Α-zirconium Hydrogen Phosphate Research Articles

Hybrid Membranes Based on Zirconium Phosphonates

Phosphonates with the composition Zr(PO3(CH2)nPh)2 with n = 0, 1, and 3 are synthesized. Hybrid membranes based on an MF-4SK membrane and the synthesized phosphonates are made. The influence of the dopant, its concentration, and synthesis method on the ion-conducting properties of the membranes is studied in comparison with hybrid membranes based on α-zirconium hydrogen phosphate. The reasons for the effect of the dopant on the conducting properties are discussed.

Synthesis of benzimidazoles by two methods (C–H functionalization and condensation reaction) catalyzed by α-zirconium hydrogen phosphate-based nanocatalyst

In this report, two heterogeneous nanocatalysts based on α-zirconium hydrogen phosphate were applied. These heterogeneous catalysts have demonstrated the promising catalytic activity for the synthesis of 2-substituted benzimidazoles in two different methods. One of these reactions is the functionalization of the C–H bond and the formation of C–N bond, and the other reaction involves the condensation reaction between aldehydes and 1,2-phenylenediamine. The activity of both catalysts was compared in two methods, and the superior catalyst was introduced. The prepared catalysts are easily separated from the reaction mixture by centrifugation and reused several times without significant loss of activity.

First-principles calculations on structure and electronic properties of α-zirconium hydrogen phosphate

AbstractLayered zirconium hydrogen phosphate intercalation compounds can be easily tuned, leading to potential applications in many fields, specifically by introducing them in different polymeric composites as nanofillers. Employing first-principles density functional theory based calculations, we have investigated ground state electronic structure properties of α-zirconium hydrogen phosphate (α-ZrP). We discuss the structure and electronic band structure, where projected density of states calculations have been discussed to understand the different atomic orbitals contributions to electronic bands. ZrP has numerous properties of interest for use in many semiconductor device structures, specifically, layered zirconium hydrogen phosphate has substantial promise for both optical devices and for high power electronics due to its large direct band gap. Our structural calculations suggest that layered zirconium hydrogen phosphate exhibits monoclinic structure. The calculated structural parameters and band gap are in good agreement with available experimental data.

Fabrication and characterization of biocompatible nacre-like structures from α-zirconium hydrogen phosphate hydrate and chitosan

Composite materials with an ordered layered structure resembling that of nacre were fabricated by layer-by-layer assembly making use of presynthesized α-zirconium hydrogenphosphate hydrate (ZrP) platelets and chitosan. These two biocompatible materials were chosen in view of possible applications in the biomedical field, e.g., as bone or joint replacement implants. The effect of different concentrations of the inorganic ZrP platelets and the organic components (chitosan) on the composite assembly and structure was investigated. A high concentration of chitosan (0.1wt.%) resulted in a misalignment of the inorganic platelets, while at very low concentrations (0.001wt.%), the substrate was not fully covered by the polymer, again leading to misalignment. Also, the concentration of the α-ZrP platelets affected the composite assembly and structure. The number of dipping cycles was varied between 70 and 220, yielding a maximum thickness of approximately 6μm. The pH value of the chitosan solution was also varied to investigate its influence on the composite assembly. The mechanical properties of the composites were tested with a nanoindenter. For samples prepared with the same number of dipping cycles, higher values of Young’s modulus and hardness were obtained with improved alignment of the platelets in the samples. For samples prepared with 220 dipping cycles, a Young’s modulus of 2.6GPa and a hardness of 70MPa were observed. Important general relationships are recognized between the preparation parameters, the degree of order within the nacre-like films and the resulting mechanical properties.

New zirconium hydrogen phosphate alkyl and/or aryl phosphonates with high surface area as heterogeneous Brønsted acid catalysts for aza-Diels–Alder reaction in aqueous medium

New zirconium hydrogen phosphate alkyl and/or aryl phosphonates of general formula Zr(PO 3OH) 2−( x + y )(PO 3R) x (PO 3R 1) y have been prepared as amorphous solids. The presence of hydrophobic groups such as Me, Ph and Pr and their percentage have an important role in the definition of the corresponding solid structure. All the prepared solids are micro- and mesoporous and show an extraordinary surface area (200–380 m 2/g). The Brønsted acid catalytic activity of the solids was tested on the direct aza-Diels–Alder reaction of 2-cyclohexen-1-one with N-PMP- pCl-benzaldimine in aqueous medium. The hydrophobic groups on the solid catalyst surface favor reagents’ diffusion toward the acidic sites, aiding proton transfer to reagents, increasing the catalytic activity of the prepared solids compared with the layered α-zirconium hydrogen phosphate (α-ZrP).

Aza-Diels–Alder reaction of Danishefsky's diene with immines catalyzed by porous α-zirconium hydrogen phosphate and SDS under solvent-free conditions

The aza-Diels–Alder reaction between benzaldimines 1 and Danishefsky's diene in solvent-free conditions is reported for the first time. The reaction occurs rapidly at 30 °C and is catalyzed by porous α-zirconium hydrogen phosphate (p-αZrP) in the presence of sodium dodecyl sulfate (SDS). The yields were excellent. The recycling of the catalyst has also been investigated.

Nafion/Zirconium Phosphate Composite Membranes for PEMFC Operating at up to 120 ° C and down to 13 % RH

Nafion/zirconium phosphate (ZP) composite membranes of different structures containing in situ precipitated ZP, crystalline layer-structured α-zirconium hydrogen phosphate , and three-dimensional-network zirconium hydrogen phosphate were synthesized. The ZP materials used have different structure and surface properties (specific surface area, zeta potential, and particle morphology). The composite membranes were studied in an proton exchange membrane fuel cell (PEMFC) over a range of relative humidity (RH) from 13 to 50% at temperatures of 80 and . At the operating temperature of , all studied composite membranes demonstrated significant improvement in performance under dehydrating conditions compared to unmodified Nafion membranes. Among the tested membranes, the Nafion/α-ZPL composite membrane demonstrated the highest performance at at all RH values, especially at 13% RH. At 26 and 50% RH, the performance of Nafion/α-ZPL and Nafion/19% ZP in situ membranes were close, and the performance of the Nafion/ZPTD membrane was the lowest. The effects of filled polymer pore constriction, scaffold formation, membrane structure, and surface properties of the ZP particles on the membrane performance in PEMFCs are discussed in the paper.

Intercalation of aminonaphthalenes into α-zirconium hydrogenphosphate

Intercalates of 1- and 2-aminonaphthalene (1-AN and 2-AN), 1,5- and 1,8-diaminonaphthalene (1,8-DAN) and 2-aminoanthracene (2-AA) into α-Zr(HPO 4) 2·H 2O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, molecules of aminonaphthalenes are protonated in the interlayer space. 1,5-diaminonaphthalene (1,5-DAN) molecules are arranged in a monomolecular way in the intercalate. The other guest molecules form partially interdigitated bilayers in the interlayer space.

Zirconium Phosphate and Modified Zirconium Phosphates as Supports of Lipase. Preparation of the Composites and Activity of the Supported Enzyme

Biocomposites with enzymatic activity were obtained by adsorption of lipase from Candida rugosa on the surface of different layered zirconium phosphates and phosphonates such as α-zirconium hydrogenphosphate, solid dispersions of zirconium phosphate in silica, zirconium carboxyethanephosphonate, zirconium phosphate-carboxyethanephosphonate, zirconium benzenephosphonate, and zirconium phosphate-benzenephosphonate. All the supports were characterized for chemical composition, BET specific surface area, surface ion exchange capacity, and X-ray diffraction patterns. The adsorption process at 4 °C was studied as a function of time of equilibration of the support with the lipase solutions (0.5 mg/mL) and as a function of the amount of protein present in the equilibrating solution. The activities of biocomposites with the different supports, at different protein loadings, were obtained by determining the amount of acetic acid produced by catalyzed hydrolysis of p-nitrophenylacetate. The best results in terms of ...

Intercalation compounds of α-zirconium hydrogen phosphate with Rh 3+ ions and Rh 3+-diamine complexes. Part II. Their behaviour towards CO, CO 2 and H 2 and their use in the CO catalytic oxidation

The reactivity of Rh 3+ ions and Rh 3+-diamine α-Zr(HPO 4) 2·H 2O complexes intercalated in α-zirconium hydrogen phosphate towards small molecules (CO, O 2, H 2) was studied. The compounds only containing Rh 3+ ions, of composition ZrH x Rh y (PO 4) 2·4H 2O ( x = 2 – 3 y; 0 < y ≤ 0.66) react with CO at atmospheric pressure and temperatures ranging from 80 to 100°C, and undergo selective reduction of Rh 3+ to Rh 1+. The resulting materials containing Rh 1+ are reoxidized to Rh 3+ by molecular dioxygen under the same pressure and temperature conditions. The simultaneous action of a CO O 2 mixture determines the catalytic oxidation of the CO to CO 2 and the system acts as a stable catalyst of this reaction. At higher temperatures, the reduction of Rh 3+ is no longer selective and in these conditions Rh 0 is formed, which escapes from the support and causes its deactivation. Similar behaviour is found in systems containing Rh 3+-diamine complexes, which react with CO at temperatures higher than 120°C and undergo an irreversible reduction of Rh 3+ to Rh 0. The reaction with H 2 (70 < T < 100°C) also causes a non selective reduction of the Rh 3+ to Rh 1+ and Rh 0. The progress over time of the catalytic activity of some compounds with different contents of Rh 3+ in converting CO to CO 2 has shown not only that these materials maintain a constant catalytic activity, indicating the stability of the systems to the loss of metal during working cycles, but also that Rh 3+ supported in these matrixes is more active and selective in this type of reaction than Rh 3+ in solution.

Preparation, Characterization, and Structure of α-Zirconium Hydrogen Phosphate Hemihydrate

A hemihydrate form of layered zirconium phosphate was obtained by reacting ZrO2 with concentrated H3PO4 (17 M) at 230°C for 2 days, Zr(HPO4)2 · 0.5H2O crystallizes in the monoclinic symmetry with cell constants a = 9.1478(5) Å, b = 5.3242(3) Å, c = 15.288(1) Å, β = 103.848(6)°, space group C2/c. It undergoes a reversible phase transition at about 70°C, without losing the lattice water; the interlayer distance is reduced to 7.30 Å and the symmetry changes to the trigonal one (a = 5.3743(5) Å, c = 21.982(2) Å, space group R3̄ ). The crystal structure of the hemihydrate phase at room temperature was determined by using 36 unambiguously indexed reflections, obtained by the decomposition of the X-ray diffraction pattern, in a conventional single-crystal analysis. A geometric model was assumed for the high-temperature phase. Refinement of the crystal structures was performed by the Rietveld method. In the low-temperature phase, the crystallization water forms interlayer hydrogen bonds with the P-OH of the α-layers, which accounts for the very long times or the elevated temperature required for complete dehydration to occur. Accordingly, the hemihydrate does not transform into the monohydrate phase even when dipped into boiling water and it does not seem obtainable from partial dehydration of the monohydrate form.

Conductivity variations in composites of α-zirconium phosphate and alumina

Composite proton-conducting solid electrolytes have been formed from α-zirconium hydrogen phosphate (α-Zr(HPO 4) 2·H 2O, α-ZrP) and aluminas (Al 2O 3) in varying mole ratios. Conductivity variations as a function of temperature have been characterised and compared to that for a delaminated α-ZrP (no alumina). There are no appreciable conductivity enhancements on composite formation, but conductivity for materials ca. 50 mole% in alumina can be comparable to the delaminated material. Differential scanning calorimetry shows the composites to have different thermal properties to simple admixtures. High resolution 31P NMR studies show reaction to form aluminium phosphate at the interface between components.

Intercalation compounds of α-zirconium hydrogen phosphate with heterocyclic bases and their ac conductivity

Intercalation compounds of α-zirconium hydrogen phosphate with diazoles (pyrazole, imidazole) and diazines (pyridazine, pyrimidine and pyrazine) were prepared by equilibrating the host matrix, pre-swelled with ethanol and/or 1-butanol, with diluted solutions of the bases, for one to two weeks. Composition data and interlayer distance values suggest that the guests are accommodated in the interlayer region as a monolayer of molecules lying flat or slightly tilted with respect to the surface of the sheet. The ac conductivities of diazole intercalates, determined by impedance measurements on pellets over a temperature range of 80–160°C, are higher than those of diazine. At 120°C the pirazole intercalate had a conductivity of 1.4×10 -6S cm -1 (9×10 -6S cm -1 when the intercalate was prepared in pellicular form). The data have been tentatively interpreted on the basis of a transport mechanism involving proton transfer from protonated guest molecules to a nonprotonated neighbour ones, followed by the rotation of the neutral (or protonated) species.

Influence of the guest molecules on the protonic conduction of anhydrous intercalation compounds of α-Zirconium hydrogen phosphate with diamines

α-ω alkyl diamines can be intercalated into α-layered zirconium hydrogen phosphate with the formation of compounds of formula α-Zr(HPO 4) 2·N 2H 4(CH 2) n . Anhydrous intercalates with n=0, 2, 3, 4, 5 were characterized by X-ray powder diffractometry and thermogravimetric analysis in order to determine the temperature range at which the anhydrous phase is stable. The ac conductivity was measured with platinum black electrodes on pellets in a dry argon atmosphere. The highest conductivity (}2×10 -6 S cm -1 at 180°C) and the lowest activation energy (0.74 eV) were found for the hydrazine intercalate. At the same temperature the conductivity of the other intercalates is at least 3 orders of magnitude lower with activation energies in the range 0.9 to 1.2 eV, thus showing the protonic transport to be markedly influenced by the basic strength of the diamine.

TPD study of NH 3 adsorbed by different phases of zirconium phosphate

Thermodesorption of NH 3 has been used to measure the acidity of α-zirconium hydrogen phosphate and different phases obtained from this material by thermal treatments. It was found that samples treated at temperatures lower than 300 °C, consisting of hydrated or anhydrous α-phases, adsorbed an amount of ammonia corresponding almost to neutralization of all acidic -POH groups and formation of a well-characterized diammonium phase. Samples treated at t ≥ 400 °C, in which partial or total condensation of interlayer -POH groups occurred, showed a strongly reduced capacity for adsorption of NH 3, because of the formation of P-O-P bridges between layers which hindered diffusion of NH 3. After pretreatment of Zr hydrogen phosphate at 600 °C, the TPD spectrum of ammonia adsorbed at room temperature showed only the signal of NH 3 adsorbed by surface -POH sites, indicating that its interaction with internal sites was now precluded. From the shape of the TPD curves from these samples information on the strength of surface acidic sites was deduced.

α-zirconium hydrogenphosphate, monohydrate. preparation, chemical properties and ac conductivity

The preparation of zirconium hydrogenphosphate, monohydrate (αZrP) was performed by two methods giving materials with slightly different properties. It is shown that the particle size of αZrP depend upon the method of preparation and the washing procedures, and that the ac conductivity decreases with increasing particle size (5 x 10 -6 to 5 x 10 -5 Ω -1 cm -1 at 20°C). The activation energy has been determined to 0.25 eV/mol (between 20°C and about 100°C) independent of the particle size, showing αZrP to be a surface ion conductor.