Synthesis and mechanism of particle- and flower-shaped ZnSe nanocrystals: Green chemical approaches toward green nanoproducts

A nontoxic, simple, cheap, and reproducible strategy, which meets the standard of green chemistry, is introduced for the synthesis of ZnSe nanoparticles and nanoflowers. The production of these green nanomaterials can be readily scaled up and performed directly at ambient condition without affecting their qualities. The experimental results show that the as-synthesized ZnSe nanoparticles and nanoflowers with a zinc blende structure have a narrow size distribution without resorting to any postsynthetic size-selective procedure. A systematic study of the nanocrystal formation process indicates the following properties. (i) The amount of precursors plays a greater role in the determination of the nanoparticle size than other reaction parameters. Variation of this parameter allows us to tune the nanoparticle size in the high-temperature annealing process. This tunability is interpreted well by the growth kinetics. (ii) The limited ligand protection mechanism cannot be employed to explain the formation of our nanoflowers. Instead, a new growth mechanism is proposed. Upon heating at high temperature, a mononuclear Zn complex converts to a polynuclear Zn complex with multiple Zn atoms. Each Zn atom grows into one ZnSe nanoparticle after the injection of Se solution. These nanoparticles closely connect and thus look like nanoflowers.