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