Effect of Cu addition on TiO2 surface properties and photocatalytic performance: X-ray Absorption Spectroscopy analysis

In this work, 1 wt% Cu doped TiO2 was prepared by incipient wetness impregnation by using pure TiO2 which was synthesized by sol-gel method. From XRD results, the enlargement of TiO2 unit cells was observed which indicated the incorporation of Cu into TiO2 lattice. The optical property showed more visible region absorption of Cu-doped TiO2 sample which was due to a reduction of band gap energy. Ti K-edge XANES spectra of pure and doped TiO2 confirmed the anatase (Ti4+) form while Cu K-edge XANES of Cu-doped catalyst presented the oxidation state of Cu as Cu2+ in octahedral symmetry. The EXAFS spectra of Ti K-edge and Cu K-edge of 1 wt% Cu/TiO2 evidenced the substitution of Cu into Ti site by observing the variation in bond distance between probe atom and the neighboring environment. According to the photodegradation performance study, the photodegradation rate of Cu-doped TiO2 under UV irradiation exhibited almost 2 times higher than that of pure TiO2. The enhancement of photocatalytic activity can be proofed by Ti L-2,L-3-edge XANES spectra. These results indicated that Cu acts as an electron trapping site which resulted from the creation of impurity energy levels below the conduction band of TiO2. Moreover, an oxygen vacancy production upon the addition of Cu can also trap an excited electron from the valence band of TiO2. Therefore, the electron scavenger behavior together with oxygen vacancy can suppress the electron-hole recombination, yielding more electrons and holes to further undergo the reaction.