Phosphates, modified zirconium

The ability to modify the backbones of LMP structures with phosphonates allows for wide flexibility in the design of new materials containing photoactive binuclear metal cores. The goal of our initial studies has been to demonstrate that a ligating functionality within the gallery is accessible for reaction with a bimetallic core. To demonstrate these initial objectives, we have chosen to study zirconium phosphate modified with alkyl carboxylate, which is a good ligand of bimetallic cores. 

Chen LC, Yu TL, Lin HL, Yeh SH (2008) Nafion/PTFE and zirconium phosphate modified Nafion/PTFE composite membranes for direct methanol fuel cells. J Membr Sci 307 10-20... 

Crystalline and modified zirconium phosphate Since protons cannot diffuse on the anhydrous surface of an a-layer, the conductivity of anhydrous ZrP is expected to come from protons jumping between oxygens belonging to the side faces of adjacent layers (see Fig. 16.2). The conductivity values of anhydrous ZrP , ZrP(p, and ZrPjs,, determined by applying an electric field perpendicular to the flat surfaces of the pellets, are shown in Fig. 16.5 in the case of ZrP p, the parallel conductivity is also reported. 

Schafer et al. used several spectroscopic techniques to characterize the surface species on phosphate-modified zirconia particles. Their results show that phosphate merely adsorbs on the surface of zirconia under the mildest phosphate concentration, i.e., neutral pH, room temperature, and short contact times. However, at acidic pH and higher temperarnres, esterification of the phosphate with surface hydroxyls takes place as the kinetic barriers are overcome. The solid NMR studies clearly show the presence of covalently bound phosphate. This phosphate modification effectively blocks the sites responsible for the strong interaction of certain Lewis bases with the zirconia surface, resulting in a more biocompatible stationary phase. Unlike fluoride-modified zirconia, phosphate-modified zirconia behaves as a classic cation exchanger and not as a mixed-mode medium analogous to hydroxyapatite, despite spectroscopic evidence of zirconium phosphate formation on the surface. This limits the applicability of the supports, as most proteins and enzymes are anionic at neutral pH. Nevertheless, its ability to separate proteins with high p/ values still deserves much attention. The preparative-scale separation of murine IgGs from a fermentation broth demonstrates the utiUty of the supports for solutes that are retained. 

Malinauskas A, Ruzgas T, Gorton L (2000) Electrochcamcal study of the redox dyes Nile Blue and Toluidine Blue adsorbed on graphite and zirconium phosphate modified graphite. J Electroanal Chem 484 55-63... 

Figure 3. Three basic strategies for the incorporation of multiply bonded metal-metal guest species into vanadyl and zirconium phosphate host layers, (a) The direct intercalation of solvated M—— M cores into the native layered phosphate host structure, (b) Incorporation of M—— M complexes with ancillary ligands containing a Lewis basic site, (c) Coordination of M—— M cores with ligands provided from modified phosphate layers.

Both aluminum oxide and zirconium oxide are catalytically interesting materials. Pure zirconium oxide is a weak acid catalyst and to increase its acid strength and thermal stability it is usually modified with anions such as phosphates. In the context of mesoporous zirconia prepared from zirconium sulfate using the S+X I+ synthesis route it was found that by ion exchanging sulfate counter-anions in the product with phosphates, thermally stable microporous zirconium oxo-phosphates could be obtained [30-32]. Thermally stable mesoporous zirconium phosphate, zirconium oxo-phosphate and sulfate were synthesized in a similar way [33, 34], The often-encountered thermal instability of transition metal oxide mesoporous materials was circumvented in these studies by delayed crystallization caused by the presence of phosphate or sulfate anions. 

Phosphate and sulphate modifiers were incorporated by the addition of appropriate amounts of 0.01 M sulphuric or phosphoric acid to a pre-calcined aerogel followed by further calcination at 873 K. Samples are labeled as X-SiZr (y) where X refers to either sulphated (S) or phosphated (P) samples, and y refers to the mole ratio of sulphate/phosphate relative to zirconium in the preparation method. For comparison purposes, samples of zirconia and sulphated zirconia were also prepared. This was achieved via precipitation from zirconium isopropoxide (Aldrich 70 wt.%). The same H2O Zr propanol ratios were employed as used during the preparation of the mixed oxides. A sulphated zirconia, prepared by the use of sulphuric acid as hydrolysis catalyst was prepared for comparative purposes and had a nominal S Zr ratio of 0.30 1. A further sample was prepared where segregation of components was induced by thermal treatment by calcination at 1373 K for 6 h.of the non-treated SiZr (0)... 

The existing method for preparing crystalline zirconium phosphate is firstly to precipitate the amorphous form from a mixture of phosphonic acid and zirconyl chloride and secondly to reflux the amorphous form in 12M phosphoric acid for several days after washing the amorphous form free of chloride. This gives the a-form. Not only is this a time consuming process, but the amorphous form is difficult to filter. We aimed to develop a one step process to the crystalline material by using crystal habit modifiers. 

Table 5 - Phenol Hydroxylation Using Zirconium Phosphates Made with Crystal Habit Modifiers...

Most of the reported inorganic fillers used to modify Nafion are composite where the inorganic particles (usually nanoparticles) are located in the membrane bulk. Most of them are prepared using the recast method, where the filler nanoparticles dispersed in a solvent are mixed with Nafion ionomer dispersion in the same solvent or a compatible one. The solution is cast on a Petri dish or a plane surface at high temperature to form the recast composite membrane. An alternative method adopted to prepare Nafion composites with silica [31, 32, 41, 95], functionalized silica [35], and zirconium and titanium phosphate [41], is the in situ sol-gel reaction method, schematized in Fig. 6.5. 

Inorganic/PVA composites have been also considered, including sulfonic or phosphonic modified silica, titania, hydroxyapatite, heteropoly acids, zirconium phosphate, and montmorillonite. Hybrid organic-inorganic PVA composite membranes, like PVA/Ti02/PSSA, PVA/SiOa/SSA/, PVA/PWA/sPEEK/PWA, PVA/Si02/PPA, etc., have been reported. 

Layered a-zirconium phosphate and its modified and intercalated phases... 

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