Cieslak, Emilia
(2010).
Imaging and analysis of natural and manufactured nanoparticles.
University of Birmingham.
Ph.D.
Abstract
Nanotechnology, a new science discipline, which studies design, characterization, production and applications of materials with sizes 1-100 nm, has marked a new breakthrough in technological development. It promises to revolutionise many aspects of modern life. However, with increasing markets and industrial scale of production, nanomaterials (NMs) became a potential, but largely unknown, risk to human health and the environment. Carbon based NMs including carbon nanotubes (CNTs) and fullerenes are an important class of NMs and are further studied in this thesis. Potential fate and behaviour of single-walled CNTs (SWCNTs) was investigated in natural waters using transmission electron microscopy (TEM) and atomic force microscopy (AFM). There was a focus on CNT interactions with natural aquatic colloids along with the impacts of other solution conditions at environmentally relevant levels. Similar research on fullerenes C60 was also undertaken, as a part of a wider study investigating fish ecotoxicology of fullerenes. Nanoscale atmospheric particles were imaged and analysed with AFM. Additionally, a pilot study on metal speciation in SWCNTaq was conducted to determine partitioning of Ni, Y, Cd, Cu and Cr between particle-bound, labile and dissolved fractions with a view to better understand the role of SWCNTs in trace metals binding (and thus influencing their transport, chemistry and bioavailability). The results indicate that SWCNTs in aquatic systems are likely to interact with natural nanoscale material. The experiments showed that SWCNTs in aqueous suspensions are stabilised with humic acid (probably by surface coating formation) and precipitated by divalent cations, while monovalent cations did not exhibit such destabilising effects. 95-100 % of yttrium (catalyst residue) was retained by the ultrafiltration membrane at all studied conditions indicating its particulate or particlebound speciation. On the other hand, the majority of chromium was dissolved. In general, the presence of humic acid decreased dissolved and labile metal species whereas Ca2+ had the opposite effect. Comparison of TEM and AFM results showed that both techniques are suitable to study suspended SWCNTs and produced consistent and complementary quantitative and qualitative results. An improved protocol (involving ultracentrifugation) for TEM specimen preparation was tested with aqueous suspensions of SWCNTs and nC60. It shortened the analysis time and improved reproducibility. The results show that fullerenes form very stable aqueous suspensions. However, the majority of the dispersed C60 occurs in microscale, rather than nanoscale aggregates, with only ca. 2% of material by mass between 1 and 100 nm. Visualisation of C60 in the presence of natural aquatic colloids did not show such strong interactions as in case of SWCNTs. Two analysed size fractions of atmospheric nanoparticles collected with an inertial impactor proved to be significantly contaminated with particles in the size range of 1-10 nm, which was attributed mainly to the diffusive mechanism of impaction for the imaged material.
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