Remotion of the antibiotic tetracycline by titania and titania-silica composed materials

Removal of the antibiotic tetracycline (TC) by TiO2 and the mesoporous binary system TiO2-SiO2 have been studied in batch experiments by performing adsorption isotherms/kinetics and photodegradation kinetics under different conditions of pH, supporting electrolyte concentration, temperature, adsorbent amount, and TiO2-loading. On the one hand, the adsorption of TC on the studied materials is strongly dependent on pH, increasing as pH decreases. The adsorption mechanism, controlled by diffusion processes, is strongly related to electrostatic attractions and H-bond formations mainly between amide, carbonylic and phenolic groups of the antibiotic and the functional groups of TiO2. The adsorption capacity at constant pH increases in the order TiO2 < TiO2-SiO2 mainly due to the highly surface area that the silica offers and to the homogenously dispersion of the TiO2 nanocrystallites. On the other hand, the photodegradation rate is affected by the presence of the studied materials at several pH, although its photocatalytic activities are more important at pH 7 or lower. The photodegradation mechanisms seem to be related to the formation of OH center dot radicals which are responsible for the decomposition of TC. The composed titania-silica materials might act not only as an excellent adsorbent but also act as an alternative photocatalyst for pollution control. (C) 2011 Elsevier B.V. All rights reserved.