Catalyst-free growth of quasi-aligned nanorods of single crystal Cu3Mo2O9 and their catalytic properties.

We propose a simple and catalyst-free method to grow quasi-aligned single crystalline Cu(3)Mo(2)O(9) nanorods in terms of a mechanism differing from the conventional vapor-solid (VS) and vapor-liquid-solid (VLS) ones for chemical vapor deposition (CVD) methods by directly heating Cu foils in a mixed atmosphere of MoO(3) vapor and air. High quality Cu(3)Mo(2)O(9) nanorods can be simply grown in a temperature range from 450 to 550 degrees C whose diameter, length, and distribution density are dependent on both heating temperature and time. Interestingly, the growth rate at 550 degrees C drops significantly after 6 h. All nanorods grow along the [010] direction. On the basis of a proposed growth model, the nucleation of Cu(3)Mo(2)O(9) nanorods is believed to be governed by formation of initial polycrystalline Cu(x)O protuberances with nanoscale diameters on Cu foils which may act as growth "templates". This novel method can be applied to grow other similar tertiary transition metal oxide nanostructures on substrates with large sizes. Most importantly, these Cu(3)Mo(2)O(9) nanorods decrease the ignition temperature of Printex U model soot from 600 to 438 degrees C, being in between 200 and 450 degrees C of the exhaust of diesel-powered combustion engines, which are therefore expected to be a potential efficient and environmentally friendly catalyst for diesel exhaust combustion.