Alumina Hollow Fiber Research Articles

Asymmetric Al2O3 and PES/Al2O3 hollow fiber membranes for green tea extract clarification

Green tea (Camellia sinensis) leaves are particularly rich in polyphenols. Here we propose the clarification of green tea extract by an innovative process consisting of a two-stage filtration through asymmetric alumina (Al2O3) hollow fibers, which we specially designed for this application by the phase inversion technique. The fibers presented outer sponge like-layers, mainly responsible for the membrane selectivity (turbidity of green tea extract was reduced by 90%) and mechanical strength (135 MPa), and an inner finger-like layer that reduced the resistance to flux permeation (water permeability of 2.56 × 10−9 m3 s−1 m−2 Pa−1). In order to increase the membrane retention coefficient, we deposited a polyethersulfone (PES) coating layer on the fiber outer surface. This polymeric layer further reduced the green tea extract turbidity by 97.8% in the permeate. As a consequence, no team cream formed even after 30 days of refrigerated storage. Thus, the membranes that we conceived enabled to obtain a product with superior clarity and stability. Additionally, a mathematical description of flux decay during the filtration processes showed that cake formation and internal pore blockage models better described flux decay through Al2O3 and PES/Al2O3 hollow fibers, respectively.

Covalent Self-Assembly in Two Dimensions: Connecting Covalent Organic Framework Nanospheres into Crystalline and Porous Thin Films.

Insolubility of covalent organic frameworks (COFs) in organic solvents is one of the major obstacles for the potential application of these extended networks such as drug delivery, sensing, optoelectronics, and semiconductor device fabrication. The present work proposes a unique way to make uniform, solution-processable, crystalline, and porous COF nanospheres directly from the homogeneous solution of amine and aldehyde via spatial and temporal control of the nucleation and growth. This strategy of direct nucleation simultaneously showcases the caliber to tune the size of the COF nanospheres from 25 to 570 nm. We have also demonstrated the concept of mesoscale covalent self-assembly of those solution-processable COF nanospheres in the liquid-liquid interface (DCM-water bilayer) for the very first time, transmuting them into self-standing COF thin films with long-range ordered arrangements in two dimensions. The crystalline and porous (with TpAzo showing highest SBET of 1932 m2 g-1) free-standing COF thin films could be fabricated in a wide range of thicknesses from as low as 21 nm to as high as 630 nm. Both β-ketoenamine (TpAzo, TpDPP) and imine (TpOMeAzo, TpOMeDPP) linked COF thin films have been synthesized via mesoscale covalent self-assembly of the solution-processable COF nanospheres illustrating the generality of this eloquent methodology. Further, the solution processability has been tested and utilized to cast COF thin films uniformly in the inner and outer surface of an alumina hollow fiber membrane. The COF thin film-alumina hollow fiber membrane composites have showcased promising selective molecular separation of He and O2, He and CO2, and He and N2.

Decompression stripping of carbon dioxide from rich monoethanolamine through porous hydrophobic modified ceramic hollow fiber membrane contactor

In this study, commercial alpha alumina powder was used to fabricate hollow fiber membrane by phase inversion spinning method. The fabricated alumina hollow fiber membrane was confirmed to have high chemical and thermal stability based on thermogravimetric analysis and contact angle measurement. When CO2 stripping characteristics were examined by introducing decompression membrane contactor process in the stripping part of amine absorption process, increase in degree of vacuum resulted in increased CO2 stripping flux. In liquid to lumen operation under decompression pressure of 61.325 kPa and absorbent flow rate of 9 ml/min, CO2 stripping flux was 45.75 × 10−4 mol/m2·s. Existing articles on membrane contactor stripping were mostly N2 sweep type and reported CO2 stripping flux of 1–24 mol/m2·s, whereas the present study achieved stripping performance that was approximately 2–40 times higher. Decompression stripping of porous ceramic hollow fiber membrane contactor can be viewed as a promising process since it did not cause the phenomenon of decrease in CO2 purity due to N2 and showed similar or greater CO2 stripping flux than previously reported membrane contactor stripping processes.

Thin carbon hollow fiber membrane with Knudsen diffusion for hydrogen/alkane separation: Effects of hollow fiber module design and gas flow mode

Recovery of heavier hydrocarbons, C2~C4 olefins and paraffins, from gas streams is of great importance economically. In this study, asymmetric carbon hollow fiber membranes (CHFMs) were prepared by a one-step vacuum-assisted dip coating and pyrolysis, and investigated for H2/CO2, H2/C2H6, and H2/C3H8 separations. To increase the mechanical strength of the CHFMs, a porous alumina hollow fiber with ID/OD = 2 mm/4 mm was used as the supporting material. A solution of polyetherimide in N-methyl-2-pyrrolidone was used as the casting solution. The effects of (1) membrane preparation parameters, (2) fiber packing densities, (3) fiber packing arrangement, and (4) gas flow configuration (inside-out or outside-in) on the gas-separation performance were also investigated. The results showed that decreasing the concentration of the casting dope and the number of coating cycles was found to be the most effective approach to increase the H2 permeance, while maintaining the H2/CO2 selectivity. Further, as the fiber packing density was increased from 5.54% to 38.78% for the hexagonal packing configuration, the H2 permeance increased from 362.04 GPU to 711.61 GPU, without any decrease in the gas selectivity. The as-prepared CHFM exhibited the maximum gas permeance of 711.61 GPU for H2 and the following gas selectivity: 2.79, 4.65, and 5.34 towards H2/CO2, H2/C2H6, and H2/C3H8, respectively. The successful preparation and modularization of the CHFM is advantageous and industrially relevant for several gas-separation applications, such as H2 energy production from CO2, C2H6, and C3H8, and olefins/paraffins recovery.

Flow synthesis of a novel zirconium-based UiO-66 nanofiltration membrane and its performance in the removal of p-nitrophenol from water

In this work, a thin zirconium-based UiO-66 membrane was successfully prepared on an alumina hollow fiber tube by flow synthesis, and was used in an attempt to remove p-nitrophenol from water through a nanofiltration process. Two main factors, including flow rate and synthesis time, were investigated to optimize the conditions for membrane growth. Under optimal synthesis conditions, a thin UiO-66 membrane of approximately 2 μm in thickness was fabricated at a flow rate of 4 mL·h-1 for 30 h. The p-nitrophenol rejection rate for the as-prepared UiO-66 membrane applied in the removal of p-nitrophenol from water was only 78.1% due to the existence of membrane defects caused by coordinative defects during membrane formation. Post-synthetic modification of the UiO-66 membrane was carried out using organic linkers with the same flow approach to further improve the nanofiltration performance. The result showed that the p-nitrophenol rejection for the postmodified membrane was greatly improved and reached over 95%. Moreover, the post-modified UiO-66 membrane exhibited remarkable long-term operational stability, which is vital for practical application.

Micro-structured and reinforced spinel hollow fiber membranes: Influence of sintering temperature and ceramic powder composition

Spinel hollow fiber membranes were succoessfully prepared by the phase inversion and sintering technique using mixtures of dolomite and alumina as powder precursors. Different mass proportions of dolomite to alumina were evaluated, as well as different sintering temperatures. According to XRD analyses, spinel was formed when dolomite and alumina mixtures were sintered at temperatures higher than 1100 °C. Spinel hollow fiber membranes which were produced with 25 wt% of dolomite into alumina and sintered at 1350 °C presented an asymmetric pore size distribution with pore sizes varying from 0.16 to 5.29 μm and porosity of 43%. Dolomite additions at proportions greater than 25 wt% produced symmetric hollow fiber membranes due to the relative large particle size of raw dolomite. Spinel hollow fibers sintered at 1350 °C presented mechanical resistance of 54.88 ± 4.25 MPa, which represents an increase of 49% if compared to the mechanical resistance of pure alumina hollow fibers sintered at the same temperature. However, this increase in mechanical resistance was associated to a decrease in membrane permeability. The spinel hollow fiber membrane sintered at 1350 °C was successfully applied for oily wastewater treatment, with oil rejection of 94.5%.

Photoreduction of chromium(VI) in microstructured ceramic hollow fibers impregnated with titanium dioxide and coated with green algae Chlorella vulgaris.

Here we propose an innovative photocatalytic hybrid system for the reduction of hexavalent chromium (Cr(VI)) from aqueous solutions. The hybrid system was composed of titanium dioxide (TiO2) immobilized in the micro-voids of asymmetric alumina hollow fibers and of the green algae Chlorella vulgaris coated on the outer sponge-like layer of the fiber. The photoreduction of Cr(VI) was systematically studied in different systems: single systems with TiO2 or algae; the synergistic system of algae combined with TiO2; and the proposed hybrid system composed of TiO2 and algae supported in ceramic hollow fibers. Morphological and energy dispersive spectroscopy analyses showed that TiO2 and the algae were properly supported in the substrate (alumina hollow fibers). For an initial Cr(VI) concentration of 10 mg L-1 and dosages of 1 g L-1 of TiO2 and algae, the hybrid system resulted in total Cr(VI) reduction after 16 h of process. Additionally, the efficiency of the hybrid system for Cr(VI) reduction was reduced in only 9% after 5 cycles of reuse and in 42% after 10 cycles of reuse. Thus, micro-structured ceramic hollow fibers impregnated with TiO2 and decorated with the green algae C. vulgaris was efficient for Cr(VI) reductions.

Scalable One‐Step Gel Conversion Route to High‐Performance CHA Zeolite Hollow Fiber Membranes and Modules for CO2 Separation

Efficient separation of CO2 from other molecules such as CH4, N2, and hydrocarbons is a key problem in many energy production and greenhouse gas reduction schemes. Zeolite materials demonstrate attractive gas separation properties, but their industrial application as membranes in gas separation are elusive because of high cost and low reproducibility of conventional fabrication techniques. A facile method is demonstrated for the fabrication of high‐silica CHA zeolite membranes on low‐cost alumina hollow fiber substrates by a one‐step direct gel conversion method, along with a detailed characterization of the CHA hollow fiber membranes. To demonstrate the scalability of the method, 20 hollow fiber (710 μm OD and 390 μm ID) membranes are synthesized in the same batch and assembled into a module. Under dry conditions, the membranes show an excellent CO2 permeance up to 3500 GPU (1 Gas Permeation Unit = 3.348 × 10−10 mol m−2 s−1 Pa−1) and an excellent CO2 separation performance (e.g., CO2/CH4 separation factors up to 210 in the 1–7 bar feed pressure range). In addition, the membranes exhibit a considerable increase in CO2 selectivity under humid (saturated water vapor) conditions with moderate permeance drops. This study opens a promising new path for accelerated development of low‐cost zeolitic membranes for gas separation technology.

Fabrication of lanthanum-based perovskites membranes on porous alumina hollow fibre (AHF) substrates for oxygen enrichment

Abstract In this work, two types of lanthanum-based MIEC perovskite oxides, namely La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and La0.6Sr0.4Co0.2Ni0.8O3-δ (LSCNi), were deposited onto porous alumina hollow fibre (AHF) substrates and used for oxygen enrichment. Such structure was developed to shorten oxygen ion diffusion distances in dense membranes and simultaneously leading to higher oxygen flux. The perovskite oxides were prepared using Pechini sol-gel method and deposited via a vacuum-assisted technique. The deposition of lanthanum-based membranes onto the outer and inner sides of the porous AHF has been facilitated through numerous microchannels in the AHF substrates. The effects of operating temperature and argon sweep gas flowrate on oxygen permeation flux of lanthanum-based AHF membrane were investigated. The results revealed that the oxygen permeation flux of LSCF-AHF and LSCNi-AHF increased with operating temperatures due to the improvement of bulk diffusion and surface exchange properties after the lanthanum-based perovskite deposition. Higher oxygen flux was observed for LSCNi-AHF as LSCNi possessed balanced oxygen ionic and electronic conductivities as compared to LSCF membranes. Benefitting from improved oxygen activation and vacancy generation properties after Ni substitution into the B-site ion of LSC perovskite, a dramatic increased oxygen fluxes up to 4.5 mL/min·cm2 was observed at 950 °C. The present work demonstrated a feasible method for fabricating oxygen transport membrane (OTM) using porous AHF substrates

Feasibility study of CAU-1 deposited on alumina hollow fiber for desalination applications

This work investigated the feasibility of a metal–organic framework (MOF), Christian-Albrechts-University (CAU-1), deposited on alumina hollow fiber for desalination applications. CAU-1 membranes, synthesized using the solvothermal approach, were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and contact angle measurement. The performances of the CAU-1 membranes were tested using forward osmosis (FO). Using a configuration of active layer facing feed, the CAU-1 membrane (M6) had the highest flux of 18 L m−2 h−1 with a reverse solute value of 0.079 kg m−2 h−1. The M6 membrane was further tested using a configuration of active layer facing draw. Surprisingly, the flux moved from the high salt concentration to low salt concentration, obeying the reverse osmosis phenomenon under low pressure. At 10,000 ppm of salt concentration, M6 membrane showed solute fluxes of 4.07 and 3.07 L m−2 h−1 for NaCl and MgSO4 with rejections of 75% and 65%, respectively. Guest molecules and an amine group in CAU-1 were responsible in affecting the performance of the membrane for desalination application.

Synthesis and performance evaluation of zeolitic imidazolate framework-8 membranes deposited onto alumina hollow fiber for desalination

This work describes the development of zeolitic imidazolate framework-8 (ZIF-8) membranes on modified alumina hollow fiber for desalination by forward osmosis. Effects of different seeds (ZnO, NiO and PDA) and sodium formate on in-situ deposition of ZIF-8 were studied in relation to the membrane’s morphology and performance. XRD result shows that ZIF-8 was successfully synthesized in the presence of sodium formate. FESEM images showed PDA modified support was unsuccessful in producing well defined and dense ZIF-8 membrane layer even after another ZIF-8 re-deposition due to its minimal amount. The NiO modified support was also found unsuccessful, as ZIF-8 crystals were formed in clusters. On the contrary, dense ZIF-8 membrane was successfully prepared on ZnO modified support with SF-1 synthesis solution producing bigger ZIF-8 crystal and thinner ZIF-8 membrane than as of SF-2. Water flux performance in forward osmosis showed that NiO/ZIF-8, PDA/ZIF-8 and PDA/ZIF-8 (re-deposition) membranes gave negative water fluxes of -50 kg/m2·h, -5.2 kg/m2·h and -1.7 kg/m2·h with reverse solutes of 42.66 mol/m2·h, 27.42mol/m2·h and 3.22 mol/m2·h, respectively, indicating the solute from draw solution diffused into the feed solution. However, ZIF-8 membrane prepared using SF with molar ratio of 1, on the ZnO modified support had a water flux of 13.3 kg/m2·h, reverse solute of 0.95 kg/m2·h and salt rejection of 52.1%. When the SF ratio was increased to 2, the ZIF-8 membranes showed a water flux of 12.5 kg/m2·h, reverse solute of 1.64 kg/m2·h and salt rejection of 54.9%. The moderate salt rejection could be associated with defects in the ZIF-8 membranes due to poor grain boundaries.

Photocatalytic nanofiber-coated alumina hollow fiber membranes for highly efficient oilfield produced water treatment

Cost-effective purification technology of oilfield produced water (OPW) is becoming a global challenge for future petroleum exploration and production industry. Energy-efficient operation of membrane separation is potentially promising. However, severe fouling problem of oil droplets demands new robust and fouling-resistant membranes with high permeability and rejection efficiency. Here, we propose a photocatalytic nanofiber-coated inorganic hollow fiber membrane suitable for OPW treatment. The membrane was fabricated by coating polyacrylonitrile (PAN) nanofiber incorporated with graphitic carbon nitride (GCN) photocatalyst on an alumina (Al2O3) hollow fiber membrane. While the highly porous coating made of smooth hydrophilic nanofibers facilitated water permeation, the coating effectively captured oil droplets in its opening, resulting in a better rejection efficiency of oil contaminants. Its sparse mesh morphology prevented oil contaminants to form dense fouling film on the membrane surface and maintained high permeate flux even after 180 min filtration. The best permeate flux of 640 L·m−2·h−1 and oil rejection percentage of 99% were recorded for 180 min crossflow filtration of OPW at 2 bar along with the highest pure water flux of 816 L·m−2·h−1. The photocatalytic activity of GCN enabled the coating to degrade the captured oil contaminants under UV irradiation, demonstrating permeate flux of 577 L·m−2·h−1 and oil rejection of 97% after three cycles of 180 min filtration. The excellent fouling resistance and cleaning performances of the membrane are considerably beneficial for a long-term repeated filtration operation. This work will motivate researchers to develop nanofiber-coated hollow fiber membranes for future membrane separation technology.

High-flux NaA zeolite pervaporation membranes dynamically synthesized on the alumina hollow fiber inner-surface in a continuous flow system

A continuous flow system that can make the process variable more stable was proposed to prepare NaA zeolite membranes on the inner-surface of alumina hollow fiber, in which the gel solution was recirculated and only preheated at the required section, thus avoiding the unnecessary depletion of the nutrients in the bulk. The influence of synthesis parameters including temperature, flow rate and time over the property of obtained membrane were investigated. The thickness and the morphology of the membranes were explored by SEM. Their separation performance for dehydration of ethanol/water mixture was tested in a pervaporation (PV) set-up with the feed flowing through the membranes’ lumen-side, which varied significantly when the feed flowed at different rates. The reason was inquired by studying the PV behavior at different operating conditions. It was found that the boundary layer resisted the heat transfer, leading to the lower temperature of PV at membrane surface than that of the feed, therefore, the intrinsic PV performance of the membrane could hardly be obtained when the feed flew at low rate. The optimal performance of 19.7 kg/m2 h for the permeation flux and more than 80,000 for the separation factor was tested at the flow rate of 148 mL/min with 90 wt% ethanol/water solution at 348 K, yielding an unprecedented PV performance to our knowledge. The results revealed the high reproducibility and uniformity of the membranes prepared by continuous flow system, as well as that the zeolite membranes located on ceramic hollow fiber inner-surface possessed a competitive advantage of PV performance especially of the permeation flux, which have not been realized by the previous studies and may generalize to the other zeolite or metal-organic frameworks (MOF) membranes.

High Performance of Asymmetric Alumina Hollow Fiber Membranes for the Clarification of Genipap (Genipa americana L.) Fruit Extract

Membrane filtration processes represent a suitable alternative for fruit juice treatment, but the applied membrane should present high stability and permeability. Here, we propose the development and application of ceramic asymmetric hollow fiber membranes for genipap extract clarification. Genipap is an exotic fruit from Central and South America with considerable concentration of phenolic and iridoid compounds. The dual-layer ceramic hollow fiber membrane was fabricated by a single-step co-extrusion and co-sintering process. The developed hollow fibers presented the desired asymmetric structure, with an inner finger-like region that guaranteed a suitable permeate flux (191 L h−1 m−2 at 1 bar), while the outer sponge-like layer was responsible for solid retentions and for the membrane mechanical resistance. Reductions in turbidity, total polyphenol content, and genipin concentration were of 52, 17, and 4%, respectively. Mathematical modeling of the experimental flux decay showed that pore blocking was the main fouling mechanism during filtrations of genipap extract through the asymmetric hollow fibers. The presence of microchannels with larger pore size in the inner surface of the fiber probably mitigated cake formation. The increase in the transmembrane pressure from 1 to 2 bar did not improve the permeation flux through the membrane since the fouling layer resistance was considerably higher at 2 bar than at 1 bar. Thus, asymmetric ceramic hollow fibers are suggested for juice fruit clarification with improved permeate flux and clarification degree.

Highly permeable photo-catalytic mesoporous aluminum oxide membrane for oil emulsion separation

This work describes the development of photocatalytic mesoporous aluminum oxide (alumina) membranes for oil emulsion separation. The mesoporous alumina membrane was deposited on alumina hollow fiber using hydrothermal synthesis. Aluminum nitrate nonahydrate, Al(NO3)3.9H2O, cetyltrimethylammonium bromide (CTAB), and urea were used in the preparation of the mesoporous alumina membranes. The successfully prepared mesoporous alumina membranes on ceramic support were then deposited with copper-doped ceria, which acted as photocatalyts, using the sol-gel Pechini method. The results showed that the membranes had an excellent separation performance in separating 1000 ppm polyethylene glycol and 1000 ppm bovine serum albumin when the samples were calcined at 800 °C. Under UV irradiation, there was a remarkable increase in the permeability of water through the membrane. The photocatalytic mesoporous alumina membrane showed a permeability of 1422 L/h m2 bar with 92% oil emulsion rejection. An excellent increase in the performance can be associated with the production of superoxide radical and hydroxyl radicals by the photocatalytic membrane once exposed to UV light.

Nanostructure depositions on alumina hollow fiber membranes for enhanced wetting resistance during membrane distillation

Omniphobic alumina hollow fiber membranes were developed for direct contact membrane distillation (DCMD) with a low surface tension feed in this study. Alumina hollow fiber (HF) membranes were prepared as the membrane substrates, and chemical bath deposition methods were applied to deposit ZnO nanorods and nanoparticles on the HF membranes. The SEM, EDX, and AFM analyses showed that the ZnO nanostructures were effectively deposited on the membrane surfaces and able to increase the surface roughness. After surface fluorination by FAS17, the HF membranes deposited by ZnO nanorods and nanoparticles demonstrated contact angles of 128.7° and 138.1° for a 90% v/v ethanol/water mixture, both of which were higher than 114.8° for the pristine HF membrane without ZnO nanostructures. In the DCMD experiments with the sequential addition of SDS from 0.2 to 2.0 mM, the HF membranes with ZnO nanostructures exhibited superior wetting resistances with low surface tension feeds compared to that of the pristine HF membranes. Moreover, the HF membranes with the deposited ZnO nanoparticles had the best wetting resistance, and the permeate water flux was maintained for 24 h using a 2.0 mM SDS (70 °C 1 M NaCl) solution as an initial feed. The results not only suggested that the deposition of nanostructures enhanced the wetting resistance of the alumina hollow fiber membranes to low surface tension liquids but also showed the promise of utilizing these membranes for the desalination of low surface tension wastewaters.

Effect of substrate curvature on microstructure and gas permeability of hollow fiber MFI zeolite membranes

Literature data show that gas permeability of MFI zeolite membrane varies depending on the geometry of supports. The present work investigates the effects of the surface curvature of substrates on the microstructure and the gas permeation property of supported zeolite membranes. MFI zeolite membranes were grown on porous alumina hollow fibers with different diameters (surface curvature) by the secondary growth method. Single gas permeation and H2/CO2 binary gas separation from 25 to 300 were conducted to study the membrane quality. The zeolite membranes on supports of larger surface curvature have higher permeability and lower selectivity due to the presence of more inter‐crystalline gaps in the zeolite layer formed during the template removal step. The effects of the support surface curvature (and geometry) on zeolite membrane microstructure and gas permeation characteristics are semi‐quantitatively analyzed by a transport model considering both structural change and gas diffusion in micropores. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3419–3428, 2018

Preparation, characterizations and performance evaluations of alumina hollow fiber membrane incorporated with UiO-66 particles for humic acid removal

Humic acid removal requires ceramic membranes incorporated with metal organic framework (MOF) to display remarkable stability over water. Recent work has shown UiO-66, a Zr-based MOF, as an emerging material with the potential to fulfill this requirement. This work investigated the preparation, characterization and performance of UiO-66 particles deposited on alumina hollow fiber membranes. Concentrations of Zr precursors and synthesis period were varied in the preparation of UiO-66 using solvothermal synthesis. The presence of UiO-66 particles was characterized using the field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) mapping, x-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analysis. Pure water flux and humic acid rejection tests were carried out on both pristine alumina hollow fiber membranes and alumina hollow fiber membranes deposited with UiO-66 particles. In the former, a high pure water flux value of 231.24 L m−2 h−1 was recorded, while in the latter the recorded value dropped to 9.36 L m−2 h−1. Pristine ceramic hollow fiber membranes used to separate humic acid (1 g L−1) from an aqueous solution showed a rejection rate of 98%. When UiO-66 particles were deposited on the ceramic membranes, the solute flux of the membranes increased to 68.36 L m−2 h−1. Surprisingly, it was found that 99% humic acid was rejected from a feed solution using the membranes incorporated with UiO-66 particles. Findings showed that the weight loading of the UiO-66 particles on the alumina hollow fiber membranes was very low, showing a reading of only approximately ~ 0.01 g. Based on the adsorption-desorption analysis, at high pH values (≥ 9), UiO-66 particles and humic acid displayed a similar surface charge, creating a repulsion effect during the filtration process. UiO-66 particles on alumina hollow fiber membranes showed excellent stability, making it viable for water purification applications.

Removal of nickel from aqueous solution using supported zeolite-Y hollow fiber membranes.

This work describes the development of supported zeolite-Y membranes, prepared using the hydrothermal method, for the removal of nickel from an aqueous solution. Alumina hollow fibers prepared using the phase inversion and sintering technique were used as an inert support. The supported zeolite-Y membranes were characterized using the field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and the water permeation and rejection test. The performance of the supported zeolite-Y membranes for heavy metal removal using batch adsorption and filtration test was studied using the atomic absorption spectroscopy (AAS). The adsorption study shows that the removal of nickel was pH-dependent but affected by the presence of α-alumina. The seeded zeolite-Y membrane gave the highest adsorption capacity which was 126.2mgg-1. This enabled the membrane to remove 63% of nickel ions from the aqueous solution within 180min of contact time. The adsorption mechanism of nickel onto the zeolite-Y membrane was best fitted to the Freundlich isotherm. The kinetic study concluded that the adsorption was best fitted to pseudo-second-order model with higher correlation coefficient (R2 = 0.9996). The filtration study proved that the zeolite-Y membrane enabled to reduce the concentration of heavy metal at parts per billion level.

Performance of ceramic membrane in vacuum membrane distillation and in vacuum membrane crystallization

Membrane crystallization (MCr) is emerging as an interesting candidate to extract additional freshwater and raw materials from high-concentrated solutions. Traditionally, MCr has been carried out by using polymeric membranes that have limited chemical and mechanical stability. These shortcomings can be overcome by using ceramic membranes. The current study describes the preparation and testing of two hydrophobic ceramic membranes synthesized trough sol-gel process, and combined phase-inversion and sintering method. The first membrane (CM-L) was synthesized by coating hydrophobic polymethylsilsesquioxane aerogels on alumina membrane supports via a sol-gel process. The membrane showed stable hydrophobic character in membrane distillation and crystallization tests but very low flux. To obtain high flux, a second type (CM-S) membrane was prepared by applying Fluoroalkylsilanes (FAS) (1H, 1H, 2H, 2H‑perfluorooctyltriethoxysilane) hydrophobic agent at the relatively thin and more porous as-sintered alumina hollow fibers. The suitability of both membranes for MCr process was analyzed by crystallizing NaCl and LiCl. By using 1 M NaCl and 13 M LiCl aqueous solutions, and under the same operative conditions, CM-S membrane exhibited average flux higher than CM-L membrane. The performance of both the membranes, in terms of hydrophobic character, remained stable throughout the performed tests.