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

Abstract

Mo2N decorated TiO2 nanowires were obtained via impregnating titanate nanowires with a mixture of (NH4)6Mo7O24 and hexamethylenetetramine, followed by the calcination at 600–800 oC in N2 atmosphere. The results show that only Mo6+ species can be found in the sample calcined at 600 oC while Mo element is still dominantly in the form of Mo6+ with a negligible amount of γ-Mo2N (namely Moδ+, 0 ​< ​δ ​< ​4) and Mo4+ at 700 oC. In the sample calcined at 800 oC, however, ultrasmall γ-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 γ-Mo2N-absent sample obtained at 800 oC is dominantly in the form of inert rutile TiO2, the introduction of γ-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 γ-Mo2N and TiO2 nanowires. Furthermore, 5% γ-Mo2N decorated TiO2 exhibit better photocatalytic activity due to its higher surface area and more heterojunctions between γ-Mo2N and TiO2. This γ-Mo2N decorated TiO2 photocatalyst can broaden the practical scope of rutile TiO2 and have a promising potential in photocatalytic application.