Methyl orange adsorption by microporous and mesoporous TiO2-SiO2 and TiO2-SiO2Al2O3 composite xerogels

We investigate the adsorption behavior of methyl orange (MO) on composite xerogels. Mesoporous TiO2-SiO2 and TiO2-SiO2-Al2O3 xerogels are prepared by hydrolysis of tetraethyl orthosilicate (TEOS), tetrabutyl orthotitanate (TBOT), and AlCl3 . 6H(2)O using HCl as a catalyst and cetyltrimethylammonium bromide (CTAB) as a templating agent. The corresponding microporous xerogels are also prepared without addition of CTAB. These xerogels are then characterized by XRD, FTIR, and BET. We find that MO is adsorbed by the mesoporous xerogels in acidic solutions, showing Langmuir type adsorption isotherms. We also find that the adsorption decreases with increasing temperature. It is suggested that adsorption exhibits a sieve effect and that MO is adsorbed through electrostatic attraction and hydrogen bonding between MO and the xerogels.