Zirconium phosphate preparation

Particularly, in the case of proton-conducting zirconium phosphate prepared via in situ growth within the preformed membrane,the proton conductivity of the highly dispersed filler may have some significance at high temperature and low humidity, where the conductivity of pure Nafion strongly decreases. 

Inspired by the separation ability of cyclic selectors such as cyclodextrins and crown ethers, Malouk s group studied the synthesis of chiral cyclophanes and their intercalation by cation exchange into a lamellar solid acid, a-zirconium phosphate aiming at the preparation of separation media based on solid inorganic-organic conjugates for simple single-plate batch enantioseparations [77-80]. 

An example of the modular preparation of the cyclophane 3 from the substituted bipyridine 2 and a general tripeptide 1 is shown in Scheme 3-3. The host molecule 3 contains a pre-organized binding pocket. The overall basicity of such molecules also facilitates their intercalation within the lamellas of acidic zirconium phosphate, thus making this chemistry well suited for the desired application. 

X-Ray diffraction studies have identified a distorted octahedral environment about zirconium in KZr2(P04)3, and the structures of zirconium phosphates have been discussed in terms of their utility as chemical sieves.Some preparative and structural aspects of the normal sulphates of zirconium and hafnium have been reviewed and X-ray studies have shown that the sulphates Zr20(S04)3,5H20 and Hf20(S04)3,5H20 are isostructural and are more accurately represented as M2(OH)2(S04)3,4H20. Other studies of zirconates and hafnates and related mixed oxide systems are summarized in Table 2. 

Addition of a soluble Zr(IV) salt to phosphoric acid results in the precipitation of a gelatinous amorphous solid. The stoichiometric crystalline zirconium phosphate can be prepared by refluxing zirconium phosphate-gel in concentrated phosphoric acid [5]. The procedures for synthesis of zirconium phosphate have been described in detail elsewhere [6]. 

Adsorption of mercury. All chemicals used were Merck or Baker analytical quality reagents, unless stated otherwise. From the commercially available adsorbents the following were used silica gel 60 A porosity, 0.063-0.200 mm particle size (Merck) charcoal 0.3-0.5 mm particle size, gas-chromatographic quality (Merck) alumina R Woelm hydrous zirconium oxide HZ0-1, 100-200 mesh, (Bio-Rad). Except for zirconium phosphate, which was prepared according to Amphlett ( ), all other sorbents were prepared by coating (precipitation) on acid-purified silica gel, as described in (1 ). The Si0 -NH was prepared according to Leyden et al (11). L... 

Another preparative method in which the rate of precipitation is slow involves slow decomposition of zirconium fluoro complexes [14], These are first prepared by adding an appropriate amount of hydrofluoric acid (HF) to the zirconyl salt and these complexes are decomposed in the presence of phosphoric acid, with a slow stream of nitrogen or water vapor passing through the system. The rate of precipitation of zirconium phosphate is controlled by the rate of removal of HF from the system, and when this is very slow, a highly crystalline a-ZrP is obtained. The gamma form of the metal phosphate differs significantly from the alpha and current discussion will be concerned with the latter phase. 

Figure 3 Partial schematic structure of ot-zirconium phosphate lamallae and its preparation.

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. 

It is known that non-aqueous synthesis has been effectively applied in the preparation of various metal phosphates, including amine-containing aluminum, gallium, indium, zinc and cobalt phosphates with three-dimensional open-framework structures [17-24]. Moreover, phosphates with a layered or chain structure can been crystallized from non-aqueous media [25, 26]. Since the fluoride ions mineralizer was introduced into the synthesis of zirconium phosphates, several zirconium phosphate fluorides with novel structures have also been developed. 

Table 2. Influence of the solvent on the preparation of zirconium phosphates.

Sol-gel methods are used to prepare a heterogeneous, nanometer composite of calcium zirconium phosphate and strontium zirconium phosphate, Cao.sSro.sZrsOn. In this composite, individual domains both expand and contract upon heating, leading to a material with virtually zero thermal expansion over the range 0-500 °C. 

In an application of the Paal-Knorr pyrrole synthesis, the synthetic equivalents 3 of 1,4-ketoaldehydes were prepared by the radical addition of ketones 4 to vinyl pivalate. Treatment of the intermediates 3 with amines gave pyrroles 5 <03SL75>. Other new extensions of this popular pyrrole synthesis include the preparation of a number of pyrroles from hexane-2,5-dione and amines under solvent-free conditions in the presence of layered zirconium phosphate or phosphonate catalysts <03TL3923>, and the development of a solid-phase variant of this reaction <03SL711>. Likewise, the preparation of iV-acylpyrroles from primary amides and 2,5-dimethoxytetrahydrofuran in the presence of one equivalent of thionyl chloride has also been reported <03S1959>. 

The zirconium oxide cannot be regenerated, and should be discarded after use. The zirconium phosphate may be regener ated by passing through it about 400 ml. of 4 JIf nitric acid or perchloric acid and washing away the excess acid with water, as in the preparation of fresh material. After several cycles or prolonged standing, however, the phosphate will become pasty, and it must then be replaced. 

Advancements in the preparation of new PLS s nearly parallels that of the zeolite and zeolite-like phases. Initially the pillared smectite clays were investigated but the quest for new materials with new properties led to e qiloring the pillaring of other layered phases. These include, most notably, the layered zirconium phosphates, double hydroxides (hydrotalcites), sihcas and metal oxides. The parallel paths of discovery in new material compositions for the layered phases and the microporous (zeoUte) phases are summarized in Table 1. A conq>arison between the pore architectures of the zeohtes and the two dimensional PLS is shown in Table 2. 

In contrast to the conventional approach whereby various organic groups are subsequently bound to a previously prepared surface, we have been synthesizing a broad series of anchored, layered-structure solids by precipitating the pre-derived phosphonate salts with tetravalent metal ions. The two-dimensional backbone has the zirconium phosphate structure however, substituted for hydroxylic groups are the desired organics, oriented away from the basal surfaces in a bilayered fashion in the interlayer region. 

We have prepared other mixed composition pillared compounds irtiich have as their non-pillaring group the hydroxyl moiety, and thus are simply relatives of zirconium phosphate in which the layers are spread at a fixed distance apart. These products behave as expected in titration and ion-exchange experiments, and will not be further discussed here. 

Antimicrobial nanoflbers of poly(e-caprolactone) (PCL) were prepared by electrospinning of a PCL solution with small amounts of Ag-loaded zirconium phosphate (AgZ) nanoparticles for potential use in biomedical applications [41]. SEM, EDX, and XRD investigations of the electrospun flbers confirmed that Ag-containing nanoparticles were incorporated and well-dispersed in smooth PCL nanoflbers [41]. In another study, PCL-based polyurethane (PCL-PU) nanoflbers containing Ag nanoparticles for use in antimicrobial nanofllter applications were prepared by... 

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