Formation of hydroxyl radicals and kinetic study of 2-chlorophenol photocatalytic oxidation using C-doped TiO₂, N-doped TiO₂, and C,N Co-doped TiO₂ under visible light

This work reports on synthesis, characterization, adsorption ability, formation rate of hydroxyl radicals (OH^•), photocatalytic oxidation kinetics, and mineralization ability of C-doped titanium dioxide (TiO₂), N-doped TiO₂, and C,N co-doped TiO₂ prepared by the sol–gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy were used to analyze the titania. The rate of formation of OH^• for each type of titania was determined, and the OH-index was calculated. The kinetics of as-synthesized TiO₂ catalysts in photocatalytic oxidation of 2-chlorophenol (2-CP) under visible light irradiation were evaluated. Results revealed that nitrogen was incorporated into the lattice of titania with the structure of O-Ti-N linkages in N-doped TiO₂ and C,N co-doped TiO₂. Carbon was joined to the Ti-O-C bond in the C-doped TiO₂ and C,N co-doped TiO₂. The 2-CP adsorption ability of C,N co-doped TiO₂ and C-doped TiO₂ originated from a layer composed of a complex carbonaceous mixture at the surface of TiO₂. C,N co-doped TiO₂ had highest formation rate of OH^• and photocatalytic activity due to a synergistic effect of carbon and nitrogen co-doping. The order of photocatalytic activity per unit surface area was the same as that of the formation rate of OH^• unit surface area in the following order: C,N co-doped TiO₂ > C-doped TiO₂ > N-doped TiO₂ > undoped TiO₂.