiscale membranes. To do so, we employed different techniques including electrochemical impedance spectroscopy, PG-NMR and QENS. Experimental Field Gun Emission-Scanning Electron Microscopy (FG-SEM), High Resolution Transmission Electron Microscopy were used to characterize the microstructure of the hybrid membranes while Small Angle Neutron Scattering (SANS) was performed to study the hybrid organic/inorganic interfaces. In-plane proton conductivity was determined as function of temperature and humidity. Electrochemical impedance spectroscopy (EIS), 2H NMR relaxation and 1H pulsed field gradient NMR (PFGNMR), quasielastic neutron scattering (QENS) were used to study the proton transport at various scales. Results Hybrid organic-inorganic membranes were fabricated by electrospinning in controlled atmosphere (Relative Humidity ~ 20% and T = 25°C) on aluminum foil which serves as counter electrode. The electrospun solution consists of dissolved polymer and pre-hydrolyzed silica precursors. After processing and heat treatment at 70°C, the hybrid membrane is homogenous, flexible with a thickness ranging from 10 to 100 mm depending on the volume of the used hybrid solution. Characterization techniques including FG-SEM, SANS and HR-TEM demonstrated that the fibers in the membrane are composed of an alternation of a thin layer of polymer and oblong functionalized silica domains connected to each other to form a continuous network. To characterize the proton transport in the electrospun hybrid organic-inorganic membranes, their proton conductivities were measured at 80°C under various relative humidity (RH) conditions. We found that this complex architecture gives rise to efficient proton transport as conductivity values superior to 100 mS/cm is achieved at 80°C under 80% relative humidity. Lately, macroscopic diffusion coefficient was measured by EIS and values compare well with Nafion, confirming the fast transport of hydrated proton through the membrane. Unexpectedly, hydrated proton and water molecule interact with the silica network, giving rise to local diffusion coefficient one order of magnitude lower than Nafion (PG-NMR and QENS) but diffuse rapidly throughout the membrane, as the diffusion coefficient of water is comparable to Nafion for the range of 1 to 10 mm. Conclusion In contrast to what it has been observed in Nafion, we found that the water diffusion coefficient (m to Å) can be locally slowdown (2 x 10-6 cm2/s) due to weak interactions with the silica network but diffusion coefficient determined by EIS is high (9.6 x 10-6 cm2/s) at least comparable to one observed in Nafion, the state of art at the mm scale. Acknowledgements The authors would like to thank ANR MéconPrhy for the financial support.

Advances in Porous Organic-Inorganic Composite Membranes

Advances in Porous Organic-Inorganic Composite Membranes

Lagp-Based Composite Membrane for Rechargeable Aqueous Li-Air Battery

Novel high efficiency grid-scale high energy density storage systems, such as rechargeable Li-air batteries (LABs), are urgently needed to enable and manage a more wide-spread utilization of renewable energy sources. Among these organic electrolyte LABs offer the highest gravimetric energy density, but they suffer from limited cyclability and poor energy efficiency due to the high over-potential during charge and discharge. LABs relying on aqueous catholytes promise somewhat lower theoretical capacity but a higher potential to reach theoretical limits in practical devices. In these systems catholytes with high solubility for the discharge product enhance the cycle efficiency and power performance. The fast ion-conducting electrolyte membrane is the key component of an aqueous Li-air battery, as it protects the lithium anode from reacting chemically with the catholyte solution. Here, an inorganic-organic hybrid membrane based on NASICON-type Li1.5Al0.5Ge1.5(PO4)3 (LAGP) ceramics and PEO:PVDF:LiBF4 with a thickness of 100-150 μm is designed and tested inside an aqueous LAB. By varying the mass fraction of the ceramic and polymer constituents mechanical properties and ionic conductivity of the membrane were optimized yielding conductivities of 5×10-4 S cm-1. The membrane in an Li-air cell also has to be stable in contact with the lithium anode. Cyclic voltammetry of the membrane up to 4 V vs. Li/Li+shows only two distinct peaks of cathodic deposition and anodic dissolution of the anode, confirming the wide electrochemical window of the membrane. To identify a suitable solid electrolyte:catholye couple, the membrane was immersed in an aqueous solution of LiCl (10M) and the changes in the structure and conductivity were monitored. Geometry and XRD pattern of the membrane are almost identical before and after immersion for 20 days, while the conductivity of the membrane increases with immersion time. Figure 1 demonstrates the schematic design of the cell. Hybrid inorganic-organic membrane is placed between lithium anode and catholyte in the reaction chamber (cell). The catholyte is circulated between the cell and a reservoir. The air cathode consists of finely dispersed Pt on multi-walled carbon nanotube arrays on a carbon fiber cloth, so that oxygen reduction and formation are effectively catalyzed. Room temperature charge/discharge profiles of a cell cycled in the voltage range of 1.5 to 4.5 V for the first 10 cycles are shown in Figure 2. The cell is operated with a constant current density of 0.5 mAcm-2. Both charge and discharge cycles are limited to one hour. During the first cycle, the cell shows charge and discharge plateaus at 4.0 V and 2.6 V, respectively. The equilibrium potential is considerably increased compared to cells without a continuous supply of the catholyte; all other components remaining the same. To further enhance the energy efficiency of the LAB we explore ways to reduce the internal cell resistance by optimizing membrane thickness and patterning, as well as by tailoring charge transfer processes at the electrode:electrolyte:catholyte interfaces. Figure 1

Organic-inorganic materials containing nanoparticles of zirconium hydrophosphate for baromembrane separation.

Organic-inorganic membranes were obtained by stepwise modification of poly(ethyleneterephthalate) track membrane with nanoparticles of zirconium hydrophosphate. The modifier was inserted inside pores of the polymer, a size of which is 0.33 μm. Inner active layer was formed by this manner. Evolution of morphology and functional properties of the membranes were investigated using methods of porosimetry, potentiometry and electron microscopy. The nanoparticles (4 to 10 nm) were found to form aggregates, which block pores of the polymer. Pores between the aggregates (4 to 8 nm) as well as considerable surface charge density provide significant transport numbers of counter ions (up to 0.86 for Na+). The materials were applied to baromembrane separation of corn distillery. It was found that precipitate is formed mainly inside the pores of the pristine membrane. In the case of the organic-inorganic material, the deposition occurs onto the outer surface and can be removed by mechanical way. Location of the active layer inside membranes protects it against damage.

Facile synthesis of zirconia doped hybrid organic inorganic silica membranes

Hybrid organic inorganic silica membranes are interesting candidates for gas-separation applications due to their excellent hydrothermal stability. However, up to now these membranes lack the separation performance required to separate hydrogen from carbon dioxide. In this work a procedure for doping zirconia into the hybrid silica matrix is reported, resulting in an improved H2/CO2 permselective membrane compared with non-doped hybrid silica membranes. Zirconia doped 1,2-bis(triethoxysilyl)ethane (Zr-BTESE) was synthesized by sol–gel chemistry, using zirconyl nitrate as the zirconium source. By optimization of the sol reaction conditions (i.e. reaction time and temperature) a homogenous sol was obtained. Defect-free membranes were obtained by adjusting the concentration of the dip-coating solution. The doped membranes showed a slight decrease in hydrogen permeance from 4.4×10−7 to 1.8×10−7molm−2s−1Pa−1 as compared to an undoped BTESE membrane, but a large increase in H2/CO2 (from 4 to 16) and H2/N2 (from 12 to 100) permselectivity was observed.

Sol–gel hybrid membranes loaded with meso/macroporous SiO2, TiO2–P2O5 and SiO2–TiO2–P2O5 materials with high proton conductivity

In this work, highly conductive hybrid organic–inorganic membranes loaded with SiO2, TiO2–P2O5 and SiO2–TiO2–P2O5 meso/macroporous particles were prepared via a sol–gel process. Meso/macroporous particles were incorporated to hybrid membranes, for improving water retention and enhancing electrochemical performance. These particles with a polymodal pore size distribution were prepared by templating in highly concentrated emulsions, the particles showed a specific surface area between 50 m2/g (TiO2–P2O5) and 300 m2/g (SiO2–TiO2–P2O5). The particles were dispersed in a hybrid silica sol and further sprayed onto glass paper. The films were polymerized and sintered; those loaded with meso/macroporous particles had a homogenous distribution. High temperature proton conductivity measurements confirmed a high water retention. Conductivity of these materials is higher than that of Nafion® at higher temperatures (120 °C) (2·10−2 S/cm). This study provides processing guideline to achieve hybrid electrolytes for efficient conduction of protons due to their high surface area and porous structure.

Class II Hybrid Organic-inorganic Membranes Creating New Versatility in Separations

Class II Hybrid Organic-inorganic Membranes Creating New Versatility in Separations

Ion-fuelled L-Phenylalanine controlled pumping by hybrid membrane materials

We report organic–inorganic membrane materials for controlled translocation of ion-pairs along directional conduction pathways. The supramolecular/sol–gel combined procedure has been realised in two steps. First, the self-organization properties of 3-(ureidoarene)propyltriethoxysilane compound, 1 in aprotic solvents were determined, revealing the formation of supramolecular oligomers, in the self-assembly step. They led in a second sol–gel transcription step to hybrid membrane materials. Then, the transport of organic molecules of variable charge, like L-Phenylalanine can be directionally tuned, via ion-fuelled membrane polarization phenomena. Using this strategy, the transport of the cationic, zwitterionic and anionic forms of the L-Phenylalanine can be controlled and directionally oriented from the feed to strip phase and vice versa.

Hybrid organic–inorganic membranes from size exclusion deposition of fluorescent, octylene-bridged polysilsesquioxane particles

Hybrid organic–inorganic membranes were prepared by size exclusion deposition of fluorescent, octylene-bridged polysilsesquioxanes (OBP) nanoparticles onto ceramic membrane supports. Acid-catalyzed, sol-gel polymerization of 1,8-bis(triethoxysilyl)octane (BESO) was shown by dynamic light and scattering electron microscopy to afford spherical nanoparticles that, after 3–4 weeks, were sufficiently large enough to block the pores in porous, ceramic membranes with a 1.5nm cut-off. The OBP particles were deposited by drawing a low concentration sol through the ceramic membrane. The OBP particles blocked the pores with an intractable, tightly packed layer 3μm in thickness. The efficacy of size exclusion deposition was verified by incorporation of small amounts of a fluorescent, dansyl co-monomer into the particles and inspection of the membrane cross section by confocal fluorescence microscopy.

A facile synthesis of proton-conducting organic–inorganic membranes

Hybrid organic–inorganic proton conducting membranes based on arylsulfonic acid (Ar-SO3H) groups and poly(ethylene glycol) (PEG) units were easily obtained in one step synthesis by co-hydrolysis and polycondensation of 2-(4-Chlorosulfonylphenyl)ethyl trimethoxysilane and bis-silylated polyethylene oxide. The hydrolysis of SO2Cl groups into SO3H was achieved during the sol–gel process by the in situ generated HCl acting as catalyst for the hydrolysis and polycondensation reactions. All membranes were characterized by 1H, 13C and 29Si MAS solid-state NMR, elementary analysis, Scanning Electron Microscopy (SEM) and X-ray photoelectron (XPS) spectroscopy. Their thermal and thermomechanical properties were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), respectively.. The thermomechanical and conductive properties were found to be dependent on the PEG chain length and the PMMA amount. The proton conductivities of these materials were found to be approximately 10−2Scm−1 at 20°C.

Organic–inorganic hybrid proton exchange membrane based on polyhedral oligomeric silsesquioxanes and sulfonated polyimides containing benzimidazole

A new series of organic–inorganic hybrid proton exchange membranes (PEMs) were prepared using sulfonated polyimides containing benzimidazole (SPIBIs) and glycidyl ether of polyhedral oligomeric silsesquioxanes (G-POSS). SPIBIs were synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 5-amino-2-(4-aminophenyl) benzimidazole (APBIA) and 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS). The organic–inorganic cross-linked membranes can be prepared by SPIBIs with G-POSS by a thermal treatment process. The cross-linking density of the membranes was evaluated by gel fractions. The water uptake, swelling ratio, mechanical property, thermal behavior, proton conductivity, oxidative and hydrolytic stability of the cross-linked organic–inorganic membranes were intensively investigated. All the cross-linked membranes exhibit high cross-linking density for the gel fraction higher than 70%. Compared to pristine membranes (SPIBIs) and membranes without benzimidazole groups (SPI), the anti-free-radical oxidative and hydrolytic stabilities of cross-linked membranes are significantly higher. The anti-free-oxidative stability of SPIBI-100-P (cross-linked SPIBI membrane with 100% degree of sulfonation) is nearly four-fold higher than that of SPIBI-100. The proton conductivity of the cross-linked membranes ranges from 10−3 S cm−1 to 10−2 S cm−1 depending both on the degree of sulfonation (DS) of the SPIBI and temperature.

Effect of heat treatment on pervaporation separation of aqueous salt solution using hybrid PVA/MA/TEOS membrane

Heat treatment is believed to be an important step in controlling the morphology and properties of polymer based membranes. In this study, hybrid organic–inorganic membrane based on poly(vinyl alcohol) (PVA), maleic acid (MA) and tetraethyl orthosilicate (TEOS) was synthesised via a sol–gel route. The effects of heating temperature and heating time on pervaporation separation performance of aqueous salt solution were studied in relation to swelling and hydrophilic properties, the free volume, salt transport properties, and water diffusivity of the membrane. The free volume of the hybrid membrane under different heat treatment conditions were well correlated with the pervaporation testing results. With increasing heating temperature or time, the fractional free volume of the hybrid membrane was reduced due to a more compact structure by crosslinking among PVA, MA and TEOS. As a result, the water flux decreased and the salt rejection increased. The salt transport properties followed a similar trend as the water uptake, indicating the hydrated NaCl was solvated by water in the membrane phase.

A closer look at the development and performance of organic–inorganic membranes using 2,4,6-tris[3(triethoxysilyl)-1-propoxyl]-1,3,5-triazine (TTESPT)

2,4,6-Tris[3(triethoxysilyl)-1-propoxy]-1,3,5-triazine (TTESPT) is a new precursor for preparing membranes. The TTESPT-derived silica membrane exhibits a significant degree of selectivity for C3H6–C3H8 ∼37 at a permeation temperature of 50 °C, which greatly surpasses the upper-bounds of selectivity and permeance trade-off of carbon membranes. This indicates the potential for further development toward C3H6–C3H8 separation applications.