Non-functionalized Membrane Research Articles

A self-cleaning thermocatalytic membrane for bisphenol a abatement and fouling removal

Thermocatalytic, ceramic microfiltration membranes for continuous micropollutants removal and simultaneous degradation of organic fouling were synthesized by integrating a Sr0.85Ce0.15FeO3 (SCF) perovskite in alumina membranes and tested for the bisphenol A (BPA) abatement under different experimental conditions. Scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX) characterization techniques were used to characterize the samples. The effect of water flux, BPA concentration and temperature on the BPA and fouling removal was investigated in detail. Up to 55 % of BPA was removed by filtration of a 9.6 mg L−1 BPA solution at 40 °C and a flux of 25 LMH. Degradation studies with BPA feed concentrations of 3.4, 5.5 and 9.6 mg L−1 showed higher degradation rate by the membrane with higher concentrations of BPA. Furthermore, the rate of BPA degradation increases with lower permeate flux, due to the longer retention time of pollutant in the membrane. Membranes were fouled with humic acid to study the thermocatalytic fouling removal. After fouling, membranes were rinsed to remove external, removable fouling, which was followed by 20–120 min of thermal treatment at 40 °C. This showed up to complete recovery of permeability by reduction of hydraulic resistance from the internal fouling in the membranes. No effect of heat treatment was observed for fouled non-functionalized membranes. Hence, the novel membrane studied in this article is a promising solution for simultaneous degradation of micropollutants and recovery of permeability during filtration, e.g. in wastewater treatment.

On the Choice of Different Water Model in Molecular Dynamics Simulations of Nanopore Transport Phenomena.

The water transport through nanoporous multilayered graphene at 300k is investigated using molecular dynamics (MD) simulation with different water models in this study. We used functionalized and non-functionalized membranes along with five different 3-point rigid water models: SPC (simple point charge), SPC/E (extended simple point charge), TIP3P-FB (transferable intermolecular potential with 3 points-Force Balance), TIP3P-EW (transferable intermolecular potential with 3 points with Ewald summation) and OPC3 (3-point optimal point charge) water models. Based on our simulations with two water reservoirs and a porous multilayered graphene membrane in-between them, it is evident that the water transport varies significantly depending on the water model used, which is in good agreement with previous works. This study contributes to the selection of a water model for molecular dynamics simulations of water transport through multilayered porous graphene.

Lyotropic Liquid Crystal-Based Membranes for Water Remediation: Fabrication, Characterization and Performance Evaluation.

In water remediation, biomimetic membranes are gaining much attention due to their selectivity, dynamic stability, nontoxicity, and biocompatibility. Lyotropic liquid crystals (LLCs) are self-organizing networks that can conform to an array of geometries with high pore densities. As such, LLCs are excellent membrane materials for water applications because they are water insoluble and are manipulated to conform to an array of morphologies that provide natural water channels that are readily tunable in size. They have the ability to create uniform pores, between the range of 1 and 5 nm, with large surface areas. Thus, this work focuses on the design, fabrication, and characterization of LLC-modified Janus-type membranes for forward osmosis applications. Physical characterization of the membranes was performed using scanning electron microscopy (SEM), and the results show an open-pore radius and the presence of both finger- and sponge-like pores depending on membrane preparation. The contact angle assessment indicates that as the membranes are further modified with other polymers (e.g., PAN), higher hydrophilicity and surface energy are achieved. Moreover, the Brunauer–Emmett–Teller (BET) analysis showed a significant variation in the pore distribution between membranes. Functionalized membranes presented satisfactory water flux and superior salt rejection compared to nonfunctionalized membranes. SupPACMoDS membranes are 83% more efficient at preventing salt back flux than the nonmodified version. This is credited to the thickness and pore structure provided by the PAN support layer in the membrane.

Simple and low cost dithizone-functionalized polymer membranes as a tool for mercury preconcentration and monitoring in aqueous bodies. Preliminary results using X-ray absorption near-edge structure (XANES).

<p>Here the effectiveness of cation selective membranes, produced for divalent mercury (Hg2+) preconcetration from aqueous bodies, is examined. To this end, the behavior of PVC-based membranes, functionalized with dithizone for mercury complexation, is examined by means of Energy Dispersive X-ray Fluorescence (EDXRF) and total reflection - X-ray absorption near-edge structure (TXRF–XANES) techniques. In our previous works, we successfully immobilized dithizone on PVC-based thin film substrates, creating novel Hg-selective membranes, and identified the optimal experimental parameters affecting mercury sorption from water samples. Nonetheless, the question remains, to what extent dithizone is responsible for mercury complexation on the membrane surface, or it just improves the membrane’s active surface area thus simply improving the adsorptive effect. Using the EDXRF technique it appears that membranes functionalized with dithizone has a much higher efficiency (by up to threefold) in preconcetrating mercury from water matrices, compared to the non-functionalized membranes. Then, the membranes were also examined by means of TXRF–XANES and it was identified that indeed mercury-dithizone complex is produced on the membrane surface, which is responsible for the much higher mercury sorption, compared to the non-functionalized membranes. Also, the XANES mercury-dithizone spectrum is presented. Given polymer membrane simple manufacturing procedure and their low cost this study works towards establishing a new method for very low concentration mercury analysis (sub-ppb levels) as well as mercury collection from aqueous bodies, provided that the membranes are produced and used in large-scale routine works.</p>

Hydrophobic ceramic capillary membranes for versatile virus filtration

In this study, we present hydrophobic yttria-stabilized zirconia capillary membranes conditioned for virus filtration. These macroporous ceramic filters (d50 = 150 nm) efficiently extract viruses regardless of their surface charge with high throughput rates. For hydrophobic functionalization of the ceramic membranes we used two different silanes, n-hexyltriethoxysilane (HTS, C6-chain) and n-octyltriethoxysilane (OTS, C8-chain), in three different molarities. The virus retention of the membranes is tested in dead-end mode by intracapillary virus feeding using two small bacteriophages as model species: MS2 and PhiX174. Virus retention increases most strongly for hydrophobic capillaries functionalized with 0.05 M OTS, showing a virtually complete retention with log-reduction values (LRVs) of ~ 9 for both bacteriophages compared to the non-functionalized membrane with LRVs of 0.3 ± 0.1 for MS2 and 3.4 ± 0.2 for PhiX174. The functionalized membranes allow a high membrane flux of ~ 150 L/(m2hbar), with throughput rates up to ~ 400 L/(m2 h) while maintaining high filtration efficiency. Even under varying feed conditions using only mono- or divalent salt ions or pH values ranging from 3 to 9, retention capacities of the capillary membranes are high. Accordingly, such hydrophobic ceramic membranes offer a versatile alternative to conventional polymeric membranes for virus removal with greatly improved membrane flux.

Bacteriophage-based strategies for biofouling control in ultrafiltration: In situ biofouling mitigation, biocidal additives and biofilm cleanser

The ability of bacteriophages to infect and destroy specific bacteria makes them promising antimicrobial agents in industrial processes. In this study, potential strategies of bacteriophage-facilitated biofouling control during membrane ultrafiltration (UF) were investigated through use of the model T4 bacteriophage and the model host bacterium, Escherichia coli. In the dead-end filtration mode, phages were immobilized on the membrane surface to serve as biocidal agents and inhibit the propagation of bacteria in situ. After 6 h of filtration, a 36% flux reduction was observed for the T4-functionalized membrane in comparison to 71% for the non-functionalized membrane. Surface modification of the membrane using O2 plasma treatment resulted in increased numbers of bound phage and enhanced biofouling resistance of the membrane. Introducing the phage into the feed of a cross-flow filtration system effectively mitigated the water flux reduction of the membrane caused by bacterial growth. By modifying the concentration of phage additives, the growth of bacteria was delayed, inhibited, or eliminated. Phage treatment changed the structure of biofilms on the membrane surface and facilitated in situ biofilm cleaning. A 20% greater recovery in water flux was observed for the biofilm-contaminated membrane following phage-assisted cleaning when compared to the membrane cleaned via a physical washing process. Taken together, these results show that bacteriophage assisted anti-biofouling strategies have the potential to mitigate biofouling in membrane processes in an environmentally friendly manner.

Palladium nanoparticle binding in functionalized track etched PET membrane for hydrogen gas separation

In this work, track-etched poly (ethylene terephthalate) (PET) membranes having different pore sizes were functionalized by the carboxylic groups and the amino groups. Palladium (Pd) nanoparticles of average diameter 5 nm were synthesized chemically and deposited onto pore walls as well as on the surface of these pristine and functionalized membranes. Effect of Pd nanoparticles binding on these membranes were explored and aminated membrane were found to bind more Pd nanoparticles due to its affinity. The morphology of these composite membranes is characterized by Scanning Electron Microscope (SEM) for confirmation of Pd nanoparticle deposition on pore wall as well as on the surface. Gas permeability of functionalized and non-functionalized membranes for hydrogen and carbon dioxide has been examined. From the gas permeability data of hydrogen (H2) and carbon dioxide (CO2) gases, it was observed that these membranes have higher permeability for H2 as compared with CO2. Due to absorption of hydrogen by Pd nanoparticles selectivity of H2 over CO2 was found higher as compared to without Pd embedded membranes. Such type of membranes can be used to develop hydrogen selective nanofilters for purification/separation technology.

Amino-Functionalized Ceramic Capillary Membranes for Controlled Virus Retention.

A straightforward chemical functionalization strategy using aminosilanes for high-flux yttria-stabilized zirconia capillary membranes is presented (macroporous, d50 = 144 nm, open porosity =49%, membrane flux ∼150 L/(m(2)hbar)). Three different aminosilanes with one, two or three amino groups per silane molecule, namely 3-aminopropyltriethoxysilane (APTES), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AE-APTES) and N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA), are used to generate the amino-functionalized membranes. With a higher number of amino groups per silane molecule increased loading capacities between 0.44 and 1.01 accessible amino groups/nm(2) membrane are achieved. Streaming potential measurements confirm that the zeta-potential of the membrane surface is converted from negative (non-functionalized) to positive (amino-functionalized). By operation in dead-end filtration mode using the model virus MS2 (diameter = 25 nm, IEP = 3.9) the virus retention capacity of the amino-functionalized membranes is significantly increased and log reduction values (LRVs) of up to 9.6 ± 0.3 (TPDA) are obtained whereas a LRV < 0.3 is provided by the non-functionalized membranes. Long-term dead-end filtration experiments for 1 week reveal a high stability of immobilized aminosilanes (TPDA), being robust against leaching. By iterative backflushing with desorption buffer MS2-loaded membranes are successfully regenerated being reusable for a new filtration cycle. The presented functionalization platform is highly promising for controlled virus retention.

A comparative experimental study on the deviation of the ideal selectivity in HDTMS-functionalized and untreated ceramic structures with pores in the upper mesoporous range

Mesoporous ceramic capillary membranes with mean pore sizes of about 20 nm are prepared as model structures to investigate the influence of an altered surface chemistry on the flow behavior of gases. To modify the membrane surface, a wet chemical silanization process with hexadecyltrimethoxysilane (HDTMS) is used to gain an alkyl-functionalized surface. Structural and surface characterizations show that the surface chemistry is altered without affecting the mean pore diameter. For the non-functionalized membrane, single gas permeation measurements at 20 °C reveal ideal permselectivities which are in good agreement with the Knudsen theory. In contrast, the HDTMS-functionalized membrane shows permselectivities regarding carbon dioxide (CO2) which deviate about 20% from Knudsen theory. The gas permeation measurements further indicate a relative flow enhancement for CO2 in comparison to nitrogen (N2), argon (Ar) and methane (CH4). Adsorption and desorption isotherms of CO2 and N2 at 20 °C show a decreased specific adsorption capacity for both gases, while the adsorption selectivity for CO2/N2 is increased. This indicates a weaker interaction of gas molecules and membrane surface due to HDTMS functionalization. This weaker gas–solid interaction along with the increased adsorption selectivity is proposed as reason for the experimentally observed deviation of the permselectivities from Knudsen theory.

Solid phase extraction membranes with submicron multifunctional adsorbent particles

Asymmetric polyethersulfone membranes with submicron particles comprising crosslinked poly(glycidyl methacrylate-co-2-acrylamido-2-methylpropane sulfonic acid) were prepared by a combination of a traditional liquid phase inversion process for making membranes with photopolymerization and crosslinking of functional monomers included in the casting solution. Scanning electron microscope images of the membrane cross-section revealed a hybrid structure with an interconnected network of submicron particles embedded within the porous polyethersulfone support. Permeation of toluidine blue solutions through non-functionalized membranes showed a dramatic effect of 2-acrylamido-2-methylpropane sulfonic acid concentration in the casting solution on the dynamic adsorption performance. The epoxide groups present in glycidyl methacrylate copolymer were transformed into amine functionalities by ring opening under alkaline conditions. Permeation of dilute Cu2+ solutions through functionalized membranes demonstrated that the plate height for some of these membranes was an order of magnitude smaller than for commercial particle-filled membranes used in solid phase extraction.

Laccase immobilization on titania nanoparticles and titania-functionalized membranes

Bio-catalytic degradation of recalcitrant micropollutants with enzymes such as laccase provides an environmentally attractive alternative to the conventional filtration and adsorption processes. However, enzyme loss and denaturation remain key challenges for their potential use in water treatment applications. In this work, laccase immobilization on TiO2 nanoparticles and TiO2 blended polyethersulfone (PES) membranes were investigated due to TiO2's chemical stability, ease of functionalization, and architecture. Different surface modification and functionalization strategies on support materials were compared based on enzyme loading, apparent activity, activity recovery, and stability. When coupling agent 3-aminopropyltriethoxysilane (APTES) and cross-linker glutaraldehyde (GLU) were applied sequentially, effective coupling of laccase was achieved based on 2,2′-azino-bis-(3-ethyl benzothiazoline-6-sulfonic acid) (ABTS) assays. TiO2 functionalized PES membrane showed better enzyme immobilization efficiency than the non-functionalized membrane. Optimal performance was observed for PES membrane containing 4wt% TiO2, where TiO2 not only provided the enzyme coupling sites but also affected the membrane surface morphology and hydrophilicity to favor the enzyme immobilization. These bio-catalytic membranes also displayed good enzyme stability, tolerance to wider pH range and vigorous filtration conditions required for water treatment applications. Kinetic study also indicated that the enzyme affinity to assay substrate was maintained after immobilization when compared with packed bed and batch reactors.

Osteogenic activities of MC3T3-E1 cells on heparin-immobilized poly(caprolactone) membranes

The aim of this study was to investigate the effects of heparin on the activity of osteoblast-like cells seeded on poly(caprolactone) (PCL) membranes. The membranes were prepared by solvent-casting technique in ~150 µm thickness. Then they were treated with 1,6-hexanediamine solution and functionalized with covalently bound heparin. The morphology, proliferation, and differentiation of MC3T3-E1 preosteoblasts on these membranes were investigated in vitro. The heparin functionalized PCL membranes, compared to non-functionalized membranes, significantly stimulated osteoblast proliferation. The Scanning electron microscope images confirmed the stimulative effect of covalently bound heparin on the osteoblast-like cell proliferation. The alkaline phosphatase and osteocalcin levels for cells proliferated on heparin containing PCL membranes were higher than that of nonfunctionalized membranes.