Solid–Solid Interactions on Active Adsorbents

Abstract

IN recent years the diffuse spectral reflectance properties of various solid systems have been investigated^1,2, and several analytical applications have been developed^3–5. Often it has been reported advantageous to mix the optically absorbing substance with an inactive powdered diluent such as sodium or potassium fluoride. When this is done the reflectance spectrum of the absorbing substance is sharpened and clarified in many cases. More pronounced effects have been obtained when a so-called active adsorbent powder such as chromatographic alumina or silica gel is substituted for the inactive diluent. In an attempt to study the nature of the changes brought about by active adsorbents in the solid state, pilot experiments have been carried out using Michler's ketone (4,4′-bisdimethylamino-benzophenone) mixed with active alumina. Michler's ketone has a well-defined absorption spectrum in transmittance in solution and reflectance from the solid, and is quantitatively removed from solution in a non-polar solvent by alumina. In a typical experiment 1 and 2 mgm. of the powdered ketone were mixed with 3 gm. of acidic and basic alumina (Woelm) and the solid mixtures allowed to stand for several days at room temperature in sealed containers. Visual changes slowly occurred in these systems until in appearance they were virtually identical with alumina on which the ketone had been adsorbed from a solution as in ordinary column chromatography. It is suggested that the two phenomena involve essentially the same adsorption process, differing only in rate.