TiO(2)/high-silica zeolite composite synthesized by a sol-gel method was applied for the removal of sulfamethazine (SMT) antibiotic from water, and simple models including both adsorption and photocatalytic decomposition were developed. In this study, two types of models were constructed: a synergistic model that included the interaction between the zeolite and TiO(2) in the composite, and an individual model, which did not include the interaction. We obtained rate constants for adsorption, desorption and photocatalytic decomposition experimentally, and compared them with the results calculated using the synergistic and individual models. The individual model predicted that ca. 55% of SMT would be removed from the system after 6h of treatment; however, our experiments showed that 80% of the SMT was removed, suggesting the existence of another reaction pathway. Therefore, a synergistic model was constructed, in which, part of the SMT was adsorbed onto the zeolite within the composite, desorbed from the zeolite and migrated to the TiO(2), and was then photocatalytically decomposed. Experiments were carried out with varying amounts of the TiO2-zeolite composite, and the synergistic model was validated. We estimated that 10% of the desorbed SMT was photocatalytically decomposed without being released into the water. When TiO(2)-zeolite composite concentrations were 0.04, 0.12 and 0.20g/L, and the treatment time was 6h, the proportions of the total decomposition of SMT that occurred via this synergistic reaction pathway were calculated as 52.2%, 58.6% and 66.7%, respectively. In other words, over half of the SMT was decomposed through the synergistic reaction, which played a very significant role in the overall removal of SMT (the remainder of the SMT was decomposed through simple photocatalysis on the TiO(2)).
Keywords: Adsorbent; Composite; Modeling; Photocatalyst; Synergistic reaction.
Copyright © 2014 Elsevier B.V. All rights reserved.