Dual-layer Hollow Fiber Research Articles

TiO2-embedded dual-layer mullite hollow fiber membranes for efficient removal of Persistent organic pollutants from wastewater

Persistent organic pollutants (POPs) are toxic pollutants that harm the environment and ecosystems. This study presents a novel approach to develop a dual-layer hollow fiber ceramic membrane for phenolic compound removal. A co-extrusion-based phase inversion process and co-sintering techniques were employed to fabricate the membrane, and the effects of TiO2 loadings on the outer layer were investigated. Characterization techniques, including FTIR, SEM, EDX, and zeta potential analysis, were used to analyze the mullite and TiO2 powders and membranes. The membrane’s performance was evaluated through rejection tests of POPs at various concentrations (10, 500, and 1000 ppm) and fouling assessments were conducted. The results showed that the M−MT0.6 membrane, with a mean pore size of 0.0245 μm, effectively rejected benzoic acid (81.45 %), gallic acid (91.45 %), and hydroquinone (74.49 %) from wastewater, achieving the highest permeate flux (1320.50 L/m2·h) for gallic acid at 10 ppm. Additionally, M−MT0.6 exhibited minimal fouling over a 1-h filtration cycle, with the lowest fouling rate (35.1 %) recorded at 1000 ppm for BA, attributed to effective backwashing. However, higher fouling rates were observed at 10 ppm for BA (90.10 %) and HQ (83.50 %). Overall, this study demonstrates the potential of the novel membrane for effective removal of POPs from industrialwastewater.

Preparation of ultra-high permeability dual-layer Al2O3 hollow fiber supports for zeolite membrane fabrication

Four-channel dual-layer Al2O3 hollow fiber with ultra-high permeability and mechanical strength was prepared by co-extrusion and co-sintering technique for the first time and used as support for NaA zeolite membranes fabrication. The macroporous inner layer of the Al2O3 hollow fiber, composed by large Al2O3 particle, gives supports the high permeability and mechanical strength, while the thin out layer, composed by small particles, provides an even and smooth surface for zeolite membrane growth. By using SiO2 as the sintering aid, the sintering temperature of the inner layer was reduced and match with that of the outer layer. The effects of SiO2 adding amount, sintering temperature, Al2O3 particle size and their content on the structure and properties of the prepared hollow fiber were investigated systematically. At a sintering temperature of 1520 °C, a dual-layer hollow fiber with surface pore size of 0.38 μm and fracture load of 24.52 N, exhibits pure water flux as high as 22.23 m3 m 2 h−1 bar−1. The NaA membrane prepared on this support achieved a flux of 14.14 kg m−2 h−1 and a separation factor >10,000 in pervaporation separation of EtOH/H2O solution (90 wt%, 75 °C). This work provides an efficient and low-cost way to prepare ceramic hollow fiber support for high-performance zeolite membrane fabrication.

Carbon quantum dots (CQDs) incorporated dual-layer hollow fibers for pervaporative dehydration of ethanol

Pervaporative ethanol dehydration is a promising approach to concentrate ethanol from biofuel stocks. In this study, we have fabricated high performance dual-layer cellulose triacetate (CTA)/Ultem hollow fiber membranes incorporated with a small amount of superhydrophilic carbon quantum dots (CQDs) via the immiscibility induced phase separation (I2PS) method. The flow rates of the inner- and outer-layer dopes were firstly optimized. Subsequently, various small amounts of CQDs were added into the inner- and outer-layer dope solutions to explore their impacts on membrane structure and separation performance. It was found that the incorporation of a reasonably small amount of CQDs, whether to the inner or outer layer of I2PS membranes, could significantly enhance the mechanical properties and pervaporation performance by altering their structures. The most effective membrane containing 0.2 wt% CQD in the outer layer (0.2CQD_OL) demonstrated exceptional pervaporation performance. Using an 85 wt% ethanol feed solution, this membrane achieved a total flux of 4306 ± 130 g m−2h−1 (equivalent to a water permeance of 33.28 mol m−2h−1 kPa−1) and a water content of approximately 95 wt% (equivalent to a mole-based selectivity of 153) in the permeate over a 172 hr long-term test. A comparison with literature underscores the superior performance of this newly developed I2PS membrane, particularly in terms of water permeance. In summary, the CQD-embedded CTA/Ultem HF membranes demonstrate substantial potential for industrial applications in the pervaporative ethanol dehydration.

Novel self-cleaning PVDF/MoO3/ZnO/GO dual layer hollow fiber photocatalytic membrane with excellent photocatalytic performance of EDCs removal and energy storage capability

Endocrine-disrupting chemicals (EDCs) have a wide range of detrimental effects on health, particularly on the human endocrine system. Efflux This research study involves the application of - molybdenum trioxide, zinc oxide and graphene oxide (MoO3/ZnO/GO) with polyvinylidene fluoride (PVDF) membrane as photocatalytic dual layer hollow fiber (DLHF) membrane as novel energy storage photocatalytic membrane towards efficient degradation of EDCs under visible light illumination. Ternary MoO3/ZnO/GO was synthesized using hydrothermal method and was embedded on the surface of dual layer hollow fiber membrane by dry-wet spinning method by varying the GO loading at 0.1, 0.25 and 0.5 wt%. The results indicated that the 0.5 PVDF/MoO3/ZnO/GO DLHF photocatalytic membrane exhibited improved wettability, high porosity, good water flux, and exceptional EDCs removal, achieving removal rates of 73.08%, 75.80%, 73.65%, 100%, 95.57%, and 53.50% for 1 mg/L BPA, 1 μg/L BPA, 2 μg/L gabapentin, 1 μg/L diclofenac, 10 μg/L caffeine, and 6 μg/L nonylphenol, respectively after 240 min of light exposure. Besides, energy storage capability achieved 96.07% rejection of 1 mg/L BPA in dark condition while stability and reusability test showed 0.5 PVDF/MoO3/ZnO/GO DLHF achieve 74.02% regeneration efficiency after 3 consecutive cycles. Furthermore, the photocatalytic properties of 0.5 PVDF/MoO3/ZnO/GO DLHF could assure a self-cleaning property and increase its lifetime. The PVDF/MoO3/ZnO/GO DLHF photocatalytic membrane served as a versatile 3-in-1 solution, enhancing photocatalytic degradation and rejection capabilities while also serving as a promising energy storage material with self-cleaning properties for removing EDCs from aquatic environments, regardless with or without the presence of light.

Construction of micro-tubular proton-conducting ceramic electrochemical reactor (MT-PCER) for ammonia production at atmospheric pressure

Micro-tubular ceramic electrochemical reactors have attracted significant interest due to their high packing density, large electrode specific surface area, and long triple phase boundaries (TPBs). In this work, a micro-tubular proton-conducting ceramic electrochemical reactor (MT-PCER) with a unique microstructure is facilely constructed for ammonia synthesis at atmospheric pressure. BaCe0.7Zr0.1Y0.2O3-δ (BCZY as the electrolyte)/Ni–BaCe0.7Zr0.1Y0.2O3-δ (Ni-BCZY as the catalytic cathode) dual-layer hollow fibers with open finger-like pores on the inner surface are first fabricated using a modified co-spinning/co-sintering process to form a basic MT-PCER. Fe-based catalyst was then coated into these open finger-like pores in Ni-BCZY layer as an additional catalytic cathode of the MT-PCER. The unique open finger-like pores structure of the basic MT-PCER decreases the mass transfer resistance and also provides space for loading additional catalysts, contributing towards the higher catalytic performance of the MT-PCER. However, the Faradaic efficiency for ammonia formation remained low, indicating that the cathode catalyst required further improvement. This fabrication technique provides a flexible method to adjust the cathode catalysts to optimize the catalytic performance of the MT-PCERs.

Cathode tailoring of micro-tubular protonic ceramic electrochemical reactors for CO2 hydrogenation

Protonic ceramic electrochemical reactors (PCER), having the advantages of high efficiency, adjustability, and scalability, exhibit great potential in energy storage such as conversion of CO2 into high-value chemicals. Designing critical components like the electrolyte and electrodes of electrochemical reactors is essential to widen commercial applications. The present work constructed a three-layer microtubular PCER (MT-PCER) for CO2 hydrogenation. BaCe0.5Zr0.3Y0.2O3-δ (BCZY) was used as the electrolyte material to prepare BCZY/Ni-BCZY/Ni triple-layer hollow fibers (TLHFs) by a phase-inversion based co-spinning/co-sintering process. Porous Ni-BCZY was the catalytic functional (cathode) layer, and the metallic Ni composed the current collector layer. Results indicated that CO2 conversion and CH4 selectivity were significantly enhanced when the NiO content in the cathode layer increased from 40 % to 60 %, while there was no significant change for the content continuously increasing to 80 %. Compared with the reactor employing dual-layer hollow fibers, the Ni collector layer in TLHFs presented a remarkable intensification of the methanation performance. As a result, the MT-PCER with 60 % NiO content in the cathode layer and utilizing the Ni current collector was the recommended reactor structure, which possessed the CO2 conversion of 29.8 %, CH4 selectivity of 50.9 %, CH4 yield of 15.2 %, and faradaic efficiency of 43.6 % at 700 °C and 2 V applied voltage. The adjusted design of the TLHF facilitated the advancement of the performance and efficacy of the MT-PCER, promoting carbon capture, utilization, and storage processes.

Structural tailoring of the current collector/anode dual-layer hollow fibers to enhance the performance of micro-tubular protonic ceramic fuel cells

Micro-tubular protonic ceramic fuel cells (MT-PCFCs) offer significant advantages in energy utilization and storage, including high stability/durability and intermediate working temperature. Inefficient intraluminal current collection and costly fabrication processes are challenges for high-performance MT-PCFCs. Herein, hierarchically structured Ni/Ni–BaCe0.7Zr0.1Y0.2O3-δ dual-layer hollow fibers (DLHFs) have been fabricated by the phase-inversion assisted co-spinning/co-sintering technique. By adjusting the viscosity of anode suspension, the DLHFs' microstructure is tailored and optimized for porosity, pore size, and thickness of collector layer and spongy region. After assembling MT-PCFCs, effects of DLHFs’ microstructure on fuel cell performance are investigated, revealing that a thinner spongy region reduces gas transfer resistance, lowers polarization impedance, and enhances fuel cell performance. A maximum power density of 687.1 mWcm−2 for the optimum MT-PCFC is reached at 700 °C. The innovative DLHF design enhances current collecting efficiency for MT-PCFCs and exhibits potential in other micro-tubular applications, such as hydrogen pumps and electrochemical reactors.

Dual layer hollow fiber photocatalytic membrane based on TiO2-WO3@GO composite with catalytic memory and enhanced anti-fouling and self-cleaning properties for oilfield-produced water treatment

Oilfield-produced water (OPW) is a complex wastewater that is difficult to treat causing significant harm to the environment. Photocatalytic membranes are emerging for OPW treatment. However, they suffer significant fouling due to the inability to self-clean during prolonged treatment. They also require continuous photo assistance to sustain the catalytic process. This limits their applications in the absence of light referred to as memory catalysis. This work reported the fabrication of a unique ternary photocatalyst TiO2-WO3@GO/PVDF dual-layer hollow fiber (DLHF) photocatalytic membranes for photodegradation and memory catalysis of total organic carbon (TOC) in OPW. The photocatalytic membranes were fabricated via phase inversion and co-extrusion method varying (0,1,3,5) wt% of the TiO2-WO3@GO photocatalyst. The membranes were characterized and their performances for TOC removal under visible light and memory catalysis were evaluated. The membranes exhibited excellent TOC degradation, rejection, anti-fouling, self-cleaning, and catalytic memory. The WO3 was responsible for electron storage within the system and improved the absorptive capacity of TiO2 in the visible range while the GO promoted the electron-hole transfer creating abundant active sites for photocatalytic reaction. The 3 wt% loaded membrane showed the best TOC rejection of 98.62 % after 6 h of operation, water and permeate fluxes of 99.51 L/m2h, and 76.54 L/m2h respectively. The membrane showed good catalytic memory in the dark with a TOC rejection of 68.56 % after 6 h, OPW flux recovery ratio (FRR), and TOC rejection of 91.35 % and 89.76 % respectively after 5 cycles of operation under visible light. This work is expected to bring a paradigm shift toward the fabrication of memory catalytic membranes for wastewater treatment.

ZIF-8 membranes on ZIF-8-PVDF/PVDF dual-layer polymeric hollow fiber supports for gas separation

ZIF-8 membranes have attracted extensive research attention due to their ease of synthesis, stable properties, and wide applicability. Compared to expensive inorganic supports, organic polymer supports are more flexible and inexpensive. However, addressing the issue of weak adhesion between the surface of the organic support and the ZIF-8 membrane layer poses a significant challenge. In this study, we present a strategy for preparation of ZIF-8 membrane by the fabrication of an asymmetric dual-layer polymeric hollow fiber support using polyvinylidene fluoride (PVDF) as the material. The outer layer of the support is composed of PVDF embedded with ZIF-8 seeds, while the inner layer consists of pure PVDF. This approach addresses the weak adhesion between the support and the ZIF-8 membrane layer formed through a one-step solvothermal crystallization process. The effects of ZIF-8 seed size, content, and crystallization conditions on the membrane structure and performance are investigated. Under the synergistic molecular sieving effects of ZIF-8 continuous membrane layer and ZIF-8 crystals within the outer layer of the support, larger gas molecules are difficult to penetrate the membrane layer, making the resulting membrane highly selective for the gas separation. Under the optimal fabrication conditions, the H2 permeability of the ZIF-8 membrane is determined to be 1.52 ± 0.1 × 10−7 mol·Pa−1·s−1·m−2, with a H2/N2 ideal separation selectivity of 69.5 ± 4. This method demonstrates simplicity and high reproducibility for preparation of ZIF-8 membranes on dual-layer hollow fibers, and it is expected to be extended to the growth and fabrication of other MOF membranes.

ZIF-8-based dual layer hollow fiber mixed matrix membrane for natural gas purification

To prevent pipe damage and lower operating costs, natural gas must be cleaned of pollutants like carbon dioxide (CO2) and hydrogen sulphide (H2S). High selectivity of the functional material in the mixed matrix membranes (MMMs) allows for a more efficient gas separation compared to traditional polymeric membranes. However, poor dispersion and compatibility between the functional material and the polymer matrix become one of the major problems of MMMs. The use of zeolite imidazole (ZIF-8) in MMMs has been explored for its ability to separate CO2/CH4 due to its versatile gas molecule diameter range and effective CO2 adsorption. In this study, the effects of ZIF-8 at various loadings were examined on the physical and chemical properties of dual layer hollow fiber MMMs and gas separation efficiency. Following the successful production of 86.25 nm ZIF-8 nanoparticles, ZIF-8-based DLHF MMMs were created. The results showed that 0.5 wt% ZIF-8 loading provided the best results, with excellent interaction between the polymer PSf and the inorganic filler ZIF-8, strong heat resistance, and chemical stability. Increased CO2 permeability and CO2/CH4 ideal selectivity by 72.5 % and 1196.2 % respectively, compared to the unmodified membrane. It was inferred through this study that minimal loading of 0.5 wt% ZIF-8 in the DLHF MMMs improved their ability to separate gases, making them a good option for capturing CO2.

Scale Design of Dual-Layer Polyphenylsulfone/Sulfonated Polyphenylsulfone Hollow Fiber Membranes for Nanofiltration.

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.

Photodegradation of Bisphenol a in Water via Round-the-Clock Visible Light Driven Dual Layer Hollow Fiber Membrane

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.

Sodium hypochlorite activated dual-layer hollow fiber nanofiltration membranes for mono/divalent ions separation

The tailoring of nanofiltration membranes for the precise separation of mono/divalent ions often involves complicated procedures to modify the surface chemistry and structure. Herein, an efficient sodium hypochlorite (NaClO) activation method is developed to tune the selective layer of cross-linked polyimide (PI)/polyethersulfone (PES) dual-layer hollow fiber membranes. By oxidizing the hydroxyl and imine groups while hydrolyzing the amide groups in the cross-linked structure, the membranes are effectively tailored with the negatively charged surface and a more open pore structure with 0.47 nm mean effective pore size. The NaClO-activated membranes show over 97.85% rejection of Na2SO4 while the NaCl rejection decreases from 93.83% to − 19.85% during treating the mixed ions solutions. The fabricated membranes with high separation efficiency and long-term stability exhibit vast potential for the separation of mono/divalent ions in industries. Moreover, the elaborated NaClO activation mechanism potentially gives fundamentals for the modification of the PI membranes with cross-linked structures for other applications.

Fabrication and characterization of dual-layer hollow fiber membranes incorporating poly(citric acid) grafted GO with enhanced antifouling property for water treatment

ABSTRACT Membrane fouling which occurs during filtration process is a perennial issue and could lead to reduced separation efficiency. In this work, poly(citric acid) grafted graphene oxide (PGO) was respectively incorporated into matrix of single-layer hollow fiber (SLHF) and duallayer hollow fiber (DLHF) membranes, aiming to improve membrane antifouling properties during water treatment. Different loading of PGO ranging from 0 to 1 wt% was first introduced into the SLHF in order to identify the best PGO loading for the DLHF preparation with its outer layer modified by nanomaterials. The findings showed that at the optimized PGO loading of 0.7 wt%, the resultant SLHF membrane could achieve both higher water permeability and bovine serum albumin rejection compared to the neat SLHF membrane. This is owing to the improved surface hydrophilicity and increased structural porosity upon the incorporation of optimized PGO loading. When 0.7 wt% PGO was introduced only to the outer layer of DLHF, the cross-sectional matrix of the membrane was altered, forming microvoids and spongy-like structure (more porous). Nevertheless, the BSA rejection of the membrane was improved to 97.7% owing to the presence of inner selectivity layer that was produced from different dope solution (without PGO addition). The DLHF membrane also demonstrated significantly higher antifouling properties compared to the neat SLHF membrane. Its flux recovery rate is 85%, i.e., 37% better than that of neat membrane. By incorporating hydrophilic PGO into the membrane, the interaction of the hydrophobic foulants with the membrane surface is greatly reduced.

10-Year Historical Development of Dual Layer Hollow Fiber Hemodialysis Membranes

Hollow fiber membranes have been employed to purify blood from within the heart of hemodialysis process, namely dialyzer. In the past 10 years, the interest on the utilization of dual layer hollow fiber (DLHF) membranes has arisen due to the innovative idea of combining adsorption and diffusion processes into one step. This short review outlines the historical development of DLHF hemodialysis membranes that spans from year 2012 to year 2022. The motivation and the outcome from the first and the second generation DLHF hemodialysis membranes are discussed. In addition, the use of DLHF membranes in other hemodialysis-related application is presented. This short review would provide a perspective for membranologists to recognize the issues in DLHF hemodialysis membranes and to work their way to finding the real solutions.

Microstructure tailoring of the BaCe0.7Zr0.1Y0.2O3-δ(BCZY)/Ni-BCZY dual-layer hollow fibers by co-spinning/co-sintering for high performance micro-tubular protonic ceramic fuel cells (MT-PCFCs)

Micro-tubular protonic ceramic fuel cells (MT-PCFCs) exhibit substantial advantages such as high energy conversion efficiency, large volumetric power density, and intermediate operating temperature. The performance of MT-PCFCs is highly dependent on the microstructure of the microtubes. In this study, BaCe0.7Zr0.1Y0.2O3-δ(BCZY)/Ni-BCZY (electrolyte/anode) dual-layer hollow fibers (DLHFs) are fabricated in a single step by co-spinning/co-sintering technique, which significantly reduces manufacturing time and cost. The relationship between the MT-PCFCs performance and the microstructure of the DLHFs is investigated. By adjusting the cermet powder content and the spinning rate, the microstructure of DLHFs is tailored and optimized to achieve the best performance for the MT-PCFCs. Experimental results indicate that the anode structure with thick finger-like voids inside and thin sponge-like interlayer closely attached to the thin electrolyte film is favorable to obtain high performance MT-PCFCs. A maximum power density of 554.5 mW cm-2 for the optimal MT-PCFC is achieved at 700 ℃.

Thin-Film Composite Matrimid-Based Hollow Fiber Membranes for Oxygen/Nitrogen Separation by Gas Permeation.

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.

Hybrid Inorganic Organic PSF/Hap Dual-Layer Hollow Fibre Membrane for the Treatment of Lead Contaminated Water

Lead (Pb) exposure can be harmful to public health, especially through drinking water. One of the promising treatment methods for lead contaminated water is the adsorption-filtration method. To ensure the cost-effectiveness of the process, naturally derived adsorbent shall be utilised. In this study, hydroxyapatite particles, Ca10(PO4)6(OH)2 (HAP) derived from waste cockle shell, were incorporated into the outer layer of polysulfone/HAP (PSf/HAP) dual-layer hollow fibre (DLHF) membrane to enhance the removal of lead from the water source due to its hydrophilic nature and excellent adsorption capacity. The PSf/HAP DLHF membranes at different HAP loadings in the outer layer (0, 10, 20, 30 and 40 wt%) were fabricated via the co-extrusion phase inversion technique. The performance of the DLHF membranes was evaluated in terms of pure water flux, permeability and adsorption capacity towards lead. The results indicated that the HAP was successfully incorporated into the outer layer of the membrane, as visibly confirmed by microscopic analysis. The trend was towards an increase in pure water flux, permeability and lead adsorption capacity as the HAP loading increased to the optimum loading of 30 wt%. The optimized DLHF membrane displayed a reduced water contact angle by 95%, indicating its improved surface hydrophilicity, which positively affects the pure water flux and permeability of the membrane. Furthermore, the DLHF membrane possessed the highest lead adsorption capacity, 141.2 mg/g. The development of a hybrid inorganic-organic DLHF membrane via the incorporation of the naturally derived HAP in the outer layer is a cost-effective approach to treat lead contaminated water.

Use of Nucleating Agent NA11 in the Preparation of Polyvinylidene Fluoride Dual-Layer Hollow Fiber Membranes.

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.

Fabrication of CO2-tolerant SrFe0.8Nb0.2O3-δ/SrCo0.9Nb0.1O3-δ dual-layer 7-channel hollow fiber membrane by co-spinning and one-step thermal process

CO2-tolerant membranes are crucial for oxyfuel combustion systems utilizing oxygen permeable membranes. A newly constructed dual-layer 7-channel hollow fiber membrane consisting of SrFe0.8Nb0.2O3-δ (SFN) porous outer layer and SrCo0.9Nb0.1O3-δ (SCN) hollow fiber inner layer has been successfully fabricated by co-spinning and one-step thermal process (OSTP) approach in this work. The outer layer can have different porous structures depending on the graphite content of the spinning solution. In the OSTP approach, the in-situ reactive sintering of the membrane materials results in the two layers being well adhered and mechanically robust. At 900 °C under 80% CO2-containing in sweeping gas, the oxygen flux of SFN/SCN dual-layer hollow fiber membrane with the porous layer of 91.8 μm was 1.98 mL min−1 cm−2, about 7.1 times as much as the SCN hollow fiber membrane (0.28 mL min−1 cm−2) in the same situations. The porous SFN outer layer was demonstrated to prevent membrane performance degradation effectively. Furthermore, the SFN/SCN dual-layer membrane operated in a 20% CO2-containing atmosphere for at least 200 h, maintaining an oxygen flux of 3.20 mL min−1 cm−2 without degradation. As a result of these findings, the SFN/SCN dual-layer 7-channel hollow fiber membrane has significant application potential in CO2 capture for oxyfuel combustion.