Search Results (13)

This work presents methods of obtaining polymeric hollow-fiber membranes produced via the dry–wet phase inversion method that were published in renowned specialized membrane publications in the years 2010–2020. Obtaining hollow-fiber membranes, unlike flat membranes, requires the use of a special installation for their production, the most important component of which is the hollow fiber forming spinneret. This method is most often used in obtaining membranes made of polysulfone, polyethersulfone, polyurethane, cellulose acetate, and its derivatives. Many factors affect the properties of the membranes obtained. By changing the parameters of the spinning process, we change the thickness of the membranes’ walls and the diameter of the hollow fibers, which causes changes in the membranes’ structure and, as a consequence, changes in their transport/separation parameters. The type of bore fluid affects the porosity of the inner epidermal layer or causes its atrophy. Porogenic compounds such as polyvinylpyrrolidones and polyethylene glycols and other substances that additionally increase the membrane porosity are often added to the polymer solution. Another example is a blend of two- or multi-component membranes and dual-layer membranes that are obtained using a three-nozzle spinneret. In dual-layer membranes, one layer is the membrane scaffolding, and the other is the separation layer. Also, the temperature during the process, the humidity, and the composition of the solution in the coagulating bath have impact on the parameters of the membranes obtained. Full article

This study assesses the effects of different polytetrafluoroethylene (PTFE) particle sizes and concentrations on the performance of dual-layer membranes in direct contact membrane distillation (DCMD). Specifically, particle sizes of 0.5 μm, 1 μm, and 6 μm were systematically evaluated at concentrations of 0 wt%, 2 wt%, 4 wt%, and 6 wt%. Comprehensive analyses, including scanning electron microscopy (SEM), liquid entry pressure (LEP), contact angle, thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), atomic force microscopy (AFM), permeate flux, nitrogen gas permeation, and salt rejection, were employed to characterize the membranes. Under conditions of a feed temperature of 70 °C and a salt concentration of 8000 ppm for a 24 h duration, the results clearly indicated that a 0.5 μm PTFE particle size combined with a 6 wt% concentration exhibited the highest performance. This configuration achieved a permeate flux of 11 kg·m²/h and a salt rejection rate of 99.8%. The outcomes of this research have significant implications for the optimization of membranes used in DCMD applications, with potential benefits for sustainable water treatment and energy conservation. Full article

Partial oxidation of methane (POM) is a prominent pathway for syngas production, wherein the hydrogen in syngas product can be recovered directly from the reaction system using a hydrogen (H₂)-permeable membrane. Enhancing the efficiency of this H₂ separation process is a current major challenge. In this study, Ce_0.8Y_0.2O_2-δ-BaCe_0.8Y_0.2O_3-δ (YDC-BCY) hollow fiber (HF) membranes were developed and characterized for their H₂ permeation fluxes. Firstly, YDC and BCY ceramic powders were synthesized using the sol-gel method, followed by the fabrication of YDC-BCY dual-phase ceramic HF membranes using a combined phase inversion–sintering process. Characterization using SEM, powder XRD, EDS, and electrical conductivity tests confirmed the phases of the prepared powders and HF membranes. Well-structured YDC and BCY powders with uniform particle sizes were obtained after calcination at 900 °C. With the addition of 1 wt.% Co₂O₃ as a sintering aid, the YDC-BCY dual-phase HF membrane achieved densification after sintering at 1500 °C. Subsequently, the influences of sweep gas composition and temperature on the hydrogen permeation of the YDC-BCY HF membranes with YDC/BCY molar ratios of 2:1, 3:1, and 4:1 were investigated. At 1000 °C and a sweep-gas flow rate of 120 mL·min⁻¹, the YDC-BCY HF membrane with a YDC/BCY molar ratio of 4:1 exhibited a peak hydrogen flux of 0.30 mL·min⁻¹ cm⁻². There is significant potential for improving the hydrogen permeation of dual-phase ceramic membranes, with future efforts aimed at reducing dense layer thickness and enhancing the membrane material’s electronic and proton conductivities. Full article

This study focuses on the synthesis and characterization of dual-layer sulfonated polyphenylenesulfone (SPPSu) nanocomposite hollow fiber nanofiltration membranes incorporating titanium dioxide (TiO₂) nanoparticles through the phase inversion technique. Advanced tools and methods were employed to systematically evaluate the properties and performance of the newly developed membranes. The investigation primarily centered on the impact of TiO₂ addition in the SPPSu inner layer on pure water permeability and salt rejection. The nanocomposite membranes exhibited a remarkable three-fold increase in pure water permeability, achieving a flux of 5.4 L/m²h.bar compared to pristine membranes. The addition of TiO₂ also enhanced the mechanical properties, with an expected tensile strength increase from 2.4 to 3.9 MPa. An evaluation of salt rejection performance using a laboratory-scale filtration setup revealed a maximal rejection of 95% for Mg₂SO₄, indicating the effective separation capabilities of the modified dual-layer hollow fiber nanocomposite membranes for divalent ions. The successful synthesis and characterization of these membranes highlight their potential for nanofiltration processes, specifically in selectively separating divalent ions from aqueous solutions, owing to their improved pure water flux, mechanical strength, and salt rejection performance. Full article

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) that can cause adverse effects on human health. The incorporation of materials as visible light photocatalysts and its energy storage capability allow for the photodegradation of BPA, especially in the absence of a light source. To date, there have been no significant studies regarding energy storage in membrane technology, with only a focus on the suspension form. Hence, this study was conducted to degrade the pollutant through a co-extrusion process using a mixture of copper (II) oxide and tungsten oxide as the photocatalyst and energy storage materials, respectively. Both materials were embedded into polyvinylidene (PVDF) membranes to produce a Cu₂O/WO₃/PVDF dual-layer hollow fiber (DLHF) membrane. The outer dope extrusion flow rate was set at 3 mL/min, 6 mL/min, and 9 mL/min with photocatalyst:polymer ratios of 0.3, 0.50, and 0.7 Cu₂O/WO₃/PVDF, respectively. The performance of the membranes for each ratio was evaluated using 2 ppm of BPA with visible light irradiation. The results showed that each membrane’s outer and inner layers featured finger-like void structures, while the intermediate part had a sponge-like structure. The membrane with the photocatalyst:polymer ratio of 0.5 was hydrophilic and had a high porosity of 54.97%, resulting in a high flow of 510 L/m²h. Under visible light irradiation, a 0.5 Cu₂O/PVDF DLHF membrane with a 6-mL/min outer dope flow rate was able to remove 97.82% of 2-ppm BPA without copper leaching into the water sample. Under dark conditions, the DLHF sample showed the capability of energy storage performance and could drive certain degradation after lighting off up to 70.73% of 2-ppm BPA. The photocatalytic DLHF membrane with the ratio of 0.5 was the most optimal due to its potential morphology and ability to degrade a large amount of BPA. It is important to emphasize that usage of materials with the capability for energy storage can provide a significant contribution toward more practical membranes, so photodegradation can occur even in dark conditions. Full article

In recent years, the need to reduce energy consumption worldwide to move towards sustainable development has led many of the conventional technologies used in the industry to evolve or to be replaced by new alternatives. Oxygen is a compound with diverse industrial and medical applications. For this reason, obtaining it from air is one of the most interesting separations, traditionally performed by cryogenic distillation and pressure swing adsorption, two techniques which are very energetically expensive. In this sense, the implementation of membranes in a hollow fiber configuration is presented as a much more efficient alternative to carry out this separation. The aim of this work is to develop cost-effective multilayer hollow fiber composite membranes made of Matrimid and polydimethylsiloxane (PDMS) for the separation of oxygen and nitrogen from air. PDMS is used as a cover layer but can also enhance the performance of the membrane. In order to compare these two materials, three different configurations are studied. First, integral asymmetric Matrimid hollow fiber membranes were produced using the spinning method. Secondly, by using dip-coating method, a PDMS dense selective layer was deposited on a self-made polyvinylidene fluoride (PVDF) hollow fiber support. Finally, the performance of a dual-layer hollow fiber membrane of Matrimid and PDMS was studied. Membrane morphology was characterized by SEM and separation performance of the membranes was evaluated by mixed-gas permeation experiments. The novelty presented in this work is the manufacture of hollow fiber membranes and the way Matrimid is treated. This makes it possible to develop much thinner dense layers than in the case of flat-sheet membranes, which leads to higher permeance values. This is a key factor when implementing this technology on an industrial scale. Membranes prepared in this work were compared to the current state of the art, reporting quite good performance for the dual-layer membrane, reaching O₂ permeance of 30.8 GPU and O₂/N₂ selectivity of 4.7, with a thickness of about 5–10 μm (counting both selective layers). In addition, the effect of operating temperature on the membrane permeances has been studied experimentally; we analyze its influence on the selectivity of the separation process. Full article

Polyvinylidene fluoride (PVDF) dual-layer hollow fiber membranes were simultaneously fabricated by thermally induced phase separation (TIPS) and non-solvent induced phase separation (NIPS) methods using a triple orifice spinneret (TOS) for water treatment application. The support layer was prepared from a TIPS dope solution, which was composed of PVDF, gamma-butyrolactone (GBL), and N-methyl-2-pyrrolidone (NMP). The coating layer was prepared from a NIPS dope solution, which was composed of PVDF, N,N-dimethylacetamide (DMAc), and polyvinylpyrrolidone (PVP). In order to improve the mechanical strength of the dual-layer hollow fiber, a nucleating agent, sodium 2,2′-methylene bis-(4,6-di-tert-butylphenyl) phosphate (NA11), was added to the TIPS dope solution. The performance of the membrane was evaluated by surface and cross-sectional morphology, water flux, mechanical strength, and thermal property. Our results demonstrate that NA11 improved the mechanical strength of the PVDF dual-layer hollow fiber membranes by up to 42%. In addition, the thickness of the coating layer affected the porosity of the membrane and mechanical performance to have high durability in enduring harsh processing conditions. Full article

Hollow-fiber membranes are widely used in various fields of membrane processes because of their numerous properties, e.g., large surface area, high packing density, mass production with uniform quality, obvious end-of-life indicators, and so on. However, it is difficult to control the pores and internal properties of hollow-fiber membranes due to their inherent structure: a hollow inside surrounded by a wall membrane. Herein, we aimed to control pores and the internal structure of hollow-fiber membranes by fabricating a dual layer using a dual nozzle. Two different pore formers, polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP), were separately prepared in the dope solutions and used for spinning the dual layer. Our results show that nanoscale pores could be formed on the lumen side (26.8–33.2 nm), and the open pores continuously increased in size toward the shell side. Due to robust pore structure, our fabricated membrane exhibited a remarkable water permeability of 296.2 ± 5.7 L/m²·h·bar and an extremely low BSA loss rate of 0.06 ± 0.02%, i.e., a high BSA retention of 99.94%. In consideration of these properties, the studied membranes are well-suited for use in either water treatment or hemodialysis. Overall, our membranes could be considered for the latter application with a high urea clearance of 257.6 mL/min, which is comparable with commercial membranes. Full article

Bisphenol A (BPA) is amongst the endocrine disrupting compounds (EDCs) that cause illness to humans and in this work was removed using copper (I) oxide (Cu₂O) visible light photocatalyst which has a narrow bandgap of 2.2 eV. This was done by embedding Cu₂O into polyvinylidene fluoride (PVDF) membranes to generate a Cu₂O/PVDF dual layer hollow fiber (DLHF) membrane using a co-extrusion technique. The initial ratio of 0.25 Cu₂O/PVDF was used to study variation of the outer dope extrusion flowrate for 3 mL/min, 6 mL/min and 9 mL/min. Subsequently, the best flowrate was used to vary Cu₂O/PVDF for 0.25, 0.50 and 0.75 with fixed outer dope extrusion flowrate. Under visible light irradiation, 10 mg/L of BPA was used to assess the membranes performance. The results show that the outer and inner layers of the membrane have finger-like structures, whereas the intermediate section of the membrane has a sponge-like structure. With high porosity up to 63.13%, the membrane is hydrophilic and exhibited high flux up to 13,891 L/m²h. The optimum photocatalytic membrane configuration is 0.50 Cu₂O/PVDF DLHF membrane with 6 mL/min outer dope flowrate, which was able to remove 75% of 10 ppm BPA under visible light irradiation without copper leaching into the water sample. Full article

In this study, a triblock copolymer was used as additive to fabricate new dual layer hollow fiber membranes with a hydrophilic active inner surface in order to improve their fouling resistance. The polymeric components of the solutions for membrane fabrication were poly(ether sulfone), poly(N-vinyl pyrrolidone), and the triblock copolymer. The additive consists of three blocks: a middle hydrophobic poly(ether sulfone) block and two outer hydrophilic alkyl poly(ethylene glycol) blocks. By varying the additive concentration in the solutions, it was possible to fabricate dual layer hollow fiber membranes that are characterized by a hydrophilic inner layer, a pure water permeance of over 1800 L/(m² bar h) and a molecular weight cut-off of 100 kDa similar to commercial membranes. Contact angle and composition determination by XPS measurements revealed the hydrophilic character of the membranes, which improved with increasing additive concentration. Rheological, dynamic light scattering, transmission, and cloud point experiments elucidated the molecular interaction, precipitation, and spinning behavior of the solutions. The low-molecular weight additive reduces the solution viscosity and thus the average relaxation time. On the contrary, slow processes appear with increasing additive concentration in the scattering data. Furthermore, phase separation occurred at a lower non-solvent concentration and the precipitation time increased with increasing additive content. These effects revealed a coupling mechanism of the triblock copolymer with poly(N-vinyl pyrrolidone) in solution. The chosen process parameters as well as the additive solutions provide an easy and inexpensive way to create an antifouling protection layer in situ with established recipes of poly(ether sulfone) hollow fiber membranes. Therefore, the membranes are promising candidates for fast integration in the membrane industry. Full article

Dual-layer hollow fiber (DLHF) nanocomposite membrane prepared by co-extrusion technique allows a uniform distribution of nanoparticles within the membrane outer layer to enhance the membrane performance. The effects of spinning parameters especially the air gap on the physico-chemical properties of ZrO₂-TiO₂ nanoparticles incorporated PVDF DLHF membranes for oily wastewater treatment have been investigated in this study. The zeta potential of the nanoparticles was measured to be around –16.5 mV. FESEM–EDX verified the uniform distribution of Ti, Zr, and O elements throughout the nanoparticle sample and the TEM images showed an average nanoparticles grain size of ~12 nm. Meanwhile, the size distribution intensity was around 716 nm. A lower air gap was found to suppress the macrovoid growth which resulted in the formation of thin outer layer incorporated with nanoparticles. The improvement in the separation performance of PVDF DLHF membranes embedded with ZrO₂-TiO₂ nanoparticles by about 5.7% in comparison to the neat membrane disclosed that the incorporation of ZrO₂-TiO₂ nanoparticles make them potentially useful for oily wastewater treatment. Full article

In clinical practice, the catheter has to be placed at an accurate position during anesthesia administration. However, effectively guiding the catheter to the accurate position in deeper tissues can be difficult for an inexperienced practitioner. We aimed to address the current issues associated with catheter placement using a novel smart assistance system for blood vessel catheter placement. We used a hollow introducer needle embedded with dual wavelength (690 and 850 nm) optical fibers to advance the tip into the subclavian vessels in anesthetized piglets. The results showed average optical density changes, and the difference between the absorption spectra and hemoglobin concentrations of different tissue components effectively identified different tissues (p < 0.05). The radial basis function neural network (RBFNN) technique was applied to distinguish tissue components (the F-measure value and accuracy were 93.02% and 94%, respectively). Finally, animal experiments were designed to validate the performance of the proposed system. Using this system based on oximetry, we easily navigated the needle tip to the target vessel. Based on the experimental results, the proposed system could effectively distinguish different tissue layers of the animals. Full article

The presence of bisphenol A (BPA) in various water sources has potentially led to numerous adverse effects in human such as increased in blood pressure and derangement in liver function. Thus, a reliable treatment for the removing BPA is highly required. This present work aimed to study the efficiency of visible light driven photocatalytic dual-layer hollow fiber (DLHF) membrane for the removal of BPA from water and further investigated its detrimental effects by using an in-vivo model. The prepared membranes were characterized for their morphology, particles distribution, surface roughness, crystallinity and light absorption spectra. The removal of 81.6% and 86.7% in BPA concentration was achieved for N-doped TiO₂ DLHF after 360 min of visible and UV light irradiation, respectively. No significant changes for all three groups were observed in liver function test meanwhile the rats-exposed to untreated BPA water shows significance blood pressure increment contrary to rats-exposed to treated BPA water. Similarly, the normal morphology in both jejunum and ileum were altered in rats-exposed to untreated BPA water group. Altogether, the presence of N-doped TiO₂ in DLHF are shown to significantly enhance the photocatalytic degradation activity under visible irradiation, which effectively mitigates the effect of BPA in an in-vivo model. Full article