Structure of zirconium phosphate gels produced by the sol - gel method

Abstract

Several zirconium phosphate (ZrP) gels of various water contents produced by a sol - gel method were investigated. They were found to be the polymer-class gels using the method of small-angle neutron scattering. X-ray diffraction analysis revealed that their solid-phase framework was formed from branched fragments (layers and blocks) of -ZrP crystal structure. These gels are strongly fluctuating systems when they are on the scale of . Their fluctuation character is shown to be described by two parameters: a correlation radius and a fractal dimension D. It was found that and almost did not depend on the water content and that D increased from to when the water content decreased from 50% to 0% as the gels were dried to a temperature of . Simultaneously, substantial shrinkage of granules, a decrease in porosity and ion-exchange capability, and formation of blocks from -phosphate layers occurred with decrease in the water of the hydrogel as it dried. A probable description of the evolution of the ZrP-gel structure with variation in the water content during drying is suggested on the basis of the data obtained.

Electrical characterization of ion conducting biopolymeric gel complexes

“…The observed micropeaks in XRD pattern of gel state confirm that strong fluctuations are observed in hydrogel and dry gel, which were almost independent of water content in it; however, decrease in porosity in dry-gel affected the LRO. The observed similar phenomenon was also found to exist in Zirconium phosphate gels [20]. The overall data obtained by XRD analysis of this present specimen provide a basis for most probable gel structure.…”

Dehydration of fructose to 5-hydroxymethylfurfural in sub-critical water over heterogeneous zirconium phosphate catalysts

“…38 The phosphate-to-zirconium ratio was close to 2 (1.8-2) in all samples (see Table 1), which is relevant to its basic formula Zr(O 3 POH) 2 AEnH 2 O, where n depends on the drying method and degree of crystallinity. 26 As shown in Table 1, a small deviation from the ratio 2 was obtained for these samples. However, in general, the crystals obtained after refluxing have approximately the same composition as the amorphous sample.…”

“…31 It has been previously shown that amorphous forms of ZrP solids could change to semi-crystalline and crystalline forms by refluxing in concentrated phosphoric acid, while increasing with refluxing time. 26 Therefore, in Table 1 the crystallinity increased from entry A1 toward F1. All the prepared samples, including the amorphous to crystalline forms, were calcined at two temperatures, 300 and 600°C for 3 h. The data for the calcined samples are also shown in Table 1 …”

“…ZrP solids have been primarily used as ion exchangers. 26 However, the use of these solids as catalysts in various reactions such as dehydration, isomerization, polymerization, and alkylation has received considerable attention during the last few years, [27][28][29] as attested to by the numbers of papers and patents that have recently been published. In the presence of different ZrP solids, the dehydration of alcohols, 30 esterification of acetic acid with ethanol, 31 oxidation of propene, 32 and dehydration of cyclohexanol 28 have been widely studied.…”

Accumulation of zirconium phosphate by a Serratia sp.: a benign system for the removal of radionuclides from aqueous flows

“…The structure (amorphous, semicrystal or crystal) of ZrP depends on the method used for its synthesis (Bogdanov et al 1997). However, the stoichiometric P to Zr ratio is 2 (e.g.…”