Exploring Variables in Aqueous Synthesis of Zinc Oxide Nanoparticles

Zinc oxide is commonly found in sunblock and antibacterial creams. For these technologies and many others, the habit and size of crystals, connected to their surface properties, are important to be able to reproducibly synthesize. This research into the aqueous synthesis of zinc oxide nanoparticles with water as a solvent is an extension of previous work using ethanol as a solvent, with the eventual goal of bacterial remediation. While previous studies used zinc sulfate and zinc acetate reactants, zinc chloride was used here. This exploratory research examined many variables: zinc molarities (0.005-0.05), sodium hydroxide molarities (0.05-0.5), presence or absence of guar gum, and time for mixing were all altered in a controlled fashion. The passivating agent, guar gum, was included to inhibit growth, limiting particle size. X-ray diffraction and particle size data were collected on prepared samples. Analysis showed consistent synthesis of zinc oxide, but none of the trials resulted in nanoparticles; smallest sizes were on the order of 1-3 mm, and typical sample size averages were 25-50 mm. Measured pH, dependent on sodium hydroxide amount, showed no correlation to particle size, but smaller particle sizes tended to favor lower molarities of both zinc chloride and sodium hydroxide. In addition, warmer temperatures (room temperature versus ≈70 °C) led to larger particle sizes; thereafter, experimentation was restricted to room temperature. Exploratory synthesis with water has enabled the development of fundamental knowledge for growth from aqueous solutions, and the potential ability to use inexpensive, abundant water as a solvent for useful materials