Adsorption of Chromate and Arsenate by Amino-Functionalized MCM-41 and SBA-1

We report the characteristics of aminosilane-grafted mesoporous silicas as adsorbents of oxyanions in acidic conditions. Mono-, di-, and triamino-functionalized silicas were prepared to examine the influence of amino group density. The triaminosilane-grafted mesoporous silica adsorbed more chromate and arsenate than expected from the increased number of sites, suggesting stable complex formations. Functionalized SBA-1 showed larger adsorption capacities than MCM-41 derivatives. The adsorption capacity was independent of the average surface density of monoamino groups, demonstrating domain formation of fixed silanes. These structural characteristics on molecular and meso scales may offer insights into understanding the mechanism of heterogeneous oxyanion capture by amino-functionalized solids, which are promising inexpensive reagents for reducing toxic anion pollution.