Increase In Water Permeability Research Articles

Preparation and performance evaluation of carboxylic acid containing polyamide incorporated microporous ultrafiltration PES membranes

Improved ultrafiltration membranes were prepared by the phase inversion technique via immersion precipitation of synthesized carboxylic acid containing polyamide (CPA) and polyethersulfone (PES) in dimethylacetamide. The CPA was synthesized and characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance, thermogravimetric analysis, and differential scanning calorimetry analyses. Next, the influence of CPA adding and its different concentrations on the performances and membrane structure were investigated. The obtained membranes were characterized by means of FTIR in the attenuated total reflection mode, scanning electron microscopy, and contact angle. The membrane performance studies revealed that the presence of CPA in the membrane structure increased water permeability while reducing protein fouling. It turned out that the PES/CPA membranes had better porosity, more hydrophilic surface, and more vertically finger‐like pores in comparison with the bare PES membrane. When the CPA concentration in the blending solution reached 1 wt%, the water permeability increased from 7.3 to 153.6 L/m2 h1. The attenuated total reflection‐FTIR analysis confirmed that CPA was captured in the membrane matrix.

Use of halophilic aquaporin for preparation of biomimetic thin film composite membrane

A new aquaporin from a moderate halophile, Halomonas elongata, for fabrication of desalination membrane is introduced in this study. For activity comparison, H. elongata aqp gene and E. coli aqpZ gene were cloned into pGEX-4T-2 vector and expressed in E. coli BL21 cells. E. coli AqpZ (EcAqpZ) appeared as tetrameric form, whereas H. elongata aquaporin (HeAqp) was found mostly as monomers in SDS-PAGE analysis. Light scattering measurements showed that incorporation of aquaporins into the liposomes vesicles resulted in increase in water permeability. HeAqp and EcAqpZ were embedded in 200 nm DOPC liposomes and immobilized with m-phenylene-diamine (MPD) and trimesoyl chloride (TMC) salt rejection layer on polysulfone membrane (PSf). Water with 800 mM NaCl concentration was used for salt rejection experiments. Increasing aquaporin concentration resulted in increase in water permeability of Halomonas aquaporin embedded membranes. % salt rejection of HeAqp and EcAqp incorporated PSf membranes were increased by three fold as compared to control membrane. Salt rejection and water permeability of HeAqp embedded PSf membrane was three and 25 fold higher than that of control membrane, respectively. H. elongata aquaporin, a halophilic aquaporin, was shown to be a suitable candidate for preparation of desalination membranes.

Simple Model on Water Retention and Permeability in Soil Mixed with Lignocellulose Fibres

Natural or lignocellulose fibres have been widely used for reinforcing soils in geotechnical infrastructures by using their mechanical reinforcement. However, less attention has been taken to the hydraulic properties of soil-lignocellulose fibre composites, namely Soil Water Retention Curve (SWRC) and soil water permeability. These hydraulic properties are the key parameters when conducting transient seepage analysis in reinforced slope stability calculation. Till now, there is no model yet that can capture SWRC and water permeability of soil-lignocellulose fibre composite. This technical note aims to develop a new and simple model for predicting the SWRC and water permeability of soils mixed with lignocellulose fibres. The model considers the void ratio change by incorporating the air void from fibres. The void ratio function is then fed into a void-ratio-dependent SWRC model. SWRCs and water permeability of soils mixed with two lignocellulose fibres (jute and coir) were measured systematically to provide high quality data to validate the proposed model. There were three replicates for each case. It shows that the presence of pore structures in natural fibres reduced air entry value of soils from 8 kPa to 2–3 kPa, while it had no effects on desorption rates. Moreover, those pores in lignocellulose fibres increased the water flow path, resulting in increased water permeability. As demonstrated by dye tracer experiments, the increased water flow was along the cellulose, hemicellulose fibrils inside the fibre and soil-fibre interface. The comparisons between experimental measurements and model predictions indicate that the proposed simple model can capture the effects of natural fibres on soil hydraulic properties quite well, with the maximum discrepancy less than 15% and 28% for SWRC and water permeability, respectively.

Durability of steel fibre reinforced rubberised concrete exposed to chlorides

This study assesses the durability and transport properties of low water/binder ratio (0.35) steel fibre reinforced rubberised concrete (SFRRuC) mixes, which are proposed to be used as flexible concrete pavements. Waste tyre rubber is incorporated in concrete as fine and coarse aggregate replacement and blends of manufactured steel fibres and recycled tyre steel fibres are used as internal reinforcement. The fresh, mechanical and transport properties of plain concrete are compared with those of SFRRuC mixes having different substitutions of rubber aggregates (0, 30 and 60% by volume). The chloride corrosion effects due to exposure to a simulated accelerated marine environment (intermittent wet-dry cycles in 3% NaCl solution) is also evaluated. The results show that, although water permeability (e.g. volume of permeable voids and sorptivity) and chloride ingress increase with rubber content, this increase is minor and water and chlorides permeability are generally within the range of highly durable concrete mixes. No visual signs of deterioration or cracking (except superficial rust) were observed on the surface of the concrete specimens subjected to 150 or 300 days of accelerated chloride corrosion exposure and a slight increase in the mechanical properties is observed. This study shows that the examined low water/binder SFRRuC mixes promote good durability characteristics, making these composite materials suitable for flexible concrete pavement applications.

Hemocompatibility and antifouling properties of PEGMA grafted Polyethersulfone/aminated halloysite nanotubes mixed matrix membrane

The aim of this study was to evaluate the permeation performance and hemocompatibility of polyethersulfone (PES) membrane after mixing with halloysite nanotubes (HNTs), followed by grafting poly (ethylene glycol) methyl ether metacrylate (PEGMA). HNTs were modified by (3-aminopropyl)triethoxysilane (APTES) to facilitate dispersion in PES matrix. Incorporation of 2wt% HNTs not only could increase water permeability of the PES membrane from about 580 to 840 L/m2.h.bar, but also improved mechanical strength of the membrane and could be an appropriate sublayer for composite membrane preparation. Grafting PEGMA could inhibit proteins attachment and platelets adhesion on the PES mixed matrix membrane.

Impact of bacterial streamers on biofouling of microfluidic filtration systems.

We investigate the effect of biofouling in a microfluidic filtration system. The microfluidic platform consists of cylindrical microposts with a pore-spacing of 2 μm, which act as the filtration section of the device. One of our key findings is that there exists a critical pressure difference above which pronounced streamer formation is observed, which eventually leads to rapid clogging of the device with an accompanying exponential decrease in permeate flow. Moreover, when streamers do form, de-clogging of pores also occurs intermittently, which leads to small time scale fluctuations [O(101 s)] superimposed upon the large time scale [O(102 min)] clogging of the system. These de-clogging phenomena lead to a sharp increase in water permeation through the microfluidic filtration device but rates the water quality as biomass debris is transported in the permeate. Streamer-based clogging shares similarities with various fouling mechanisms typically associated with membranes. Finally, we also show that the pH of the feed strongly affects biofouling of the microfluidic filtration system.

Synthesis of polyamide thin-film nanocomposite membranes using surface modified imogolite nanotubes

Nanocomposite membranes were synthesized using unmodified and surface modified imogolite nanotubes. Membranes were through interfacial polymerization of polyamide onto polyacrylonitrile (PAN) macroporous supports. Surface modification was done using two different polymers: polyvinylpyrrolidone (PVP) and polydimethylsiloxane (PDMS). These polymers were selected to improve nanotube dispersion in chloroform and n-hexane solvents which were used during membrane synthesis. The structural and surface-chemical properties of the nanotubes and the synthesized thin-films were characterized and correlated with membrane performance. Surface modification resulted in an increased mass loading of nanotubes into the polyamide thin-films. This corresponded to an increase in water permeability, going from 1 mg/g to 2.5 mg/g as the mass loading increased from 1.47 × 10–12 m/Pa s to 3.59 × 10–12 m/Pa s. Increases in water permeability were attributed to increases of the pore size from 3.967 to 4.357 nm within the membrane due to the interior space of the nanotubes and to changes in the cross-linking density surrounding the nanotube within the thin-film.

Water/salt transport properties of organic/inorganic hybrid films based on cellulose triacetate

The synergized optimization of water flux and salt rejection by blending with inorganic fillers has been achieved for the polyamide (PA) thin film nanocomposite (TFN) membrane. However, it is difficult to characterize its mass transport properties due to the very thin and heterogeneous PA film. In this work, we select cellulose triacetate (CTA) as the base to prepare hybrid films and their transport properties were studied according to solution-diffusion theory. A series of inorganic fillers, such as reduced graphene oxide (RGO), zeolites, ZIF-8, SiO2 and graphene oxide (GO) were incorporated. The SEM and EDX results indicate a less than 1 wt% filler content for a uniform dispersion. The blending of inorganic fillers leads to enhanced glass transition temperature (Tg) and density, little effect on the water transport property but dramatically decreased salt permeability values, which are nearly ten-fold of that of the CTA film. The blending of GO can densify and hydrophilize CTA simultaneously, which is most promising for a desalination application. The increased water uptake should contribute to its increased water permeability, while the decreased free volume size and FFV value and various interactions between the ions (Na+, Cl-) and GO sheets account for salt permeability decrease.

P-299 - Short-term regulation of Aquaporin-5 by combined phosphorylation and pH

Aquaporin-5 (AQP5) is a membrane water channel widely distributed in human tissues that was found up-regulated in different tumors and considered implicated in carcinogenesis. AQP5 phosphorylation was reported to increase its expression and trafficking, resulting in increased membrane abundance. Interestingly, AQP5 is mostly found phosphorylated in tumor tissues. However, the effects of phosphorylation on channel activity as well as its sensitivity to extracellular acidification have not been investigated so far. In this work, using a yeast model of heterologous expression, we investigated the effect of protein phosphorylation and pH sensitivity as a mechanism of AQP5 short-term regulation. We observed that external acidification alone (pH 5) does not affect AQP5 activity. However, AQP5 phosphorylation induced by intracellular cAMP renders the protein channel prone to pH sensing, resulting in marked increase in water permeability when pH is raised to 7.4. The mechanism of gating may involve intracellular phosphorylation of AQP5 with consequent change in protein conformation and channel pore widening. In this new open configuration, deprotonation of residues occurring at pH 7.4 may support an increased water transport capacity of the AQP5 protein.

Selective removal of divalent cations by polyelectrolyte multilayer nanofiltration membrane: Role of polyelectrolyte charge, ion size, and ionic strength

We fabricated polyelectrolyte multilayer (PEM) nanofiltration (NF) membranes using a layer-by-layer (LbL) method for effective removal of scale-forming divalent cations (Mg2+, Ca2+, Sr2+, and Ba2+) from feedwaters with different salinities. Two polymers with opposite charges, polycation (poly(diallyldimethylammonium chloride), PDADMAC) and polyanion (poly(sodium 4-styrenesulfonate), PSS), were sequentially deposited on a commercial polyamide NF membrane to form a PEM. Compared to pristine and PSS-terminated membranes, PDADMAC-terminated membranes demonstrated much higher rejection of divalent cations and selectivity for sodium transport over divalent cations (Na+/X2+) due to a combination of both Donnan- and size-exclusion effects. A PDADMAC-terminated membrane with 5.5 bilayers exhibited 97% rejection of Mg2+ with selectivity (Na+/Mg2+) greater than 30. We attribute the order of cation rejection (Mg2+ > Ca2+ > Sr2+ > Ba2+) to the ionic size, which governs both the hydration radius and hydration energy of the cations. The ionic strength (salinity) of the feed solution had a significant influence on both water flux and cation rejection of PEM membranes. In feed solutions with high ionic strength, abundant NaCl salt screened the charge of the polyelectrolytes and led to swelling of the multilayers, resulting in decreased selectivity (Na+/X2+) and increased water permeability. The fabricated PEM membranes can be potentially applied to the pretreatment of mild-salinity brackish waters to reduce membrane scaling in the main desalination stage.

Age-Related Changes in Water Transport by Corneal Endothelial Cells in Rats

Senescence-associated alterations in structure and function of cornea make it more sensitive to traumas and disease. Trauma of cornea leads to edema and vision impairment and only corneal transplantation remains the effective for vision correction. Role of aquaporins for cornea endothelium function, as well as age-related changes of their activity, are not entirely understood. Herein, we studied changes with age the water permeability (Pf) of the plasma membranes of the corneal endothelial cells and the level of expression in them of the mRNA genes of the water channels of the aquaporins AQP1 and AQP3 in Wistar and senescence-accelerated OXYS rats. From the age of 3 to 18 months, Pf in Wistar rats increased, in OXYS - decreased and was twice lower than in Wistar rats. The expression of aqp1 mRNA (studied by RT-PCR) in the endothelium was the same in Wistar and OXYS rats at the age of 3 months. By the age of 18 months, it increased only in Wistar rats and became twice higher than in OXYS rats. The expression of aqp3 mRNA in the endothelium of 3-month-old OXYS rats was half that of Wistar rats and did not change with age, while in Wistar rats it decreased and at 18 months was 4 times lower than in 3 months. We supposed that increased water permeability of endothelial cells in Wistar rats is adaptive and compensates for the decrease in endothelial cell density with age, while the accelerated aging of OXYS rats abolishes this compensation.

Acid post-treatment of sol-gel-derived ethylene-bridged organosilica membranes and their filtration performances

This study investigated the effect of acid post-treatment on the filtration performance of organosilica membranes. The membranes were prepared from 1,2-bis(triethoxysilyl)ethane (BTESE) via sol-gel processing with different H2O/BTESE molar ratios. Fourier-transform infrared spectra significant residual ethoxy groups within membranes derived from sols with low H2O/BTESE ratios, after firing at 300 °C in N2. The ethoxy groups within the membranes were hydrolyzed to hydroxide groups by immersing the membranes in hydrochloric acid (HCl). This rendered the membranes more hydrophilic. The hydroxyl groups may have promoted the formation of hydrophilic pores, which would in turn promote water permeation. The HCl-treated membranes showed higher water permeability than the original BTESE-derived membrane. The effect of HCl treatment was more pronounced for the membrane prepared with the lowest H2O/BTESE ratio of 1, resulting in approximately three times higher water permeability than the original membrane. Membranes prepared from sols with low H2O/BTESE ratios showed improved solute rejection and increased water permeability, upon HCl treatment. This was attributed to cross-linking in the organosilica matrix via the condensation of newly-formed hydroxyl groups, that caused the narrowing or blocking of large pores.

Effects of row deep tillage for the growth base formed by piling up soil in damp lowlands behind coastal sand dunes to construct coastal disaster prevention forest belts on the Kujukuri coastline, Japan

ABSTRACT To successfully afforest coastal forest belts ensuring high disaster prevention, growth bases for them have been constructed by piling up soil in the low wetlands along the Kujukuri coastline. Ground surfaces in such bases are often covered with water because of soil compaction, leaving them susceptible to stagnant water. Water stagnation in soil is problematic, potentially interfering with afforesting coastal forests. Therefore, row deep tillage was conducted for parts of growth bases to combat the poor physical properties of the existing soil. Here, we surveyed soil profiles and measured vertical soil hardness distribution in two forest stands with piling up soil to evaluate the effectiveness of tillage for man-made soil. Soil hardness measurements indicated that the vertical areas with ‘soft’ and ‘hard/consolidated’ soil alternately appeared in growth base profiles. Generally, soil of the dense and very hard layers was apt to be formed by strong compaction of the filled-up soil because of heavy machinery usage during growth base preparation. Such dense and hard soils in the untilled areas of the profiles were also observed in this study. By contrast, it was confirmed that row deep tillage drastically improved soil physical properties, i.e., decreased hardness and increased water permeability, because the sequential hardened subsoil layers were well-broken-up. Moreover, it was observed many thick and large roots penetrated deeper layers with deep tillage areas. These results suggest that row deep tillage of hardened soil is quite effective at securing the areas and providing the physical conditions for deeply penetrated roots into deeper soils, which increases healthy root development. They show the effects of soil hardness reduction and water permeability improvement have been maintained for two decades, at least, after construction. These findings will be useful for alleviating some problems of soil compaction, water stagnation, and tree-growth hindrance that have been encountered on afforestation sites with man-made soil.

Efficient dye removal from aqueous solution by high-performance electrospun nanofibrous membranes through incorporation of SiO2 nanoparticles

Abstract In this study, novel chitosan/poly(vinyl alcohol) (PVA)/SiO2 nanocomposite ENMs were prepared to improve the mechanical strength and permeation properties of ENMs. The effect of various concentrations of SiO2 in the spinning solution (0, 0.5, 1.0 and 2.0 wt %) on the morphology, fiber diameter, porosity, thermomechanical properties, and permeability of the synthesized membranes was investigated. The prepared affinity membranes were utilized for the removal of dye from colored wastewater. Incorporating SiO2, as a reinforcing agent, was found to increase the compaction resistance of the nanocomposite ENMs. With the addition of 0.5 wt % of SiO2, the Young's modulus of the prepared membranes almost doubled from 0.74 MPa for chitosan/PVA ENM to 1.69 for nanocomposite ENM. The major finding was that with the incorporation of 1.0 wt % SiO2, a marked increase in both water permeability and dye rejection is attained. The optimized nanocomposite membrane provided 98% Direct Red 23 rejection and 1711 l/m2h flux under 0.4 bar transmembrane pressure. As a result, this study provides valuable insights into the preparation of high-performance and robust nanocomposite ENMs for the wastewater treatment.

Effect of unmodified and modified montmorillonite on the properties of PCL based ultrafiltration membrane for water treatment applications

This work presents the preparation of membranes using polycaprolactone (PCL), a biodegradable polymer incorporating unmodified and modified nanoclay using phase inversion technique. The membranes prepared with the incorporation of 0.1g to 0.4g of unmodified nanoclay and 0.05 g to 0.15g of modified nanoclay were studied with respect to porosity, hydrophilicity, chemistry, mechanical and thermal properties and morphological characteristics. The results showed that the membrane incorporated with unmodified nanoclay has enhanced strength and porosity compared to the membrane with modified nanoclay and neat PCL. An increase in water permeability is shown by the incorporation of unmodified nanoclay and contact angle measurement results revealed an increased hydrophilicity with a decrease in membrane roughness which was confirmed using AFM analysis. The surface morphology was examined using SEM analysis and the results revealed that on adding unmodified nanoclay, the average pore size decreased from 6.2μm to 4.5μm and for membranes with modified nanoclay, the average pore size was found to be 1μm. The prepared membranes were tested for the rejection of Congo Red and the performance were analysed.

Unveiling the Susceptibility of Functional Groups of Poly(ether sulfone)/Polyvinylpyrrolidone Membranes to NaOCl: A Two-Dimensional Correlation Spectroscopic Study.

A clear understanding of membrane aging process is essential for the optimization of chemical cleaning in membrane-based facilities. In this study, two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (CoS) analysis was first used to decipher the sequential order of functional group changes of NaOCl-aged poly(ether sulfone)/polyvinylpyrrolidone (PES/PVP) membranes. The synchronous maps showed 12 major autopeaks in total. Based on the asynchronous maps, a similar aging sequence of membrane groups was clearly identified at three pHs (i.e., 6, 8, and 10): 1463, 1440, and 1410 (cyclic C-H structures) > 1662 (amide groups) > 1700 (succinimide groups) > 1320, 1292 (S═O asymmetric) > 1486, 1580 (aromatic structures) > 1241 (aromatic ether bands) > 1105, 1150 cm-1 (O═S═O symmetric). Among them, membrane chlorination occurred at 1241, 1410, and 1440 cm-1. Moreover, the initial degradation of PVP and the subsequent transformation of PES could be highly responsible for the increased water permeability and the enlargement of membrane pores, respectively, both leading to serious fouling with humic acid filtration. In summary, the 2D-FTIR-CoS analysis is a powerful approach to reveal the interaction mechanisms of NaOCl-membrane and could be also useful to probe the process of membrane fouling and chemical cleaning.

Enhanced water transport and salt rejection through hydrophobic zeolite pores

The potential of improvements to reverse osmosis (RO) desalination by incorporating porous nanostructured materials such as zeolites into the selective layer in the membrane has spurred substantial research efforts over the past decade. However, because of the lack of methods to probe transport across these materials, it is still unclear which pore size or internal surface chemistry is optimal for maximizing permeability and salt rejection. We developed a platform to measure the transport of water and salt across a single layer of zeolite crystals, elucidating the effects of internal wettability on water and salt transport through the ≈5.5 Å pores of MFI zeolites. MFI zeolites with a more hydrophobic (i.e., less attractive) internal surface chemistry facilitated an approximately order of magnitude increase in water permeability compared to more hydrophilic MFI zeolites, while simultaneously fully rejecting both potassium and chlorine ions. However, our results also demonstrated approximately two orders of magnitude lower permeability compared to molecular simulations. This decreased performance suggests that additional transport resistances (such as surface barriers, pore collapse or blockages due to contamination) may be limiting the performance of experimental nanostructured membranes. Nevertheless, the inclusion of hydrophobic sub-nanometer pores into the active layer of RO membranes should improve both the water permeability and salt rejection of future RO membranes (Fasano et al 2016 Nat. Commun. 7 12762).

Atomic layer deposition of Al 2 O 3 on porous polypropylene hollow fibers for enhanced membrane performances

Abstract Porous polypropylene hollow fiber (PPHF) membranes are widely used in liquid purification. However, the hydrophobicity of polypropylene (PP) has limited its applications in water treatment. Herein, we demonstrate that, for the first time, atomic layer deposition (ALD) is an effective strategy to conveniently upgrade the filtration performances of PPHF membranes. The chemical and morphological changes of the deposited PPHF membranes are characterized by spectral, compositional, microscopic characterizations and protein adsorption measurements. Al2O3 is distributed along the cross section of the PP hollow fibers, with decreasing concentration from the outer surface to the inner surface. The pore size of the outer surface can be easily turned by altering the ALD cycles. Interestingly, the hollow fibers become much more ductile after deposition as their elongation at break is increased more than six times after deposition with 100 cycles. The deposited membranes show simultaneously enhanced water permeance and retention after deposition with moderate ALD cycle numbers. For instance, after 50 ALD cycles a 17% increase in water permeance and one-fold increase in BSA rejection are observed. Moreover, the PP membranes exhibit improved fouling-resistance after ALD deposition.

Membrane Cholesterol Reduces Polymyxin B Nephrotoxicity in Renal Membrane Analogs

Polymyxin B (PmB) is a “last-line” antibiotic scarcely used due to its nephrotoxicity. However, the molecular basis for antibiotic nephrotoxicity is not clearly understood. We prepared kidney membrane analogs of detergent-susceptible membranes, depleted of cholesterol, and cholesterol enriched, resistant membranes. In both analogs, PmB led to membrane damage. By combining x-ray diffraction, molecular dynamics simulations, and electrochemistry, we present evidence for two populations of PmB molecules: peptides that lie flat on the membranes, and an inserted state. In cholesterol depleted membranes, PmB forms clusters on the membranes leading to an indentation of the bilayers and increase in water permeation. The inserted peptides formed aggregates in the membrane core leading to further structural instabilities and increased water intake. The presence of cholesterol in the resistant membrane analogs led to a significant decrease in membrane damage. Although cholesterol did not inhibit peptide insertion, it minimized peptide clustering and water intake through stabilization of the bilayer structure and suppression of lipid and peptide mobility.

Effect of aggregate exposing and curing agent on the performance of exposed aggregate concrete

As the most important part of exposed aggregate concrete (EAC), the surface zone usually attracts much attention. This paper presents an investigation on the effect of aggregate exposing and curing agent on the properties and microstructure of EAC by a range of analytical techniques. The results show that a gradual reduction of compressive strength, a significant increase of abrasion resistance, obvious increase of carbonation depth and slight increase of chloride & water permeability are observed when the surface aggregates are exposed. The chloride permeability, water permeability and carbonation depth are reduced, and compressive strength and abrasion resistance of EAC are significantly enhanced by applying the curing agent. The microhardness of surface zone around aggregate is lower than that of matrix after aggregate exposing, but can be significantly increased by curing agent. The surface zone is deteriorated after exposing aggregate, but the surface zone and near-surface zone become denser after applying the curing agent. The curing agent penetrates into the concrete by 4–5mm and reacts with hydration products. The mechanical properties and durability of EAC are improved due to the increase of hydration degree and formation of new products such as CaSiO3 by application of curing agent.