Mode of Oleic Acid Adsorption on Rice Hull Ash Cristobalite

Fourier transform infrared spectroscopy was used to investigate the adsorption of oleic acid (OA) onto dry rice hull ash (RHA) silica. Adsorption partially occurred by surface hydrogen bonding of the carboxylic acid. There was also formation of carboxylate ions by reaction of OA with residual potassium oxide. These ions were strongly bound by the ash. Isopropanol inhibited OA adsorption by H-bonding and encouraged desorption of H-bonded OA, but without itself being significantly bound. RHA with 40% moisture also adsorbed a small amount of OA by H-bonding and reacted with OA to form and adsorb carboxylate ions.