Effects of cerium dopant concentration on structural properties and photocatalytic activity of electrospun Ce-doped TiO₂ nanofibers

Electrospun (Formula presented.) and Ce-doped (Formula presented.) nanofibers were prepared with 0.5, 2.0 and 8.0 % weight Ce. The structural properties and phase composition were characterized using high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction and X-ray absorption near edge spectroscopy (XANES) at the Ti K-edge. The undoped nanofibers are composed of an assembly of (Formula presented.) nanoparticles and their crystal structure is a mixture of anatase and rutile phases with an anatase:rutile volume ratio close to 3:1. As Ce is introduced, the nanoparticles decrease in size and the rutile phase volume decreases. Ce (Formula presented.)-edge XANES probed the local structure of Ce dopants. At 0.5 % Ce, most Ce ions are incorporated in the (Formula presented.) charge state but, at 2 % Ce, the majority are (Formula presented.). Visible light absorption indicated that (Formula presented.) act as shallow acceptors that only participate in absorption of wavelengths below 420 nm but (Formula presented.) impurity states are associated with absorption of wavelengths up to 550 nm. Photocatalytic performance of the nanofibers was assessed by measuring the degradation of adsorbed Rhodamine B in aqueous solution under visible and ultraviolet light. The 0.5 % Ce-doped (Formula presented.) nanofiber showed the best visible-light photocatalytic activity, which is probably due to the majority presence of (Formula presented.). At higher Ce concentration, the photocatalytic reaction rate was lower than undoped nanofibers, indicating that recombination at the (Formula presented.) sites is rate limiting.