Amine-functionalized ordered mesoporous silicas as model materials for liquid phase acid capture

Uptake of dilute aqueous acetic acid was compared using primary, secondary, tertiary amines, and quaternary ammonium grafted ordered mesoporous silica. Primary amine and quaternary ammonium grafted samples showed the highest uptake, 0.21 mmol acetic acid/g SBA-15, with secondary and tertiary amines showing nominally lower, 0.18 mmol/g, at 0.5 mmol aminosilane loaded per gram SBA-15. Solution conditions during uptake were varied to conclude that only associated acetic acid could be bound and that the mechanism relied heavily on electrostatic interactions. The aminosilane packing density was found to be crucial to performance with variation depending on the ligand bulk as well as the silica support's pore size. Relevant solution conditions for cellulose depolymerization were also explored by comparing uptake of multiple organic acids and with dextrose added. Here, it was shown that the most hydrophobic organic acid was preferentially extracted, and the uptake was enhanced in the presence of dextrose.