Synthesis and ageing transformations of manufactured metal oxide nanomaterials

Abstract

With the increased use of manufactured nanomaterials (MNMs) and increased environmental and human exposure, “nanosafety”, the assessment of hazards from MNMs, has become a major research objective. Despite this, the field has yet to advance sufficiently due to challenges in characterisation and in linking systematically physicochemical properties to toxicity. In order to understand what makes a nanomaterial harmful, toxicity studies need to be carried out. Yet these need to be performed on a range of well-characterised comparable MNMs with systematically varied properties. Furthermore, most nanoparticles undergo transformations and react in ways that change their behaviour and properties over time resulting in aged nanoparticles. These no longer have the same characteristics of their pristine counterparts, which in turn could influence their toxicity. Therefore thorough understanding of the behaviour and ageing processes that the MNMs can undergo is also necessary. The aim of this work was to develop and fully characterise a library of comparable nanoparticles with a range of core chemistries, but the same capping. Following this behavioural and ageing studies of the MNMs in the different scenarios were carried out. A library of metal oxide NMs based on a polyvinylpyrrolidone (PVP) capped ceria synthesis was developed and extensively characterised. The protocol was successfully modified to produce PVP capped zinc oxide and copper oxide of comparable sizes (c. 5, 7 and 20 nm). Characterisation was carried out by Dynamic Light Scattering (DLS), Zeta Potential, Ultra-Violet-Visible Light Spectroscopy (UV-VIS), Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy Electron Energy Loss Spectroscopy (STEM-EELS), Fourier Transform Infra-red (FT-IR), X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS) and Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) so as to confirm the success of the synthesis and gain valuable information on NM characteristics. Results suggest that the tested protocol was successful in creating stable PVP capped metal oxide NMs of reproducible sizes and that a common mechanism hypothesis holds true. The metal oxide core had mixed valency oxides when the metal was stable in multiple valency states. Additionally, PVP was found to play a significant role in the synthesis of the MNMs influencing both their physical and chemical properties [excerpt].