The last advances on the application of INCA (Ionomer Nc Analysis) methodology for a better understanding of perfluorinated ionomers are reported and discussed. It was found that INCA is a very suitable technique for the determination of the melting temperature (Tm) of un-crystallized and semi-crystalline perfluorinated ionomers. Furthermore, for these determinations, it is even more precise than dynamic mechanical analysis, a method essentially developed for polymers in which the water-uptake is negligible. Of interest, it is the information that INCA methodology gives on the phenomenon of the water-uptake memory of perfluorinated ionomers.

The possibility of increasing the working temperature of fuel cells using Nafion as ionomer membranes by a new annealing procedure in the presence of dimethylsulfoxide or tributylphosphate as annealing agents has been investigated. The extent of annealing was derived by the shift of nc/T plots of annealed membranes (nc is the index of counter-elastic force) relatively to the plot of as received membranes. nc/T plots can be used as a powerful analytical method useful for deriving quantitative information on the annealing extent and for obtaining information on the melting temperature of the semi-crystalline phase grown during annealing. It was found that, by using an annealing temperature of 140 degrees C in the presence of an annealing agent, an important effect on the thermal stability of Nafion membranes was obtained. The increased thermal stability was related to the increase of the original semi-crystalline phase which acts as a physical cross-linker so that the mechanical properties are no longer lost at the glass transition temperature but at the melting point of the semi-crystalline phase. The use of nc/T plots as analytical tools for detecting and understanding important ionomer properties was denominated as Ionomer nc Analysis (INCA).

In order to increase the stability of Nafion conductivity at temperatures higher than 100°C, composite membranes made of recast Nafion filled with different percentages of zirconium phosphate (ZrP) were investigated. The membrane preparation was carried out by a simple synthetic procedure based on the use of solutions of ZrP precursors in dimethylformamide. The formation of insoluble α-type ZrP nanoparticles within the Nafion matrix was proved by 31P-MAS NMR and X-ray diffractometry. The membranes were characterized by TEM microscopy, ion-exchange capacity determinations, static stress–strain mechanical tests and conductivity measurements as a function of filler loading, at controlled relative humidity (r.h.) and temperature. An increasing filler loading results in enhanced membrane stiffness and in lower conductivity compared with pure recast Nafion. At 90% r.h. and 100°C, the conductivity decreases from ≈0.07Scm−1 for pure Nafion to ≈0.03Scm−1 for the composite membrane containing 25wt.% ZrP. Systematic conductivity measurements as a function of r.h. and temperature were carried out to draw a stability map for the conductivity of pure recast Nafion and of a composite membrane filled with 10wt.% ZrP. These maps provide for each r.h. value the maximum temperature at which the conductivity remains stable for at least 150h. The effect of zirconium phosphate is to increase the stability of conductivity at high temperature, with a gain up to 20°C. This stability enhancement has been ascribed to the higher stiffness of the composite membrane.

Zirconium phosphate sulfophenylenphosphonates of general formula Zr(HPO4)2−x(SPP)x·nH2O, with SPP = O3PC6H4SO3H and x in the range 0.4–1.35, were precipitated from solutions containing H3PO4, H2SPP and ZrF62−. The SPP/HPO4 ratio in the solids is equal to the H2SPP/H3PO4 ratio in the starting solutions for x ≤ 1 and lower for x > 1. The results coming from 31P MAS NMR, X-ray powder diffraction, FTIR-PAS spectroscopy and density measurements, as well as from the intercalation of α,ω-alkyl diamines in Zr(HPO4)1.00(SPP)1.00, suggest that the solids have a layered structure built up by the packing of symmetric α-layers where SPP and HPO4 groups are uniformly distributed on both layer faces. Proton conductivity, at 100 °C and 70% relative humidity, increases with x and reaches a maximum of 0.04 S cm− 1 for x = 1.35. The conductivity of Zr(HPO4)0.65(SPP)1.35·nH2O was determined as a function of the water content at 100 °C and compared with that of Nafion 117 and of a sulfonated polyetherketone.

Gels of amorphous and α-layered Zr(HPO4)1.0(O3PC6H4SO3H)1.0, hereafter Zr(SPP), in DMF were used to prepare composite proton conducting membranes based on polyvinylidene fluoride (PVDF) with Zr(SPP) loading from 5 to 25 wt.%. The membranes prepared with α-Zr(SPP) are less compact and homogeneous than those obtained with the amorphous filler. In the latter membranes, the size of the filler particles, determined by TEM microscopy, is in the range of 10–20 nm. Proton conductivity and water content of the membranes made of amorphous Zr(SPP) were determined as a function of temperature from 80 to 130 °C, at 90% RH, and as a function of RH, at 100 °C. In all cases the conductivity is nearly constant up to 120 °C and decreases irreversibly at higher temperatures. With increasing filler loading up to 25 wt.%, the conductivity increases by a factor of 30 and reaches 2·10−3 S/cm, at 120 °C and 90% RH; under these conditions, the H2O/SO3H molar ratio is 8.5. Moreover, in the RH range 60–90%, H2O/SO3H increases with RH from 5 to 8.5, while the conductivity rises by an order of magnitude independent of filler loading. The membrane linear swelling in water at 80 °C was also investigated and discussed on the basis of the filler hydration.

A composite of gamma -zirconium phosphate (gamma -ZrP) and silica (40% in weight of gamma -ZrP) was prepared by hydrolysis of tetraethylsilicate in the presence of exfoliated gamma -ZrP. The exfoliation of gamma -ZrP was obtained in 1:1 (v/v) acetone/water solution at 80 degreesC. The presence of silica prevented the re-aggregation of the exfoliated gamma -ZrP lamellae. After heating at 650 degreesC, the greater part of gamma -ZrP was present in the composite as bilamellar packets of zirconium phosphate acid pyrophosphate while about 20% was transformed into alpha -Zr(O3POH)(2). The surface acid P-OH groups of these lamellar species (about 1. 1 meq. g(-1)) were not destroyed by thermal treatment up to 750 degreesC. The composite exhibited a specific surface area of 421 m(2) g(-1) of which about 191 m(2) g(-1) was attributable to exfoliated lamellae of zirconium phosphate.The catalytic properties of the composite were preliminarily investigated for the conversion of ethylbenzene to styrene at different temperatures and different EB/O(air) ratios as a function of the contact time. The results are compared with pure gamma -ZrP calcined at 650 degreesC. Catalytic activity was strongly influenced by the total amount of the surface acidic groups of the samples. The gamma -ZrP/SiO2 composite showed a higher conversion rate (about five times) than calcined gamma -ZrP. (C) 2001 Elsevier Science B.V. All rights reserved.

Titanium phosphate sulfophenylphosphonate, Ti(HPO4)1.00(O3PC6H4SO3H)0.85(OH)0.30·nH2O was synthesised and characterized by X-ray diffraction, solid state NMR, impedance measurements, TG and DSC analysis. The MAS-NMR spectrum of 31P nucleus presents two resonances characteristic of monohydrogen phosphate and sulfophenylphosphonate groups coordinated to three Ti(IV) atoms through three non-protonated oxygen atoms. Water content, protonic conductivity (σ) and activation energy for conduction (Ea) were determined in the range 20 to −20°C for materials equilibrated at relative humidity (r.h.) in the range 5–90%. By increasing the number of water molecules per sulfonic group from 2 to 14, σ rises by 3 orders of magnitude up to about 0.1 S cm−1, while Ea decreases from 12.6 to 4.3 kcal/mol. Measurements were also carried out at 100°C as a function of relative humidity in the range 30–100%; σ values higher than 0.1 S cm−1 were found at r.h. ≥65%. The titanium phosphonate was used as a filler of Nafion 1100 hybrid membranes. At 100°C and 80% r.h., the conductivity of the hybrid membranes containing from 5% to 20% phosphonate loading is very similar to that of a Nafion 1100 membrane prepared in-house by casting technique, but it drops by an order of magnitude when the loading is increased to 30%.

A good exfoliation of layered gamma-zirconium phosphate in aqueous medium at room temperature has been obtained by intercalation of short alkylamines such as methyl-, dimethyl- and ethyl-amine. No appreciable exfoliation was observed when butylamine or longer alkylamines were intercalated, while intermediate behavior was obtained with the intercalation of propylamine. Since a good exfoliation of this layered compound is an essential step for its functionalization by topochemical reactions with phosphonic or phosphinic acids, the amine intercalation compounds and the various steps of the intercalation processes were investigated in order to obtain information on the mechanism of the exfoliation and a model of this mechanism is proposed. The use of the colloidal dispersion of exfoliated lamellae for the preparation of auto-consistent and flexible membranes as well as thin supported films of gamma-zirconium phosphate is described.

A pillared crown ether derivative of gamma-zirconium phosphate containing 4,4'-bis(dihydroxyphosphoryl)dibenzo-18-crown-6 groups covalently bound to inorganic layers has been prepared by a topotactic reaction in 1:1 water-acetone mixture at 80 degrees C. It was found that the original gamma-zirconium phosphate was already completely converted into a pillared phase (interlayer distance 1.9 nm) when similar to 15% of the interlayer dihydrogen phosphate groups were replaced with 4,4'-bis(dihydroxyphosphoryl)dibenzo-18-crown-6. The interlayer distance of this phase was found to increase progressively up to 2.1 nm with the gradual increase of the replacement to 50%. For higher replacement, a discontinuous transition of this latter phase to a new one(interlayer distance 2.6 nm) was finally observed. Some preliminary computer structural models of the crown ether conformations in the interlayer regions of these pillared phases were derived.

A pillared α-zirconium phosphite-diphosphonate with interlayer porosity has been obtained by means of a new synthetic strategy. It is based on the use of mixtures of phosphorous and diphosphonic acid having a cross-section greater than the free area associated with each -POH group in the α-zirconium phosphate layer (0.24 nm2). Under these conditions, the six adjacent sites of each diphosphonic group acting as a pillar cannot be occupied, for steric reasons, by other diphosphonic groups. These sites can, however, be occupied by the small phosphite groups, and a pillared compound is thus formed in which there are six small phosphites around each pillar. If the cross-section of the pillar is not uniform, and if its central cross-section is smaller than the terminal parts (i.e. a pillar with bases), interlayer porosity may be created. A suitable diphosphonic acid, 4,4′-(3,3′,5,5′-tetramethyl)biphenyl diphosphonic acid, was synthesised and a compound of composition Zr(HPO3)1.2(O3P-R-PO3)0.4 (R = 3,3′,5,5′-tetramethylbiphenyl) obtained. The specific surface area was 405 m2/g with negligible mesoporosity, while the micropore volume was 0.16 cm3/g with a micropore distribution around 0.5 nm. A structural model of this covalently pillared layered solid is reported and discussed.

The topotactic reaction of gamma-ZrPO(4)[O(2)P(OH)(2)].2H(2)O (gamma-ZrP) with benzenediphosphonic acid was examined in water and in acetone-water mixtures. This reaction was found to take place in water only on the external surface of the microcrystals, and pillared compounds were never obtained, even after very long reaction times. On the contrary, covalently pillared compounds were quickly obtained in acetone-water mixtures. The mechanism of the latter topotactic reaction was investigated by determining the rate of the phosphate groups released and the rate of the benzenediphosphonates taken up by gamma-ZrP over a long time (50 days). These data showed that pillared derivatives of gamma-ZrP can be obtained because colloidal dispersions of exfoliated lamellae are formed in acetone-water mixtures. The diphosphonate group acts initially as a monovalent species, replacing only one dihydrogen phosphate group on the surface of the exfoliated gamma-lamellae. The colloidal and partially derivatized lamellae thus formed can interact with each other by forming polylamellar pillared systems. When the number of pillared lamellae exceeds a given value (usually 5-6), flocculation of the colloidal gamma-ZrP takes place. Topotactic reactions between packets of pillared lamellae may also continue in the flocculated system. Therefore, the average number of the pillared lamellae slowly increases over time.

A series of α-pillared zirconium phosphite-diphosphonates of general formula Zr(O3PH)x(O3P-C6 H4-PO3)y was prepared in water, dimethylsulfoxide-water andn -propanol-water, by changing the ratios and the concentrations of the reagents. Pure mesoporous solids with a large surface area (230 to 400 m2 g-2) and a great pore volume (0.3 to 0.7 cm3 g-2) were obtained. These materials showed a narrow distribution of pores that was tuneable over the range 4–14 nm diameter by simply varying the conditions of preparation, especially the concentration of the reagents. The formation of interparticle mesoporosity has been attributed to edge-edge interactions between rigid packets of a few pillared α-layers giving rise to stable aggregates with a house of cards structure.

The preparation and properties of layered metal phosphates and phosphonates can be understood on the basis of octahedra-tetrahedra building block chemistry. A large variety of engineered solids for specific applications can be obtained, ranging from ion-exchange, intercalation of polar molecules and catalysis on pillared compounds with functionalised micro- and meso-cavities to materials with high protonic conduction and non-linear optic properties. Important recent developments are the etherogeination of crown ethers, formation of interpillar cavities with variable volume and the coordination chemistry of transition metal ions entrapped on layered surfaces.

After a brief illustration of the structures of three-layered zirconium phosphates, some general concepts on the influence of the structural characteristics on the distribution of the pillars, as well as some general strategies used to obtain microporous pillared compounds, are discussed. The synthesis of covalently pillared α-zirconium phosphite diphosphonates is first described and the use of pillars with bases for the creation of microporosity in the interlayer region is reported. The structure of a microporous compound in which the pillar with bases 3,3',5,5'-tetramethyl-biphenyldiphosphonate was used (interlayer microporosity 405 m 2 g -2 , micropore volume 0.16 cm 3 g -2 , pore size 0.5 nm), is described. The controversial results reported in the literature for microporous compounds of α-zirconium phosphate pillared with inorganic polyoxycations are also discussed. Particular emphasisis is then given to recent results on the preparation of microporous compounds by topotactic pillaring of γ-zirconium phosphate with organic radicals. The preparation and structure of the compound pillared with ≈25% of biphenyldiphosphonate groups is illustrated. A large specific surface area (≈320 m 2 g -2 ), a great micropore volume (0.12 cm 3 g -2 ) and a narrow micropore distribution with an average diameter of 0.58 nm, was obtained. The topotactic pillaring of γ-zirconium phosphate with nonrigid pillars and with crown ethers, as well as the encouraging prospects for the preparation of microporous and thermally stable compounds from γ-ZrP pillared with polyoxycations, are then examined. Finally, the possibility of preparing microporous solids by pillaring the recently discovered ZrPO 4 Cl(dmso) with dicarboxilates, is reported.

Some organic derivatives of layered α- and γ-zirconium phosphates bear ionogenic groups and accordingly, they are inorgano-organic ion-exchangers. Because of the presence of organic groups in the interlayer region, particular selectivities for some radionuclides may be expected; however, their use in nuclear reprocessing or treatment of radioactive wastes can be permitted only if their stability to ionising radiation is also sufficiently good. A preliminary investigation was carried out on the resistance to massive doses of ionising radiation of two typical inorgano-organic derivatives with a layered structure of α-type, namely Zr[HOOC(CH2)2PO3]2 and Zr(C6H5PO3)2. The resistance of the original phosphonic acids used for the synthesis of the above compounds was also examined. The first compound was easily degraded while the second one was sufficiently stable even at doses of 3 × 106 Gy. This fact is promising for the potential use of some inorgano-organic ion-exchangers in the nuclear industry and further research on their stability towards ionising radiation is therefore of interest.

The intercalation of crystal violet (CV+) into the ethanol form of a-zirconium phosphate has been investigated. X-ray powder diffraction patterns of samples with increasing dye loading showed that a pure phase (interlayer distance 2.2 nm) was obtained at a dye loading of 22% of the maximum ion-exchange capacity. Computer models and calculations based on dye dimensions and the structure of the host showed that this phase possesses dye loading and an interlayer distance very near to the maximum values, i.e., about 25% and 2.14 nm, respectively, that can be obtained if the crystal violet is intercalated as a monolayer of dye cations placed perpendicular to the inorganic layers of the host. The decrease of the interlayer distance to 1.8 nm with drying was attributed to a change on the inclination of dye molecules inside the interlayer space after the solvent is eliminated. The absorption spectra measured by diffuse reflectance spectroscopy showed maxima around 430 and 640 nm due to the protonation of the dye by the acidic P-OH groups of alpha-zirconium phosphate, exhibiting pK values in the range from similar to 0 (430 nm) to similar to 1 (640 nm). The dye-dye interaction in the perpendicular orientation caused absorption around 510 nm assigned to stacked (CV+)(n) layers.

The rates of the topotactic reactions between gamma-zirconium phosphate and phenylphosphonic acid in water and water-acetone mixtures at various temperatures were investigated. The slow rates of the process in aqueous medium or in water-acetone mixtures at temperatures lower than 50 degrees C were attributed to a slow interdiffusion of O(2)P(OH)(2)(-) and O(2)P(OH)(C(6)H(5))(-) groups in the interlayer region of gamma-ZrP. Similar to ion-exchange processes, the replacement begins in the external part of the interlayer region and progresses toward the central region with the formation of an advancing phase boundary. In water-acetone mixtures at temperatures higher than 60 degrees C an exfoliation of gamma-ZrP was found. Thus, the initial process is very fast since the substitution can take place directly on the surface of the exfoliated gamma-lamellae. However, after a certain degree of substitution, a flocculation of the colloidal dispersion, which slows down the rate of the further topotactic substitution, was observed. Some considerations on the topotactic substitution occurring on the surface of the exfoliated lamellae and on the mechanism of the diffusion of the exchanging species in the interlayer region are also reported.

NiO electrodes, prepared by pressing NiO and α-zirconium phosphate powders (1:1 or 1:2 in weight) were anodically doped with Ni(III). The use of these electrodes as solid references of gas sensors based on solid state protonic conductors has been investigated. A very low drift of potential (≤0.1 mV per day) and an exchange current density of the order of about 2 μA/cm2 were found. Because of the good stability of its potential and the relatively high exchange current density, this kind of electrode can be suitably used as both reference and as counter-reference electrode in potentiometric and amperometric sensors, respectively.