Experimental study on the bandgap narrowings of TiO2 films calcined under N2 or NH3 atmosphere

The anatase nanoparticulate TiO2 films were calcined at temperatures ranging from 500 °C to 650 °C under nitrogen and ammonia atmospheres, respectively. The bare and calcined films were characterized by Raman spectroscopy, atomic force microscope, ultraviolet–visible absorption spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activities were evaluated by studying the decomposition of methylene blue. With the same crystalline phases and same N dopant concentrations, the films calcined in NH3 exhibited much larger redshifts of the photoabsorption edges and much higher visible-light photocatalytic efficiencies than the films calcined in N2, indicating the incorporation of hydrogen played an important role in the bandgap narrowing.