Organic-inorganic Composite Membranes Research Articles

Natural redox mediator anthraquinone aloe-emodin facilitated the in-situ mineralized γ-FeO(OH) membrane for the removal of tannic acid through photocatalytic-PMS activation

The growing utilization of Traditional Chinese Medicine (TCM) has resulted in an increase in wastewater. Herein, a new kind of organic-inorganic redox mediator membrane by immobilizing γ-FeO(OH) and aloe-emodin(AE) with the characteristic large π-conjugation anthraquinone structure on PVDF membrane was innovatively achieved. AE exhibiting both electron deficiency and redox activity possesses a co-catalyst role in degradation of tannic acid (TA), aiding in the separation of charge carriers through the sequential hydrogenation and dehydrogenation of AE. The removal rates of TA were 92.8 % in the tannic acid solution and 60.3 % in the simulated rhubarb wastewater by the AE-γ-FeO(OH) membrane under PMS+Vis conditions in 45 min. Also, they show a higher recovery of pure water flux and owning good fouling performance. Overall, this current work presents a novel approach for the design and preparation of organic-inorganic photocatalytic composite membrane using readily available natural products for the purification TCM wastewater.

Combining dip-coating and rotate-drying to preparation of PDMS on SiC tubular support with macropore for high pervaporation performance

High-performance polydimethylsiloxane (PDMS)/ceramic tubular pervaporation membranes have potential in industrial separation applications, but realizing the preparation of PDMS layer on the ceramic supports with micrometer-scale pore size (0.8 μm or 4.3 μm) for improving performance remains a challenge. We report a strategy (combined dip-coating and rotate-drying, DCRD) to preparation of PDMS on silicon carbide (SiC) tubular support with macropore. Response surface methodology was employed to optimize the dip-coating process, and the influence of friction velocity on tubular composite membranes was investigated. The results indicate that pulling speed, casting solution viscosity, and their interaction have significant effects on the pervaporation performance of PDMS/SiC tubular composite membranes. Moreover, increasing friction velocity results in uneven PDMS layer thickness, which in turn impacts the pervaporation performance of the composite membrane. Furthermore, the rigid structure of SiC restricts the movement of PDMS polymer chains, enabling the composite membrane to maintain stable pervaporation performance at higher isobutanol feed concentrations (3 wt%) or elevated feed temperatures (60 °C). After continuous operation for 200 h, the developed PDMS/SiC tubular composite membrane consistently maintained the total flux of 650 g m−2 h−1 and the separation factor of 39 for isobutanol/water. Eventually, this novel fabrication method offers new insights into the preparation of various other organic-inorganic tubular composite membranes.

Effect of composite membrane flux behavior on oily wastewater treatment: Predicting and optimizing based response surface methodology and AI

The use of inorganic-organic composite membranes or mixed matrix membranes in membrane technology has gained worldwide recognition as a reliable method for producing drinkable water and effectively treating and purifying wastewater. This study aimed to create a model using response surface methodology (RSM) and artificial neural network (ANN) that can accurately predict and optimize the flux behavior of a membrane made of a polymeric-ceramic composite material for oil-water separation. In addition, as mentioned earlier, the optimization of the factor has been achieved through the use of RSM to establish the most optimal mode for the oil-water separation process. The findings of the RSM analysis show that the projected R2 value of 0.9764 closely matches the Adjusted R2 value of 0.9789, indicating a strong agreement between the two. Furthermore, the ANN modeling exhibited significant agreement with the actual data. The ANN model achieved a high level of performance, with an R-squared value of 0.9998 and a mean squared error (MSE) of 2.57E-03. The results were obtained by employing a model structure comprising two concealed layers, with the initial concealed layer comprising 3 neurons and the subsequent concealed layer comprising 10 neurons. The RSM was tweaked to find that the best flow mode happened when the oil emulsion level was 107.117 mg/L, the transmembrane pressure (TP) was 134.219 kPa, and the time period was 12.836 s.

Preparation and characterization of high flux cellulose acetate/hydroxyapatite composite ultrafiltration membranes for water treatment

In this study, we prepared cellulose acetate/hydroxyapatite (CA/HA) composite ultrafiltration membranes for water treatment. The organic-inorganic composite ultrafiltration membranes were prepared by doping different contents of HA nanoparticles into the CA by phase inversion method. The structure and morphology of the HA nanoparticles and membranes were characterized by X-ray diffraction, Fourier infrared spectroscopy and Scanning electron microscopy. Thermogravimetric analysis was used to describe thermal characteristics. The contact angle value and wettability test were used to determine the hydrophilicity of the polymer membrane. In addition, fluxes and rejection rates were tested at different pollutant concentrations and different pH values. The pore size and porosity gradually increased and the hydrophilicity and thermal stability of membrane were improved with the deposited HA content. With the addition of 5 wt% HA, the tensile strength of the membrane reached a maximum value of 2.80 MPa. The fluxes of pure water, CR, MB and BSA were 152.23, 111.25, 125.69 and 87.47 L/(m2·h), while the rejection rates of CR, MB and BSA were 99.99 %, 92.91 % and 99.99 %, respectively. In addition, the rejection decreased with increasing dye concentration and showed higher rejection under alkaline conditions. On the whole, the produced CA/HA composite membranes exhibited significantly higher permeability and rejection rates, offering them a lot of potential for water treatment applications.

Short-side-chain perfluorosulfonic acid incorporated with functionalized silane-based hybrid membrane for the application of energy devices

A unique functionalized organosilane (FOSi) is synthesized and prepared as a hybrid organic-inorganic composite membrane (OICM) using short-side-chain perfluorosulfonic acid (SSC-PFSA) at a large scale for vanadium redox flow battery (VRFB). The OICM solution is fabricated by using 75 wt % of SSC-PFSA and 25 wt % of FOSi and cast with the help of Roll to Roll (R2R) film casting equipment. The OICM's proton conductivity and performance are comparable to the Nafion membrane, owing to additional hydrophilic fields in the hybrid membrane. The OICM possesses proton conductivity of 0.13 S/cm and an ion exchange capacity of 1.44 meq/g, even though the water uptake has been lowered than the PFSA owing to better dispersion of FOSi. OICM has a low vanadium permeability (1.52 × 10−6 cm2/min) and remarkable selectivity, which is a significant benefit. Consequently, over 45th cycles, the OICM performs comparably to Nafion in energy efficiency combined with coulombic and voltage efficiency. The unit cell-test with OICM shows a normalized coulombic efficiency due to low permeability than PFSA and high voltage efficiency due to high proton conductivity. Hence OICM divulges a promising path to developing an alternative membrane for energy devices.

A facile strategy for the preparation of carbon nanotubes/polybutadiene crosslinked composite membrane and its application in osmotic energy harvesting

The osmotic energy between riverine water and seawater can be converted into electricity by reverse electrodialysis (RED). However, the facile fabrication of advanced RED membranes with high energy conversion efficiencies, large areas, and excellent mechanical properties remains a challenge. Carbon nanotubes (CNTs) exhibit excellent conductivity and provide suitable channels for ion transport but cannot form membranes independently, which limits the related applications in osmotic energy conversion. Herein, a new organic–inorganic composite membrane is prepared by combining hydroxyl-terminated polybutadiene as a matrix and carbon nanotubes as transport nanochannels. The nanotubes are pre-subjected to plasma treatment to increase the surface charge density and transport capacity of the nanochannels, improving the ion selectivity and energy conversion efficiency. Under actual seawater/river water conditions, the developed membrane delivers a power density of ∼5.1 W/m2 and shows good mechanical strength (219 MPa). Our work provides a facile solution to the problem posed by the inability of ideal nanochannels to form membranes independently and paves the way for the application of RED membranes in osmotic energy conversion.

Fabrication of a Fish-Bone-Inspired Inorganic-Organic Composite Membrane.

Biological materials have properties like great strength and flexibility that are not present in synthetic materials. Using the ribs of crucian carp as a reference, we investigated the mechanisms behind the high mechanical properties of this rib bone, and found highly oriented layers of calcium phosphate (CaP) and collagen fibers. To fabricate a fish-rib-bone-mimicking membrane with similar structure and mechanical properties, this study involves (1) the rapid synthesis of plate-like CaP crystals, (2) the layering of CaP-gelatin hydrogels by gradual drying, and (3) controlling the shape of composite membranes using porous gypsum molds. Finally, as a result of optimizing the compositional ratio of CaP filler and gelatin hydrogel, a CaP filler content of 40% provided the optimal mechanical properties of toughness and stiffness similar to fish bone. Due to the rigidity, flexibility, and ease of shape control of the composite membrane materials, this membrane could be applied as a guided bone regeneration (GBR) membrane.

Organic-inorganic composite membrane-based transport membrane condenser: Performance of waste recovery from hot gas mixture of CO2 and water vapor

Recovering the waste heat from the stripped gas (i.e., the gas mixture of CO2 and water vapor) using the transport membrane condenser is an effective approach to reduce the regeneration heat consumption in CO2 chemical absorption process. To decrease the capital expenditure of transport membrane condenser, this study prepared an inexpensive organic–inorganic composite membrane through adding the hydroxylated boron nitride (BN-OH) into the polyvinylidene fluoride (PVDF) during membrane preparation via nonsolvent induced phase separation. Then the composite membrane was placed in a membrane cell as the transport membrane condenser to recovery the waste heat of simulated stripped gas. The results showed that when compared to the single PVDF membrane, the addition of BN-OH improves the pore uniformity, thermal conductivity, and porosity of membrane. Among all the prepared composite membranes, the composite membrane adding 5 wt% nano-sized BN-OH particles exhibits the best waste heat recovery performance. Furthermore, a decrease in the membrane thickness in addition to an increase in polyvinylpyrrolidone dosage during membrane preparation enhances the waste heat recovery performance, however deteriorates the mechanical strength of membrane. Moreover, the organic–inorganic composite membrane prepared in this study demonstrated a good stability of waste heat recovery performance during a long-term operation, showing a potential in the rich solvent-split modified carbon capture process to achieve a low capital expenditure and a high waste heat recovery performance.

High-Toughness and High-Transparency Recyclable Poly(vinyl alcohol)-Based Organic–Inorganic Composite Membranes

High-Toughness and High-Transparency Recyclable Poly(vinyl alcohol)-Based Organic–Inorganic Composite Membranes

Proton Conducting Organic-Inorganic Composite Membranes for All-Vanadium Redox Flow Battery.

The quest for a cost-effective, chemically-inert, robust and proton conducting membrane for flow batteries is at its paramount. Perfluorinated membranes suffer severe electrolyte diffusion, whereas conductivity and dimensional stability in engineered thermoplastics depend on the degree of functionalization. Herein, we report surface-modified thermally crosslinked polyvinyl alcohol-silica (PVA-SiO2) membranes for the vanadium redox flow battery (VRFB). Hygroscopic, proton-storing metal oxides such as SiO2, ZrO2 and SnO2 were coated on the membranes via the acid-catalyzed sol-gel strategy. The membranes of PVA-SiO2-Si, PVA-SiO2-Zr and PVA-SiO2-Sn demonstrated excellent oxidative stability in 2 M H2SO4 containing 1.5 M VO2+ ions. The metal oxide layer had good influence on conductivity and zeta potential values. The observed trend for conductivity and zeta potential values was PVA-SiO2-Sn > PVA-SiO2-Si > PVA-SiO2-Zr. In VRFB, the membranes showcased higher Coulombic efficiency than Nafion-117 and stable energy efficiencies over 200 cycles at the 100 mA cm-2 current density. The order of average capacity decay per cycle was PVA-SiO2-Zr < PVA-SiO2-Sn < PVA-SiO2-Si < Nafion-117. PVA-SiO2-Sn had the highest power density of 260 mW cm-2, while the self-discharge for PVA-SiO2-Zr was ~3 times higher than Nafion-117. VRFB performance reflects the potential of the facile surface modification technique to design advanced membranes for energy device applications.

Pore-filling membrane containing solely zirconium phosphonates with high content through in-situ conversion

Organic-inorganic composite membranes are used in various applications, especially as proton-conducting electrolyte membranes for proton-exchange membrane fuel cells (PEMFCs). This study proposed a method to fill a flexible porous substrate solely with high amounts of inorganic (approximately 48 wt%) nano-zirconia precursor, surface-modified by acetylacetone (AcAc-Zr). AcAc-Zr can be converted to zirconium phosphate (ZrPi) in situ, and several other zirconium phosphonates, such as zirconium aminotris-methylene-phosphonate (ZrATMP) and zirconium 1-hydroxyethane-1,1-diphosphonate (ZrHEDP). Transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) analysis revealed that the pores were continuously filled with ZrPi, indicating that ZrPi has a percolated structure in the membrane, beneficial for their proton conduction. The proton conductivities of the membranes, including ZrPi, ZrHEDP, and ZrATMP, were sufficiently high, on the order of 1 mS cm−1 at 80 °C and 95% relative humidity.

A Brief Overview of the Microstructural Engineering of Inorganic-Organic Composite Membranes Derived from Organic Chelating Ligands.

This review presents a concise conceptual overview of membranes derived from organic chelating ligands as studied in several works. The authors' approach is from the viewpoint of the classification of membranes by matrix composition. The first part presents composite matrix membranes as a key class of membranes and makes a case for the importance of organic chelating ligands in the formation of inorganic-organic composites. Organic chelating ligands, categorized into network-modifying and network-forming types, are explored in detail in the second part. Four key structural elements, of which organic chelating ligands (as organic modifiers) are one and which also include siloxane networks, transition-metal oxide networks and the polymerization/crosslinking of organic modifiers, form the building blocks of organic chelating ligand-derived inorganic-organic composites. Three and four parts explore microstructural engineering in membranes derived from network-modifying and network-forming ligands, respectively. The final part reviews robust carbon-ceramic composite membranes as important derivatives of inorganic-organic hybrid polymers for selective gas separation under hydrothermal conditions when the proper organic chelating ligand and crosslinking conditions are chosen. This review can serve as inspiration for taking advantage of the wide range of possibilities presented by organic chelating ligands.

Silk Nanofibril-Palygorskite Composite Membranes for Efficient Removal of Anionic Dyes.

To develop membrane materials with good performance for water purification that are green and low cost, this work reports an organic-inorganic composite membrane composed of silk nanofibrils (SNFs) and palygorskite (PGS). To improve the stability of the the composite membrane, genipin was used as a crosslinking agent to induce the conformational transition of SNF chains from random coils to β-sheets, reducing the swelling and hydrolysis of the membrane. The separation performance can be adjusted by tailoring the component ratio of the nanomaterial. The results showed that these membranes can effectively remove anionic dyes from water, and they exhibit excellent water permeability. The SNF-based membrane had strong mechanical and separation properties, and the PGS could tune the structure of composite membranes to enhance their permeability, so this green composite membrane has good prospects in water treatment and purification applications.

Inorganic-organic composite membranes containing amino-functionalized mesoporous silica loaded phosphotungstic acid with enhanced fuel cell performance and stability

In this work, phosphotungstic acid (HPW) modified amino-functionalized mesoporous silica (AMS) as an inorganic filler (AMS@HPW) is incorporated into sulfonated poly (aryl ether sulfone) (SPAES) to prepare inorganic-organic composite membrane. The fabricated silica possesses a mesoporous structure with a surface area of 488.74 m2/g. The amino modification of silica acting as a “bridge” loads more HPW and promotes the compatibility between inorganic fillers and SPAES. The obtained SPAES/AMS@HPW composite membranes effectively inhibit HPW leakage and display better stability and fuel cell property due to the acid-base interaction and hydrogen-bond networks. Especially, the SPAES/AMS@HPW-1.0 membrane displays 18.4% higher proton conductivity (175.5 mS/cm) at 90 °C and 22.3–28.5% higher power density (470.4–678.4 mW/cm2) at 60%–100% RH than the original membrane. In addition, the SPAES/AMS@HPW-1.0 membrane still maintains stable voltage output and shows lower voltage decay (0.331 mV/h) and hydrogen permeation current density (8.28 mA/cm2) than Nafion 112 after the durability test.

Interfacial Tailoring of Polyether Sulfone-Modified Silica Mixed Matrix Membranes for CO2 Separation.

In this work, in situ polymerization of modified sol-gel silica in a polyether sulfone matrix is presented to control the interfacial defects in organic-inorganic composite membranes. Polyether sulfone polymer and modified silica are used as organic and inorganic components of mixed matrix membranes (MMM). The membranes were prepared with different loadings (2, 4, 6, and 8 wt.%) of modified and unmodified silica. The synthesized membranes were characterized using Field emission electron scanning microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, thermogravimetric analyzer, and differential scanning calorimetry. The performance of the membranes was evaluated using a permeation cell set up at a relatively higher-pressure range (5-30 bar). The membranes appear to display ideal morphology with uniform distribution of particles, defect-free structure, and absence of interfacial defects such as voids and particle accumulations. Additionally, the CO2/CH4 selectivity of the membrane increased with the increase in the modified silica content. Further comparison of the performance indicates that PES/modified silica MMMs show a promising feature of commercially attractive membranes. Therefore, tailoring the interfacial morphology of the membrane results in enhanced properties and improved CO2 separation performance.

Surface Mineralization of the TiO2-SiO2/PES Composite Membrane with Outstanding Separation Property via Facile Vapor-Ventilated In Situ Chemical Deposition.

Conventional polymeric membranes are broadly employed in water treatment processes; however, most of them suffer from relatively low water permeance and severe membrane fouling phenomena owing to their relatively hydrophobic nature. In this work, a novel class of inorganic-organic composite membranes was developed through a newly developed vapor-ventilated in situ chemical deposition method, where the Ti and Si precursors were first hydrolyzed and then conferred into metal oxides to form a continuous TiO2-SiO2 modification layer. Owing to the distinct physicochemical properties, the Ti and Si precursors were leveraged as quasi-molecular regulators to tune the membrane surface chemistry and pore aperture (within the nanoscale) to benefit highly efficient water purification by underpinning the rapid transport of water molecules and featuring an excellent fouling-resistant and fouling-releasing property against typical pollutants. The as-developed TiO2-SiO2/PES composite membrane showed a high water permeance of 187.4 L·m-2·h-1·bar-1, together with a relatively small mean pore aperture of 4.2 nm, showing an outstanding permeating efficiency among state-of-the-art membranes with a similar separation accuracy. This study provides a paradigm shift in membrane materials that could open avenues for developing high-performance inorganic-organic composite membranes for complex wastewater treatment.

Preparation of high permeance thin-film composite nanofiltration membrane on macroporous ceramic support

Thin-film composite (TFC) nanofiltration (NF) membranes have been widely used in water purification processes. In harsh conditions, however, the application of TFC membrane was limited by selectivity loss because of swelling or dissolution. In this study, a defect-free polyamide (PA) layer was directly prepared on a tubular alumina ceramic membrane with a pore size of 100 nm to compensate these shortcomings. The ceramic support, owing to its superior hydrophilicity, showed excellent affinity with aqueous diamine monomers, preventing defects caused by large pore sizes. Besides, the narrow aperture distribution of support is conductive to control the water-oil interface at an appropriate position that the active layer can form near the support by simple air-drying. Different morphologies and performances were easily obtained by changing the monomer concentration and reaction time. The resulting organic–inorganic composite membrane exhibited pure water permeance of 21.7 LMH/bar and desirable rejection to Na2SO4 of 99.0%. Moreover, the prepared NF membrane showed satisfactory compaction resistance at pressure from 2 to 12 bar owing to the excellent mechanical strength of the support. The inorganic support also endowed the TFC membrane with good performance stability even at 75 °C and after soaking in different organic solvents for one week.

Organic-inorganic composite ultrafiltration membrane with anti-fouling and catalytic properties by in-situ co-casting for water treatment

Organic-inorganic composite membranes have received much attention for superior water-treatment performance, where manipulating distribution of inorganic nanoparticles in membrane matrix remains a great challenge. Therefore, an in-situ co-casting was developed to modulate distribution of nanoparticles in membrane matrix for preparing multifunctional dual-layer manganese dioxide-polyvinylidene fluoride (MnO2-PVDF) composite ultrafiltration membrane. Results showed MnO2-PVDF membranes possessed apparent bi-layer structure and nanoparticles were distributed uniformly on the surface and upper layer. Such a configuration improved hydrophilicity with a maximum pure water permeance of 1012.97 L/m2·h·bar and displayed excellent mechanical strength. From anti-fouling tests, 7.5 wt% MnO2-PVDF membrane presented the highest flux recovery of 83.2%, and low fouling propensity in either bovine serum albumin (BSA) solution or secondary effluent. The enhanced anti-fouling resulted from less attractive or even repulsive interactions between MnO2-PVDF membranes and foulants. Furthermore, the MnO2-PVDF membrane could accomplish ∼100.0% water flux recovery by a facile peroxymonosulfate (PMS) cleaning, following BSA fouling. Similarly, the catalytic capability of MnO2-PVDF membrane for PMS was evidenced through the removal of various organic pollutants. In long-term operation, the composite membrane displayed excellent stability and low Mn ion leaching. Our results provide a promising route for structural regulation and development of organic-inorganic composite membranes for water treatment.

Design of bentonite/polyurethane composite membrane with a high flux in treatment of organic wastewater by using the pigment volume concentration theory

The flux and rejection rate of the membrane in wastewater treatment are main factors to evaluate the efficiency of membrane separation. In this study, bentonite was added into polyurethane (PU) as a pigment to prepare a type of composite membrane. The properties of composite membrane were designed and regulated by the pigment volume concentration (PVC) theory to optimize the flux and rejection rate in organic wastewater treatment. FT-IR spectra showed the interaction between bentonite and PU matrix that the swelling degree depended on this synergistic effect. The hydrophilic surface of membrane was contributed by bentonite particles in PU matrix. The PVC of the 3# composite membrane (11.81%) was closest to the critical pigment volume concentration (CPVC). The rejection rate of methylene blue was 97.28%, and at the same time, the water flux was 48.52 L·m−2·h−1. In addition, the rejection rates of typical organic pollutants such as Rhodamine B, phenol and industrial wastewater reached 95.32%, 96.84% and 97.16%, and the fluxes were 36.36 L·m−2·h−1, 41.58 L·m−2·h−1 and 38.84 L·m−2·h−1, respectively. This kind of inorganic-organic composite membrane has the potential to be applied to organic wastewater treatment. This study provides a new method for designing composite membranes by using the PVC theory.

High mechanical strength conductive inorganic–organic composite membranes for chiral separation and in situ cleaning

Enantiomeric separation based on membrane techniques has the advantages of energy efficiency, sustainable operation, and no additives, but there are no commercially available chiral membranes. The main reasons restricting the development of chiral membranes are separation specificity, poor mechanical properties, and membrane fouling. Therefore, we developed a novel chiral membrane with a stainless steel mat mesh as the base and β-cyclodextrin blended in cellulose acetate as the functional layer. The organic layer was loaded on the inorganic base by nonsolvent-induced phase inversion, and the two post treatments were optimized. The results indicate that the optimal percent enantiomeric excess (ee%) was 96.98 ± 5.22 % for d,l-tryptophan, 46.38 ± 1.65 % for d,l-phenylalanine, 11.50 ± 2.52 % for (RS)-propranolol, and 5.16 ± 0.88 % for (RS)-warfarin. The mechanical properties of stainless steel chiral composite membranes are better than those of other chiral membranes, and the Young's modulus values reached 3234 MPa. In addition, ultrasonic cleaning and electrolytic cleaning were successfully tested to solve the membrane fouling problem, and a comparative study indicated that electrolytic cleaning has low energy consumption and is a fast and effective cleaning method that can achieve flux recovery. These results indicate that conductive chiral membranes can achieve long-term separation of chiral compounds and have great potential for industrial applications.