LAUSR

Abstract The manner how nano building blocks assemble into hierarchical architectures exerts a tremendous influence on gas-sensing performance of the metal oxides. Herein, we focus on tuning the 1D nanorods into 3D hierarchical urchins with various assembly densities, aiming at investigating the effect between gas diffusion and charge transfer. Via modulating the additive amount of NaOH, loose-, moderate- and close-assembled SnO 2 nanourchins aggregated with nanorods were successfully prepared, respectively. The relationships of nanorond assembly behavior to specific surface and average pore size of the urchin-like nanostructures were discussed in detail. A comparison study reveals that an enhanced gas sensing performance for the sensor made of the moderate-assembled SnO 2 nanourchins towards ethanol occurs over the other two, implying that perhaps there exists an optimizing assembly density range which provides not only enough space for gas diffusion but also sufficient contact network for charge transfer, in terms of good contacts among nanorods in an urchin-like sphere and among nanorods from adjacent spheres.