Visible-Light-Driven N−F−Codoped TiO₂ Photocatalysts. 1. Synthesis by Spray Pyrolysis and Surface Characterization

Novel photocatalytic materials, yellow-colored N−F-codoped TiO 2 (NFT) powders, were synthesized from a mixed aqueous solution containing TiCl 4 and NH 4 F by spray pyrolysis (SP). The resulting powders were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), NH 3 -temperature-programmed desorption (NH 3 -TPD), X-ray photoelectron spectroscopy (XPS), and N 2 adsorption. FE-SEM images and N 2 adsorption confirm that the NFT powders possessed spherical particles with a highly porous surface morphology. The doped N and F concentrations in the NFT powders depended significantly on the SP temperature and ranged from 0.10 to 0.26 and from 0.11 to 0.40 atomic % (at. %), respectively. NH 3 -TPD measurement indicates that the surface of the NFT powder was strongly acidic. Moreover, by investigating the characteristics of the TiO 2 precursor hydrolysis and the thermal decomposition behaviors of the other components in the starting solution, we elucidated the reasons for the formation of porous NFT powders, which we ascribed to the enormous gas evolution from NH 4 F during TiO 2 particle formation and the template role played by NH 4 Cl.