A Dopant Replacement-Driven Molten Salt Method toward the Synthesis of Sub-5-nm-Sized Ultrathin Nanowires

The high-temperature molten-salt method is an important inorganic synthetic route to a wide variety of morphological phenotypes. However, its utility is limited by the fact that it is typically incapable of producing ultrathin (<5 nm diameter) nanowires, which have a crucial role in novel nanotechnology applications. Herein, a rapid molten salt-based synthesis of sub-5-nm-sized nanowires of hexagonal tungsten oxide (h-WO3) that is critically dependent on a substantial proportion of molybdenum (Mo) dopant is described. This dopant-driven morphological transition in tungsten oxide (WO3) may be attributable to the collapse of layered structure, followed by nanocluster aggregation, coalescence, and recrystallization to form ultrathin nanowires. Interestingly, due to the structural properties of h-WO3, the thus-formed ultrathin nanowires are demonstrated to be excellent photocatalysts for the production of ammonia (NH3) from nitrogen (N-2) and water. The ultrathin nanowires exhibit a high photocatalytic NH3-production activity with a rate of 370 mu mol g(-1) h(-1) and an apparent quantum efficiency of 0.84% at 420 nm, which is more than twice that obtained from the best-performing Mo-doped W18O49 nanowire catalysts. It is envisaged that the dopant replacement-driven synthetic protocol will allow for rapid access to a series of ultrathin nanostructures with intriguing properties and increase potential applications.