A novel mixed zirconium phosphate/phosphonate based on glyphosine, of formula Zr2(PO4)H5(L)2·H2O [L = (O3PCH2)2NCH2COO], was synthesized in mild conditions. The compound has a layered structure that was solved ab initio from laboratory PXRD data. It crystallizes in the monoclinic C2/c space group with the following cell parameters: a = 29.925(3), b = 8.4225(5), c = 9.0985(4) Å, and β = 98.474(6)°. Phosphate groups are placed inside the sheets and connect the zirconium atoms in a tetradentate fashion, while uncoordinated carboxylate and P-OH phosphonate groups are exposed on the layer surface. Due to the presence of these acidic groups, the compound showed remarkable proton conductivity properties, which were studied in a wide range of temperature and relative humidity (RH). The conductivity is strongly dependent on RH and reaches 1 × 10(-3) S cm(-1) at 140 °C and 95% RH. At this RH, the activation energy of conduction is 0.15 eV in the temperature range 80-140 °C. The similarities of this structure with related structures already reported in the literature were also discussed.
Reaction of cerium ammonium nitrate and tetrafluoroterephthalic acid in water afforded two new metal-organic frameworks with UiO-66 [F4_UiO-66(Ce)] and MIL-140 [F4_MIL-140A(Ce)] topologies. The two compounds can be obtained in the same experimental conditions, just by varying the amount of acetic acid used as crystallization modulator in the synthesis. Both F4_UiO-66(Ce) and F4_MIL-140A(Ce) feature pores with size < 8 Å, which classifies them as ultramicroporous. Combination of X-ray photoelectron spectroscopy and magnetic susceptibility measurements revealed that both compounds contain a small amount of Ce(III), which is preferentially accumulated near the surface of the crystallites. The CO2 sorption properties of F4_UiO-66(Ce) and F4_MIL-140A(Ce) were investigated, finding that they perform better than their Zr-based analogues. F4_MIL-140A(Ce) displays an unusual S-shaped isotherm with steep uptake increase at pressure < 0.2 bar at 298 K. This makes F4_MIL-140A(Ce) exceptionally selective for CO2 over N2: the calculated selectivity, according to the ideal adsorbed solution theory for a 0.15:0.85 mixture at 1 bar and 293 K, is higher than 1900, amongst the highest ever reported for metal-organic frameworks. The calculated isosteric heat of CO2 adsorption is in the range of 38-40 kJ mol-1 , indicating a strong physisorptive character. CeO(TFBDC)•H2O [F4_MIL-140A(Ce)] 548 mg (1mmol) of cerium ammonium nitrate [(NH4)2Ce(NO3)6), CAN] and 238 mg (1 mmol) of tetrafluoroterephthalic acid (H2TFBDC) were dissolved in 50 ml of deionized (DI) water in a round bottom flask. The solution was heated to 110 °C under stirring and refluxed for 24 h. The obtained yellow solid was collected and washed three times with DI water and once with acetone. The solid was then dried in oven at 80 °C for 24 h. Yield: 73% (calculated on the basis of Ce). Elemental analysis: C = 22.7% exp. (23.4% calc.), H = 0.76% exp. (0.49% calc.) CeO0.67(OH)0.67(TFBDC)•3H2O [F4_UiO-66(Ce)] 548 mg (1 mmol) of CAN, 238 mg (1 mmol) of H2TFBDC and 6 mL (100 mmol) of acetic acid were dissolved in 45 ml of DI water in a round bottom flask. The solution was heated to 110 °C under stirring and refluxed for 24 h. The obtained yellow solid was collected and washed three times with DI water and once with acetone. The solid was then dried in oven at 80 °C for 24 h. Yield: 66% (calculated on the basis of Ce). Elemental analysis: C = 23.5% exp. (22.6% calc.), H = 2.19% exp. (1.57% calc.) Analytical procedures Powder X-Ray Diffraction (PXRD). PXRD patterns were collected in reflection geometry with a 40 s step-1 counting time and with a step size of 0.016° 2θ on a PANalytical X'PERT PRO diffractometer, PW3050 goniometer, equipped with an X'Celerator detector by using the Cu Kα radiation. The long fine focus (LFF) ceramic tube operated at 40 kV and 40 mA. The pattern
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 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.
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