Deposition of ultrasmall γ-Mo2N nanocrystals on TiO2 nanowires and their promotion effect on photocatalytic activity

Mo2N decorated TiO2 nanowires were obtained via impregnating titanate nanowires with a mixture of (NH4)(6)Mo7O24 and hexamethylenetetramine, followed by the calcination at 600-800 degrees C in N-2 atmosphere. The results show that only Mo6+ species can be found in the sample calcined at 600 degrees C while Mo element is still dominantly in the form of Mo6+ with a negligible amount of gamma-Mo2N (namely Mo delta+, 0 < d < 4) and Mo4+ at 700 degrees C. In the sample calcined at 800 degrees C, however, ultrasmall gamma-Mo2N nanocrystals with an average size of about 3.3 nm can be observed on the surface of TiO2 nanowires. The photocatalytic activity test reveals that, although the gamma-Mo2N-absent sample obtained at 800 degrees C is dominantly in the form of inert rutile TiO2, the introduction of gamma-Mo2N nanocrystals can significantly improve its performance to be more than doubled in methyl orange (MO) removal percentage, increasing from 36.5% to 75.5% after 2h irradiation (high-pressure mercury lamp), due to the formation of heterojunction between gamma-Mo2N and TiO2 nanowires. Furthermore, 5% gamma-Mo2N decorated TiO2 exhibit better photocatalytic activity due to its higher surface area and more heterojunctions between gamma-Mo2N and TiO2. This gamma-Mo2N decorated TiO2 photocatalyst can broaden the practical scope of rutile TiO2 and have a promising potential in photocatalytic application.