Synthesis of zinc sulfide nanospheres by spray pyrolysis
Kaus, Mark Joseph
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The focus of this research was to synthesize zinc sulfide nanostructures because of their various applications that can range from bioimaging to photocatalysis. Zinc sulfide nanoparticles can provide unique photonic, electronic and catalytic properties that make them of interest for all of these applications. Using spray pyrolysis, ZnS nanoparticles can be created with a simple, continuous and reproducible method that can be quite easily controlled. We used two polymer templates in the process of creating nanospheres. These were poly (ethylene glycol) methyl ether (PEG) and polyvinylpyrrolidone (PVP), which were used to control the internal morphology of the nanospheres. A droplet-to-particle conversion was used to create spherical nanoparticles with either a hollow or porous geometry depending on the polymer template used. The process uses a zinc acetate and thiourea precursor solution for the formation of zinc sulfide. In solution, these precursors react to form a bis-thiourea zinc acetate (BTZA) complex, which precipitates as the solvent evaporates in the high temperature furnace. After the solvent completely evaporates, the BTZA complex decomposes to produce zinc sulfide. When PEG is used, the BZTA precipitates on the droplet surface, with PEG segregating to the core. This ultimately leads to formation of hollow nanospheres. However, when PVP is used as the polymer template, it interacts strongly with the bis-thiourea complex and ZnS such that the PVP and ZnS precipitate together throughout the droplet. Once the evaporation of the solvent occurs, the polymer template pyrolyzes at high temperatures such that pores are left throughout the newly formed ZnS nanospheres. However, in our reactor system, pyrolysis of the polymer templates was incomplete, and the hollow or porous nanospheres contained significant residual polymer. Complete polymer pyrolysis may be possible at longer residence time.