Effects of acid washing treatment on the adsorption equilibrium of volatile organic compounds on titanate nanotubes

Gravimetric techniques were employed to determine the adsorption capacities of titanate nanotubes (TNT) for volatile organic compounds (VOC), including n-hexane, benzene, toluene, p-xylene, m-xylene, and o-xylene, at isothermal conditions of 15, 20 and 25 °C. TNT were prepared via a hydrothermal treatment of TiO2 powders in a 10 M NaOH solution at 150 °C for 24 h, and subsequently washed with HCl aqueous solution of different concentrations. Effects of the alteration of microstructures of TNT, induced by the acid washing process (or the sodium content), on the organic vapors adsorption were discussed. The experimental data were correlated by well-known vapor-phase models including BET and GAB models. Isosteric heats of adsorption were calculated and heat curves were established. Equilibrium isotherms of VOC on TNT were type II, characterizing vapor condensation to form multilayers. The specific surface area and pore volume of TNT were the dominating factors for the determination of its VOC adsorption capacity. The GAB isotherm equation fitted the experimental data more closely than the BET equation. Thermal data showed that the adsorption of VOC on TNT was primarily due to physical forces and TNT exhibited energetically heterogeneous surfaces.