Heterogeneous photo-electro-Fenton process using different iron supporting materials

In this work, the application of heterogeneous photo-electro-Fenton processes using iron supported on Nafion membranes and ion exchange amberlite and purolite resins is studied. Spectroscopic and TOC results using as a model pollutant an aqueous Orange II dye solution indicate that the process can be carried out with any of the iron supporting materials under study. While the resins can incorporate between 59 and 65 mg Fe/g of substrate, a Nafion membrane can fix 45 mg Fe/g of supporting material. Iron desorption analysis after a photo-electro-Fenton degradation test on the other hand, indicates that the ion exchange resins and the Nafion membrane hold more than 90% of iron. An alkaline rinse after the activation exchange process for the amberlite resin and the Nafion membrane, results in a larger stability of the fixed iron species.     

Studies of a high temperature proton exchange membrane based on incorporating an ionic liquid cation 1-butyl-3-methylimidazolium into a Nafion matrix

High temperature proton exchange membranes based on Nafion were prepared by incorporating the polymer with ionic liquid cation 1-butyl-3-methylimidazolium (BMIm) and doping with phosphoric acid (PA). We found that using the hydroxide form rather than the chloride form of BMIm incorporated more readily the BMIm cation into Nafion film. A mole ratio of about 2 of BMIm cation to Nafion repeat unit, i.e., λ_BMIm/Nafion, was reached with the hydroxide form BMIm. The incorporated BMIm cation enhanced the doping of phosphoric acid into Nafion. A proton conductivity of 10.9 mS cm⁻¹ and a tensile stress at break of 5.3 MPa were achieved, respectively, with a composite membrane of Nafion/2.3BMIm/5.2PA in molar ratio at 160 °C without humidification.     

Preparation of poly(acrylic acid)/poly(vinyl alcohol) membrane for the facilitated transport of CO2

Poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) membrane was prepared for the facilitated transport of CO₂. The carrier of CO₂ was monoprotonated ethylenediamine and was introduced in the membrane by ion exchange. The ion‐exchange capacity of the membrane was 4.5 meq/g, which was much higher than that of the Nafion 117 membrane. The membrane was highly swollen by the aqueous solution. Much higher selectivity of CO₂ over N₂ and higher CO₂ permeability were obtained in the PAA/PVA membrane than in the Nafion membrane because of the higher ion‐exchange capacity and solvent content. The highest selectivity was more than 1900 when the CO₂ partial pressure in the feed gas was 0.061 atm. Effects of ion‐exchange capacity, membrane thickness, and annealing temperature in conditions of membrane preparation on membrane performance were investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 936–942, 2001     

Novel anion exchange membranes having fluorocarbon backbone: Preparation and stability

Anion exchange membranes with excellent durability were prepared by chemical modification of Nafion. The modification was achieved by transformation of the sulfonic acid group into quaternary ammonium group. Namely, Nafion membrane was first converted into an amide-type membrane. Reduction of the carbonxyl group to methylene followed by quaternarization with alkyl iodide resulted in the formation of an anion exchange membrane. The electric resistance of the resulting membranes depends on the equivalent weight of the starting membranes (4.4–6.0 Ω cm² in 0.5N NaCl). The characteristics of the membranes are the excellent stability toward chemical substances such as organic solvents, oxidizing agents, acids, etc. For example, the membranes are stable in aqueous saturated chlorine solution at 60°C for 1000 hr.     

Synthesis of organic-inorganic composite membrane by sol-gel process

Silica was succesfully incorporated into cation exchange polymer membranes, CL-25T and Nafion 417, utilizing sol-gel process. As dipping time increased, increase in silica uptake in membrane was observed. In Nafion 417 membrane, no relationship was found between the silica uptake and the change in ion exchange capacity. But CL-25T which has larger pores than Nafion 417 shows proportional decrease in ion exchange capacity with increasing silica uptake. It suggests that the pore structure of membrane and the size control of silica sol are important to modify the structure of composite membranes. In CL-25T membranes modified by silica, the transport rate of IPA (isopropyl alcohol) increased with increasing OH^- concentration on the pore surface.     

Industrial application of Nafion-systems in rearrangement-aromatisation, transesterification, alkylation, and ring-closure reactions

Nafion, a perfluorinated sulphonic acid ion-exchange polymer, is known to be a very strong Brønsted acid. Thus, Nafion NR 50 and Nafion/SiO₂ with 15 wt.% Nafion-loading were selected, in order to elucidate the potential for rearrangement-aromatisation of ketoisophorone (KIP) to 2,3,5-trimethylhydroquinone diacetate (TMHQ-DA) in presence of acetic acid anhydride as acylating agent, transesterification of TMHQ-DA to 2,3,6-trimethylhydroquinone monoacetate (TMHQ-1-MA) and reaction of isophytol (IP) with trimethylhydroquinone (TMHQ) to (all-rac)--tocopherol. For the rearrangement-aromatisation of KIP to TMHQ-DA supported Nafion/SiO₂ was markedly more active than the unsupported Nafion NR 50. Both Nafion-systems generally revealed remarkably high selectivity, which ranged up to 94 GC-a% TMHQ-DA at high conversion. The major side-product was 3,4,5-trimethylcatechol diacetate. In case of Nafion/SiO₂, pre-treatment under vacuum and especially grinding of the extrudates seemed to increase activity at comparably high selectivity. Recycling Nafion/SiO₂ after filtering and rinsing with acetic acid anhydride led to gradually decreasing activity. Without intermediate isolation of TMHQ-DA, Nafion/SiO₂ was active and selective for the formation of TMHQ-1-MA. Using the Nafion systems in the reaction of IP and TMHQ revealed that remarkably high conversion of IP (>95%) and compared with zinc chloride/Brønsted acid or BF₃-catalysed reaction good yields (≈92%) and selectivities were obtained. We found a strong dependency on the solvent polarity. In further experiments, the recovery of the catalyst was tested.     

Studies on syntheses and permeabilities of special polymer membranes: 50. Transport of metal ions against their concentration gradient through water-insoluble poly(styrene sulphonic acid) membrane

Water-insoluble cation exchange membranes were prepared by heat treating membranes made of poly(styrene sulphonic acid) and poly(vinyl alcohol). Transport of metal ions through the above cation exchange membrane against their concentration gradient was investigated under various conditions. The transport in this system, where one side of the membrane in a diaphragm cell was acidic and the other alkaline, was influenced significantly by the initial H⁺ ion concentration on the acidic side. The selectivity of metal ions in diffusive transport depended on the size of their hydrated ions and that in transport against their concentration gradient was due to the affinity between the metal ions and the carrier fixed to the membrane.     

Modification of Nafion membrane using poly(4‐vinyl pyridine) for direct methanol fuel cell

Perfluorinated membrane such as Nafion (from Du‐Pont) has been used as a polymer electrolyte membrane. Nafion 117 membrane, which was usually used as the electrolyte membrane for the polymer electrolyte membrane fuel cell (PEMFC), was modified by using poly(4‐vinyl pyridine) (P4VP) to reduce the methanol crossover, which cause fuel losses and lower power efficiency, by the formation of an ionic crosslink structure (sulfonic acid‐pyridine complex) on the Nafion 117 surface. Nafion film was immersed in P4VP/N‐methyl pyrrolidone (NMP) solution. P4VP weight percent of modified membrane was controlled by changing the concentration of P4VP/NMP solution and the dipping time. P4VP weight percent increased with increasing concentration of dipping solution and dipping time. The thickness of the P4VP layer increased with increasing concentration of dipping solution and dipping time when the concentration of the dipping solution was low. At high P4VP concentration, the thickness of the P4VP layer was almost constant owing to the formation of acid–base complex which interrupted the penetration of P4VP. FTIR results showed that P4VP could penetrate up to 30 µm of Nafion 117 membrane. Proton conductivity and methanol permeability of modified membrane were lower than those of Nafion 117. Both decreased with increasing concentration of dipping solution and dipping time. Methanol permeability was observed to be more dependent on the penetration depth of P4VP. Water uptake of the modified membrane, the important factor in a fuel cell, was lower than that of Nafion 117. Water uptake also decreased with increasing of P4VP weight. On the basis of this study, the thinner the P4VP layer on the Nafion 117 membrane, the higher was the proton conductivity. Methanol permeability decreased exponentially as a function of P4VP weight percent. Copyright © 2006 Society of Chemical Industry     

Transport of proton in polymeric ionic exchange membranes in relation with the dissociated sorbed acid

The transport of proton in ion exchange membranes in contact with HCl and H₂SO₄ solutions is studied. The membranes are the Nafion® 117 cation exchange membrane and, on the other hand, the Selemion® AAV and the Morgane ARA anion exchange membranes. Sorption and water content measurements combined with the radiotracer technique point out the low dissociation degree of the acid present in the membrane phase. This low dissociation leads to the excellent permselectivity towards proton of the Nafion membrane, and it is also the factor which decreases the proton leakage in the two studied anion exchange membranes.     

Novel grafted nafion membranes for proton‐exchange membrane fuel cell applications

Novel poly(glycidyl methacrylate)‐grafted Nafion–phosphoric acid membranes for direct‐oxidation methanol fuel cells were prepared with a potassium persulfate chemical initiation system for the first time. The introduced epoxy groups were converted to amine groups through a reaction with ethylenediamine, which consequently doped with phosphoric acid ( PO₃H) groups. The latter significantly contributed to enhancing the ion‐exchange capacity, mechanical properties, and thermal stability. Factors affecting the modification steps were studied. Changes in the chemical and morphological structure were verified through Fourier transform infrared spectroscopy, TGA, and scanning electron microscopy characterization. Various grafting percentages (GP%'s) up to 32.31% were obtained. As a result, the thickness of the grafted membranes increased. Furthermore, the methanol permeability of the modified membranes was reduced with increasing grafted polymer content compared with that of the Nafion membrane. An 83.64% reduction in the methanol permeability was obtained with a polymer grafted content of 18.27%. Finally, the efficiency factor for all of the modified Nafion membranes was enhanced compared with that of Nafion. A fourfold improvement was obtained with membranes with a GP% of 18.27% as a maximum value. Such promising results nominate the used technique as a one for the improvement of Nafion membrane efficiency. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Overlimiting mass transfer through cation-exchange membranes modified by Nafion film and carbon nanotubes

Eight cation-exchange membranes different in the surface morphology and the degree of hydrophobicity were studied by contact angle, voltammetry and mass transfer rate measurements. One series of membranes was prepared starting from heterogeneous MK-40 membranes, and another, from homogeneous Nafion? 117 membranes. Coating a membrane with a thin film of Nafion resulted in increasing surface hydrophobicity, while the doping of the Nafion surface film with carbon nanotubes (CNT) led to an unexpected decrease in hydrophobicity. It was found however that after 100 h operation of a Nafion? 117 membrane coated with a Nafion film doped with CNT, the contact angle increased from 51 to 81°. This increase in the surface hydrophobicity was accompanied by a significant rise in overlimiting transfer rate, more than 1.5 times, under the same voltage. High correlation between the overlimiting mass transfer rate and the degree of hydrophobicity was observed also in all studied cases: more hydrophobic surface leads to a higher mass transfer rate. The effect is explained by increasing electroconvection occurring as electroosmosis of the second kind: the slip of water over a hydrophobic surface enhances the tangential velocity of electroconvective vortex having its maximum at a distance of several hundreds of nm from the surface.     

多孔有机笼在聚丙烯腈纳米纤维表面固载及其复合质子交换膜

质子交换膜（PEM）是质子交换膜燃料电池的核心部件,需具备选择性地快速传递质子的特性。多孔有机笼具有高比表面积、良好的化学稳定性和高吸水特性以及三维连通的质子传递路径,可提升PEM的质子传导性能。本文将多孔有机笼（CC3）原位固载到聚丙烯腈（PAN）纳米纤维表面,与Nafion复合制备了CC3/PAN-Nafion复合质子交换膜,对其结构和性能进行了研究,结果表明：CC3的固载改变了纤维的微观形貌,增加了纤维直径,使纳米纤维比表面积从9.57m²/g增加到113.6m²/g;将CC3/PAN引入复合膜显著提升了CC3/PAN-Nafion的热稳定性、吸水性、阻醇性以及质子传导性能,其中CC3/PAN-Nafion12在100%RH,80℃时质子传导率可达0.165S/cm,较Nafion膜提升了一倍。     

固体电解质膜对PEMFC电极动力学的影响

研究了不同种类的固体电解质膜对质子交换膜燃料电池性能的影响,采用相同组成的气体扩散电极与制作工艺,分别用Nafion 111、Nafion 112、Nafion 1135、Nafion 115、Dow 800固体电解质膜制成MEA,并组装成单电池,用极化曲线法与交流阻抗法研究了单电池的极化行为与电气特性,并用zsimwin软件模拟了电气特性参数。结果表明,随着固体电解质膜变薄,电池内阻变小,但电池开路电压却反而降低,固体电解质膜的厚度较大(如Nafion 115)或较小(如Nafion 111)都会使电极双电层微分电容变小,使电极电化学反应动力学变差,离子交换容量大的电解质膜电导率大,电极电荷传递阻力较小,反应阻抗小。     

Highly methanol resistant and selective ternary blend membrane composed of sulfonated PVdF‐co‐HFP,sulfonated polyaniline and nafion

Partially sulfonated poly(vinylidene fluoride‐co‐hexafluoro propylene)/partially sulfonated polyaniline (SPVdF‐co‐HFP/SPAni) binary blend membranes have shown promising results in terms of low methanol permeability and high membrane selectivity compared to Nafion‐117 membrane. However, the proton conductivity and IEC of this binary blend membrane was much lower than Nafion‐117. It was found that incorporation of minimal quantity of Nafion within SPVdF‐co‐HFP/SPAni blend membrane at a constituent weight % ratio of SPVdF‐co‐HFP:SPAni:Nafion = 50:40:10 induced significant improvements in ion‐exchange capacity (IEC), proton conductivity and tensile strength over that of the binary blend membrane. In addition, the SPVdF‐co‐HFP/SPAni/Nafion ternary blend membrane exhibited much lower methanol permeability, higher membrane and relative selectivities and comparable IEC to Nafion‐117. In effect, presence of minimal quantity of Nafion induced significant positive attributes to the ternary blend membrane; and assisted in reaching a balance between material cost and properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43294.     

Fabrication and Characteristics of Poly(benzimidazole/fluoro/ether/siloxane/amide)/Sulfonated Polystyrene/Silica Nanoparticle-Based Proton Exchange Membranes Doped With Phosphoric Acid

Novel poly(benzimidazole/fluoro/ether/siloxane/amide) (PBFESA) was developed for the formation of hybrid proton exchange membrane. Afterward, phosphoric acid doped PBFESA/PS-S/SiNPs was prepared with PBFESA, sulfonated polystyrene (PS-S), and 0.1–2 wt% silica nanoparticles (SiNPs). Tensile strength of acid doped PBFESA/PS-S/SiNPs nanocomposites increased from 63.9 to 68.1 MPa with increasing SiNPs loading. They had higher ion exchange capacity (IEC) of 2.3–3.3 mmol/g and proton conductivity of 1.9–2.7 S/cm at 80°C (higher than perfluorinated Nafion 117 membrane 1.1 × 10^?1 S/cm). A H₂/O₂ fuel cell using PBFESA/PS-S/SiNPs 2 (IEC 3.3 mmol/g) showed better performance than Nafion 117 at 40°C (30% RH).     

Partially Sulfonated Poly(vinylidene fluoride) Induced Enhancements of Properties and DMFC Performance of Nafion Electrolyte Membrane

Partially sulfonated poly(vinylidene fluoride) (SPVdF) has been prepared by incorporation of sulfonic acid groups within poly(vinylidene fluoride), using chlorosulfonic acid as the sulfonating agent. The degree of sulfonation (DS) has been varied by modulating the duration of the sulfonation reaction. Blending of SPVdF (having DS = 36.78%) with Nafion at a constituent wt.% ratio of SPVdF:Nafion = 70:30 has resulted in the fabrication of polymer electrolyte membrane with superior properties compared to pristine Nafion‐117 membrane. This particular blend composition exhibited a proton conductivity value of 3.6 × 10⁻² S cm⁻¹ (i.e. ∼12.5% increase over Nafion‐117), a methanol permeability value of 6.81 × 10⁻⁷ cm² s⁻¹ at 6M methanol concentration (i.e. ∼99.31% decrease from Nafion‐117) and a corresponding membrane selectivity value of 5.29 × 10⁴ Ss cm⁻³ (i.e. an increase of approximately two‐orders of magnitude over Nafion‐117) at 20 °C. In addition, this blend composition has also exhibited (a) better heat stability at temperatures as high as 160 °C by virtue of it possessing higher glass transition temperature, (b) higher storage modulus, (c) higher stress relaxation at high angular frequency and (d) superior DMFC performance at high methanol feed concentration in presence of humidified, as well as, non‐humidified air as the catholyte, compared to Nafion‐117 membrane.     

Ion‐exchange membrane based on poly(styrene sulfonic acid‐co‐n‐(2‐hydroxyethyl) acrylamide)

A new ion‐exchange membrane was prepared by blending a copolymer of poly(styrene sulfonic acid‐co‐N‐(2‐hydroxyethyl) acrylamide) with poly(vinylidene fluoride). The dissolution of the copolymer into water was prevented by the crosslinked network formed by condensation reaction between N‐(2‐hydoroxyethyl) acrylamide (HEAA) units. The reaction was caused after film‐forming the blend. Swellability in water, ion‐exchange capacity, ion conductivity, and mechanical properties of the membrane were investigated and compared with those of a well‐known ion‐exchange membrane, Nafion 117. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2788–2796, 2007     

Nafion®—titania nanocomposite proton exchange membranes

Proton exchange membranes consisting of Nafion^® and crystallized titania nanoparticles have been developed to improve water‐retention and proton conductivity at elevated temperature and low relative humidity. The anatase‐type titania nanoparticles were synthesized in situ in Nafion solution through sol–gel process and the size of the formed titiania nanoparticles is in the range of 3–6 nm. The formed nanoparticles are well‐dispersed in Nafion solution at the titania concentration of 5 wt %. The glass transition temperature of the formed Nafion‐titania composite membrane is about 20^oC higher than that of plain Nafion membrane. At elevated temperature (above 100°C), the Nafion‐titania nanocomposite membrane shows higher water uptake ability and improved proton conductivity compared to pure Nafion membrane. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study of adsorption and desorption performance of acid dyes on anion exchange membrane

The adsorption and desorption performances of CI Acid Red 18 and CI Acid Red 88 on an anion exchange membrane were studied. The effects of temperature, time, pH value and inorganic salt on the adsorption were investigated. The results showed that temperature and pH value had nearly no influence on the dye adsorption. The addition of inorganic salt (sodium sulphate) in the dye solution had a definite influence on the adsorption. The adsorption of the two acid dyes was in accordance with the pseudo‐second order dynamics model. The Langmuir adsorption model could describe the adsorption processes well. The membrane was more effective on CI Acid Red 18, which has three sulphonic groups. In the desorption process, different solutions were applied to investigate the desorption performance of the two acid dyes. The desorption percentage could reach ca. 90% using a mixture of ethanol, sodium chloride and water as the desorption solution. The anion exchange membrane could be reused.     

乙烷质子交换膜燃料电池的研究

研究了以乙烷作为燃料、全氟磺酸高分子膜(Nafion膜)作为质子交换膜、Pt或Pt-Ru作为电极催化剂主要组分、并通过掺杂Nafion膜作为电极内的离子导体构成的燃料电池电化学性能.研究了两种电极催化剂:Pt与Pt-Ru复合催化剂的制备及构成的单电池在不同温度及运行时间下的电化学性能.温度增加,电池性能变好;运行时间增加,电池性能下降,在相同的温度与运行时间下,Pt-Ru复合催化剂构成的电池比Pt催化剂构成的电池极化小.通过分析电极反应产物,探讨了乙烷电极及电池的反应机理.结构为C2H6,( Pt-Ru+膜材料复合阳极)/Nafion膜/(Pt+膜材料复合阴极),O2 的质子交换膜燃料电池,在150℃时,电池的最大输出电流和功率密度分别高达70 mA·cm-2和22 mW·cm-2.