Study on the Growth of Novel Hierarchical Structure of ZnO via Vapor Phase Synthesis

We synthesized novel hierarchical structure of ZnO via simple vapor phase synthesis and investigated its applicability as a photocatalyst.

Zinc pellet (99.95 %) was loaded into the end of semi-sealed quartz tube (φ 5 cm × 40 cm), then the tube was inserted into the horizontal tube furnace which has been preheated to 950℃. In the furnace, ZnO whiskers are grown through evaporation, diffusion and oxidation process as shown in Fig 1.

Fig 1. SEM images of products(a-Sample 1, b-Sample 2)

The specific surface area of the samples was evaluated. The result shows that the specific surface area of Sample 2 is 19.5 m²/g, significantly larger than the value of 5.4 m²/g for Sample 1.

On the basis of the experimental result, we estimated that spiny tetrapod structure was grown through two steps: formation of smooth tetrapods structure and growth of spiny structure on its surface.

Fig 2. Growth mechanism of spiny tetrapod ZnO

Formation of spiny tetrapods is identified by analyzing SEM images.

Fig 3. SEM images of one leg of the spiny tetrapod

Note that Fig 3(a) and 3(b) are the comparatively initial and final stages of the spine crystals growth on the surface of tetrapod ZnO, respectively.

The trunk of a tetrapod with rough surfaces as shown in Fig 3(a), can provide a strong evidence that spine crystals grow from the secondary nucleation on the smooth tetrapod.

The formation of sheet-like nanostructures grown on the surface of the tetrapod ZnO, shown in Fig 3(b) can be interpreted as the formation of linear nuclei via agglomerated and fused zinc suboxide droplets deposited on the smooth tetrapod and their subsequent growth.

The results has been published in the "Functional Materials Letters" under the title of "Novel hierarchical structure of ZnO: Growth of spiny tetrapod via vapor phase synthesis"(http://doi.org/10.1142/S1793604725510671).