VARIABLES IN PREPARATION OF MODIFIED SILICA ADSORBENTS

Variables in a procedure for modifying the selectivity and capacity of silica, by precipitating silicic acid in the presence of the intended adsorbate, have been studied so as to optimize those qualities and improve the reproducibility. The chief factor affecting the xerogel selectivity for methyl orange relative to ethyl orange was the structure of the dye present during gelation. Capacity was increased by slow gelation rates, longer aging or drying times, and the use of pure methanol instead of acidified methanol or water for washing the gel. The amount of dye that remained in the xerogels after exhaustive extraction had no effect on the capacity or selectivity of the adsorbents. Repeated attempts to prepare stereoselective silica adsorbents for enantiomers, reported in earlier literature, resulted in failure. © 1969, American Chemical Society. All rights reserved.