Polyamide Thin Film Research Articles

Synthesis and characterization of thin film nanocomposite membranes incorporated with surface functionalized Silicon nanoparticles for improved water vapor permeation performance

The present work demonstrates the fabrication of novel thin film nanocomposite membranes incorporating surface functionalized Silicon nanoparticles (average size 15–20nm) for removal of water vapor from nitrogen gas. Silicon nanoparticles were synthesized using the inductively coupled plasma (ICP) technique. The nanoparticles were dispersed in deionized water to introduce hydroxyl functional groups on the surface. The surface functionalization was confirmed by infrared spectroscopy. The effect of nano-Si concentration on the water vapor permeation properties of the TFN membranes was investigated in detail. The hydroxyl functional groups resulted in significant improvement of surface hydrophilicity and roughness of the nanocomposite membranes which in turn enhanced the water solubilization. The small size of nanoparticles permitted extensive interaction between the nanoparticles and the thin film polyamide layer. Increase in the nano-Si concentration resulted in improvement of water vapor permeance and selectivity till 0.5w/w%, above which the selectivity decreased because of the interference in interfacial polymerization reaction due to the dilution of aqueous phase monomer and high loading of nanoparticles. Water vapor permeance in excess of 2200GPU with vapor/N2 selectivity of 501 was obtained when the nano-Si loading was 0.5w/w%. The introduction of nano-Si in the polyamide membrane improved the stability of the nanocomposite membrane such that it slightly resisted the decrease in water vapor permeance with operating temperature.

Preparation of Polyamide Thin Film Composite Memrbanes with Metal Complex Contained Polysulfone Support Layer and Evaluation of Forward Osmosis Performance

Preparation of Polyamide Thin Film Composite Memrbanes with Metal Complex Contained Polysulfone Support Layer and Evaluation of Forward Osmosis Performance

Hollow mesoporous silica nanoparticles: A peculiar structure for thin film nanocomposite membranes

Incorporation of nanomaterials into the thin film composite (TFC) membrane is a promising approach to enhance the filtration performance of the membranes. This study was aimed to fabricate a novel thin film nanocomposite (TFN) membrane hybridized with hollow mesoporous silica nanoparticles (HMSN). It was expected that the HMSN-TFN membranes could have enhanced desalination performance. The research was focused on understanding of how the HMSN incorporation could affect physicochemical properties and permeation behavior of the HMSN-TFN membranes. Spherical HMSN with an average particle size of ~70nm were fabricated by hydrothermal synthesis using soft templates. The HMSN were successfully incorporated into the selective polyamide layer in the TFN structures. The physicochemical properties of the HMSN and TFN membranes were systematically investigated using DLS, TGA, ATR-FTIR, SEM, TEM, nitrogen sorption analyser, tensiometer and XPS analysis. The HMSN-TFN membranes were more hydrophilic and performed highly improved water flux (~40%) compared with the TFC membranes, while their rejection to NaCl was not significantly changed. The HMSN-TFN membranes also displayed a higher compaction resistance than the TFC membrane, suggesting a positive interaction between the HMSN and the polyamide thin film layer. This interaction is beneficial for enhancing the strength and durability of the newly developed HMSN-TFN membranes in the high-pressure filtration process.

Single-Step Assembly of Multifunctional Poly(tannic acid)-Graphene Oxide Coating To Reduce Biofouling of Forward Osmosis Membranes.

Graphene oxide (GO) nanosheets have antibacterial properties that have been exploited as a biocidal agent used on desalination membrane surfaces in recent research. Nonetheless, improved strategies for efficient and stable attachment of GO nanosheets onto the membrane surface are still required for this idea to be commercially viable. To address this challenge, we adopted a novel, single-step surface modification approach using tannic acid cross-linked with polyethylene imine as a versatile platform to immobilize GO nanosheets to the surface of polyamide thin film composite forward osmosis (FO) membranes. An experimental design based on Taguchi's statistical method was applied to optimize the FO processing conditions in terms of water and reverse solute fluxes. Modified membranes were analyzed using water contact angle, adenosine triphosphate bioluminescence, total organic carbon, Fourier transform infrared spectroscopy, ζ potential, X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy. These results show that membranes were modified with a nanoscale (<10 nm), smooth, hydrophilic coating that, compared to pristine membranes, improved filtration and significantly mitigated biofouling by 33% due to its extraordinary, synergistic antibacterial properties (99.9%).

Facile surface modification by aldehydes to enhance chlorine resistance of polyamide thin film composite membranes

A facile two-step surface modification by aldehydes was proposed to prepare chlorine resistant polyamide (PA) thin film composite (TFC) membranes simultaneously maintaining its high separation performance. Firstly formaldehyde was employed to reduce the chlorine sensitive N-H bonds of amide groups in PA layers into the chlorine resistant N-CH2OH bonds. Then glutaraldehyde was introduced to crosslink the newborn N-CH2OH groups via the stable ether bonds aimed to tighten the polyamide inter-chains. In the statically accelerating chlorination, the two-step modified PA-TFC membranes exhibited ameliorative chlorine resistance both in the acidic and alkaline aging conditions. More importantly, the sound retention of the typical ridge-valley polyamide structure after modification revealed that it was a mild surface modification solely confined to the outmost surface of the layers and succeeded to maintain the high separation performance. A more hydrophilic surface was also obtained after modification and resulted in a better antifouling performance towards protein. Reagents involved in were all easy-to-get and reacted with each other via chemical covalent bonds, which might open a promising way to commercialize a stable chlorine-resistant polyamide thin film composite membranes simultaneously of high separation performance.

Aqueous Degradation of Polyamide Membrane Materials in Halogenated Environments

Model polyamide thin films were prepared through a controlled interfacial polymerization route known as molecular layer by layer (mLbL). Films were synthesized directly onto quartz crystals and subjected to halogenated aqueous environments that are known to cause degradation of the amide network. A quartz crystal microbalance (QCM) was used as the detection platform to ascertain mass loss due to degradation in real time. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements were also performed at various stages of the degradation sequence to elucidate the chemical and morphological changes at the surfaces respectively. Appropriate strategies for accurately comparing material degradation resistance are proposed along with modifications to the crosslinked polyamide chemistry to produce more halogen tolerant polymeric surfaces.

Evaluation of forward osmosis membrane performance and fouling during long-term osmotic membrane bioreactor study

Forward osmosis membrane performance and fouling was studied during 100 days of continuous activated sludge treatment. The purpose of the study was to compare the performance and fouling of commercial cellulose triacetate and newly developed polyamide thin film composite membranes that treated high salinity and low salinity activated sludge from two membrane bioreactors. Water flux, reverse salt flux, and specific reverse salt flux were measured to evaluate the performance of virgin and fouled membranes. Membrane autopsy was used to investigate foulant composition and compare physicochemical membrane properties before and after fouling. The results indicated that both membrane types attained steady-state water flux over 100 days, characterized by an initial decline and subsequent steady-state period. Biofouling and organic fouling caused overall water flux decline, in which foulants were identical between membrane and activated sludge types. Water flux results were similar for the two activated sludge types and demonstrated that FO membrane performance and fouling was independent of total dissolved solids, calcium, and mixed liquor suspended solid concentrations. Lastly, virgin membrane properties (i.e., hydrophilicity and surface roughness) did not contribute substantially to membrane fouling. Cellulose triacetate membranes outperformed thin film composite membranes, with lower fouling propensity, higher water flux, lower reverse salt flux, and lower specific reverse salt flux.

Ink-jet printing assisted fabrication of thin film composite membranes

Modern printing techniques may facilitate membrane fabrication methods for the creation of novel polymer compositions and coatings. The interfacial polymerization reaction between diamine and triacyl chloride monomers is a highly efficient method to achieve currently used RO and NF thin film composite membranes. Here we present our investigation of the interfacial polymerization process using an ink jet printer for the application of an amine monomer to an ultrafiltration (UF) support as part of the polymerization method. In this study, single and multiple coatings of m-phenylene diamine (m-PDA) were applied to the UF support, without a draining step, before application of trimesoyl chloride (TMC). The resulting polymer films were characterized using FTIR and correlated to the amount of m-PDA printed on the UF support. The amount of crosslinking in the polyamide thin film increased as more m-PDA was printed on the support as indicated by XPS oxygen/nitrogen ratios. Also, the hydrophilicity of the surfaces could be explained with respect to the amount of polyamide crosslinking. SEM images of the membrane surfaces showed the progressive morphological changes to the surface as more m-PDA was printed. Salt rejection increased and the flux decreased as the amount of printed m-PDA increased, and was explained by amount of polymer crosslinking, surface hydrophobicity, and polyamide layer thickness. Further development of ink-jet printing within the context of interfacial polymerization methods, or for other membrane coating applications may accelerate the discovery of novel membranes, and lead to deeper understanding of membrane processes. Printing as a coating method exhibits higher accuracy and controllability compared to dip coating methods, that require removal of excess liquid or droplets via difficult to control draining or other steps, and which may eventually result in an overall more efficient fabrication process.

Polyamide thin-film composite membranes for potential raw biogas purification: Experiments and modeling

Abstract This work reports on raw biogas purification method via swollen polyamide thin-film composite membranes. Experiments on permeation of gas mixture through two commercial thin-film polyamide composite (TFC) membranes were performed using an in-house permeation apparatus. The active polyamide top layer of TFC membranes was swollen by water present in a feed stream of raw biogas, whose relative humidity was higher than 85%. An effective CO2/CH4 separation was based on the significantly higher solubility of carbon dioxide in water compared to that of methane. The transport properties of both composite membranes are discussed together with the structure of membrane top active layer. One-dimensional mathematical model for flow and mass transport in the membrane cell was developed. The model enables the evaluation of the mass transport coefficients by the iterative fitting of experimental data in the co-current and counter-current flow arrangements. The model also determines concentration profiles of gas component on both sides of the membrane, which are otherwise immeasurable experimentally. The model can be used to evaluate the effect of changing the membrane area on the performance of the membrane module. Model results are discussed with respect to the required CH4 enrichment.

Direct incorporation of silver nanoparticles onto thin-film composite membranes via arc plasma deposition for enhanced antibacterial and permeation performance

We report on a new technique that incorporates silver nanoparticles (AgNPs) onto polyamide (PA) thin film composite (TFC) reverse osmosis membranes via arc plasma deposition (APD) to impart antibacterial properties and simultaneously improve membrane performance. APD allows the direct deposition of AgNPs under vacuum dry condition, overcoming the drawbacks of the conventional wet-chemical methods. AgNPs (~7.6nm in diameter) were uniformly distributed without aggregation throughout the PA selective layer with some partially implanted into the PA matrix. Ag loading could be tuned by simply adjusting the number of APD purse shots. The deposited AgNPs exhibited good leaching stability, presumably due to the strong Ag-PA chemical interaction and partially buried AgNP morphology. The resulting Ag-incorporated TFC (Ag-TFC) membrane showed the strong and long-lasting antibacterial properties for both gram-negative and -positive bacteria. Simultaneously, the Ag-TFC membrane exhibited an enhancement in water flux of approximately 40% without deterioration in NaCl rejection. These performance changes were tentatively attributed to the partial destruction of the PA layer under the high energetic APD condition along with the increased membrane hydrophilicity. Hence, the APD process provides a simple and effective route to modify membranes with functional NPs.

Preparation of spherical mesoporous aminopropyl-functionalized MCM-41 and its application in polyamide thin film nanocomposite reverse osmosis membranes

Aminopropyl-functionalized MCM-41 (NH2-MCM-41) was synthesized by the one-pot hydrothermal method using tetraethoxysilane (TEOS) and (3-aminopropyl)triethoxysilane (APTES) as silica sources, cetyltrimethylammonium bromide as template, ethanol as a cosolvent, and sodium hydroxide as the alkali source. The synthesized nanoparticles were noticeably monodisperse with standard deviation of under 10% for the mean particle size. The specific surface area, pore size, pore volume and amino group density of the NH2-MCM-41 varied with the content of APTES in the initial solution. The NH2-MCM-41-polyamide thin film nanocomposite reverse osmosis (TFN RO) membranes were obtained by interfacial polymerization of trimesoyl chloride (TMC) and m-phenylene-diamine (MPD). The hydrophilicity of the TFN RO membranes was improved by the incorporation of NH2-MCM-41 nanoparticles. The water flux of 54 L m−2 h−1 at 1.6 MPa for NH2-MCM-41-polyamide TFN RO membrane was nearly 2.8 times that of the pure polyamide thin film composite (TFC) RO membrane and the solute rejection was 96.5% with a 0.1% w/v NH2-MCM-41 loading.

Biodegradation of cellulose triacetate and polyamide forward osmosis membranes in an activated sludge bioreactor: Observations and implications

This study investigated long-term stability of forward osmosis (FO) membranes against biodegradation during prolonged exposure to activated sludge. Results show that cellulose triacetate (CTA) membranes were more resistant against biodegradation than polyamide thin film composite (TFC) ones. Nevertheless, CTA membrane biodegradation was discernible after seven months of exposure to activated sludge as manifested by an increase in the membrane average pore size, water and salt permeability, and membrane structural parameter. As a result, of prolonged exposure to activated sludge, the water and reverse salt fluxes of the CTA membrane increased; and concomitantly the rejection of a range of trace organic contaminants decreased significantly. The impact of prolonged exposure to activated sludge on the polyamide active layer of TFC FO membranes was even more severe. Our results indicate that currently available commercial CTA and polyamide TFC FO membranes may not be readily compatible for practical osmotic membrane bioreactor (OMBR) operation. Thus, the development of new and robust FO membrane materials specifically designed for membrane bioreactor operation is essential for commercial OMBR applications.

Superhydrophilic and antibacterial zwitterionic polyamide nanofiltration membranes for antibiotics separation

Superhydrophilic and antibacterial zwitterionic polyamide thin film composite nanofiltration membranes (ZTFCMs) with excellent water permeability and antibiotics selectivity were prepared through the interfacial polymerization of N-aminoethyl piperazine propane sulfonate (AEPPS) monomer with trimesoyl chloride (TMC) monomer on top of polysulfone ultrafiltration supporting membranes (PSF-UF). Chemical structures of the ZTFCMs were evaluated by attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and element analysis (EA), with membrane microstructures and hydrophilicity being examined by microscopies and water contact angle, respectively. Superhydrophilic ZTFCMs were obtained with more AEPPS content on membrane surface, and they show excellent water permeability coupled with high erythromycin (ERY) retention. For example, the water permeability and retention to ERY of the ZTFCM (AEPPS aqueous concentration is 3.0wt%) are 8.4Lm−2h−1bar−1 and 96.5% (applied pressure is 6bar), respectively. In addition, the ERY concentration of the mixed feed increases exponentially from 100.0 to 350.7mgL−1 with a treatment capacity of 61.6Lm−2h−1 during 7.25h continuous concentration operation. Furthermore, ZTFCMs show a stable and good separation performance during a long-time filtration process of 168h and exhibit an exceptional antibacterial property assessed by Escherichia coli adhesion.

Novel zwitterion functionalized carbon nanotube nanocomposite membranes for improved RO performance and surface anti-biofouling resistance

Zwitterion functionalized carbon nanotubes (CNTs) were incorporated into polyamide thin film composite membranes to improve membrane permselectivity and surface biofouling resistance. The CNTs within the polyamide layer were partially aligned via a vacuum filtration step during membrane synthesis, and the fabrication of the zwitterionic CNT/polyamide nanocomposite membranes was optimized by varying the loadings of CNTs and the crosslink density of the polyamide. The permeation flux was found to increase by approximately three-fold as the fraction of CNTs was increased from 0 to 20wt% for all the salt solutions tested in our study. The steric hindrance to transport due to the zwitterionic functional groups prevents the permeation of the majority of ions through the CNT pores, resulting in high salt rejection. The charges of the zwitterionic groups do not appear to produce a significant Donnan potential to reject ions, and thus surface charge had no effect on membrane selectivity. The semi-aligned zwitterionic CNTs appeared to be exposed at the membrane surface and interacted with the feed water to form a strong hydration layer, resulting in improved surface biofouling resistance. The adsorption rate of protein foulants on the nanocomposite membrane surface was significantly reduced compared to the control membrane without CNTs, and the adsorbed fouling layer could be easily removed by flushing with water. After washing, the nanocomposite membrane recovered 100% of the decreased water flux whereas the control membrane only recovered 10% of the decreased flux resulting in a permanent loss of 30% in water permeation.

Tailoring polyamide thin film composite nanofiltration membranes by polyethyleneimine and its conjugates for the enhancement of selectivity and antifouling property

Post modification of poly(piperazineamide) membrane with polyethyleneimine conjugates provides membranes with novel properties such as high monovalent to divalent ion selectivity and improved antifouling properties, suitable for water purification.

A practical approach to synthesize polyamide thin film nanocomposite (TFN) membranes with improved separation properties for water/wastewater treatment

TFN membranes containing 0.05 or 0.10 w/v% surface-functionalized TNTs in a PA selective layer were synthesized for better performances in water/wastewater treatment.

Water vapor permeation behavior of interfacially polymerized polyamide thin film on hollow fiber membrane substrate

Thin film polyamide layer was formed by reaction between MPD and TMC on the inner surface of polysulfone (PSf) hollow fiber membranes (HFM). Concentrations of both the aqueous and organic monomer were varied in order to study the effect on physical properties such as surface morphology, hydrophilicity, roughness and thickness of polyamide layer. Physical properties were evaluated using FTIR, scanning electron microscopy, atomic force microscopy, and water contact angle. The water vapor permeation performances of composite HFM were tested and it was observed that monomer concentration drastically affects the water vapor permeance and selectivity. Not only polyamide layer thickness, but also the hydrophilicity, and structure of the polyamide layer affect the water vapor permeance and selectivity. Increase in MPD concentration caused increase in water vapor permeance while on the other hand TMC concentration had adverse effect on the permeance. Maximum water vapor permeance (1500 GPU) and selectivity (500) were obtained by using 2.0 w/v% MPD and 0.25 w/v% TMC for interfacial polymerization. In the end, MATLAB simulations were carried out in order to estimate the membrane area required to achieve 60% water vapor removal efficiency for real site 10 MW coal fired power plant.

Performance of nanofiltration and reverse osmosis membranes for arsenic removal from drinking water

The removal of arsenic was investigated by four types of thin-film polyamide nanofiltration (NF) (NF270, NF90) and reverse osmosis (RO) (XLE, BW30) membranes in a flat-sheet module. The influence of membrane types, pressure, pH, and pre-oxidation step on the removal of arsenic (As(III)) was investigated. Initial As(III) concentration was 100 μg/l for all of the experiments. Flux was determined over a pressure range of 3.5–10 bar for both NF and RO membranes. Experiments were conducted at pH 3.5, 5, 7.5, and 10 to evaluate the effect of pH on As(III) removal. The impact of pre-oxidation and oxidant concentrations on As(III) removal were also evaluated. It was found that the percentage of As(III) removal of RO membranes were in the range of 97–99 for all transmembrane pressure applied. In the range of operating conditions, As(III) and As(V) rejection were found almost equally good by RO membranes. RO permeate met the WHO and Turkish standard for arsenic. Pre-oxidation step improved the rejection performance of NF. Nevertheless, NF permeate did not meet the standards in the range of operating conditions.

3D visualization of the internal nanostructure of polyamide thin films in RO membranes

The front and back surfaces of fully aromatic polyamide thin films isolated from reverse osmosis (RO) membranes were characterized by TEM, SEM and AFM. The front surfaces were relatively rough showing polyamide protuberances of different sizes and shapes; the back surfaces were all consistently smoother with very similar granular textures formed by polyamide nodules of 20–50nm. Occasional pore openings of approximately the same size as the nodules were observed on the back surfaces. Because traditional microscopic imaging techniques provide limited information about the internal morphology of the thin films, TEM tomography was used to create detailed 3D visualizations that allowed the examination of any section of the thin film volume. These tomograms confirmed the existence of numerous voids within the thin films and revealed structural characteristics that support the water permeance difference between brackish water (BWRO) and seawater (SWRO) RO membranes. Consistent with a higher water permeance, the thin film of the BWRO membrane ESPA3 contained relatively more voids and thinner sections of polyamide than the SWRO membrane SWC3. According to the tomograms, most voids originate near the back surface and many extend all the way to the front surface shaping the polyamide protuberances. Although it is possible for the internal voids to be connected to the outside through the pore openings on the back surface, it was verified that some of these voids comprise nanobubbles that are completely encapsulated by polyamide. TEM tomography is a powerful technique for investigating the internal nanostructure of polyamide thin films. A comprehensive knowledge of the nanostructural distribution of voids and polyamide sections within the thin film may lead to a better understanding of mass transport and rejection mechanisms in RO membranes.

Immobilization of silver nanoparticle-decorated silica particles on polyamide thin film composite membranes for antibacterial properties

We present a new strategy to strongly and effectively immobilize silver nanoparticles (AgNPs) on polyamide thin film composite membranes to endow antibacterial activity. This method relies on the immobilization of relatively large silica particles (SiO2, ~400nm in diameter), where AgNPs of ~30nm in diameter are tightly and densely bound (AgNP@SiO2), on the membrane surface using cysteamine as a covalent linker. The formation of multiple Ag–S chemical bonds between a “bumpy” AgNP@SiO2 and the rough membrane surface provides a great leaching stability of AgNPs and AgNP@SiO2. AgNP@SiO2 particles were well distributed over the entire membrane surface without severe aggregation. The surface coverage of the membrane by AgNP@SiO2 was tuned by adjusting the deposition time and AgNP@SiO2 particle concentration. The AgNP@SiO2-immobilized membrane showed excellent antibacterial properties against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, even with a relatively low particle coverage. Importantly, the separation performance (water flux and salt rejection) of the membrane was not impaired by particle immobilization. These beneficial effects are attributed mainly to the sparse and good distribution of AgNP@SiO2, which can reinforce the antibacterial activity of AgNPs while having a negligible impact on the hydraulic resistance.