Transformation of Zinc Oxide Nanoparticles under Environmentally Relevant Conditions

Velintine, Valach Andrian (2020) Transformation of Zinc Oxide Nanoparticles under Environmentally Relevant Conditions. Masters thesis, University Malaysia Sarawak (UNIMAS).

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Abstract

The productions of nanoparticles in nanotechnology industries keep increasing as the demands increase each year due to its unique properties of nanoparticles that can be fully utilized. Zinc oxide (ZnO) nanoparticles is one of the examples that has attracted scientists to produce in larger scales production especially in the consumer products. Without realizing the consequences, ZnO nanoparticles will be released into the environment in various ways either directly or indirectly. Once released, ZnO nanoparticles may be dissociated into Zn2+ ions which is toxic to the environment and eventually effects on human health. In this study, two commercially available zinc oxide (ZnO) nanoparticles of size 50 nm and 100 nm were purchased and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), surface area Brunauer-Emmet-Teller (BET) and Fourier transform infrared (FTIR) spectroscopy. The transformation of ZnO nanoparticles under environmental relevant conditions were also studied. Water chemistry such as pH and ionic strength play important roles in the release of Zn2+ ions. The presence of humic acid and exposure to sunlight could also affect the dissolution of ZnO nanoparticles. XRD and TEM confirmed that the size of the particles was in the range stated at the labels. The dissolutions were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). It was found that the dissolution of ZnO nanoparticles is higher at pH 1 and decreased as the pH increased to pH 11. Dissolution of ZnO nanoparticles also showed pH dependency whereby for both sizes, the dissolution increased when pH decreased. This study also indicates that the fate of ZnO nanoparticles is highly dependent on water chemistry. At higher pH, dissolution of ZnO was limited by solubility equilibrium, because of the negative charge of humic acid, it alters the surface charge of ZnO nanoparticles, attracts them and preventing the particles to aggregates and precipitate. In the presence of humic acid also slowed down the release of Zn2+ ions in aquatic environment. The adsorption of humic acid onto ZnO nanoparticles is observed to follow Langmuir isotherm. Exposure to sunlight encouraged the dissolution of ZnO nanoparticles.

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