Doctor of Philosophy
Institute for Superconducting and Electronic Materials
The study of nanomaterials is an area of extensive research due to the size and shape dependent properties that arise as a result of confinement to the 1 - 100 nm scale. Materials at this scale exhibit new properties that are neither those of the corresponding bulk or individual molecules making up the material. One reason for this is thought to be due to the fact that, at this scale, many of the atoms making up the material lie at its surface, and so, an interface between the material and its surroundings is formed that it is not observed in the corresponding bulk or individual atoms of the material. This can lead to the generation of new or improved physical, chemical, magnetic and biological properties in nanomaterials compared to their larger scale counterparts. Implementation of nanomaterials, such as nanoparticles, into consumer products have also been shown to have a positive impact on the quality life of the general public. One such example of this is the application of inorganic metal oxide nanoparticles in therapeutic sunscreen products. Sunscreens containing these nanoparticles, namely titanium dioxide (TiO2) and zinc oxide (ZnO), protect the skin from harmful solar ultraviolet (UV) radiation and thus contribute to the prevention of erythema (sunburn), immunosuppression, premature skin ageing and skin cancer. The size reduction of these materials to the nanoscale has been shown to improve their optical UV absorbance properties and increase transparency of formulations containing these nanomaterials in comparison to their microsized or bulk counterparts. However, as a consequence of this nano-phenomenon, the photocatalytic potential of these nanoparticles is also exponentially increased. Like a double-edged sword, absorption of UV radiation by these nanoparticles can also lead to the generation of reactive free radical species, which have the capacity to degrade other organic components in a sunscreen formulation. The ability for these sunscreen based nanoparticles to generate free radicals is also of concern if they make contact with viable cells within the skin after topical application. Generation of free radical species within cells can result in a state of oxidative stress, a condition that has been implicated in a number of physiological and neurological diseases as well as cancer development. Although a significant number of studies have suggested these particle remain on the surface of the skin, inconsistencies in some results and discrepancies in the sampling methodologies used have still left the scientific community, and the general public, divided on the continued safe use of these nanoparticles. Investigations into alternative inorganic UV filters with complementary properties to those currently used but without the potential toxicological effects has yielded a limited number of candidate materials. More extensive research has focussed on methods for minimizing or removing the free radical generating potential of TiO2 and ZnO and comprise manipulation of the phase composition, particle morphology and surface chemistry. In this thesis work, we investigate different potential coating materials for TiO2 based nanomaterials and assess their suitability based on their impact towards UV light absorption and photocatalytic/phototoxic potential in hopes of improving the safety of sunscreen based inorganic UV filters.
Morlando, Alexander, Next Generation Inorganic Nanomaterials for Sunscreening Applications, Doctor of Philosophy thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2020. https://ro.uow.edu.au/theses1/901
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.