Single-layer Membrane Research Articles

Dual-layer BaCe0.8Y0.2O3-δ-Ce0.8Y0.2O2-δ/BaCe0.8Y0.2O3-δ-Ni hollow fiber membranes for H2 separation

Ceramic ion-conducting membrane technology is one of the promising options for hydrogen separation to replace the conventional expensive cryogenic distillation methods. In order to achieve high H2 permeation flux, designing multi-phase membranes possessing high mixed protonic and electronic conductivities in asymmetric structure with a thin dense separating layer is an important strategy for future novel membrane development. Multi-phase dual-layer BaCe0.8Y0.2O3-δ (BCY)-Ce0.8Y0.2O2-δ (YDC)/BCY-Ni hollow fiber membrane with excellent hydrogen permeability was developed by a single-step co-extrusion technique in this work. The thickness of the dense layer of the membrane can be controlled by the powder content of BCY-YDC in the spinning suspension. When the content of BCY-YDC was lowered from 65 to 45 wt%, the thickness of the dense layer was decreased from 33.5 to 14.5 μm. The thin dual-phase BCY-YDC dense layer determines the H2 permeation and the porous BCY-Ni support layer provides the mechanical strength and catalytic effect for surface exchange reactions. Compared to the BCY-YDC single-layer membrane, the H2 flux of such dual-layer asymmetric membrane with dense layer of 17.0 μm was improved significantly by a factor of 2 reaching 0.566 mL cm−2 min−1 at 900 °C under the hydrogen partial pressure difference of 50 kPa. A long term permeation test for 240 h confirmed the high operational stability of the prepared dual layered hollow fiber membrane. The good membrane performance is directly sourced from the excellent integration of the dual layers prepared in one step and thin thickness of the densified separating layer with catalytic porous support.

Biphasic Calcium Phosphate Sphere Graft Combined with a Double-Layer Non-Crosslinked Collagen Membrane Technique for Ridge Preservation: A Randomized Controlled Animal Study.

The purpose of this study was to compare the histologic and radiologic differences between single- and double-layer collagen membrane techniques in flapless ridge preservation. The mandibular fourth premolar and first molar of four beagle dogs were used in the experiment. Mesial roots of the teeth were extracted and root canal treatment was performed at the distal roots. Ridge preservation was performed at the extraction sites using synthetic bone graft material. A single layer (control group) or double layer (test group) of non-crosslinked collagen membrane was applied following bone graft application. Three months later, the animals were sacrificed and micro-computed tomography (micro-CT) and histomorphometric analyses were conducted. Nonparametric Mann–Whitney test was performed to compare between the control and test groups. The vertical difference between buccal and lingual crests of control and test groups was 1.28 ± 0.41 and 0.53 ± 0.37 mm, respectively (p = 0.026). The mineralized bone area in control and test groups was 31.48% ± 7.41% and 42.25% ± 9.73%, respectively (p = 0.041). Within the limit of this study, ridge preservation using the double-layer membrane technique showed a reduced buccal bone resorption and improved new-bone formation in the ridge compared to that using the single-layer membrane technique.

Alumina double-layered ultrafiltration membranes with enhanced water flux

In the present work, γ-alumina double-layered ultrafiltration (UF) membranes with novel gradient pore-sized active layers and single-layered UF membranes were produced using an approach of tightening the pore size of alumina microfiltration (MF) membranes. With the processes of sol-gel, dip coating and sintering, the achieved single- and double-layered UF membranes displayed similar performance in particle size retention, and the double-layered membrane expressed better properties than the single-layered UF membrane in terms of water flux, resistance and anti-fouling. Compared to the MF membrane, the prepared UF membranes displayed improved hydrophilicity and enhanced particle size retention behavior, but lower flux, higher resistance and weaker anti-fouling performance. However, the UF membrane with double layers exhibited values of flux and resistance in the same order of magnitude as those of the MF membrane. The produced alumina double-layered membranes with enhanced flux are of great potential in UF of water.

Optical Characteristic Investigation on an Underwater Adjustable Focus Solar Concentrator with Single-Layer Membrane

Optical Characteristic Investigation on an Underwater Adjustable Focus Solar Concentrator with Single-Layer Membrane

Examination of Selection and Combination of Water-Absorbing Agent to Blend with Polyvinyl Alcohol (PVA) in Preparing CO2-Separation Membrane with High-Performance

In the present study, the selection and combination of the water-absorbing agent to blend with polyvinyl alcohol (PVA) for the preparation of a high-performance CO2-separation membrane were examined by evaluating the separation performance of the resulting membrane. The separation performance of a two-layer membrane prepared by stacking and a single-layer membrane prepared by blending were also compared, where the latter was found to be superior. The selection of a water-absorbing agent with higher water absorption and compatibility with PVA is important in the preparation of a high-performance separation membrane by blending. The high-performance CO2-separation membrane was prepared by blending PVA with two types of water-absorbing agents. In addition, the variation in the composition ratio of two water-absorbing agents further improved the CO2-separation performance. Accordingly, the high-performance CO2-separation membrane was successfully prepared by combining PVA with two water-absorbing agents.

Theoretical guidance for fabricating higher flux hydrophobic/hydrophilic dual-layer membranes for direct contact membrane distillation

In this study, a new simultaneous heat and mass transfer theoretical model of the membrane distillation process operating under direct contact membrane distillation (DCMD) mode has been developed for the hydrophobic/hydrophilic dual-layer composite membranes. Using the proposed model, a criterion parameter (β) was derived to determine whether the flux will be increased for the prepared hydrophobic/hydrophilic composite membranes. A flux ratio (γDL/SLM) of dual-layer to single-layer membrane was also developed to predict the DCMD flux performance of the composite membranes. To validate the theoretical model, three sets of dual-layer hydrophobic/hydrophilic composite membranes and single-layer hydrophobic membranes with defined total thicknesses (240 μm, 260 μm, and 285 μm) and different thickness ratios (δ/δo=3.69, 2.48 and 2.19) were purposefully fabricated using electrospinning technique. Theoretical modelling results were compared with the experimental data in terms of DCMD flux ratio. The experimental data of flux ratios for the three sets of fabricated membranes at 60 °C, γDL/SLE, are 2.75, 1.97 and 1.80, respectively, which fit well with the model prediction values (γDL/SLM= 2.96, 2.18, and 1.97) within high agreement level at a relative standard deviation of 9.6%. Furthermore, the flux ratio of DL2 to SL2 membranes (dual-layer and single-layer membranes with 260 μm total thicknesses and δ/δo=2.48 thickness ratio) at different feed inlet temperatures still maintain a high degree of consistency with model values. Overall, the results show the experimental data agree well with the theoretical model prediction for the flux ratio within relative standard deviation of 10.1%, thereby confirming the validity of the proposed model. Additionally, a critical value of the thickness ratio (χ) was calculatedχ=1+1β, this value could provide useful guidance to design a highly efficient hydrophobic/hydrophilic dual-layer composite membrane for DCMD applications in the future work.

Paper Stacks for Uniform Rehydration of Dried Reagents in Paper Microfluidic Devices

Spatially uniform reconstitution of dried reagents is critical to the function of paper microfluidic devices. Advancing fluid fronts in paper microfluidic devices drive (convect) and concentrate rehydrated reagents to the edges, causing steep chemical gradients and imperfect mixing. This largely unsolved problem in paper microfluidics is exacerbated by increasing device dimensions. In this article, we demonstrate that mixing of dried reagents with a rehydrating fluid in paper microfluidics may be significantly enhanced by stacking paper layers having different wicking rates. Compared to single-layer paper membranes, stacking reduced the “non-reactive area”, i.e. area in which the reconstituted reagents did not interact with the rehydrating fluid, by as much as 97% in large (8 cm × 2 cm) paper membranes. A paper stack was designed to collect ~0.9 ml liquid sample and uniformly mix it with dried reagents. Applications of this technology are demonstrated in two areas: (i) collection and dry storage of sputum samples for tuberculosis testing, and (ii) salivary glucose detection using an enzymatic assay and colorimetric readout. Maximizing the interaction of liquids with dried reagents is central to enhancing the performance of all paper microfluidic devices; this technique is therefore likely to find important applications in paper microfluidics.

Embedding topography enables fracture guidance in soft solids

The natural topographical microchannels in human skin have recently been shown to be capable of guiding propagating cracks. In this article we examine the ability to guide fracture by incorporating similar topographical features into both single, and dual layer elastomer membranes that exhibit uniform thickness. In single layer membranes, crack guidance is achieved by minimizing the nadir thickness of incorporated v-shaped channels, maximizing the release of localized strain energy. In dual layer membranes, crack guidance along embedded channels is achieved via interfacial delamination, which requires less energy to create a new surface than molecular debonding. In both membrane types, guided crack growth is only temporary. However, utilizing multiple embedded channels, non-contiguous crack control can be maintained at angles up to 45° from the mode I fracture condition. The ability to control and deflect fracture holds great potential for improving the robustness and lifespan of flexible electronics and stretchable sensors.

Comprehensive Study of Morphological Modification of Dual-Layer Hollow Fiber Membrane

The NiO–YSZ/LSCF–YSZ dual-layer hollow fiber membrane receives increasing attention which is due liable to quick changes in properties during co-extrusion followed by the co-sintering method. The effect of mixed bore liquid of water + ethanol + n-methyl-2-pyrrolidone and co-sintering temperature on physical and chemical characteristics of the obtained membrane was systematically explored in this study. Here, the characterization of the membrane was inspected using scanning electron microscope–energy-dispersive X-ray, three-point bending, mercury porosimetry, X-ray diffraction and nitrogen tightness tests as well as the oxygen permeation test. Results indicated that membrane prepared using 100% water as a bore liquid produced a sandwich structure. On the contrary, by employing 40:10:50% of water/ethanol/NMP as a mixed bore liquid and sintering for 8 h at 1300 °C, an open-channel structure in the microstructure gives a good porosity as tested using mercury porosimetry, mechanical properties and nitrogen permeability with no secondary phases. In addition, the co-sintering effect was examined by increasing temperature to 1400 and 1500 °C. However, an impurity phase of LaZr2O7 was formed which is due to the chemical reaction of La and Sr into YSZ structure. Oxygen permeate concentration through the dual-layer membrane was found to be slightly different as compared to the single-layer hollow fiber membrane. The results further suggest that the outer layer should be tighter and thinner to enhance the oxygen ion diffusion.

Mechanically Robust Nanofibrous Xerogel Membrane for One‐Pass Removal of Trace Water in Oil

AbstractRemoval of trace water from oil is essential for a high‐performance fuel supply system. Trace water in fuel is a crucial contributor to frequent system maintenance and failure. In this work, an electrospun polyacrylic acid/polyvinyl alcohol (PAA/PVA) nanofibrous xerogel membrane (NFM) is prepared to remove trace water in oil. Based on the optimization of the weight ratio and the crosslinking conditions of PAA/PVA, the resultant NFM shows remarkable water‐retaining capacity (swelling ratio of 124.8 g/g) and rapid absorption property. The optimal membrane displays a small average pore size of 523.2 nm, high porosity of 79.6% as well as robust tensile strength of 8.1 MPa. Additionally, after just one pass through a single layer membrane (thickness of 35 ± 3 µm and areal density of 3.5 ± 0.5 g m−2), the milky oil containing 1 wt% water is clarified and the water content reduced to 130 ppm. With extensive water being absorbed into the 3D network (different with the conventional separation mechanism) as well as good compatibility with oil, a multilayer pleated scheme may provide a practical methodology for enhancing fuel oil properties and performances.

Double-Layer Tympanic Membrane Graft in Type I Tympanoplasty.

Some discussion remains among otologists regarding the best grafts for tympanic membrane closure. It is unclear whether double-layer grafts are superior to single-layer and whether single-layer cartilage is superior to fascia or perichondrium alone. The objective of the current study was to examine the relative efficacy of single-layer versus double-layer tympanic membrane grafting techniques. A retrospective review of the medical records was used to address the objective of the study. Patients operated on in an over/under technique by the same surgeon underwent single-layer perichondrium or single-layer perichondrium with a cartilage island, or a double-layer of perichondrium combined with periochondrium with a cartilage island. The outcomes assessed were tympanic membrane reperforation and hearing improvement. A total of 135/177 (76%) perichondrium grafts had no reperforation, and 43/55 (78%) perichondrium with cartilage island grafts had no reperforation; 352/390 (90%) of the double-layer closures had no reperforation. There was no statistically significant difference in reperforation rates between the 2 single-layer techniques (P = .926). The difference in reperforation rates after the double-layer closure versus the perichondrium single-layer closure was statistically significant (P = .001), as was the difference in reperforation rates after the double-layer closure versus the cartilage island single-layer closure (P = .02). All 3 groups showed statistically significant hearing improvement postoperatively (P < .0001). Preoperative hearing levels (P = .179), postoperative hearing (P = .857), and decibels of hearing improvement (P = .356) were the same for all 3 groups. Double-layer closure gives lower tympanic membrane reperforation rates than does single-layer closure, as well as similar hearing outcomes.

Capillary effect in Janus electrospun nanofiber membrane for oil/water emulsion separation

Janus electrospun nanofiber membranes (J-ENMs) have attracted considerable interest as membranes for oil-in-water emulsion separation due to the opposite properties on each side of the membrane. Such properties can provide capillary effect and achieve water unidirectional transportation. However, the capillary effect on performances of the J-ENMs is still obscure. Therefore, it is highly important to investigate the relation of pore size, capillary pressure, and fluid flux of them. For this study, J-ENMs, which have a dual-layer structure with hydrophilic polyacrylonitrile (PAN) and hydrophobic polystyrene (PS) nanofibrous membranes simultaneously, were fabricated via the electrospinning process. Among the fabricated membranes, the large pore sizes of the PS layer of J-ENMs affected capillary pressure leading to a pure water flux increase of nine times that of the small pore size. For emulsion flux, oil droplets can pass through a large pore of the PS layer easily and can cause a decrease in emulsion flux. Nevertheless, the emulsion flux of J-ENMs was 1.7 times higher than that of single layer membrane, which showed a promising application for the oil/water separation field.

Etching gas-sieving nanopores in single-layer graphene with an angstrom precision for high-performance gas mixture separation.

One of the bottlenecks in realizing the potential of atom-thick graphene membrane for gas sieving is the difficulty in incorporating nanopores in an otherwise impermeable graphene lattice, with an angstrom precision at a high-enough pore density. We realize this design by developing a synergistic, partially decoupled defect nucleation and pore expansion strategy using O2 plasma and O3 treatment. A high density (ca. 2.1 × 1012 cm-2) of H2-sieving pores was achieved while limiting the percentage of CH4-permeating pores to 13 to 22 parts per million. As a result, a record-high gas mixture separation performance was achieved (H2 permeance, 1340 to 6045 gas permeation units; H2/CH4 separation factor, 15.6 to 25.1; H2/C3H8 separation factor, 38.0 to 57.8). This highly scalable pore etching strategy will accelerate the development of single-layer graphene-based energy-efficient membranes.

High-permeance polymer-functionalized single-layer graphene membranes that surpass the postcombustion carbon capture target

A single-layer nanoporous graphene membrane functionalized with CO2-phillic polymers shows extremely fast, selective CO2 transport.

Charged nanoporous graphene membranes for water desalination.

Water desalination using positively and negatively charged single-layer nanoporous graphene membranes are investigated using molecular dynamics (MD) simulations. Pressure-driven flows are induced by the motion of specular reflection boundaries with a constant speed, resulting in a prescribed volumetric flow rate. Simulations are performed for 14.40 Å hydraulic pore diameter membrane with four different electric charges distributed on the pore edges. Salt rejection efficiencies and the resulting pressure drops are compared with the previously obtained base-line case of 9.9 Å diameter pristine nanoporous graphene membrane, which exhibits 100% salt rejection with 35.02 MPa pressure drop at the same flow rate. Among the positively charged cases, q = 9e shows 100% and 98% rejection for Na+ and Cl- ions respectively, with 35% lower pressure drop than the reference. For negatively charged pores, optimum rejection efficiencies of 94% and 93% are obtained for Na+ and Cl- ions for the q = -6e case, which requires 60.6% less pressure drop than the reference. The results indicate the high potential of using charged nanoporous graphene membranes in reverse osmosis (RO) desalination systems with enhanced performance.

Continuously Tunable Pore Size for Gas Separation via a Bilayer Nanoporous Graphene Membrane

Pore size is a crucial factor impacting gas separation, but difficult to control for a single-layer nanoporous graphene membrane. Here, we propose a bilayer design of a nanoporous graphene membrane...

Nanoindentation of circular multilayer graphene allotropes

Nanoindentaion has been proposed as an efficient technique to measure mechanical single-layer two-dimensional (2D) materials via combining the membrane theory with the indentation data. However, for multilayered structures of 2D materials, significant discrepancy exists between the Young’s modulus obtained from the existing membrane model and those from other methods. Here we develop a multilayer indentation model by taking the multilayer effect into account in the previous membrane model. We show that the present model can accurately predict the Young’s modulus of multilayered 2D carbon materials. For few layer graphene and twin graphene structures, the deviation of the Young’s moduli obtained by the present model are both within a reasonable range, while the error caused by the direct use of the previous single-layer membrane model increases with the number of layers. The present model provides an efficient tool to extract the mechanical properties of 2D materials from the nanoindentation data of their multilayered structures.

Electrospun tri-layer membranes for H2/Air fuel cells

Dual nanofiber electrospinning was used to fabricate a series of multi-layer fuel cell membranes with high proton conductivity and low in-plane water swelling, using 825 EW perfluorosulfonic acid (PFSA) ionomer and polyamide-imide (PAI). The relative flow rates of the two polymer solutions were adjusted during electrospinning to create multiple layers with different PFSA/PAI weight ratios. After electrospinning, fiber mats were transformed into dense membranes with a total thickness of 20 µm by heating and compaction, where each layer had the same composite morphology: a PFSA ionomer matrix with an embedded network of reinforcing PAI fibers. Tri-layer films were fabricated with surface layers composed of 95 wt% PFSA and 5 wt% PAI and an inner (reinforcing) layer that was enriched in PAI (25–60 wt% PAI), with either a uniform PFSA/PAI composition or with a symmetric PFSA/PAI compositional gradient. The thickness of the inner layer (uniform or gradient composition) was adjusted so that the effective/average composition of the entire membrane was 80 wt% PFSA and 20 wt% PAI. As compared to a single layer membrane with a uniform distribution of PAI fibers in a PFSA matrix, the tri-layer membrane structures exhibited dramatically less in-plane swelling (5–6% vs. 11%) with no loss in proton conductivity. For a slightly different system, with alternating layers of neat PFSA and 70/30 PFSA/PAI, increasing the number of layers from 3 to 5, 7, or 9 had no effect on proton conductivity (because the overall membrane composition was held constant) and did not further reduce the membrane in-plane swelling.

Selective Filtration of Fluids in Materials with Slit-Shaped Nanopores

Problems associated with a qualitative increase in the selectivity of fluid filtration remain the major challenge in a variety of areas such as fluid transport through porous materials and media, ion separation, water desalination and purification, and many others. A promising way to solve these problems is to design and develop membranes with slit-shaped nanopores. In the paper, we studied the selectivity and permeability of slitshaped nanosized pores in the natural mineral (hydroxyapatite) with the use of the nonequilibrium molecular dynamics approach with all-atom models. We showed that the subnanometer-wide slit-shaped pores in hydroxyapatite are able to demonstrate both good salt rejection and relatively high water permeability. In particular, the numerically predicted water permeability of hydroxyapatite with 0.4 nm thick slit-shaped nanopores reaches about 200 L/(m2 h bar) that is higher than that of commercial membranes and has the same order of magnitude as the theoretically predicted water permeability through single-layer MoS2 nanoporous membranes. An increase in the nanopore thickness is accompanied by a multiple growth in permeability, which is comparable with advanced 2D-CAP (2D-conjugated aromatic polymer) membranes, but in so doing the filtration selectivity is lost. The results show that nanoporous materials with the connected network of slit-shaped nanopores is a promising filter material for water treatment including seawater desalination and other important technical and environmental applications.

AA'-Stacked Trilayer Hexagonal Boron Nitride Membrane for Proton Exchange Membrane Fuel Cells.

Hexagonal boron nitride (h-BN) and graphene have emerged as promising materials for proton exchange membranes because of their high proton conductivity and chemical stability. However, the defects and grain boundaries generated during the growth and transfer of two-dimensional materials limit their practical applicability. Here, we report the fabrication of membrane electrode assemblies using large-area single-oriented AA'-stacked trilayer h-BN (3L-BN), which exhibits very few defects during the growth and transfer, as a proton exchange membrane for use in fuel cell systems. The fuel cell based on AA'-stacked 3L-BN showed a H2 permeation current density as low as 2.69 mA cm-2 and an open circuit voltage (OCV) as high as 0.958 V; this performance is much superior to those for cells based on Nafion (3.7 mA cm-2 and 0.942 V, respectively) and single-layer h-BN (10.08 mA cm-2 and 0.894 V, respectively). Furthermore, the fuel cell with the AA'-stacked 3L-BN membrane almost maintained its original performance (OCV, maximum power density, and H2 permeation current density) even after 100 h of an accelerated stress test at 30% RH and 90 °C, while the fuel cells with the Nafion and single-layer BN membranes exhibited severely deteriorated performances. The stability of the cell based on the AA'-stacked 3L-BN membrane was better because the membrane prevented gas crossover and suppressed the generation of reactive radicals during cell operation.