Pressure-assisted self-assembly technique for fabricating composite membranes consisting of highly ordered selective laminate layers of amphiphilic graphene oxide

We prepare highly ordered flexible layers of graphene oxide (GO) on modified polyacrylonitrile substrates by the pressure-assisted self-assembly technique. This composite membrane shows excellent performance during the pervaporation separation of a 70 wt.% isopropyl alcohol (IPA)/water mixture: 99.5 wt% water in permeate and 2047 g m⁻² h⁻¹ permeation flux. Despite the specific GO deposition increase from 4.3 to 43.3 × 10⁻⁵ g cm⁻² (ninefold layer thickness growth), its effect on the permeation flux is not significant, as manifested by only a little decrease in the flux. At 70 °C feed temperature, the permeate water concentration remains 99.5 wt% and the permeation flux reaches 4137 g m⁻² h⁻¹. The high selectivity may be due to the dense GO film consisting of highly ordered and packed laminates, allowing water but inhibiting IPA molecules to pass through. GO is demonstrated to be amphiphilic: water molecules adsorb first at the hydrophilic edge (hydroxides) and then rapidly diffuse through the hydrophobic core (mainly carbon), forming a water passage channel that promotes high permeation flux. When water molecules permeate through the GO layers, they accumulate and form a monolayer structure that pushes the successive layers away from each other, leading to widening of the d-spacing.     

Oxygen permeation through dense La0.1Sr0.9Co0.8Fe0.2O3−δ perovskite membranes: Catalytic effect of porous La0.1Sr0.9Co0.8Fe0.2O3−δ layers

The oxygen permeation performance of a number of La_0.1Sr_0.9Co_0.8Fe_0.2O_3−δ (LSCF1982)-based membranes, consisting of dense LSCF1982 layer with/without porous LSCF1982 layer, was analyzed on the basis of the thickness of the dense layer and catalytic effect of the porous layer. A 0.27 mm thick dense membrane gives oxygen permeation flux ($J_{O_2}$) of 2.33 sccm min⁻¹ cm⁻² at 900 °C, which is increased to 3.55 sccm min⁻¹ cm⁻² on applying a porous layer of LSCF1982 onto the dense membrane. The membrane gives a stable flux for 300 h. The flux was further improved by reducing the thickness of the dense LSCF1982 layer and at 950 °C a flux of 4.47 sccm min⁻¹ cm⁻² is obtained with 0.012 mm thick membrane.     

Preparation processes and characterizations of alumina-coated alumina support layers and alumina-coated natural material-based support layers for microfiltration

Recently, porous ceramic membranes have become a subject of significant interest due to their outstanding thermal and chemical stability. To reduce the high manufacturing costs of these porous ceramic membranes, recent research has focused on the utilization of inexpensive natural materials. However, there have not been any well-established direct comparisons of the membrane properties between typical alumina-based membranes and novel natural material-based membranes. Therefore, we compared alumina-coated alumina support layers (with average pore sizes ranging from 0.10 µm ~0.18 µm), alumina-coated diatomite-kaolin composite support layers (with an average pore size of 0.12 µm), and alumina-coated pyrophyllite-diatomite composite support layers (with an average pore size of 0.11 µm) via the dip-coating method and subsequent heat treatment ranging from 1200 °C–1400 °C for 1 h. The pure water permeability of the alumina-coated diatomite-kaolin composite support layer and the alumina-coated pyrophyllite-diatomite composite support layer was found to be approximately 2.0×10² L m⁻² h⁻¹ bar⁻¹, which is similar to that of an alumina-coated alumina support layer. Therefore, we suggest that the average pore size of an alumina-coated natural material-based support layer can be effectively controlled while exhibiting acceptable water permeability.     

Macro-porous dolomite hollow fibers sintered at different temperatures toward widened applications

Ceramic hollow fibers from natural dolomite with different pore structures have been designed. The unique hollow fibers were produced by the phase inversion method and applying different sintering temperatures. The hollow fiber precursor presented coagulated polymers through the fiber thickness due to the high granulometric size of the used dolomite material (11.3–47.2 µm). The fiber sintered at 400 °C presented mechanical strength of 4.5 MPa and water permeability of 84.7 L h⁻¹ m⁻² kPa⁻¹. The increase in the sintering temperature up to 1250 °C resulted in fragile hollow fibers due to dolomite transformations that resulted in gas release and a significant mass loss of 33.7%. At 1350 °C, the liquid phase sintering mechanism occurred and the dolomite hollow fiber sintered at 1350 °C presented mechanical strength of 5.5 MPa and water permeability of 2219 L h⁻¹ m⁻² kPa⁻¹. Doloma dissolution in water was investigated and calcium concentration was increased from 0.72 (pure water) to 2.905 ppm for a contact time from 4 h between the fiber sintered at 1250 °C and pure water. However, this dissolution did not decrease the mechanical resistance of the fiber. These results suggest the potential of applying natural dolomite for producing low cost membranes or substrates. The hollow fiber sintered at 400 °C is suggested to be used as a proper separation medium, while the hollow fiber sintered at 1350 °C may be used as a substrate for the deposition of a separation layer to be used in gas separations. The high porosity of the fiber sintered at 1250 °C suggests its application as a support for the impregnation of functional materials. Thus, depending on the applied sintering temperature the dolomite membrane can be used in different applications.     

A thermodynamically stable La2NiO4+δ/ Gd0.1Ce0.9O1.95 bilayer oxygen transport membrane in membrane-assisted water splitting for hydrogen production

A bilayer configuration of mixed ion-electron conducting La₂NiO_4+δ and oxygen-ion conducting Gd_0.1Ce_0.9O_1.95 (LNO/GDC10) was proposed for hydrogen production by water-splitting and its properties were measured as a function of temperature, reducing gas CO content and water vapor pressure during the hydrogen production by water-splitting. The hydrogen production flux increased with increasing water vapor pressure and oxygen chemical potential to a maximum of 0.12 cm³ (STP)/min-cm² with 23.25% CO/76.75% CO₂ (40 sccm)/balance He (60 sccm) gas mixture on the oxygen-permeate side and wet N₂ (pH₂O=0.49 atm) on the oxidizing side at 900 °C. The stability of the bilayer membrane was tested in a very low oxygen partial pressure (pO₂) on the oxygen-permeate side. The presence of GDC10 on the oxygen-permeate side of the bilayer prevented the direct exposure of LNO to very low pO₂ and thus protected it from decomposition, even at pO₂≈10^?15 atm.     

Improving the POM performance of YBa2Cu3O7−δ membrane reactor by Co doping

The performance of Co doped YBa₂Cu₃O_7−δ (YBCO) membrane reactor have been investigated in a process of the partial oxidation of methane (POM) to syngas. The results shows that doping YBCO membrane with a little Co can enhance its oxygen permeation flux and improve its stability in reducing atmosphere noticeably. At 900 °C, with feed flow at 50 ml/min, CH₄ 6.0 v%, SV = 12,000 h⁻¹, and Ni/ZrO₂ catalyst, CH₄ conversion rate, CO selectivity, and oxygen permeation flux can reach to 98%, 92% and 1.41 ml min⁻¹ cm⁻² respectively.     

Dynamic removal of n-hexane from water using nanocomposite membranes: Serial coating of para-aminobenzoate alumoxane,boehmite-epoxide and chitosan on Kevlar fabrics

Nanocomposite membranes were fabricated by dip-coating technique. Para-aminobenzoate alumoxane, boehmite–epoxide and chitosan were consecutively coated on the Kevlar fabric surface. The membranes were utilized for removing n-hexane from water using a gravity-driven dead-end filtration setup. UV–vis, FTIR and SEM analyses were performed for characterization. Water affinity analyses revealed highly hydrophilic nature of the modified membranes. Effect of pH was examined with the pH 2 providing the best condition for oil–water separation. Maximum flux and rejection were obtained as 1128 L m⁻² h⁻¹) and 94%, respectively. Deposited oil layer was effectively removed from the membrane surface using hot citric acid solution.     

Processing of alumina-coated clay–diatomite composite membranes for oily wastewater treatment

Crack-free alumina-coated clay–diatomite composite membranes were successfully prepared by a simple pressing and dip-coating route using inexpensive raw materials at a temperature as low as 1000 °C in air. The changes of porosity, flexural strength, pore size, flux, and oil rejection rate of the membranes were investigated while changing the diatomite content. A simple burn-out process subjected to the used membranes in air completely recovered the specific surface area, steady state flux, and oil rejection rate of the virgin membranes. The recycled membranes showed an exceptionally high oil rejection rate (99.9%) with a feed oil concentration of 600 mg/L at an applied pressure of 101 kPa. The typical porosity, pore size, flexural strength, oil rejection rate, and steady state flux of the recycled alumina-coated clay–diatomite composite membrane were 36.5%, 0.12 μm, 32 MPa, 99.9%, and 6.91×10⁻⁶ m³ m⁻² s⁻¹, respectively, at an applied pressure of 101 kPa.     

Thermal chemical vapor deposition grown graphene heat spreader for thermal management of hot spots

Graphene of different layer numbers was fabricated using thermal chemical vapor deposition (TCVD), and it was demonstrated as a heat spreader in electronic packaging. Platinum thermal evaluation chips were used to evaluate the thermal performance of the graphene heat spreaders. The temperature of a hot spot driven at a heat flux of up to 430 W cm⁻² was decreased from 121 °C to 108 °C (ΔT ≈ 13 °C) with the insertion of the monolayer graphene heat spreader, compared with the multilayer (n = 6–10) ones’ temperature drop of ∼8 °C. Various parameters affecting the thermal performance of graphene heat spreaders were discussed, e.g. layer numbers of graphene, phonon scattering, thermal boundary resistance. We demonstrate the potentials of using a complementary metal oxide semiconductor compatible TCVD process to utilize graphene as a heat spreader for heat dissipation purposes.     

Preparation and characterization of a nigerian mesoporous clay-based membrane for uranium removal from underground water

This study reports the removal of uranium in underground wastewater using a Nigerian clay-based membrane. The clay and sintered clay were characterized using XRD, XRF, TGA/DTA, FESEM and PSD. The raw clay was mixed with cassava starch (10, 15, 20 and 25 wt%) and sintered at a temperature of 1300 °C. A multi-point BET analysis of the produced clay-based membranes was conducted to determine the surface area, pore volume and average pore size. Sintering characteristics were determined by apparent porosity, bulk density and flexural strength. The radioactivity of the feed and the permeated water was counted using a gamma spectrometer with an HPGe detector. From the XRD, TGA and FESEM, 1300 °C was found to be optimum for the mullite formation from the clay. The average pore sizes of the produced membranes from the BET results were observed to be in the range from 51 to 70 Å and with a steady state flux range of the tested membranes in the range 1.92×10⁻⁵–2.09×10⁻⁴ m³ m⁻² s⁻¹. The permeation flux produced is of high quality with a rejection in the range of 1.78–2.56 Bq/l of the uranium activity by the tested membranes. This low-cost membrane will have an application for the treatment of uranium-containing wastewater from fracking, oil exploration and phosphate mining industries.     

Application of response surface methodology for modeling and optimization of membrane distillation desalination process

In this work, response surface methodology (RSM) was applied for modeling and optimization of operating parameters for water desalination by direct contact membrane distillation (DCMD) process using polypropylene membrane (PP) with low pore size. Operating parameters including vapor pressure difference, feed flow rate, permeate flow rate and feed ionic strength were selected and the optimum parameters were determined for DCMD permeate flux. The developed model for permeate flux response was statistically validated by analysis of variance (ANOVA) which showed a high value coefficient of determination value (R² = 0.989). The obtained optimum operating parameters were found to be 0.355 × 10⁵ Pa of vapor pressure difference, feed flow rate of 73.6 L/h, and permeate flow rate of 17.1 L/h and feed ionic strength of 309 mM. Under these conditions, the permeate flux was 4.191 L/(m² h). Compared to a predicted value, the deviation was 3.9%, which confirms the validity of the model for the DCMD process desalination optimization. In terms of product water quality, the DCMD process using hydrophobic PP membrane can produce high quality of water with low electrical conductivity for all experimental runs.     

CO2-tolerant Ni-La5.5WO11.25-δ dual-phase membranes with enhanced H2 permeability

Enhancing the ambi-polar conductivity of the ceramic hydrogen permeable membrane by introducing an electron conductive metallic phase is quite effective, which is helpful for the hydrogen permeation flux improvement. To develop CO₂-tolerant hydrogen permeable membranes with better hydrogen permeability, Ni-La_5.5WO_11.25-δ (Ni-LWO) cermet membranes are fabricated. The alkaline earth metal-free ceramic LWO is used as the main proton-conductive phase and Ni is used as the main electron-conductive phase. The Ni-LWO membrane exhibits good chemical stability in CO₂-containing atmosphere since its hydrogen permeability maintains well in the measurement for about 180 h. Compared with the LWO ceramic membrane, the hydrogen permeability of the Ni-LWO membrane has been improved significantly. The Ni/LWO ratio has great impact on the performance of the cermet membrane. Meanwhile, among all the dual-phase Ni-LWO membranes with different Ni/LWO volume ratios, the membrane with 60 vol% Ni shows the highest hydrogen permeation flux of 0.18 ml min⁻¹ cm⁻² at 1000 °C when the feed gas contains 50% H₂.     

Carbon composite membrane derived from a two-dimensional zeolitic imidazolate framework and its gas separation properties

The carbonization of a newly reported two-dimensional zeolitic imidazolate framework (ZIF-L) with leaf-like morphology was investigated by TG, SEM, XRD and XPS. ZIF-L flakes were thermally stable at up to 200 °C, and completely transformed into an amorphous carbonaceous material after heat treatment in nitrogen at 550 °C. A carbon composite membrane was then prepared by deposition of ZIF-L flakes on a porous alumina support and then direct carbonization of ZIF-L film. During the carbonization, the ZIF-L membrane reorganized into a nanoporous carbon composite membrane composed of ZnO nanoparticles and leaf-like carbon flakes. The resulting nanoporous carbon composite membrane exhibited a narrow micropore size distribution, and it had higher BET surface area than the ZIF-L flakes. Gas separation permeation experiments showed that the carbon composite membrane had a high H₂ permeance of 3.5 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹, and moderate H₂/N₂ and H₂/CO₂ ideal selectivities of 6.2 and 4.9, respectively. This work presents a simple and effective method for preparing functional nanoporous carbon composite membranes from ZIFs (or MOFs) for many potential applications.     

Highly conductive proton exchange membranes based on sulfonated poly(phthalazinone ether sulfone) and cerium sulfophenyl phosphate

Polymer composite membranes based on sulfonated poly(phthalazinone ether sulfone) (SPPES) and cerium sulfophenyl phosphate (CeSPP) are prepared. Three CeSPP concentrations are used: 10, 20, and 30 wt.%. The membranes are characterised by infrared spectroscopy (IR), X-ray diffraction spectroscopy, thermal gravimetric analysis, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The IR results indicate the formation of intense hydrogen bonds between CeSPP and SPPES molecules. The SEM micrographs show that CeSPP well dispersed in composite membrane. The properties of the membranes are evaluated by their water uptake, ionic exchange capacity, proton conductivity and methanol permeability. The proton conductivity of the SPPES (DS 91%)/CeSPP (30 wt.%) composite membrane (I) reaches 0.384 S/cm at 130 °C and 100% relative humidity, which is three times more than Nafion®117. CeSPP improves the conductivity of composite membranes at a low humidity. At 105 °C and 70% RH, the proton conductivity of membrane (I) is 9.1 × 10⁻² S/cm, while Nafion®117 8.8 × 10⁻³ S/cm. The methanol permeability of membrane (I) is 10⁻⁸ cm²/s. That is much lower than Nafion®117.     

High performance BaCe0.8Y0.2O3−a (BCY) hollow fibre membranes for hydrogen permeation

In this work, BaCe_0.8Y_0.2O_3−α (BCY) perovskite hollow fibre membranes were fabricated by a phase inversion and sintering method. BCY powder was prepared by the sol–gel technique using ethylenediaminetetraacetic acid (EDTA) and citric acid as the complexing agents. Gel calcination was carried out at high temperature to form the desired crystal structure. The qualified BCY hollow fibre membranes could not be achieved even the sintering was carried out at temperatures up to 1550^oC due to the poor densification behavior of the BCY material. The addition of sintering aid (1 wt% Co₂O₃) inside BCY powder as the membrane starting material significantly improved the densification process, leading to the formation of gas-tight BCY hollow fibres. The optimum sintering temperature of BCY hollow fibre membrane was 1400 °C to achieve the best mechanical strength. H₂ permeation through the BCY hollow fibre membranes was carried out between 700 and 1050 °C using 25% H₂–He mixture as feed gas and N₂ as sweep gas, respectively. For comparison purpose, the disk-shaped BCY membrane with a thickness of 1 mm was also prepared. The measured H₂ permeation flux through the BCY hollow fibres reached up to 0.38 mL cm⁻² min⁻¹ at 1050 °C strikingly contrasting to the low values of less than 0.01 mL cm⁻² min⁻¹ from the disk-shaped membrane. After the permeation test, the microstructure of BCY hollow fibre membrane was still maintained well without signals of membrane disintegration or peeling off.     

Effects of hypochlorite exposure on flux through polyethersulphone ultrafiltration membranes

Polyethersulphone ultrafiltration membranes with a nominal molecular weight cut off of 10 kDa were degraded in solutions of sodium hypochlorite over a range of pH values at 55 °C to achieve exposure measured in ppm-days of chlorine exposure. The degraded membranes were tested, using an ÄKTAcrossflow? system, for clean water flux, demineralised whey flux and protein rejection. The water fluxes for three membranes (new, 10,000 ppm-day pH 12, and 10,000 ppm-day pH 9) were found to be about 100, 200 and 400 L m^?2 h^?1, respectively with cross flow at 1 bar transmembrane pressure. However whey fluxes were about 23, 5, and 6 L m^?2 h^?1 for the same three membranes. Size exclusion chromatography of the permeates showed significant permeation of α-lactalbumin and β-lactoglobulin through membranes degraded at pH 9 for 20,000 ppm-days, while almost no permeation was found for degradation at pH 12.These results show that hypochlorite degradation affected fluxes by at least two mechanisms. It was likely that membrane pitting increased the pore size causing increased water flux and reduced protein rejection. However hypochlorite also seemed to alter the membrane surface properties, causing the protein to form a less permeable layer that reduced the flux of whey.     

New morphological Ba0.5Sr0.5Co0.8Fe0.2O3−α hollow fibre membranes with high oxygen permeation fluxes

Perovskite Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?α (BSCF) hollow fibre membranes were fabricated by a combined phase inversion and sintering technique. The membranes were characterised by XRD, SEM and tested for air separation. The membrane possesses a novel morphology consisting of one dense layer and one porous layer. Oxygen permeation fluxes through the obtained hollow fibre membranes were measured in the temperature range 650–950 °C using helium sweep gas rates from 50 to 200 mL min^?1. Experimental results indicated the oxygen permeation flux through the BSCF hollow fibre membrane sintered at 1050 °C was approximately 11.46 mL min^?1 cm^?2 at 950 °C when the helium sweep rate was kept at 200 mL min^?1. The BSCF hollow fibre membrane showed a stable oxygen permeation flux of 8.60 mL min^?1 cm^?2 over the investigated period of 120 h at 900 °C.     

Enhanced hollow fiber membrane performance via semi-dynamic layer-by-layer polyelectrolyte inner surface deposition for nanofiltration and forward osmosis applications

The layer-by-layer (LBL) polyelectrolyte deposited membranes have drawn increasing attention in various applications due to the ease of selective layer formation and their stability and versatility. In this study, the LBL deposition was performed at the inner surface of the polyethersulfone (PES) hollow fiber substrate to form composite nanofiltration (NF) membrane. The semi-dynamic deposition procedure was adopted with the aid of syringes. The newly developed inner deposited (id-LBL) membranes were then tested in NF and forward osmosis (FO) applications and the performance were compared with outer surface deposition as well as some literature data. The id-LBL membranes could not only withstand higher operating pressure but also possess superior hardness rejection especially in high concentration mixed salt solutions (more than 95% rejection to Mg²⁺ and Ca²⁺ in a 5000 ppm total dissolved salt (TDS) mixture under 4.8 bar). As for the FO process, with only two layer deposition, the id-LBL membranes also demonstrated significant performance improvement with increased water flux (up to 70 L/m² h using 0.5 M MgCl₂ as draw solution in active layer facing draw solution configuration) and reduced salt leakage (around 0.5 g/m² h using 1 M MgCl₂ draw solution in active layer facing feed water configuration). This study suggests that for hollow fiber substrate, the inner surface is more suitable for the formation of the selective layer via LBL deposition than the outer surface.     

Fabrication and characterization of bone china using synthetic bone powder as raw materials

The synthetic bone powder was studied as a raw materials for bone china, completely replacing natural bone ash raw materials. The physical and thermal properties of samples obtained by the two bone powders were tested and comparatively studied. Performance tests included pyroplastic deformation, flexural strength, bulk density, sintering shrinkage, water absorption, transmittance, thermal expansion coefficient and the thermal shock resistance. The phase composition and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that using synthetic bone powder could shorten the preparation time, reduce the sintering temperature and result in high-quality bone china. The pyroplastic deformation decreased from 9.14% to 7.92%, the three-point flexural strength increased from 123 MPa to 191 MPa, the light transmittance (at a 2-mm thickness) increased from 6.7% to 11.2%, the thermal expansion coefficient decreased from 8.24×10⁻⁶ °C⁻¹ to 7.69×10⁻⁶ °C⁻¹, and the thermal shock resistance increased from 140 °C to 180 °C. A continuous interface layer without cracks was produced by using the synthetic bone powder.     

Pervaporation separation of benzene/cyclohexane through AAOM-ionic liquids/polyurethane membranes

Supported ionic liquids/polyurethane (PU) membranes were prepared by immobilizing ionic liquids on a porous anodic aluminum oxide membrane (AAOM) support that was coated on one side with polyurethane (PU). The microstructure of all membranes was characterized using scanning electron microscopy (SEM). The pervaporation separation performance of the supported ionic liquids/polyurethane membranes was investigated for benzene/cyclohexane (Bz/Cy) mixtures. The SEM results demonstrated that the porous surface of the AAOM support was sealed by the dense polyurethane membrane and the pores of the AAOM support were impregnate with ionic liquids. The ionic liquids filling in the AAOM support enhanced the separation selectivity of Bz/Cy. The separation factor of Bz to Cy increased from 5 to 34.4 and the largest PSI of AAOM-[C₄mim]PF₆/PU membrane reached 452.54 g m⁻² h⁻¹ at 55 °C for a 50 wt.% Bz/Cy mixture. Because the polyurethane prevented the leakage of ionic liquids filled in the AAOM support, the supported ionic liquids/polyurethane membranes exhibited excellent stability.