Porous Hollow Fiber Research Articles

Tubular Diamond as an Efficient Electron Field Emitter

Herein, we present a straightforward and cost-effective procedure for producing conductive diamond tubes on the surface of porous carbon nanotube hollow fibers using successive 10-pulsed laser annealing shots and 6 h of hot filament chemical vapor deposition techniques. Room-temperature Raman and X-ray diffraction spectra reveal the signature T2g peaks near 1332.4 cm–1 and 111 planes of diamonds near 43.9°, respectively. A low turn-on field (ETO) ∼1.85 V/μm@1 μA/cm2 and a threshold field (ETH) ∼2.54 V/μm@10 μA/cm2 were observed for the tubular diamond structures. The field enhancement factor (β) was calculated at 3594 and highly stable field emission current stability was observed over a long period of 4 h. For the first time, a good insight into the field emission results of the diamond is established with the structural, electronic properties, and the work function (φ) ∼4.84 eV analysis conducted by the density functional theory simulation. Finite electronic states at the Fermi level are observed beyond a band gap, and it demonstrates the wide-band gap (4.4 eV) semiconducting nature of the diamond. The Bader charge analysis and maximum entropy method pattern revealed the negative electron affinity of the diamond, and it is responsible for the emission of electrons from the conduction band of the diamond. Besides, the accumulation of charge carriers, which contributes to the electric field emission, takes place due to the weak π bonds of carbon atoms. The low turn-on field, the high field enhancement factor, and the good field emission current stability of tubular diamond offer great prospects for future efficient and low-cost field emission devices.

Smoothing the wrinkle formation and improving dye rejection performance in porous graphene oxide membranes using high surface curvature hollow fiber substrates

Assembly of atomic-scale thin two-dimensional (2D) graphene oxide (GO) nanosheets into a membrane with macroscopic three-dimensional (3D) laminar structure is accompanied by the formation of wrinkles. The size and pattern of wrinkles, which depend on the substrate curvature and the thickness of the 3D laminar structure, adversely affect the separation performance of the membrane. Therefore, smoothing the formed wrinkles is essential to boost the separation performance of GO-based membranes. For the first time, we proposed a new approach to prepare porous hollow fiber (HF) yttria-stabilized zirconia (YSZ) substrates with small-diameter (660–790 μm, outer diameter (OD)) by stretching the nascent HF using gravitational force. Also, using a delayed phase inversion, a plurality of radial micro-channels opening from the interior surface of HFs can be realized. The resultant HF substrates show promising permeation characteristics and good fracture strength owing to their open microstructure and the robustness of YSZ. Small-diameter HF substrates (OD = 660 μm) with higher surface curvature ensured the fabrication of porous GO (PGO) membranes with better dye separation performance. The rejection of methyl red (MR, MW = 269.3 g mol−1) dye molecule for small-diameter HF PGO membranes (OD 660 μm) was 10%–167% higher than that of membranes fabricated using large-diameters (OD 1250–2600 μm). This study shed light on the fabrication of high-performance thin film membranes by tailoring the geometric features of substrates.

Improving the Blood Compatibility and the Gas Permeability of Polyether Ether Ketone Hollow Fiber Membrane Used for Membrane Oxygenator via Grafting Hydrophilic Components

As the core component of extracorporeal membrane oxygenation (ECMO) therapy for patients with severe cardiopulmonary failure, the structures and the properties of membrane oxygenator play a crucial role in determining both the efficiency of the gas exchange and the safety of the patients. Herein, with the aim of enhancing the blood compatibility, gas permeability, and durability of the membrane oxygenator, a porous polyether ether ketone hollow fiber membrane (PEEK-HFM) was prepared via a combination of melt spinning and thermally induced phase separation method. Subsequently, three different hydrophilic components including a nonionic polymer (poly(ethylene glycol), PEG), an ionic monomer (acrylic acid, AA), and a zwitterionic monomer (2-methacryloyloxyethyl phosphorylcholine, MPC) were introduced onto the PEEK-HFM surface by UV-induced grafting. The effects of different hydrophilic modifications on the surface characteristics (such as surface water wettability, surface potential, and porous morphologies) and the related properties (including mechanical performance, blood compatibility, and gas exchange permeability) were studied in detail. After grafting different hydrophilic components, not only the pore size of the corresponding PEEK-HFMs decreased compared to the unmodified PEEK-HFMs but also the surface roughness. Meanwhile, although the hydrophilic modifications resulted in the deterioration of the tensile strength of resulting PHFMs, it enhanced the blood compatibility of modified PEEK-HFMs. Moreover, among these modified membranes, the one grafted with MPC showed the best blood compatibility due to its more hydrophilic surface. Additionally, the modified membranes still maintained excellent gas permeability, ensuring the gas exchange performance between carbon dioxide and oxygen. Furthermore, a comprehensive comparison between the modified PEEK-HFMs and a commercial membrane oxygenator (poly(4-methyl-1-pentene), PMP) demonstrated that the modified PEEK-HFMs exhibited higher gas permeability, better blood compatibility, stronger gas exchange ability, and comparable tensile strength, indicating their potential as a high-efficiency option for membrane oxygenators.

Electromembrane extraction of anesthetic ketamine on-line coupled to capillary electrophoresis

The anesthetic ketamine is extracted from the sample solutions by electromembrane extraction on-line coupled with capillary electrophoresis (CE) at a short separation path. Ketamine is extracted from model acidic and alkaline aqueous solutions, or from untreated human urine as donor into an acidic acceptor solution, which acts also as background electrolyte for CE. Extraction occurs in a flow-through extraction mini probe with an internal volume of 1.1 µL, consisting of a porous hollow fiber with pores filled with nitrophenyloctyl ether as extraction liquid. The probe is immersed in a 1.5 mL vial of analyte solution, the vial is vibrationally agitated during extraction, and ketamine is extracted at 150 V for 300 s. It was found that the pH of the sample solution does not affect the extraction efficiency, i.e., it does not depend on whether ketamine is in the protonated form or as a neutral molecule during extraction; the enrichment factor is 16–19, the recovery factor 1.5 %. The calibration dependence is linear in both model samples in the concentration range 2 to 50 µM and in urine in the concentration range 2.5 to 10 µM with the same slope in both sample types. The LOD values are around 1 µM. The extraction probe is reusable. However, between runs a purification process with the probe immersed in the background electrolyte is necessary to remove ketamine trapped in the membrane liquid.

Properties of Polysulphones Synthetized for Forming of Porous Hollow-Fiber Membranes

For the first time, for the problem of hollow fiber membranes spinning, polysulfones in a wide range of molecular weights (42 000–184 000 g/mol) were synthesized in such aprotic dipolar solvents as dimethylacetamide, N-methyl-2-pyrollidone, and dimethyl sulfoxide. The dependence of the thermal and mechanical properties of polysulfones on molecular weight characteristics has been studied. A comparison of the mechanical properties of the synthesized PSF, commercial PSF Ultrason S 6010 (BASF, Germany) and PSF-150 (JSC Institute of Plastics, Russia) showed that the synthesized polymers are not inferior to commercial analogues. Some synthesized polymers surpass commercial PSF in terms of elasticity and strength modulus. Based on the study of the spinning solutions dynamic viscosity, promising PSF samples were selected for the formation of porous hollow fiber supports. It was found that hollow-fiber porous support from a PSF sample with a molecular weight of 110 000 g/mol have a high nitrogen permeability of 47.5 m3/m2 · h · bar. Such supports are promising for casting highly permeable composite membranes with a thin selective layer.

Keggin type phosphotungstic acid intercalated copper-chromium-layered double hydroxide reinforced porous hollow fiber as a sorbent for hollow fiber solid phase microextraction of selected chlorophenols besides their quantification via high performance liquid chromatography

Herein, a copper-chromium-layered double hydroxide (Cu/Cr-LDH) was synthesized by the co-precipitation method. The Cu/Cr-LDH was intercalated to the Keggin-type polyoxometalate (H3PW12O40). The modified LDH accommodated in the pores of hollow fiber (HF), to prepare the extracting device for the HF-solid phase microextraction method (HF-SPME). The method was used for the extraction of 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6- trichlorophenol from tap water, river water, and tea sample. The extracted target analytes were quantified via high-performance liquid chromatography-UV detection. The figures of merit of the method such as, linear dynamic ranges (LDRs), limit of detections (LODs) and, limit of quantifications (LOQs), were determined based on the obtained optimum condition. Based on the results, the LDR was between 1 and 500 μg L − 1 and r2 higher than 0.9960. The LODs and LOQs were obtained in the ranges of 0.28–0.36 µg L − 1 and 0.92–1.1 µg L − 1, respectively. The relative standard deviations ((RSDs% for inter-and intra-day) of the method for the extraction of target analytes were calculated in two different concentrations of (2 and 10 μg L − 1) and (5 and 10 μg L − 1) between 3.70% - 5.30% and 3.50% - 5.70%-respectively. The enrichment factors were obtained between 57 and 61. In order to investigate the accuracy of the method, also the relative recovery was obtained, between 93 and 105%. Finally, the proposed method was used for the extraction of the selected analytes in different water and tea samples.

Effect of Molecular Weight and Chemical Structure of Terminal Groups on the Properties of Porous Hollow Fiber Polysulfone Membranes

For the first time, polysulfones (PSFs) were synthesized with chlorine and hydroxyl terminal groups and studied for the task of producing porous hollow fiber membranes. The synthesis was carried out in dimethylacetamide (DMAc) at various excesses of 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A) and 4,4'-dichlorodiphenylsulfone, as well as at an equimolar ratio of monomers in various aprotic solvents. The synthesized polymers were studied by nuclear magnetic resonance (NMR), differential scanning calorimetry, gel permeation chromatography (GPC), and the coagulation values of 2 wt.% PSF polymer solutions in N-methyl-2-pyrollidone were determined. According to GPC data, PSFs were obtained in a wide range of molecular weights Mw from 22 to 128 kg/mol. NMR analysis confirmed the presence of terminal groups of a certain type in accordance with the use of the corresponding monomer excess in the synthesis process. Based on the obtained results on the dynamic viscosity of dope solutions, promising samples of the synthesized PSF were selected to produce porous hollow fiber membranes. The selected polymers had predominantly -OH terminal groups and their molecular weight was in the range of 55-79 kg/mol. It was found that porous hollow fiber membrane from PSF with Mw 65 kg/mol (synthesized in DMAc with an excess of Bisphenol A 1%) has a high helium permeability of 45 m3/m2∙h∙bar and selectivity α (He/N2) = 2.3. This membrane is a good candidate to be used as a porous support for thin-film composite hollow fiber membrane fabrication.

Near-perfect suppression of Li dendrite growth by novel porous hollow carbon fibers embedded with ZnO nanoparticles as stable and efficient anode for Li metal batteries

For the practical application of next-generation Li metal batteries (LMBs), a Li metal anode with high safety and efficiency is essential. However, LMBs still suffer from the problems caused by the growth of Li dendrites at the Li metal anode. In this study, we introduce a novel way that could dramatically suppress the growth of Li dendrites and improve the performance of LMBs. A free-standing porous hollow carbon nanofiber embedded with lithiophilic ZnO nanoparticles (P-HCNF@ZnO) is fabricated using a dual-nozzle electrospinning technique followed by carbonization. The nano-sized pores formed in the shell of hollow carbon fiber provide passages for Li ions to penetrate into the core space of the hollow fiber, and the lithiophilic ZnO particles play a decisive role in inducing and plating Li ions inside the core efficiently and uniformly. Therefore, Li ions are mostly electroplated/stripped on the internal surface of the porous hollow fibers and dendrites are rarely formed on their exterior surface even under fast lithiation conditions, while numerous Li dendrites are formed on the exterior surface of the non-porous hollow fiber electrode (HCNF@ZnO). As a result, the P-HCNF@ZnO electrode exhibits a very low over-potential of about 87 mV, a stable capacity retention of about 95% at a high current density of 1.0 mA cm−2, and a much higher performance than HCNF@ZnO in a symmetric cell test. Furthermore, in full cell tests, the LiFePO4 (LFP) battery made of lithiated P-HCNF@ZnO anode exhibits a high capacity of 175.3 mAh g−1 and a lower over-potential by 0.29 V than the reference sample. Analytical works and theoretical interpretations, elucidated that the Li metal anode made of the P-HCNF@ZnO significantly improves the performance of LMBs.

Parametric and modelling study of H2O-induced plasticization in PEI-TFC membrane for gas dehydration

Separation of moisture from gaseous mixtures, such as natural gas, humid air in food and goods storage warehouses or in sports halls and so on is of great importance. In this article, the separation of water from a wet gas stream is carried out by a TFC membrane made by interfacial polymerization on the sublayer of porous polyetherimide hollow fibers. Then the key-parameters affecting membrane efficiency is studied. The outcomes show that increasing the concentration of MPD has a substantial effect on enhancing the membrane water vapor flux. Moreover, it is disclose that increasing the concentration of TMC has the greatest effect on reducing nitrogen gas permeability and increasing the selectivity. Our findings reveals that disregarding the very low concentration of water vapor in the feed, shows a great impact on the permeance of each component compared to the pure state. Also, based on the modelling, it is obvious that for nitrogen gas in the entire pressure range, the adsorption mechanism is almost completely controlled by the Henry model, while the Langmuir adsorption mechanism is controlling for water vapor at low pressures, although at high pressures, the Henry mechanism has absolute superiority. Surprisingly, the H2O-induced plasticization impact on nitrogen permeance is more intense than on water vapor permeance. According to the modeling outputs, it is revealed that because D N2 is one to two order of magnitude lower than DH2O, water vapor permeance is much higher than that of nitrogen.

Atomic layer deposition of TiO2 on porous polysulfone hollow fibers membranes for water treatment

Numerous membranes devoted to water treatment are made of Polysulfone (PSF) and can suffer from performance deterioration because of the intrinsic hydrophobicity of this material. Modifying membrane surface allows the engineering of its physicochemical properties and can achieve improved permeability and anti-fouling efficiency by tuning the membrane hydrophilicity or porosity. Atomic layer deposition (ALD) is a unique technology that provides highly conformal and uniform coatings layers such as oxides over surfaces of three-dimensional (3D) parts, porous materials and particles. In this work, titanium dioxide (TiO2) was deposited on polysulfone hollow fibers (HF) membranes via ALD using TiCl4 and H2O as precursors. Membranes obtained with increasing number of deposition ALD cycles were tested until the pores were totally blocked. The morphology, structure and mechanical properties of membranes were not altered. The deposition was confirmed by scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) analyses. The deposition of TiO2 enhanced by 50% the water permeability and by 20% the fouling resistance of the PSF HF membranes until only 20 ALD cycles. This is accompanied by an increase of hydrophilicity and a pores size reduction.

Bioinspired hollow porous fibers with low emissivity and conductivity aluminum platelet skin for thermal insulation

Hollow porous fibers with low emissivity and conductivity aluminum platelets skin for thermal insulation.

Development of advanced method based on nanoporous membranes for separation of pharmaceutical compounds from aqueous streams: Computational simulation and analysis

In this study, we developed a novel methodology for isolation and separation of pharmaceutical compounds from aqueous solutions. Pharmaceutical pollutants are an important group of contaminants of emerging concern (CECs), which their discharge in aquatic environment may result in severe ecological impacts. Penicillin G (Pen G) is a common type of antibiotic, which its presence in drinkable water sources can increase the probability of drug resistance in bacteria. This paper aims to study the removal efficiency of Pen G antibiotic from wastewater (as the aqueous solution) using novel Amberlite LA-2-contained tributyl phosphate solvent (as the organic solution) inside a porous hollow fiber membrane contactor (HFMC). To reach this aim, a comprehensive numerical simulation has been developed based on the computational fluid dynamics (CFD) technique to solve the principal transport equations in shell, membrane and tube sections of HFMC. Evaluation of the results shows the fact that the Amberlite LA-2-contained tributyl phosphate as the organic solution removed very high percentage of existed Pen G in aqueous solution. It is perceived from the results that increase in some parameters such as the concentration of organic solution improved the dimensionless concentration (C/C 0 ) of Pen G in the HFMC and consequently enhances its removal efficiency. Also, increase in the membrane parameters like porosity, packing density and the number of fibers have positive effect on the removal efficiency of Pen G. The method developed in this study is robust and can be employed in development of advanced pharmaceutical industry with focus on green technology. • Development of a CFD model for prediction of drug removal. • Study on membrane-based separation of drugs from aqueous solutions. • Understanding the effect of process parameters on the drug separation. • Mass transfer analysis of the drug separation using porous membranes.

Pd single atom stabilized on multiscale porous hollow carbon fibers for phenylacetylene semi-hydrogenation reaction

The extremely high atom dispersion of single atom catalysts (SACs) opens up new opportunities for highly efficient catalysis. However, how to balance the easy accessibility, preparation simplicity, and recoverability for routine nanoscale catalytic supports of SACs is still a big challenge. In this work, the nitrogen doped carbon immobilized Pd SACs with high loading up to 5.6 wt%, in the form of multiscale porous hollow fibers, are prepared through a co-axial emulsion electrospinning and CO2 thermal activating method. The obtained Pd SACs carbon fibers have a bamboo-like tubular structure and multiscale pores on the tube wall, which expose the active sites accessible for reactants. The multiscale porous hollow Pd SACs exhibited both high activity and selectivity for phenylacetylene semi-hydrogenation. This universal method is also applicable for the preparation of many other 1D metal SACs such as Pt, Ru and Co, which exhibits great promising for developing easily available and efficient SACs.

Combination of in-situ electro synthesized Zn–Al-LDH@ pencil graphite fiber and three phase hollow fiber LPME for microextraction of some antibiotics in urine samples and quantification via HPLC-UV

In the present study, a combination of two useful extraction techniques including fiber solid phase microextraction based on the new synthesized sorbent and the porous hollow fiber liquid phase microextraction is reported. The selective anion-exchangeable Zn–Al-layered double hydroxide as a fiber was electrodeposited on the surface of pencil graphite substrate through simple and cost-effective method. The prepared fiber was characterized and put into the lumen of the porous hollow fiber, which was filled by alkaline solution. The obtained optimum condition for the method was as follows: donor phase HCl concentration of 0.10 mM, acceptor phase NaOH concentration of 7.60 mM and extraction time of 16 min. It is necessary to adjust the concentration of the donor phase in order to extract acidic analytes from an aqueous sample into an organic phase. The method was used for the quantification of three antibiotics including amoxicillin, ciprofloxacin and cefixime. The extracted antibiotics were analyzed by high performance liquid chromatography-ultraviolet detection (HPLC-UV). In the optimal conditions, the linearity of the proposed method was in the range of 0.50–500.00 μg L−1 for selected analytes in water and urine matrices. All calibration curves showed determination of coefficient higher than 0.9958. The limits of detection and limits of quantification were calculated to be between 0.08 and 0.16 μg L−1 and 0.28–0.56 μg L−1, respectively. In order to define the precision of the method, the inter-day and intra-day relative standard deviations were determined between 3.25 and 5.73% in the three selected concentrations. The enrichment factors (EFs) were between 46.20 and 55.81 for selected drugs. Moreover, the calculated absolute recoveries were between 69.30 and 83.71%. The relative recoveries were obtained in the range of 93.00–105.00%. The proposed method was also employed for analysis of various urine samples containing the selected drugs. The obtained recoveries indicated that the method was useful and applicable in complicated biological samples.

Surface modification of porous polyvinylidene fluoride hollow fiber membrane by sulfonated poly(ether ether ketone) coating for membrane distillation of oily wastewater

AbstractHighly porous polyvinylidene fluoride hollow fiber membranes were fabricated by a non‐solvent induced phase separation process. The membranes were modified by coating an ultra‐thin hydrophilic layer of sulfonated poly(ether ether ketone) (sPEEK) onto the inner surface. An industrial oily wastewater treatment was performed through an air gap membrane distillation (AGMD) process. From field emission scanning electron microscopy, the modified membrane showed an open structure with a large finger‐like outer layer and sponge‐like inner layer. The thickness of the coated sPEEK layer on the inner surface was about 0.5 μm. The coated membrane presented mean pore size of 36 nm and overall porosity of 73%. The inner surface water contact angle decreased from about 82° to 57°. Using Langmuir adsorption experiment, minor oil adsorption on the modified membrane surface was confirmed. A stable water flux of about 12 kg m−2 h−1 and oil rejection of 99% were found during 72 h of the AGMD process for treating the oily wastewater of NGL‐900 (Gachsaran, Iran) plant. The high flux recovery ratio of about 98% was related to the improved anti‐oil‐fouling property. The modified membrane can be a potential candidate for oily wastewater treatment through the MD processes.

Novel TiO2/GO-Al2O3 Hollow Fiber Nanofiltration Membrane for Desalination and Lignin Recovery.

Due to its greater physical–chemical stability, ceramic nanofiltration (NF) membranes were used in a number of industrial applications. In this study, a novel NF membrane was prepared by co-depositing a titanium dioxide (TiO2) and graphene oxide (GO) composite layer directly onto a porous α-Al2O3 hollow fiber (HF) support. An 8 µm-thick TiO2/GO layer was deposited to the surface of α-Al2O3 HF support by vacuum deposition method to produce advanced TiO2/GO-Al2O3 HF NF membrane. Scanning electron microscope (SEM) micrographs, energy dispersive spectrometer (EDS), X-ray powder diffraction (XRD), thermogravimetric analyzer (TGA), porosity, 3-point bending strength, zeta potential analysis, and hydrophilic properties by water contact angle are used for TiO2/GO-Al2O3 HF NF membrane characterization. The results show that the developed membrane’s MWCO ranged from 600 to 800 Da. The water flux, rejection of lignin, and sodium ions were 5.6 L/m2 h·bar, ~92.1%, and ~5.5%, respectively. In a five-day NF process, the TiO2/GO-Al2O3 HF NF membrane exhibits good lignin permeation stability of about 14.5 L/m2 h.

The thermal and light performance of triangular hollow porous polyacrylonitrile fibers reinforced by inorganic salt

In this paper, triangular hollow porous polyacrylonitrile (PAN) fibers were prepared by coaxial wet spinning inspired by silver ant hair. These PAN fibers with ideal triangular hollow cross section structure were obtained by adding inorganic salts into the cortex and core spinning solution combined with proper drawing ratio. Its strength increases to 4.3 times compared with that of the nascent fiber without inorganic salt. Subsequently, the light reflection as well as thermal insulation properties of triangular and circular hollow porous fibrous mats were compared and analyzed. The results show that the triangular hollow porous fibers have higher light reflectance and heat insulation performance than the circular fibers, which endows the fabric a shimmering gloss. This research further expands the application of hollow porous fiber in both thermal insulation field and optical field, which is conducive to the design of “heat stealth” materials and flash materials.

Electrospinning preparation of hollow porous Sn0.84Sm0.08Sb0.08O2 micro/nano fibers and their multispectral compatible stealth properties

SnO2 material has good stability, electrical conductivity and high visible light transmittance, showing great potential in the field of stealth materials. However, it is an important research topic that how to improve its multispectral compatible stealth performance, meet the requirements of combat weapons against all-round attack, and conform to the development trend of “thin, light-weight, wide-band and high-performance” stealth materials. Therefore, Sn0.84Sm0.08Sb0.08O2 micro/nano fibers material was prepared by coaxial electrospinning method combined with heat treatment process in this work. The material has a three-dimensional hollow porous fiber structure, and has a larger specific surface area and better compatible stealth performance than solid core fibers. The hollow porous Sn0.84Sm0.08Sb0.08O2 micro/nano fibers material shows good absorbing ability in X-band. When the matching thickness is 2.6 mm, its effective absorbing bandwidth is 3.51 GHz, and when the matching thickness is 2.8 mm, its lowest reflection loss(RL) is −22.51 dB at 10.3 GHz. Secondly, it has a lower infrared emissivity in the infrared detector working bands of 3–5 μm and 8–14 μm, which are 0.558 and 0.672, respectively. Finally, it has reflectivity at the laser operating wavelengths of 1.06 μm and 1.55 μm, which are 7.9% and 2.1%, respectively. The material achieves the organic unity of high absorption in the radar band, low emissivity in the infrared band and low reflectivity at the laser wavelength. At the same time, this work explores the regulation mechanism of the hollow porous structure on electromagnetic wave absorption, infrared emissivity and laser reflectivity, which provides a certain reference for the development of single-type, light-weight, high-performance multispectral compatible stealth materials.

Effect of polytetrafluoroethylene hollow fiber microstructure on formaldehyde carbonylation performance in membrane contactor

Membrane contactor is regarded as a promising method for reaction and process intensification. The feasibility of formaldehyde carbonylation to synthesize glycolic acid using polytetrafluoroethylene (PTFE) membrane contactor has been proved in our previous study. In this paper, the effect of membrane microstructure on process performance was further investigated. Three porous PTFE hollow fibers with different pore sizes and one polydimethylsiloxane (PDMS)/PTFE composite membrane with dense layer were fabricated for comparison. The physical and chemical properties of four membranes, including chemical composition, morphology, contact angle, liquid entry pressure, thermodynamic analysis and gas permeability, were systemically characterized. Experiments of formaldehyde carbonylation under different reaction conditions were conducted. The results indicated that the yield of glycolic acid increased with decreasing pore size for porous membranes, which was due to the improvement of wetting behavior. The dense layer of PDMS in composite hollow fiber could effectively prevent the solvent from entering membrane pores, thus the membrane exhibited the best performance. At reaction temperature of 120 °C and operation pressure of 3.0 MPa, the yield of glycolic acid was always higher than 90% as the mass ratio of trioxane and phosphotungstic acid increased from 0.2:1 to 0.8:1. The highest turnover frequency was up to 26.37 mol⋅g−1⋅h−1. This study provided a reference for the understanding and optimization of membrane contactors for the synthesis of glycolic acid using solvent with low surface tension.

Porous stainless steel hollow fiber-supported ZIF-8 membranes via FCDS for hydrogen/carbon dioxide separation

MOF membranes show great potential in gas separation, but there are still great difficulties in industrialization due to current complex and time-consuming synthesis methods. We successfully synthesized a series of ZIF-8 membranes on the polydopamine (PDA)-modified porous stainless steel hollow fiber substrates within 20 min using the fast current drive synthesis (FCDS) method. When the applied current density is 0.76 mA/cm2, the prepared 10 cm-length ZIF-8 hollow fiber membrane exhibits a selectivity of 14 for H2/CO2 and H2 permeance of 1.9 × 10-10 mol/(m2·s·Pa) with good stability during 120 h continuous separation. This work extends the fast and facile FCDS method for growing ZIF-8 membranes from disk-shaped substrates to cambered hollow fiber substrates and makes significant sense for accelerating MOF membranes' industrialization.