Thermal and textural characteristics of modified silica

A silica gel characterised as predominently microporous, with the remaining pores of limited dimensions which do not permit capillary condensation, is modified with aqueous solutions of acetic acid, glycine and β-alanine. The modified samples are investigated and compared with a water soaked sample by means of differential thermal analysis, thermogravimetry and i.r. spectroscopy. Textural measurements are also carried out on the parent samples and those produced in the temperature range 110–600°C. Acetic acid is both physically and chemically adsorbed; a surface ester is formed. Both amino acids are physically adsorbed but no chemical interaction has been detected. Glycine and β-alanine decompose differently when adsorbed on to the silica surface than when in the pure state. The specific surface area decreases upon modification, reaching half the value of the pure silica for the β-alanine modified sample. Pore structure analysis, shows that the microporous nature of the modified samples decreases in the modifier order acetic acid < glycine < β-alanine. The adsorbed β-alanine molecules block most of the micropores present.