CHLOROPHYLL ADSORPTION BY ALUMINA-PILLARED ACID-ACTIVATED CLAYS

Clays, acid-activated to an optimum level, have been pillared with alumina to give semi-crystalline expanded materials with surface acidities, pore volumes and average pore diameters generally higher than those of the corresponding pillared materials derived from a clay matrix not previously acid-activated. The chlorophyll adsorption capacity of the pillared acid-activated materials is significantly greater than that of pillared, nonactivated clays. The procedures used in the preparation of these pillared acid-activated clays (i.e., temperature of pillaring, method of drying and calcination temperature) have a significant influence on chlorophyll adsorption capacity because they influence both the physical and the chemical properties of the final pillared material. This variation provides a useful means of relating the various properties of the pillared materials to the chlorophyll adsorption capacity. As a result, a correlation has been demonstrated between adsorption capacity and a combination of pore volume and number of strong acid sites (of strength pK(a) < -1.5) present in the pillared material. Optimal adsorbents were obtained from freeze-dried samples prepared by exchange at 20-degrees-C and calcination in air at 500-degrees-C.