Morphology-controllable electrochemical synthesis and photoluminescence properties of ZnO nanocrystals with porous structures

Abstract

A modified electrochemical route was developed to deposit powdery ZnO nanocrystals. The approach is based on sodium citrate acting as the supporting electrolyte as well as a complex agent, Zn²⁺ ions resulting from the electro-oxidation of a Zn anode rather than zinc salts, and a H₂O–EtOH mixed-solvent as the electrolytic medium. The supporting electrolytes, electrolytic media and additives play important roles in controlling the morphology of ZnO crystals. Under the synergetic action of the complex effect of citrate ions and solvent effect of H₂O–EtOH (or electrostatic-adsorption of additives), ZnO nanoparticles could self-assemble to the nanocrystals with porous structures (such as nanospheres, nanoflowers and coral-like nanocrystals) without templates. The morphology of the ZnO crystals could evolve from nanospheres to nanorods or nanospindles by changing the electrolytic media or supporting electrolytes. A possible growth mechanism of the ZnO nanocrystals with different shapes was also discussed. In addition, further studies indicate that the prepared nanospheres (or nanoflowers) with hollow or porous structures have better photoluminescence performances than the nanorods.