Effect of hydroxyl group of carboxylic acids on the adsorption of Acid Red G and Methylene Blue on TiO₂

While TiO₂ has generated great interest in the removal of organic pollutants in recent years, the effect of the surface chemical property of TiO₂ on the adsorption performance is unclear. Here, TiO₂ samples were prepared in succinic (without hydroxyl group), malic (with one hydroxyl group) and tartaric acid (with two hydroxyl groups) by hydrolysis method and labeled as SU-TiO₂, MA-TiO₂ and TA-TiO₂, respectively. Their adsorption performance for anionic dye-Acid Red G (ARG) and cationic dye-Methylene Blue (MB) was investigated. The adsorption study indicates that the adsorption amount of ARG or MB was proportional to the alkalinity or the acidity, which is related to the number of hydroxyl group of the used acids, of the as-prepared TiO₂. Therefore, SU-TiO₂ displayed the largest adsorption capacity for ARG, while TA-TiO₂ had the highest adsorption capacity for MB. Furthermore, TA-TiO₂ can be reused at least 5 times without losing its adsorption capacity. The results indicate that the adsorption mechanism involves in the electrostatic interaction and the electron acceptor-donor interaction.