Self-assembly prismatic aggregates formed during the calcination of ZnO powders: In situ monitoring by ETA technique and their photocatalytic properties

This paper describes a unique phenomenon occurred during the calcination of ZnO powders, i.e., the ZnO particles self-assembled to form prismatic aggregates with a clear edges and faces. Field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to characterize the particle morphology and crystal structure of the calcined sample. The emanation thermal analysis (ETA) technique was used to monitor the changes of ZnO particle surface and subsurface microstructure irregularities and the occurrence of interparticle compaction phenomena under in situ conditions of heating and cooling. It was assumed from the ETA results that the driven force of the self-assembly of ZnO particles towards prismatic aggregates originated from the solid state diffusion and migration of grain boundaries. The photocatalytic tests indicated that the prismatic aggregates of ZnO calcined at 800 °C demonstrated a highest photocatalytic activity for acetaldehyde decomposition because of the enhancement of the surface-exposed high-active crystal face of (101¯0).