57 1
J. Phys. Chem. 1982, 86, 571-576
proximation to the diffusion behavior of moderately concentrated solutions.
Conclusions The conductimetric technique can be used to determine diffusion coefficients for mixed electrolytes in mixed solvents.2o Results for dilute solutions of KCl/KCl in 10% (20)We have uaed the conductimetric technique to determine ternary diffusion coefficients for dilute mixed electrolytes. The same technique may be used to determine accurate ternary diffusion coefficients for concentrated mixed e1ectrolyte.s. Our equations may also be used to determine ternary diffusion coefficients for nonelectrolytes,provided a quantity which depends linearly on the solute concentration can be accurately measured at fixed positions in the diffusion cell! (21)M. S. Chen and L. Onsager, J. Phys. Chem., 81, 2017 (1977). (22)P.S. Albright and L. J. Gosting, J. Am. Chem.SOC.,68, 1061 (1946). (23)L. G . Longsworth and D. A. MacInnes, J. Phys. Chem., 43,239 (1939).
methanol/water were in good agreement with OnsagerFuoss theory and entirely analogous to results obtained earlier for the system KC1/KCl/water.'P2 No departures from the pseudo-ternary approximation were observed. At low ionic strength, the diffusion properties of mixed strong electrolytes in multicomponent systems can be accurately predicted from data obtained on binary or pseudo-binary systems. Strongly coupled diffusion may be anticipated in mixed electrolyte solutions containing polyelectrolytes, as well as in aqueous solutions containing acids (or hydroxides).
Acknowledgment. Acknowledgment is made to the donors of the American Petroleum Research Fund, administered by the American Chemical Society, for the support of this research. (24)Harned and Owen, ref 12, Chapter 8.
Surface Texture and Crystalllnlty Behavior of Zirconium Bis(methylphosphonate) Martin B. Dines" and Peter C. Qrlf?lth OccMental Research CorpOreHon, Iwlne, Callfornk 92713 (Received: June 18, 1981; I n Final Form: September 18, 1981)
Zirconium bis(methylphosphonate),prototypical of the layered tetravalent phosphonates recently described, can be prepared with a broad variation in surface area and crystallinity. These two properties, as expected, have an inverse relationship. Using the methodology of nitrogen surface area and microporosity determination of the products obtained, we endeavored to ascertain whether the structure of the amorphous (to X-rays) high surface area solids are simply of exceedingly small particle size, or intrinsically disordered, as in glasses or dried gels. Our data tends to support the former alternative.
Introduction Recent reports have described the preparation and some physicochemical properties of a novel group of layeredstructure compounds, the tetravalent metal pho~phonates-M(O$-R)~~-~ Based upon the framework of zirconium phosphate: these salts apparently contain bilayers of appended organic groups directed away from the planar inorganic M-0-P polymeric sheets (Figure 1). It is evident that such features as presented by these unusual materials promise a variety of useful properties, such as in the area of ion exchange,&' selective sorption, and catalysis. For any such application, the nature of the surface and porosity of these substances will be an essential concern, since any interaction with a fluid phase must first occur at the interface. As with other layered materials, there is a need to define and differentiate the external from the internal or bulk surface-that vast area of potential activity between the composite layers. A complicating feature of the phosphonates is the fact that varying the conditions of preparation (coupled with the nature of the organic group present) can result in products of widely varying (1)G. Albert, U. Costantino, S. Alluli and N. Tomassini, J. Inorg. Nucl. Chem., 40, 113 (1978). (2)M. B. Dines and P. M. DiGiacomo, Inorg. Chem., 20, 92 (1981). (3)L. Maya, Znorg. Nucl. Chem. Lett., 16, 207 (1979). (4)A. Clearfield and G. D. Smith, Inorg. Chem.,8,431 (1969). (5)G. Alberti, U. Costantino and M. L. L. Giovagnotti, J. Chromatogr., 180, 45 (1979). (6)L. Maya, J. Inorg. Nucl. Chem.,43,400 (1981). (7)P. M. DiGiacomo and M. B. Dines, Polyhedron, accepted for publication. 0022-3654/82/2086-0571$01.25/0
crystallinity, as manifested in their X-ray diffraction reflection widths, which range from quite sharp (high degree of order) to exceedingly broad (scale of order less than about 30 A). The method of preparation of these materials typically involves a simple metathetical precipitation from aqueous solution containing the metal ion and the appropriate phosphonic acid (eq 1). The precipitates usually form
i -
M4+ t 2(HO),P-R
M(O,P-R),
+
4H'
(1)
immediately as very small-particle white flocs, suggesting high nucleation rates and extreme insolubility. This is confirmed by the consistently high yields obtained. Exhaustive digestion ("Ostwald ripening") of these products has relatively little effect on elevating their crystallinity unless excess phosphonic acid is present. We have found, in addition, that in the case of the zirconium salts, the use of HF as a sequestrant to inhibit release of free Zr4+ to solution has a considerable effect on increasing crystallinity and particle size. This has been reported in the case of zirconium phosphate, as well.* Other factors which have also been found to influence the crystallinity and surface texture of the products were the pH of the reaction solution and the presence of organic co-solvents such as methanol or acetone. Particle size analysis and scanning electron microscopy of the products has shown a general tendency to form (8)G . Alberti and E. Torracca, J. Inorg. Nucl. Chem., 30,317(1968).
0 1982 American Chemical Society
Dines and M i
*cllc
mure 2. CPK model of the array of hexyl groups as they would ba spaced on a basal surface. Note the non-close packlng.
area and pore behavior of several layered phosphonates (using nitrogen) in an attempt to better understand their microstructure and thus the way in which they can be expected to interact with other molecules. Our prototype compound in this study is zirconium bidmethylphosphonate). In later reports we will describe some of the systematics of mixed-component and cross-linked (pillared) phases-those compounds having more than one kind of organic group. We have relied mainly on standard techniques such as BET nitrogen adsorption and electron microscopy for this work, but will describe elsewhere our findings employing more state-of-the-art developments such as ‘magic-angle” NMR.
n
Results and Discussion It is instructive to begin with a simple model of the limiting surface area for compounds that we deal with here. If we imagine a single extended layer, which is accessible
Ill
Siructure 01 the layered phosphonates, derlved from zirconium phosphate: (I) Vlew showing the Inorganic framework; (11) situation of sites on the basal surfaces: (111) edge-on model of the structure. Flgwe 1.
WlOO-pm agglomerates composed of much smaller (
