Morphology and Gas Adsorption Properties of Palladium - Cobalt-Based Cyanogels

The morphology of cyanide-bridged palladium-cobalt (Pd-Co) gels, synthesized from aqueous solutions of Na₂PdCl₄ and K ₃[Co(CN)₆], is elucidated using nitrogen and carbon dioxide adsorption, permeability measurements, electron microscopy, and small-angle X-ray scattering. The aerogels formed from the Pd-Co hydrogels possess both micro- and mesoporosity. Electron microscopy indicates that the aerogels are constituted of spherical microporous particles; the interstices between these particles constitute the mesopores. The aerogel surfaces are found to be fractal as analyzed by gas adsorption and small-angle X-ray scattering. Both these techniques yield, within experimental error, the same surface fractal dimension of 2.6 ± 0.2 for the aerogels. The Pd-Co xerogels, unlike the aerogels, are predominantly microporous with a narrow microporosity. Transmission electron microscopy reveals that the xerogels are constituted of particles of an average size of ∼10 nm. Unlike the aerogels, the xerogels do not possess surface fractality. The mechanism of adsorption of different gases on these gels is analyzed on the basis of the gel morphologies.