Fabrication and characterization of the monolithic hydrophobic alumina aerogels

The monolithic hydrophobic mesoporous alumina aerogels were successfully synthesized by acid–base sol–gel polymerization of aluminium chloride hexahydrate (AlCl₃·6H₂O) in deionized water/alcohol solution (v/v = 3:7). To minimize shrinkage during drying, alumina hydrogels were aged in tetraethylorthosilicate (TEOS)/acetonitrile solution, and modified using trimethylchlorosilane (TMCS)/acetonitrile solution. Properties of the final product were examined by contact angle measurement, FTIR, FESEM, TEM and BET analyses. Surface modification was confirmed by FTIR spectroscopy. It was found that hydrophobic property of the alumina aerogels was affected by the contents of TMCS. When the molar ratio of TMCS to AlCl₃·6H₂O is 0.35, hydrophobic alumina aerogels shows lower bulk density (0.453 g/cm³) and higher surface area (495 m²/g) than those of unmodified alumina aerogels (0.933 g/cm³, 413 m²/g).     

Preparation of PDMS—Silica Nanocomposite Membranes with Silane Coupling for Recovering Ethanol by Pervaporation

In this article, the composite polydimethylsiloxane (PDMS) membranes supported by cellulose-acetate (CA) microfiltration membrane were successfully prepared by adding nano-fumed silica particles modified with a silane coupling reagent, NH₂-C₃H₆-Si(OC₂H₅)₃. The effects of silica content, feed concentration, and feed temperature on the pervaporation performances of the nano-composite PDMS membranes were investigated for recovering ethanol from aqueous solution by pervaporation. It was found that adding the modified silica particles significantly improved the pervaporation performances of the composite membranes. When the silica content in the membrane was 5 wt%, for a 5 wt% ethanol/water mixture at 40°C, the permeation flux of the membrane maintained about 200 g · m^?2 · h^?1 and separation factor reached the maximum value of 19.     

Effect on properties of PVDF-HFP based composite polymer electrolyte doped with nano-SiO2

Various kinds of nano-SiO₂ using different catalysts were obtained and characterized by scanning electron microscope (SEM) technique. The results showed that the nano-SiO₂ using NH₃·H₂O as catalyst presented the best morphology. Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) based composite polymer electrolyte (CPE) membranes doped with different contents of nano-SiO₂ were prepared by phase inversion method. The as-prepared CPE membranes were immersed into 1.0 M LiPF₆-EC/DMC/EMC electrolytes for 0.5 h to be activated. The physicochemical and electrochemical properties of the CPEs were characterized by SEM, X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) techniques. The results indicate that the CPEs doped with 10 % nano-SiO₂ exhibit the best performance. SEM micrographs showed that the CPE membranes have uniform surface with abundant interconnected micro-pores, and the uptake ratio was up to 104.4 wt%. EIS and LSV analysis also showed that the ionic conductivity at room temperature and electrochemical stability window of the modified membrane can reach 3.372 mS cm^?1 and 4.7 V, respectively. The interfacial resistance R _i was 670 Ω cm^?2 in the first day, then increased to a stable value of about 850 Ω cm^?2 in 10 days storage at room temperature. The Li/As-fabricated CPEs/LiCoO₂ cell also showed good charge–discharge performance, which suggested that the prepared CPE membranes can be used as potential electrolytes for lithium ion batteries.     

Optimization of Preparation Conditions for PDMS-Silica Composite Pervaporation Membranes Using Response Surface Methodology

In this article, response surface methodology was used to optimize the preparation conditions of fumed silica filled polydimethylsiloxane/cellulose acetate composite membranes. The silica loading, polydimethylsiloxane concentration, and NH₂-C₃H₆-Si(OC₂H₅)₃/silica weight ratio were considered as factors. Two regression equations, which described the effects of the three factors on the permeation flux and selectivity of the membranes, were derived from the results of 20 experiments by using a statistical software Design-Expert 7.1.4. The results revealed that the three factors had important effects on the permeation flux and the selectivity. The obtained regression equations were confirmed with another four groups of experiments. According to the regression equations, for the separation of an ethanol aqueous solution with the concentration of 10 wt%, the maximum selectivity of the membrane, 11.5 could be obtained at the feed temperature of 40°C, and the corresponding permeation flux was 197.3 g · m^?2 · h^?1. The preparation conditions for making the composite membrane with the above separation performances were: the silica loading was 5.21 wt%, the polydimethylsiloxane concentration was 13.36 wt%, and the NH₂-C₃H₆-Si(OC₂H₅)₃/silica weight ratio was 0.59.     

Silver-Doped Organic-Inorganic Hybrid Silica Membranes by Sol-Gel Method: Preparation and Hydrothermal Stability

Silver-doped methyl-modified silica membranes (Ag/M-SiO₂) have been prepared using the sol-gel method by adding AgNO₃ solution to a methyl-modified silica sol. The influence of silver-doping on the physical and chemical structures, thermal stability of –CH₃ groups, and gas permeation performance for the silica membranes were investigated. The metallic silver results from the reduction of AgNO₃ which can be completely transformed after calcined above 200°C. The Si–CH₃ vibrational bands disappear completely when the calcination temperature is increased to 600°C, which mineralized when the calcination temperature is further increased to 750°C. The doping of silver nanoparticles has nearly no influence on the chemical structure of the methyl-modified silica materials and the thermal stability of –CH₃ groups, but can make the mean pore size, total pore volume, H₂ permeability, and H₂/CO₂ selectivities of the silica membranes increase. When operated at 200°C and a pressure difference of 0.35 MPa, the H₂ permeance and H₂/CO₂ selectivity of Ag/M-SiO₂ membrane with the AgNO₃/tetraethylorthosilicate molar ratio of 0.08 is 8.99 × 10^?6 mol · m^?2 · Pa^?1 · s^?1 and 10.22, respectively. After hydrothermal treatment and regeneration, the Ag/M-SiO₂ membranes show a smaller change in gas permeances and H₂/CO₂ permselectivities than the methyl-modified silica membranes without silver-doping.     

Phthalonitrile end-capped sulfonated polyarylene ether nitriles for low-swelling proton exchange membranes

A series of phthalonitrile end-capped sulfonated polyarylene ether nitriles are synthesized via K₂CO₃ mediated nucleophilic aromatic substitution reaction at various molar ratios. The as-prepared polymer structures are confirmed by ¹H NMR and FTIR spectroscopy. The properties of membranes cast from the corresponding polymers are investigated with respect to their structures. The membranes exhibit good thermal and mechanical properties, low methanol permeability (0.01?×?10^?6–0.58?×?10^?6 cm²·s^?1 at 20 °C), and high proton conductivity (0.021–0.088 S·cm^?1 at 20 °C). The introduction of phthalonitrile is proved to increase intermolecular interaction, mainly contributing to the reduction in water uptake, swelling ratio, and methanol permeability. More importantly, its introduction does not decrease the proton conductivity, but there is a slight increase. Furthermore, the selectivity of SPEN-CN-50 can reach 4.11?×?10⁵ S·s·cm^?3, which is about nine times higher than that of Nafion 117. All the data show that the as-prepared membranes may be potential proton exchange membrane for DMFCs applications.     

Proton-conducting membranes from phosphotungstic acid-doped sulfonated polyimide for direct methanol fuel cell applications

A series of novel hybrid proton conducting membranes based on sulfonated naphthalimides and phosphotungstic acid (PTA) were prepared from N-Methyl Pyrrolidone (NMP) solutions. These hybrid organic-inorganic materials, composed of two proton-conducting components, have high ionic conductivities (9.3 × 10^?2 S cm^?1 at 60 °C, 15% PTA), and show good performance in H₂|O₂ polymer electrolyte membrane fuel cells (PEMFC), previously reported by us. Moreover, they have low methanol permeability compared to Nafion^®112. In this paper we describe, for the first time, the behaviour of these hybrid membranes as electrolyte in a direct methanol fuel cell (DMFC). The maximum power densities achieved with PTA doped sulfonated naphthalimide membrane, operating with oxygen and air, were 34.0 and 12.2 mW cm^?2, respectively; about the double and triple higher than those showed by the non-doped membrane at 60 °C.     

Synthesis and characterization of polybenzimidazole/α‐zirconium phosphate composites as proton exchange membrane

To improve the high‐temperature performance of proton exchange membranes, the polybenzimidazole (PBI)/α‐zirconium phosphate (α‐Zr(HPO₄)₂·nH₂O, α‐ZrP) proton exchange composite membranes were prepared in this study. PBI polymer containing a large amount of ether units has been synthesized from 3,3′‐ diaminobenzidine (DAB) and 4,4′‐oxybis (benzoic acid) by a direct polycondensation in polyphosphoric acid. The polymer exhibited a good solubility in most polar solvents. Inorganic proton conductor α‐ZrP nanoparticles have been obtained using a synthesis route involving separate nucleation and aging steps (SNAS). The effects of α‐ZrP doping content on the composite membrane performance were investigated. It was found that the introduction of ZrP improved the thermal stability of the composite membranes. The PBI/ZrP composite membranes exhibited excellent mechanical strength. The composite membrane with 10 wt% ZrP showed the highest proton conductivity of 0.192 S cm^?1 at 160°C under anhydrous condition. The proton conducting mechanism of the PBI/ZrP composite membranes was proposed to explain the proton transport phenomena. The experimental results suggested that the PBI/ZrP composite membranes may be a promising polymer electrolyte used in high temperature proton exchange membrane fuel cells (HT‐PEMFCs) under anhydrous condition. POLYM. ENG. SCI., 56:622–628, 2016. © 2016 Society of Plastics Engineers     

Effect of Metallic Coagulant Agents on Oily Wastewater Treatment Performance using Mullite Ceramic MF Membranes

In this paper, the effects of in-line coagulation on permeation flux (PF), fouling resistance (FR), and total organic compound (TOC) rejection (R) of synthesized mullite ceramic membranes during treatment of oily wastewater in coagulation – MF hybrid process were investigated. Four coagulant ((ferrous chloride (FeCl₂.4H₂O), ferrous sulphate (FeSO₄.7H₂O), aluminum chloride (AlCl₃.6H₂O) and aluminum sulphate (Al₂(SO₄)₃.18H₂O)) plus equal concentration of lime in the form of calcium hydroxide (Ca(OH)₂) were evaluated in the coagulation – MF hybrid process at different concentrations (0 ppm, 25 ppm, 50 ppm, and 100 ppm). The results showed that coagulation can affect the membrane filtration by changing characteristics of the oil droplets. Coagulant agents improve the membrane performance at low dosage (25 ppm) for aluminum chloride and mean dosage (50 ppm) for ferrous chloride, ferrous sulphate, and aluminum sulphate. At the best conditions (50 ppm ferrous sulphate), PF increased from 2.22 × 10^?5 to 2.76 × 10^?5 (m³/m² s), FR decreased from 4.2 × 10¹² to 5.55 × 10¹¹ (m^?1), and R increased from 93.8% to 97.1%.     

Effect of cellulose triacetate membrane thickness on forward‐osmosis performance and application for spent electroless nickel plating baths

Cellulose triacetate (CTA) forward‐osmosis (FO) membranes were prepared via the phase inversion method. The influence of thickness on the performance and morphology of CTA FO membranes was discussed in detail. When the thickness of the membrane was 50.0 ± 0.5 μm (CTA4), the prototype CTA membranes displayed a water flux of 20.2 L m^?2 h^?1 and a reverse salt transport of 14.6 g m^?2 h^?1 using 1 mol/L NaCl as the draw solution and deionized water as the feed solution during the FO process at 25 °C. In addition, the high‐performance CTA4 FO membranes have been used to process spent electroless nickel plating baths where the water flux could reach 13 L m^?2 h^?1 and NiSO₄·6H₂O crystals occurred in the feed solution of the spent electroless nickel plating baths. The recovery rates of NiSO₄·6H₂O and water from the spent electroless nickel plating baths were 44.54% and 53.53%, respectively. This study focused on improving membrane design for the FO process and finding a new method of waste liquor or wastewater treatment. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45049.     

Proton‐conductive membranes based on vanadium substituted heteropoly acids with Keggin structure and polymers

In this article, novel proton‐conducting composite membranes SPEEK/PW₁₁V and PVA/SiW₁₁V were synthesized from vanadium substituted heteropoly acids (H₄PW₁₁VO₄₀·8H₂O and H₅SiW₁₁VO₄₀·15H₂O, abbreviated as PW₁₁V and SiW₁₁V) and polymers (SPEEK or PVA) at the weight ratio 70 : 30. The membranes were characterized by the infrared spectroscopy, X‐ray powder diffraction, and scanning electron microscopy, which confirmed the maintenance of the Keggin framework and dispersion homogeneously in the polymer matrix without long‐range ordering. Their proton‐conducting properties were investigated with electrochemical impedance spectroscopy. The results show that the respective proton conductivities of SPEEK/PW₁₁V and PVA/SiW₁₁V membranes were in the order of 10^?2 and 10^?4 S cm^?1 at ambient temperature. The temperature dependence of the two composite membrane electrolytes exhibit Arrhenius behavior, and the observed activation energies to be 15.82 kJ mol^?1 for SPEEK/PW₁₁V and 14.40 kJ mol^?1 for PVA/SiW₁₁V, which indicates that the proton conduction complies with the Grotthuss mechanism. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42204.     

New organic–inorganic hybrid membranes based on sulfonated polyimide/aminopropyltriethoxysilane doping with sulfonated mesoporous silica for direct methanol fuel cells

A series of novel composite methanol‐blocking polymer electrolyte membranes based on sulfonated polyimide (SPI) and aminopropyltriethoxysilane (APTES) doping with sulfonated mesoporous silica (S‐mSiO₂) were prepared by the casting procedure. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The crosslinking networks of amino silica phase together with sulfonated mesoporous silica improved the thermal stability of the hybrid membranes to a certain extent in the second decomposition temperature (250–400°C). The composite membranes doping with sulfonated mesoporous silica (SPI/APTES/S‐mSiO₂) displayed superior comprehensive performance to the SPI and SPI/APTES membranes, in which the homogeneously embedded S‐mSiO₂ provided new pathways for proton conduction, rendered more tortuous pathways as well as greater resistance for methanol crossover. The hybrid membrane with 3 wt % S‐mSiO₂ into SPI/APTES‐4 (SPI/A‐4) exhibited the methanol permeability of 4.68 × 10^?6 cm² s^?1at 25°C and proton conductivity of 0.184 S cm^?1 at 80°C and 100%RH, while SPI/A‐4 membrane had the methanol permeability of 5.16 × 10^?6 cm² s^?1 at 25°C and proton conductivity of 0.172 S cm^?1 at 80°C and 100%RH and Nafion 117 exhibited the values of 8.80 × 10^?6 cm² s^?1 and 0.176 S cm^?1 in the same test conditions, respectively. The hybrid membranes were stable up to about 80°C and demonstrated a higher ratio of proton conductivity to methanol permeability than that of Nafion117. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Selective Permeation of Ammonia and Carbon Dioxide by Novel Membranes

Abstract

Experimental results are presented on membranes of novel composition which selectively permeate ammonia and carbon dioxide from mixtures containing hydrogen. The CO₂-selective membrane, which consists of a thin liquid film of the salt hydrate tetramethylammonium fluoride tetrahydrate, exhibits a CO₂ permeance of 4-1 × 10^?5 cm³/cm²·s·cmHg with selectivity, α(CO₂/H₂), ranging from 360-30. The NH₃-selective membrane, poly(vinylammonium thiocyanate), displays a high NH₃ permeance, 5?20 × 10^?5 cm³/cm²·s·cmHg, with α(NH₃/N₂) as high as 3600 and α(NH₃/H₂) as high as 6000. Such membranes, which retain H₂ at pressure in the feed stream, may offer new opportunities in the design of separation processes.     

Novel sulfonated multi-walled carbon nanotubes filled chitosan composite membrane for fuel-cell applications

In the present study, multi-walled carbon nanotubes (MWCNTs) were sulfonated by 1,3-propane sultone and distillation–precipitation polymerization, respectively, and then incorporated into chitosan (CS) to prepare CS/MWCNTs composite membranes for fuel cell applications. CS/MWCNTs membranes show better thermal and mechanical stability than pure CS membrane due to the strong electrostatic interaction between the  SO₃H groups of MWCNTs and the  NH₂ groups of CS, which can restrict the mobility of CS chain. The sulfonated MWCNTs provide efficient proton hopping sites ( SO₃H,  SO₃⁻ …. ₃⁺HN ), thereby resulting in the formation of continuous proton conducting channels. The composite membranes with 5 wt % of MWCNTs modified by two different ways show a proton conductivity of 0.026 and 0.025 S·cm⁻¹, respectively. In conclusion, CS/MWCNTs membrane is a promising proton exchange membrane for fuel-cell applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47603.     

Robust and reliable solid oxide fuel cells with modified thin film YSZ electrolyte

Reduce electrolyte thickness can improve solid oxide fuel cell (SOFC) performance. However, thinner electrolyte often contains prominent defects and flaws, which may decrease the yield and increase operation risk. This work proposes a method to modify the thin film YSZ electrolyte, to improve cell reliability and durability. The as-sintered anode supported half-cell with screen printed YSZ electrolyte was immersed in precursor solution of Y(NO₃)₃·6H₂O and Zr(NO₃)₄·5H₂O, and being treated under hydrothermal condition of 150°C for 12 h. As a result, the modified cells show slight increase in the OCV values. Furthermore, the hydrothermal modification effectively promotes interface sintering between YSZ electrolyte and GDC barrier layer, yielding a smaller ohmic resistance of .142 Ω·cm² (a decrease of ∼11%) and a higher peak power density of .964 W/cm² (an increase of ∼18%) at 750°C, than pristine cell. Moreover, the modified cell operates stably over 300 h, while the pristine cell presents large and irregular voltage fluctuations. This work suggests that the hydrothermal modification is an effective and promisingly industrial applicable method for thin film electrolyte recovery in SOFCs.     

Novel chitosan-piperazine composite nanofiltration membranes for the desalination of brackish water and seawater

A novel chitosan (CS)-piperazine (PIP) composite nanofiltration (NF) membrane with satisfied characteristics for brackish water and seawater desalination was successfully developed. PIP was mixed with CS during the interfacial polymerization (IP) process to enhance the NF membrane permeate flux. The resultant NF membranes were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM), contact angle. Effects of CS concentration, trimesoyl chloride (TMC) concentration, reaction time and the mixing ratio of CS/PIP on NF membrane performance were investigated thoroughly. When PIP in the aqueous phase monomers reached to 25% (w/w), the PWF (60.6 L·m^?2·h^?1) was synergistically improved by nearly 2 times without a significant reduction of Na₂SO₄ rejection (89.1%). Moreover, the NF membranes possessed excellent performance for the desalination of brackish water and seawater, which showed high potential to be applied in the desalination process for water treatment.     

Single Radiation‐Induced Grafting Method for the Preparation of Two Proton‐ and Lithium Ion‐Conducting Membranes

Summary: Two distinct types of polymer electrolyte membranes for conducting protons and lithium ions have been prepared by a radiation‐induced grafting method. The polymer electrolyte precursor (PVDF‐g‐PS) is obtained by the simultaneous grafting of styrene onto poly(vinylidene fluoride) (PVDF) followed by one of two specific treatments. This includes sulfonation with a chlorosulfonic acid/dichloromethane mixture to obtain proton (H⁺)‐conducting membranes, or activation with LiPF₆/EC/DC liquid electrolyte to obtain lithium ion (Li⁺)‐conducting membranes. The chemical structure of the obtained electrolyte membranes is verified by FT‐IR spectroscopy. Differential scanning calorimetry is used to examine the changes in the crystallinity and the thermal properties of both electrolyte membranes during the preparation process. The thermal stability of both electrolyte membranes is also evaluated using thermal gravimetrical analysis. The obtained polymer electrolyte membranes achieve superior conductivity values: 1.61 × 10^?3 S · cm^?1 for Li⁺ and 5.95 × 10^?2 S · cm^?1 for H⁺ at room temperature at a polystyrene content of 50%. The results of this work suggest that high quality H⁺‐ and Li⁺‐conducting membranes can be obtained using a single radiation‐induced grafting method.

Schematic representation of the single root for preparation of Li⁺‐ and H⁺‐conducting membranes started by radiation‐induced grafting of styrene onto a PVDF film followed by chemical treatment.     

A Unique Cross-Linking Strategy to Prepare Poly(Vinyl Alcohol)-Based Anion Conducting Membrane for Fuel Cell Applications

Anion conducting polymer electrolyte membrane (PVA/KOH/CHDMG) was prepared by cross-linking of poly(vinyl alcohol) (PVA) with 1,4-cyclohexanedimethanol diglycidyl ether (CHDMG) in the presence of KOH. FTIR, FESEM, and DSC-TGA techniques were used for the structural, morphological and thermal characterization of the membrane. The effect of cross-linking on the water uptake, thermomechanical characteristics, ionic conductivity, and chemical stability of the membranes was studied with respect to CHDMG contents. The membrane ionic conductivity at room temperature was 2.2–4.7 × 10^?3 S.cm^?1. Further, the membrane exhibited good mechanical attributes and chemical stability. Thus, these low cost membranes exhibited good prospect for application in alkaline fuel cell.     

Chitosan/CaCO3 solvent‐free nanofluid composite membranes for direct methanol fuel cells

Natural polyelectrolyte chitosan (CS) has been considered to be a promising proton‐exchange membrane material for direct methanol fuel cells due to its low cost and excellent methanol barrier ability. To further improve the ionic conductivity and mechanical property of CS, calcium‐carbonate solvent‐free nanofluids (CaCO₃‐SF) with unique flow behavior were prepared by an ion‐exchange method, and then used a novel nanofiller to modify CS to fabricate composite membranes. The surface‐grafted organic long chains on the surface of CaCO₃ nanoparticles could promote the homogeneous dispersion of CaCO₃ in the CS matrix, and thus improve the interfacial bonding and facilitate the load transfer from the matrix to stiff CaCO₃. When the content of CaCO₃‐SF was 6 wt%, the tensile strength and fracture elongation of the composite membrane were 28.25 MPa and 17.17%, respectively, which increased by 25% and 36% when compared with those of pure membrane. Moreover, the ? SO₃H groups in the structure of organic long chains could form new proton transport sites, and thus enhance the proton conductivity of the membranes. Consequently, when compared with pure CS membrane (0.0131 S cm^?1), incorporation of 6 wt% CaCO₃‐SF (0.0250 S cm^?1) exhibited about onefold increase of proton conductivity. POLYM. ENG. SCI., 59:2128–2135, 2019. © 2019 Society of Plastics Engineers     

Quaternized poly (2.6 dimethyl – 1.4 phenylene oxide)/Polysulfone anion exchange membrane reinforced with graphene oxide for methanol alkaline fuel cell application

Composite anion exchange membranes (AEM) based on quaternized poly (phenylene) oxide and polysulfone blend (QPPO/PSF) were successfully fabricated and characterized for methanol alkaline fuel cell application. To make a composite AEM, increasing graphene oxide (GO) wt.% ratios was introduced in the polymer blend. The membrane properties were enhanced by the addition of GO in comparison to the bare QPPO/PSF blend. The addition of GO resulted to a higher ion exchange capacity (IEC) of 3.21 mmol.g^?1 and an ion conductivity increase of up to 63.67 mS.cm^?1 at 80 °C. The QPPO/PSF/2%GO composite membrane reached a peak power density of 112 mW.cm^?2, which is about five (5) times more than the parent QPPO membrane at room temperature. The above results indicate that QPPO/PSF/GO is a good candidate as an anion exchange membrane for alkaline fuel cell application.