Titania-zeolite composite for tetracycline photocatalytic degradation under visible light: A comparison between doping and ion exchange.

In this study, TiO supported over embryonic Beta zeolite (BEA) was prepared for the photocatalytic degradation of Tetracycline (TC) antibiotic under visible light. The immobilization of sol-gel TiO over the zeolite increased its surface area from 33 (m/g) to 226 (m/g) and enhanced its adsorption efficiency from 8 % to 18 %. In order to expand the photocatalytic activity of TiO towards the visible light region (i.e. λ > 380 nm), two different metal sensitization techniques with Iron ions from aqueous solution of FeCl were explored. In the ion-exchange method, the substitutional cations within the TiO/BEA structure were exchanged with Fe. Whereas, in the doping technique, solgel TiO was doped with Fe during its synthesis and before its immobilization over Zeolite. Four different samples with 20, 40, 60, and 100 % w/w of TiO/BEA ratio were prepared. After testing the various ion-exchanged photocatalysts under blue and white lights, only Fe-60%TiO/BEA showed better activity compared to pure TiO under white light at TC initial concentration,  = 20 ppm. For the doped immobilized Titania with 60 wt% TiO/BEA, three different doped photocatalysts were prepared with 3 %, 7 %, and 10 % per mole Fe/TiO. All the Fe-doped TiO/BEA photocatalysts showed better activity compared to pure TiO under white light. Under solar irradiations, the 3 % Fe-doped TiO/BEA was able to degrade all TC within 120 min, while Fe-60%TiO/BEA needed 200 min, and TiO needed more than 300 min. This enhanced performance was a result of both increased surface area due to immobilization over BEA as well as iron doping by Fe that simultaneously increased the visible light absorption of TiO and minimized the charge carrier recombination effect.