Monica Pica

Preparation and proton conductivity of composite ionomeric membranes obtained from gels of amorphous zirconium phosphate sulfophenylenphosphonates in organic solvents

Amorphous zirconium phosphate sulfophenylenphosphonates (Zr(HPO4)2−x(SPP)x, where SPP = O3PC6H4SO3H and 0.5 ≤ x ≤ 1.3) were precipitated from solutions of zirconyl chloride, H3PO4 and H2SPP and characterised by thermogravimetric analysis, solid state NMR and impedance measurements. Zr(HPO4)0.7(SPP)1.3 showed the highest proton conductivity (0.07 S cm−1 at 20 °C, 90% relative humidity) and turned out to be suitable to form a gel in dimethylformamide (DMF) containing about 7 wt% solid phase. The gel was used to prepare composite membranes of sulfonated polyetherketone (I. E. C. = 0.95 meq g−1) filled with 10 and 20 wt% Zr(HPO4)0.7(SPP)1.3. SEM pictures showed that the composite membranes are dense and homogeneous with filler particles not larger than 200 nm. The proton conductivity of both composite membranes and that of a pure s-PEK membrane was determined as a function of temperature up to 150 °C, at 90% relative humidity, by means of the impedance technique. While the conductivity of the s-PEK membrane was nearly constant within the overall temperature range (7–9 × 10−4 S cm−1), the conductivity of the composite membranes was independent of temperature up to 110 °C but at higher temperatures it decreased to a value approaching the conductivity of s-PEK. In the range 80–110 °C, the conductivity of the composite membrane with 20 wt% Zr(HPO4)0.7(SPP)1.3 was around 8 × 10−3 S cm−1. The possibility that the increase of conductivity arises from the presence of filler rich and/or filler continuous conduction pathways is discussed.

Gels of zirconium phosphate in organic solvents and their use for the preparation of polymeric nanocomposites

Gels of α-zirconium phosphate (α-ZrP) in water have been prepared by exfoliation of crystalline α-ZrP induced by intercalation–deintercalation of propylamine. Although these gels are X-ray amorphous, their Raman spectra indicate that the α-type layers of the starting material remain essentially unaltered. Replacement of gel water with water miscible organic solvents has allowed the formation of α-ZrP gels in a great variety of solvents, such as alkanols, N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP), acetone, tetrahydrofuran (THF) and even chloroform. Particular attention has been devoted to α-ZrP gels in DMF. On the basis of the surface area of the dry gels, the average thickness of the particles of exfoliated α-ZrP has been estimated between 25 and 80 nm for α-ZrP percentages in the starting gels between 2.5 and 10 wt%, respectively, in agreement with SEM images. α-ZrP gels in THF have been used for the preparation of polystyrene/α-ZrP nanocomposites with filler loadings up to 8 wt%. The presence of exfoliated α-ZrP delays the beginning of thermal decomposition of the polymer by a maximum of 45 °C for 4 wt% filler loading. The state of filler exfoliation has been confirmed by transmission electron microscopy.

Advances in the Chemistry of Nanosized Zirconium Phosphates: A New Mild and Quick Route to the Synthesis of Nanocrystals

Simple addition of zirconyl propionate to phosphoric acid in alcoholic media surprisingly led to the formation, in few minutes, of transparent gels containing solvent intercalated zirconium phosphate (ZrP) nanoparticles with hexagonal shape and a planar size of about 40 nm. With the help of elemental analysis, inductively coupled plasma-optical emission spectrometry (ICP-OES), and (31)P magic angle spinning (MAS) NMR, the nanoparticle composition was formulated as Zr(R)(w)(HPO(4))(x)(H(2)PO(4))(y), in which R can be an hydroxyl or a propionate group. The stoichiometric coefficients for propanol intercalated ZrP are x = 1.43, y = 0.83, and w = 0.32. Solvent elimination at 60 °C gave rise to an increase in the x value and a decrease in the y and w values. X-ray powder diffraction analysis and transmission electron microscopy (TEM) observations showed a concomitant increase in the particle size: planar size and thickness ranged from 90 to 200 nm and from 20 to 85 nm, respectively, depending on the nature of the solvent. A possible mechanism explaining the change in the x, y, and w values, the growth of nanoparticles, and the role of the solvent is proposed. Finally, the possibility of using these gels to disperse the ZrP nanoparticles within the polymer matrix of Nafion117 is shown.

Organically Modified Zirconium Phosphate by Reaction with 1,2-Epoxydodecane as Host Material for Polymer Intercalation: Synthesis and Physicochemical Characterization

Organically modified alpha-layered zirconium phosphate samples (ZrP(C(12))(x)) containing dodecyl groups bonded to the alpha-layers through P-O-C bonds have been prepared by reaction of 1,2-epoxydodecane solutions in tetrahydrofuran (THF) with gels of partially exfoliated zirconium phosphate in THF. Two dimensional correlation solid state NMR experiments for (1)H-(13)C and (1)H-(31)P nuclei have been used to prove the formation of P-O-C bonds arising from nucleophilic attack of POH mainly to carbon 1 and, to a lesser extent, to carbon 2 of epoxydodecane. ZrP(C(12))(x) samples with x in the range from approximately 0.5 to approximately 2.0 are thermally stable up to at least 200 degrees C, and their interlayer distance increases continuously with x from approximately 20 to approximately 35 A. On the basis of structural considerations, it has been suggested that samples with low x values could intercalate aliphatic polymers. Accordingly, preliminary results have shown that molten polyethylene is intercalated in ZrP(C(12))(0.49) and ZrP(C(12))(0.73). These materials can therefore be regarded as filler candidates for polymer matrixes.

Preparation of Nano-Structured Polymeric Proton Conducting Membranes for Use in Fuel Cells

Abstract: We briefly discuss the state of the art of polymer electrolyte membrane fuel cells and suggest that the main obstacles to the commercial development of these fuel cells are essentially the high costs and poor characteristics of present proton conducting membranes. A strategy for the preparation of improved nanocomposite membranes based on the introduction of proton conducting lamell? in the polymeric matrix of present ionomeric membranes is then discussed. Due to their high proton conductivity (in some cases even higher than 10−1 S cm−1), tailor made lamellæ obtained by exfoliation of superacid metal (IV) phosphonates are particularly suitable for the preparation of these hybrid membranes. The expected positive influence of the dispersed lamellæ on important properties of proton conducting membranes, such as swelling, mechanical resistance, proton transport, and diffusion of methanol, are also discussed. The methods used to obtain good lamellar dispersions into ionomeric polymers and the preparation and main characteristics of some hybrid membranes are also briefly described. The presence of nanoparticles of metal phosphonates in the electrodic interfaces Nafion/Pt already considerably improves the electrochemical characteristics of fuel cells in the temperature range 80–130°C. The increased working temperature of the fuel cell considerably reduces CO poisoning of the platinum electrodes and allows better control of the cooling system, thus overcoming important obstacles to the development of medium temperature PEM fuel cells.

Short side chain perfluorosulfonic acid membranes and their composites with nanosized zirconium phosphate: hydration, mechanical properties and proton conductivity

Aqueous dispersions of a short side chain perfluorosulfonic acid ionomer (equivalent weight 830 g eq.−1) and gels of nanosized zirconium phosphate (ZrP) in propanol are used for the preparation, by solution casting, of composite membranes with ZrP loading up to 13 wt%. These membranes, together with reference neat ionomer membranes, are characterized by mechanical stress–strain tests and in-plane conductivity determinations under different conditions of temperature and relative humidity (RH). The membrane hydration is also determined under the environmental conditions of mechanical and conductivity measurements. The conductivity of the neat ionomer membrane, at 90 and 120 °C, is weakly dependent on temperature but strongly influenced by changes in RH going from values around 0.02 S cm−1 at 25% RH to values around 0.25 S cm−1 at 90% RH. The conductivity of the composite membranes decreases with increasing filler content being however in the range of 0.01–0.02 S cm−1 at 25% RH and in the range of 0.16–0.23 S cm−1 at 90% RH at both temperatures. On the other hand the presence of the filler results in a significant increase in the Youngs modulus (up to 80%) and in the yield stress (up to 124%) not only under ambient conditions but also at 80 °C and 80% RH.

Looking for New Hybrid Polymer Fillers: Synthesis of Nanosized α-Type Zr(IV) Organophosphonates through an Unconventional Topotactic Anion Exchange Reaction

Gels of α-type zirconium(IV) phosphate alkylphosphonates, ZP(Cn)x, were prepared by reacting, at room temperature, propanol intercalated nanosized α-zirconium phosphate (α-ZrP) with propanol solutions of alkylphosphonic acids (H2Cn, n = number of carbon atoms in the alkyl chain = 4, 5, 6), with (H2Cn/Zr) molar ratios in the range 0.4-4.0. (31)P MAS NMR showed the presence of resonances due to the phosphate and phosphonate groups bonded to the Zr atoms mainly by three oxygen atoms, as in the α-type layer. The composition of the ZP(Cn)x materials, obtained by thermogravimetric analysis, ranges from x ≈ 0.2 to x ≈ 1.1. On the basis of the NMR data and of the analysis of the X-ray patterns of gels and powders, it is inferred that the ZP(Cn)x compounds have an α-type layered structure and that the reaction between α-ZrP and H2Cn is a topotactic anion exchange process. The evolution of the X-ray patterns during propanol deintercalation is consistent with a random distribution of the alkylphosphonate groups on the α-type layers which gives rise to porous pathways in the interlayer region. To test the possibility of using ZP(Cn)x as mechanical reinforcement of a polymer matrix, a starch membrane filled with 5 wt % ZP(C6)0.54 was prepared and characterized by stress-strain mechanical tests. Besides an excellent flexibility, this membrane exhibited a proportional increase of the Youngs modulus by 230% in comparison with neat starch.

Nanosized zirconium phosphate/AgCl composite materials: a new synergy for efficient photocatalytic degradation of organic dye pollutants

A new class of AgCl-based composite photocatalysts has been quickly and easily obtained by using nanosized silver(I) exchanged α-zirconium phosphate as a precipitating agent. Different ZP/xAgCl composite catalysts, having AgCl/ZP molar ratio (x) = 0.28, 0.56, and 1.16, were prepared and characterized by X-ray diffraction analysis, scanning electron microscopy/energy dispersive X-ray spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The photocatalytic properties of the ZP/xAgCl composites, having particle size ≤1 μm, were investigated in the degradation of Rhodamine B, and compared with those of an AgCl sample, with particle size ranging from 0.5 to 2 μm. The ZP/1.16AgCl turned out to be the best photocatalyst, providing a complete chromophore structure cleavage in 15 minutes; differently, in the presence of the pure AgCl sample, the concentration of the chromophore species after 30 minutes was about half of the initial one. Moreover, the catalytic activity of ZP/1.16AgCl was evaluated for three consecutive catalytic tests, and an almost complete chromophore structure cleavage was achieved in 10 minutes during the third run.

Design and synthesis of plasticizing fillers based on zirconium phosphonates for glycerol-free composite starch films

Novel starch-based composite films were prepared by solution casting from gelatinized starch, using a new class of layered zirconium hydroxyalkyl aminophosphonates, ZrF(O3PCH2)2NH(CH2)nOH (n = 3, 4, 5), as fillers/plasticizers. These compounds were specifically designed and synthesized for this application in order to support organic polar groups, able to interact with the polymer, on robust inorganic layers. Their structures were solved ab initio from powder X-ray diffraction data. The films, loaded with 2 wt% of fillers, were studied by means of various techniques such as X-ray diffraction, scanning and transmission electron microscopy, thermogravimetry, and stress–strain tests. The obtained results highlighted the double role played by the fillers as a reinforcement for the polymer matrix and as plasticizing agents: the composites showed improved thermal and mechanical properties, along with a significant reduction of volume swelling, if compared with the glycerol-plasticized films.

Polyvinylidene fluoride/zirconium phosphate sulfophenylphosphonate nanocomposite films : microstructure and mechanical properties

Nanocomposite films made of polyvinylidene fluoride (PVDF) filled with layered zirconium phosphate sulfophenylphosphonate (ZrSPP), with filler loadings up to 20 wt%, were prepared by casting solutions containing the polymer and a ZrSPP precursor. The films were characterised by solid state 31P MAS NMR, X-ray diffraction, DSC determination, Raman spectroscopy and static stress–strain mechanical tests. The presence of the filler has two main effects on the polymer structure: (i) the fraction of crystalline polymer decreases with increasing filler loading; (ii) while the trans–trans–trans–gauche (T3G) chain conformation is predominant in neat PVDF, the composite films mainly contain TnG sequences with n appreciably larger than 3. The elastic modulus and the yield stress of all composites are higher than those of neat PVDF: in both cases a maximum is observed for 1–3 wt% ZrSPP followed by an almost linear decrease for higher loadings. The evolution of the elastic modulus of the composites is discussed on the basis of the changes in the polymer conformation and in the polymer crystalline fraction induced by the filler.