PVDF hollow fiber and nanofiber membranes for fresh water reclamation using membrane distillation

Polyvinylidene fluoride hollow fiber and nanofibrous membranes are engineered and successfully fabricated using dry-jet wet spinning and electrospinning techniques, respectively. Fabricated membranes are characterized for their morphology, average pore size, pore size distribution, nanofiber diameter distribution, thickness, and water contact angle. Direct contact membrane distillation (DCMD) performances of the fabricated membranes have been investigated using a locally designed and fabricated, fully automated MD bench scale unit and DCMD module. Electrospun nanofibrous membranes showed a water flux as high as 36 L m^?2 h^?1 whereas hollow fiber membranes showed a water flux of 31.6 L m^?2 h^?1, at a feed inlet temperature of 80 °C and at a permeate inlet temperature of 20 °C.     

Defect-sealing synthesis of vertically oriented ordered mesoporous silica membranes

Vertically oriented ordered mesoporous silica membranes have been successfully synthesized in our laboratory in the form of silica plugs filling the macron-sized straight pores of hydrophobic track-etched polycarbonate membrane support. However, these membranes have shown gaps between the plugs and support pore wall which make the membranes unfeasible for use. This paper reports on techniques of synthesis of defect-free ordered mesoporous silica membranes by filling the gaps with microporous silica. Here, the elimination of defects is achieved by filling the membrane gaps with an alkoxysilane followed by exposure to humid air to allow controlled hydrolysis and condensation resulting in the formation of microporous silica within the gaps. Molecular probing gas permeation and helium/nitrogen (or oxygen) binary separation tests, coupled with surface characterization methods, show that the final membranes contain ordered mesopores of about 2.7 nm pore diameter, running through the membrane, with gaps sealed by microporous silica having a pore size <0.55 nm.     

AFM analysis of the surface of nanoporous membranes: application to the nanofiltration of potassium clavulanate

This study presents the structural characterization of the surface of four commercial nanofiltration membranes: NF90 (polyamide) and NF (polypiperazine amide) from Filmtec^TM and NP010 and NP030 (polysulfone) from Microdyn Nadir^®, by Atomic Force Microscopy (AFM). These membranes have been studied before and after undergoing a filtration process with potassium clavulanate. The fast Fourier filtering of AFM images with very high magnification (40 × 40 nm) has allowed identifying the pore size distribution and geometry of the pores on the surface of the membrane before their use. Images between 0.5 × 0.5 and 10 × 10 μm² have allowed the study of the surface roughness of the samples before and after being used to filtrate potassium clavulanate solutions. The results of roughness and power spectral fractal dimension along with the skewness and kurtosis of the height distribution have been analyzed in terms of pore size, hydraulic permeability, and the adsorption of clavulanate for the different samples.     

Hydrogen-induced gas porosity formation in Al–4.5 wt% Cu–1.4 wt% Mg alloy

The effects of low (0.067 cm³/100 g) and relatively high (0.19 and 0.27 cm³/100 g) initial melt hydrogen concentration, solidification processing conditions, and grain refining on the formation of hydrogen-induced gas porosity in Al–4.5 wt% Cu–1.4 wt% Mg alloy have been quantitatively investigated. The study was conducted with unidirectionally cooled laboratory-size ingots solidified at 0.2–37 K/s. An optical microscope-based image analyzer and precision density measurement based on the Archimedes’ principle were used to quantify the characteristics of the hydrogen-induced porosity in the ingots. Predictably, increase in melt hydrogen concentration and decrease in solidification rate increased the amount of porosity and average pore size. However, the effect of solidification rate was greater at the very low melt hydrogen concentration (0.067 cm³/100 g). These results are consistent with reported effects of solidification rate and melt hydrogen content on porosity formation in other aluminum alloys. Addition of grain refiner slightly increased the amount of porosity and the average pore size, especially at solidification rates above 1 K/s.     

Synthesis and characterization of porous polyurethaneurea membranes for pervaporative separation of 4-nitrophenol from aqueous solution

Hydroxyterminated polybutadiene (HTPB) based porous polyurethaneurea (PUU) membranes were prepared. The porosity was developed by incorporation of lithium chloride into polymer matrix with subsequent leaching of the same in hot water. Scanning electron microscopic analysis of the prepared membrane surfaces was performed. The pervaporation performance of the synthesized membrane was studied with aqueous 4-nitrophenol solution as feed. The effects of various parameters on 4-nitrophenol separation factor and total as well as 4-nitrophenol flux were studied. Polyurethaneurea membrane was found to permeate 4-nitrophenol selectively with high separation factors for the organic component. Pore size and number of pores on the surface of the membrane were calculated from SEM image of the membranes. Effects of pore size and porosity on pervaporation flux were also investigated.     

Tape-cast ceramic membranes for microfiltration application

Alumina membrane filters in the form of thin (0.3–0.8 mm) discs of 25–30 mm diameter suitable for microfiltration application, have been fabricated by the tape-casting technique. Their pore size could be varied in the range 0.1–0.7 m and porosity in the range 25%–55% through optimization of experimental parameters. The most important factor which determines the pore size, is the initial particle size of ceramic powders used for this purpose. Temperature of firing, and also the soaking time are crucial parameters which determine the porosity. Water permeability under suction conditions varies in the range 110–900 lm^–2h^–1 depending on porosity, pore size and thickness of the membrane. Most of these membranes, particularly those with pore sizes less than 0.5 m, are found to be suitable for complete removal of bacteria from water and are also reusable after cleaning by acid or heat sterilization.     

Pore evolution model of ceramic membrane during constrained sintering

Pore size has been found to strongly depend on the sintering program in the preparation of porous ceramic membranes. In this paper, a model was developed to predict the variation in pore size and porosity of membranes during the sintering process. A comparison of shrinkage characteristics was made between the sintering processes of supported membranes and unsupported membranes. For supported membranes, the effect of restriction coming from a rigid substrate on the sintering behavior has been taken into account in the calculation. It is predicted that the pore size increases in supported membranes and decreases in unsupported membranes as the sintering temperature is increased. Calculations also showed that the loss of porosity in the supported membranes was less than that in the unsupported membranes. In order to verify reliability of this model, unsupported and supported membranes were prepared with α-Al₂O₃ powders at the sintering temperatures ranging from 1125 °C to 1325 °C. The pore size and porosity were measured by gas permeation technique and Archimedes’s method. The experimental results for the unsupported and supported α-Al₂O₃ membranes showed a good agreement with those calculated from the model. Therefore, this model provides an effective tool in predicting the porosity and the pore size of ceramic membranes at the different sintering temperatures.     

Electrodeposition of nickel nanowires and nanotubes using various templates

Nickel nanotubes and nanowires are grown by galvanostatic electrodeposition in the pores of 1000, 100, and 15 nm polycarbonate as well as in anodised alumina membranes at a current density of 10 mA cm^?2. The effects of pore size, porosity, electrodeposition time, effective current density, and pore aspect ratio are investigated. Nickel nanotube structures are obtained with 1000 nm pore size polycarbonate membrane without any prior treatment method. At the early stages of electrodeposition hollow nickel nanotubes are produced and nanotubes turn into nanowires at longer depositon times. As effective current density accounting for the membrane porosity decreases, the axial growth direction is favoured yielding nanowires rather than nanotubes. However, for smaller pore size polycarbonate membranes, nanowires are obtained even though effective current densities were higher. We believe that when the pore diameter is below a critical size, nanowires grow regardless of current density since narrow pores promote layer by layer growth of nanorods due to smaller surface area of the pore bottom compared to pore walls. Pore size has a dominant effect over effective current density in determining the structure of the fibres produced for small pores. Nickel nanowires are also obtained in the small pores of anodised alumina, which has higher aspect ratios. High aspect ratio membranes favour the fabrication of nanowires regardless of current density.     

Ionic transport in P(VdF-HFP)-PEO based novel microporous polymer electrolytes

A novel microporous polymer electrolyte (MPE) comprising blends of poly(vinylidene fluoride-cohexafluoropropylene) [P(VdF-HFP)] and polyethylene oxide (PEO) was prepared by phase inversion technique. It was observed that addition of PEO improved the pore configuration, such as pore size, pore connectivity and porosity of P(VdF-HFP) based membranes. The room temperature ionic conductivity was significantly enhanced. The highest porosity of about 65% and ionic conductivity of about 7 × 10⁻⁴ S cm⁻¹ was obtained when the weight ratio of PEO was 40%. The liquid electrolyte uptake was found to increase with increase in porosity and pore size. However, at higher weight ratio of PEO (> 40%) porosity, pore size and ionic conductivity was decreased. This descending trend with further increase of PEO weight ratio was attributed to conglomeration effect of PEO at the pores.     

Synthesis and microstructure of boron-doped alumina membranes prepared by the sol–gel method

Pure and boron-doped γ-Al₂O₃ membranes have been synthesized by the sol–gel method. The thermal stability of the unsupported alumina membrane was studied by determining the pore structure (including average pore size, pore volume and BET surface area). The average pore size of the pure alumina membrane increased sharply after sintering at temperatures higher than 1000°C. Addition of 16% boron can considerably stabilize the pore structure of the unsupported alumina membrane. The pore diameter for the B-doped membrane was stabilized within 13 nm after sintering at 1200°C for 5 h. The substantial increase in the pore size for the pure alumina membrane at the sintering temperature of 1000–1200°C was accompanied by the phase transformation from γ-Al₂O₃ to -Al₂O₃. The addition of boron can raise the temperature of this phase transformation significantly and, thus, improves the thermal stability of the membranes.     

Effect of fiber orientation in gelled poly(vinylidene fluoride) electrospun membranes for Li-ion battery applications

Battery separators based on electrospun membranes of poly(vinylidene fluoride) (PVDF) have been prepared in order to study the effect of fiber alignment on the performance and characteristics of the membrane. The prepared membranes show an average fiber diameter of ~272 nm and a degree of porosity of ~87 %. The gel polymer electrolytes are prepared by soaking the membranes in the electrolyte solution. The alignment of the fibers improves the mechanical properties for the electrospun membranes. Further, the microstructure of the membrane also plays an important role in the ionic conductivity, being higher for the random electrospun membrane due to the lower tortuosity value. Independently of the microstructure, both membranes show good electrochemical stability up to 5.0 V versus Li/Li⁺. These results show that electrospun membranes based on PVDF are appropriate for battery separators in lithium-ion battery applications, the random membranes showing a better overall performance.     

A novel approach of manufacturing Nickel Wicks for loop heat pipes using Metal Injection Moulding (MIM)

Sintered nickel powder is proposed to be used as porous wicks in loop heat pipes used for space applications such as satellites and space crafts. In this work, the manufacturing procedure for tubular wicks through novel Metal Injection Moulding (MIM) route is discussed. Nickel powder, Polypropylene powder and thermoplastic binder are used to produce feedstock for injection moulding. Ideal sintering condition identified as 900°C and 60 minutes. Porosity, pore diameter of the wicks are evaluated by geometric measurements using an electronic weight measuring machine and a micrometer and extrusion flow Porosimeter, respectively. Permeability was calculated according to the Carmen–Kozeny equation. Experimental finding shows that porosity level of 55 vol%, average pore diameter of 2.6 μm, permeability of 1.94 × 10^???12 m² and roundness of 5% have been achieved in the porous wick. SEM investigation of pore structures shows the presence of large pores which leads to enhanced porosity and interconnected fine pore network responsible for generation of required capillary pumping pressure.     

Investigating the performance of ammonium sulphate draw solution in fertilizer drawn forward osmosis process

This work investigated the performance of ammonium sulphate as a draw solution in a fertilizer drawn forward osmosis (FDFO) desalination process using thin-film composite (TFC) membrane. Performance has been assessed by the water flux, reverse permeation and the forward rejection of the feed solutes. A logarithmic relation has been determined between flux and ammonium sulphate concentration. As water flux increased, the specific reverse solute flux (SRSF) of NH₄ ⁺ and SO₄ ^2? ions dropped, which is a favourable condition. Reverse permeation values obtained at flux less than 10 L/m²/h are significantly higher than that for flux more than 10 L/m²/h. Thus, it is recommended to operate the process at a flux higher than 10 L/m²/h to avoid loss of draw solute by reverse permeation. SRSF was almost constant irrespective of ammonium sulphate concentration. TFC membrane used in this study exhibited high rejection of feed solution ions for almost all draw solution concentrations except when operated at low ammonium sulphate concentration and high feed solution concentration. In conclusion, ammonium sulphate is an efficient draw solution for FDFO process when run at water flux more than 10 L/m²/h exhibiting high osmotic pressure, low reverse solute permeation and high rejection of feed solute.     

Experimental Investigation on Steel Foams Fabricated by Sintering-Dissolution Process

This article describes a new process to manufacture open-cell steel foams. Calcium chloride anhydrous is used as a space holder. By changing the values of the main manufacturing parameters such as volume percentage, and the size and shape of the space holder, we produce different steel foam samples which cover a wide range of solid fraction, pore size, and shape. The effects of space-holder content and sintering condition such as temperature and time on the porosity of steel foam samples are discussed. The microstructure and composition of steel foam samples are observed and analyzed by scanning electron microscope and X-ray diffraction. The compressive curves of steel foams are measured by a universal testing machine. The experiment results show the compressive strength of steel foam samples with porosities between 65% and 85% is in the range of 66.4 ～ 12.9 MPa. The compressive strength depends mainly on the porosity and pore shape. The absorbed energy per unit volume (W) of steel foams with porosities between 85% and 65% is in range of 6.8 ～ 31.2 MJ/m³. Under the condition of identical porosity, the absorbed energy per unit volume (W) of steel foam is about three times of aluminum foam. In compression, steel foam specimens show heterogeneous macroscopic deformation.     

Modification of polysulfone with pendant carboxylic acid functionality for ultrafiltration membrane applications

p-Carboxyphenoxymethyl polysulfone (CPMPSF) was synthesized in two steps: (i) chloromethylation of polysulfone (PSF) by in situ generated chloromethyl radical in presence of stannic chloride in tetrachloroethane and (ii) reaction of chloromethylated PSF with p-hydroxybenzoic acid in presence of potassium carbonate in dimethylformamide. The structures of the modified PSFs were confirmed by elemental analysis, IR, ¹H–NMR and $^{{13}}$ C–NMR techniques. The PSF and CPMPSF based ultrafiltration membranes were prepared according to phase–inversion process using water as nonsolvent at 4° and 15 °C, employing casting dope having different amounts of polymer (PSF or CPMPSF), polyvinylpyrrolidone (PVP) and solvent, dimethylformamide (DMF). The membranes were characterized for their pore size, pure water flux and flux and rejection for the permeation of different molecular weight poly(ethylene glycol) (PEG) solutions and sodium chloride (NaCl) solution. The pore radius of the CPMPSF membrane which was prepared without PVP in the casting dope was about 222 Å, whereas, that of the membrane prepared in the presence of PVP (6 wt%) in the casting dope was about 124 Å. For the PSF membranes, pore radii were 80 Å (without PVP) and 176 Å (with PVP 6 wt%). The CPMPSF-based membranes exhibited higher flux and rejections for PEG and NaCl solutions, as compared to the PSF membranes, due to the presence of hydrophilic carboxylic acid group. The CPMPSF membrane exhibited about 48% rejection of NaCl when tested for 5000 ppm feed solution at 400 psi.     

Mechanical and microstructural properties of cordierite-bonded porous SiC ceramics processed by infiltration technique using various pore formers

Cordierite-bonded porous SiC ceramics were prepared by air sintering of cordierite sol infiltrated porous powder compacts of SiC with graphite and polymer microbeads as pore-forming agents. The effect of sintering temperature, type of pore former and its morphology on microstructure, mechanical strength, phase composition, porosity and pore size distribution pattern of porous SiC ceramics were investigated. Depending on type and size of pore former, the average pore diameter, porosities and flexural strength of the final ceramics sintered at 1400 °C varied in the range of ~ 7.6 to 10.1 µm, 34–49 vol% and 34–15 MPa, respectively. The strength–porosity relationship was explained by the minimum solid area (MSA) model. After mechanical stress was applied to the porous SiC ceramics, microstructures of fracture surface appeared without affecting dense struts of thickness ~ 2 to 10 µm showing restriction in crack propagation through interfacial zone of SiC particles. The effect of corrosion on oxide bond phases was investigated in strong acid and basic salt medium at 90 °C. The residual mechanical strength, SEM micrographs and EDX analyses were conducted on the corroded samples and explained the corrosion mechanisms.     

非对称膜及其复合膜结构参数的确定

根据非对称膜及其复合膜与气体渗透之间关系的数学模型，建立了通过测定气体渗透率确定膜结构参数的计算方法，并建立了相应的电算软件。可确定的膜结构参数为涂层厚度、致密层厚度、底膜和复合膜的表面平均孔径及表面孔隙率。并利用此方法确定了两种气体分离复合膜的结构参数。     

Multilayer Amorphous‐Si‐B‐C‐N/γ‐Al2O3/α‐Al2O3 Membranes for Hydrogen Purification

The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H₂ can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single‐step under high temperature conditions. In the present work, the multilayer amorphous‐Si‐B‐C‐N/γ‐Al₂O₃/α‐Al₂O₃ membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H₂/CO permeance. The α‐Al₂O₃ support has a bimodal pore‐size distribution of about 0.64 and 0.045 µm being macroporous and the intermediate γ‐Al₂O₃ layer—deposited from boehmite colloidal dispersion—has an average pore‐size of 8 nm being mesoporous. The results obtained by the N₂‐adsorption method indicate a decrease in the volume of micropores—0.35 vs. 0.75 cm³ g^?1—and a smaller pore size ?6.8 vs. 7.4 Å—in membranes with the intermediate mesoporous γ‐Al₂O₃ layer if compared to those without. The three times Si‐B‐C‐N coated multilayer membranes show higher H₂/CO permselectivities of about 10.5 and the H₂ permeance of about 1.05 × 10^?8 mol m^?2 s^?1 Pa^?1. If compared to the state of the art of microporous membranes, the multilayer Si‐B‐C‐N/γ‐Al₂O₃/α‐Al₂O₃ membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high‐temperature and high‐pressure stability.     

Integration of microfiltration and nanofiltration to promote textile effluent reuse

This study investigates the application of a hybrid microfiltration–nanofiltration (MF–NF) process for textile wastewater reclamation. Indigo blue dye was efficiently retained by an MF membrane, allowing its recovery from the concentrated stream. NF technology was successfully applied to polish textile effluent. The NF membrane was evaluated under different transmembrane pressure (8–15 bars), crossflow velocities (0.21–0.84 cm s^?1), pH (7–11), and feed temperature (20–40 °C). The best NF performance was provided at a pressure of 12 bar and a crossflow rate of 0.63 cm s^?1. The NF performance (in terms of COD, conductivity, colour, and nitrogen removal) was not influenced by pH; however, higher feed pH values resulted in increased membrane fouling. The principal cause of flux decline was due to concentration polarization. Membrane chemical cleaning was sufficient to regain the initial permeability. The NF permeate met the quality requirements for all water demands within the textile industry, while the NF concentrate could be used to wash equipment, print work screens, print paste containers, and floors. The total capital cost (CapEx) of the MF–NF system was estimated at 58,362.50 US dollars and the total operational cost (OpEx) at 0.31 US dollars per cubic metre of effluent.     

Multifunctional substrates of thin porous alumina for cell biosensors

We have fabricated anodic porous alumina from thin films (100/500 nm) of aluminium deposited on technological substrates of silicon/glass, and investigated the feasibility of this material as a surface for the development of analytical biosensors aiming to assess the status of living cells. To this goal, porous alumina surfaces with fixed pitch and variable pore size were analyzed for various functionalities. Gold coated (about 25 nm) alumina revealed surface enhanced Raman scattering increasing with the decrease in wall thickness, with factor up to values of approximately 10⁴ with respect to the flat gold surface. Bare porous alumina was employed for micro-patterning and observation via fluorescence images of dye molecules, which demonstrated the surface capability for a drug-loading device. NIH-3T3 fibroblast cells were cultured in vitro and examined after 2 days since seeding, and no significant (P > 0.05) differences in their proliferation were observed on porous and non-porous materials. The effect on cell cultures of pore size in the range of 50–130 nm—with pore pitch of about 250 nm—showed no significant differences in cell viability and similar levels in all cases as on a control substrate. Future work will address combination of all above capabilities into a single device.