One-step preparation, characterization and visible-light photocatalytic activity of Cr-doped TiO2 with anatase and rutile bicrystalline phases

Cr-doped TiO2 (Cr-TiO2) nanoparticles with anatase and rutile bicrystalline phases were synthesized by a simple one-step flame spray pyrolysis (FSP) technique. The influences of chromium doping on the phase composition, microstructures, and optical properties of Cr-TiO2 were analyzed by the methods of XRD, TEM, EPR, XPS, UV–vis diffuse reflectance spectroscopy, and nitrogen adsorption–desorption. It was revealed that Cr3+ doping not only extends the visible light response of TiO2 but also increases the content of rutile in the bicrystalline TiO2. XPS results confirmed that Cr3+ can effectively promote the formation of oxygen vacancy which is contributed to the anatase-to-rutile transformation. EPR analysis indicated that the existing state of Cr in Cr-TiO2 is closely relative to the Cr content: Cr is mainly incorporated into the crystal lattice of TiO2 when the Cr content is lower than 1 at.%, while higher Cr content is favorable to the formation of Cr2O3 clusters. The photocatalytic activities of different Cr-TiO2 photocatalytsts were evaluated in terms of the photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) under visible light irradiation. Appropriate Cr3+ doping can significantly enhance the visible-light photocatalytic activity of TiO2, which is attributed to the improvement of visible light response as well as the suitable anatase-to-rutile ratio. Excess Cr3+ doping is detrimental to the improvement of visible light photocatalytic activity, which is relative to the formation of Cr2O3 clusters as well as too high rutile content.

► Bicrystalline Cr-TiO2 was synthesized by a one-step flame spray pyrolysis technique.
► Cr3+ doping not only extends light response but also adjusts the ratio of anatase-to-rutile.
► Cr3+ doping facilitates the formation of oxygen vacancy and further promotes anatase-to-rutile transformation.
► The photocatalytic activity of Cr-TiO2 is determined by its crystal structure, Cr state, and light absorption.