Highly active TiO2−x−yNxFy visible photocatalyst prepared under supercritical conditions in NH4F/EtOH fluid

A novel N and F co-doped TiO2 (TiO2−x−yNxFy) photocatalyst is prepared by treating the TiO2 precursor in NH4F/ethanol fluid under supercritical conditions. During photocatalytic degradation of methylene blue under visible light irradiation, the as-prepared TiO2−x−yNxFy exhibits higher activity than the undoped TiO2, N-doped TiO2 (TiO2−xNx), and F-doped TiO2 (TiO2−yFy). Based on the characterizations including XRD, Raman, FTIR, TEM, PLS, UV–vis DRS, N2 adsorption–desorption isotherms, XPS and NH3-TPD, the synergetic promotions of N- and F-dopants incorporated into the TiO2 lattice are discussed based on the enhanced spectral response in visible region, oxygen vacancies, and surface acidic sites. Meanwhile, the supercritical treatment also promotes the activity owing to the increase in both the surface area and the crystallization degree of anatase, and the enhanced incorporation of N- and F-dopants into the TiO2 lattice.