Controlled ZnO hierarchical structure for improved gas sensing performance

ZnO hierarchical aggregates, assembled by either nanosheets or nanoneedles, with well-controlled morphologies were prepared using a solvothermal method at ambient temperature. It is found that the morphology transition of the hierarchical aggregates can be controlled by adjusting reactant composition. A possible growth mechanism is proposed to interpret how the nanosheet and nanoneedle aggregated structures are formed. The aggregate sample assembled by 1D building blocks has smaller surface to volume ratio, comparing to the 2D block-assembled one. However, the former shows higher gas response, while the later exhibits better selectivity as well as faster response and recovery rates. The better selectivity can be attributed to the larger specific surface area and the exposed special active planes of 2D structure.