Impact of Organic Acids on the Hardness of Silica Xerogels

In this study, silica xerogels were synthesized via the method known in the literature. Various organic acids were used as catalyst while producing xerogels via Sol-gel method and the impact of these acids on xerogels’ surface area and hardness have been examined. 4 different organic acids (some of them were already mentioned in the literature) was selected, which are citric acid, oxalic acid, sulfanilic acid, and N-(2-hydroxyethyl)iminodiacetic acid. The characterization of the produced materials was performed by FTIR, whereas their surface area was measured through BET analysis. Their hardness were measured and calculated with a diamond-tipped microhardness device. The hardest material was the silica xerogel synthesized with N-(2-hydroxyethyl) iminodiacetic acid, whereas the material with lowest hardness was the one synthesized with oxalic acid. The silica xerogel with the largest surface area was the one with the highest hardness. The data indicated that the acid added during the synthesis reaction affect the hardness of the xerogel and hardness can be associated with pKa values of the added acids.