EFFECTS OF STRUCTURAL CHANGES OF PRETREATING AGENT ON ADSORPTION BY MODIFIED SILICA ADSORBENTS

Because more selective adsorbents permit faster separations to be made, factors were studied which enhance the selectivity of silica gels prepared by the pretreatment of silicic acid hydrogels with various azo dyes, related to methyl orange, and with amines. The effects of systematically varying the structure of the pretreating agent on changes in selectivity and capacity for azo dye adsorbates were investigated. As the structure of the pretreating agent increasingly deviated from that of the adsorbate, the selectivity of the gel for that adsorbate decreased and approached that of an untreated (control) gel. An increase in hydrophilic character of ring-substituted groups of the dye present during gelation appeared to increase selectivity. For relatively simple structurally-related pretreating agents, such as substituted anilines and paminobenzenes, there was a linear relationship between the selectivity and the basicity of the amino nitrogen. However, there was no obvious relationship between the structure of the pretreating agent and the adsorbent capacity. © 1969, American Chemical Society. All rights reserved.