Physical properties of fixed-charge layer double hydroxides

The physical properties of a series of layer double hydroxides (LHD) of the farm [(CO3)(0.195(1-x))Cl-0.39x(H2O)(y)]:[Zn0.61Al0.39(OH)(2)], 0 less tha n or equal to x less than or equal to 1, 0 less than or equal to y less tha n or equal to(0.4+0.2x) have been studied. The hydration dynamics of these materials indicate that the guest layer water molecules form a hydration ri ng which defines the height of the solvated, nested Cl anion. The water mol ecules can tilt around their Ct, axis such that the height of the solvated Cl ion is a function of the number of molecules forming the hydration ring. The composition dependence of the basal spacing, determined from x-ray-dif fraction powder patterns measured as a function of humidity and temperature for these materials, is a function of both the Cl concentration (x) and th e number of guest layer water molecules (y). Distinct basal spacing curves are observed for fully hydrated, partially hydrated, and dehydrated materia ls. At x = 1 the Cl end-member material exhibits a change in stacking seque nce from a 3R polytype to a 2H polytype upon dehydration. The dehydrated fa rm of this material also exhibits a (root 3 x root 3)R30 degrees superlatti ce ordering of the Cl ions. Due to the nesting of the Cl ion and the active nature of the water molecules, the basal spacing vs x curve for the dehydr ated materials is the only curve that can be fit by the discrete finite lay er rigidity model. The interlayer rigidity parameter for LDH materials has been determined to be p = 4.84+/- 0.06 indicating that these materials are stiffer than class-II layered solids but not as stiff as class-III layered solids.