Sensitization of TiO2 by halogenated porphyrin derivatives for visible light biomedical and environmental photocatalysis

Abstract

New hybrid TiO2-based materials were obtained by impregnation of semiconductor with 5,10,15,20-tetrakis(2,6-difluorosulfonylophenyl)porphyrin (F2POH) and its zinc(II) complex (ZnF2POH). The efficient immobilization of the porphyrins on the surface of titanium dioxide was obtained due to the presence of -SO3H functional groups, which interact with the surface of TiO2. All prepared materials were thoroughly characterized in terms of their morphological, spectroscopic, electrochemical, photochemical and functional properties by diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry, photoelectrochemistry as well as biological and photocatalytic tests. The modification of TiO2 with halogenated (metallo)porphyrins allows to improve overall properties of the studied materials and assess their activity upon visible part of the electromagnetic radiation (>400 nm). Nevertheless, due to their limited stability, observed photochemical effects are quite short lived. It is shown that the fluorine atoms present in porphyrin structure modulate not only physicochemical properties of the hybrid materials but also their photoactivity in the generation of reactive oxygen species (ROS). The materials based on fluorinated porphyrins have shown photocatalytic activity in the degradation of model pollutants: 4-chlorophenol and opioid drug – tramadol. Moreover, they exhibit quite significant antibacterial activity against Gram-positive (S. aureus), notably higher than TiO2 modified with commercial tetraphenyl porphyrin (TPPS). The role of singlet oxygen, hydroxyl and iodide radicals in the performed photoinactivation processes is elucidated for all studied systems. Finally, TiO2 alone is not active against bacteria upon visible light irradiation, what implies that materials containing fluorinated and sulfonated porphyrins have improved photochemical activity and efficiency of the ROS generation. Thus, they are interesting materials especially for photodynamic inactivation of microorganisms.