Photocatalytic Degradation of Tetracycline Antibiotic by Titania Photocatalyst under Visible Light

Abstract

Antibiotics (ABs) are antibacterial compounds used to treat bacterial infections both in humans and animals. Sub-therapeutic levels of antibiotics are also given to animals and poultry to promote growth. In agricultural environments, ABs reach croplands via animal manure used as fertilizer and/or AB-contaminated water used for irrigation. ABs can leach from soil and discharge from water treatment plants and eventually contaminate both surface and underground water. Tetracyclines (TCs) are among the most widely used ABs around the world due to their low cost and wide antimicrobial spectrum. In this work, we propose solar-mediated photocatalytic degradation system using titania (TiO2) photocatalyst as a promising, efficient, cost effective, and ecofriendly method to remove TCs from water streams. TiO2 is known for its super quantum yield, low cost, non-toxicity, hydrophilicity, high photoactivity, interesting charge transport properties, and good chemical and photostability. However, what restrict the use of TiO2 in large-scale applications include its large band gap energy of (3.2 eV) which limits its activation to mere UV light, complication of recovery from slurry reactors, and aggregation of its finely dispersed particles. To expand the activity of TiO2 into the visible light region and to enhance its adsorption capacity for TC, we explored its modification via sensitization with Fe ions and via immobilization over inert supports. Beta zeolite (BEA) and silicalite were used as zeolitic supports while nano-fibrous electrospun PVDF-HFP polymeric membranes were used to facilitate the recovery of titania from reaction medium. Metal organic framework (UiO66) was also prepared and used as a support to improve the surface area and adsorption capacity of TiO2. Two different metal sensitization techniques with Iron ions from aqueous solution of FeCl3 were explored. In the ion-exchange method, the substitutional cations within the TiO2/support structure were exchanged with Fe3+. Whereas, in the doping technique, 3 solgel TiO2 was doped with Fe3+ during its synthesis and before its immobilization over support. Fe modified immobilized TiO2 catalysts were characterized using SEM, XRD, BET, UV-VIS DRS, TGA, and FTIR. The photocatalytic performance of the Fe-TiO2/support was evaluated under blue, white LED lights, and real solar irradiations for TC degradation. We also varied the reaction conditions (catalyst dosage, light power and wavelength, temperature, pH, and salt concentration) to optimize the operating conditions for TC photocatalytic degradation under visible light.