Quantification of Hydroxyl Groups from Alumina in Aluminosilicate Materials by Adsorption Isotherms

A simple and accessible method without the use of expensive and specific reagents is presented in this work for the quantification of hydroxyl groups from alumina in aluminized silica. The method is based on the differential interaction of a dye on bare silica and on aluminized silica surfaces due to the electrostatic repulsion of dye molecules by Al-OH groups in aluminized silica, and subsequent spectrophotometric quantification. The adsorbate molecule used for this study was malachite green. The difference between amount of malachite green retained on bare silica and aluminized silica remained constant when the ratio of active sites on the support to malachite green molecules was not very different. The results indicated that the method presents sensitivity and selectivity for the determination of hydroxyl groups in aluminosilicate materials with high repeatability, making possible the quantification of Al-OH in aluminosilicates without the use of sophisticated scientific instruments.