A dissertation submitted to the Faculty of Science of the University of
Witwatersrand, Johannesburg, in full fulfilment of the requirements for the degree
of Master of Science.
May 2017 / Nanomaterials (NMs) have been shown to exhibit unique physical and chemical
properties that are highly size and shape-dependent. The ability to control synthesis
of nanoparticles (NPs) with particular shapes and sizes can lead to exciting new
applications or enhancements of current systems in the fields of optics, electronics,
catalytics, biomedicine and biotechnology. Due to increased chemical pollution as
well as health concerns, biological synthesis of NMs has quickly emerged as
potentially being an eco-friendly, scalable, and clean alternative to chemical and
physical synthesis. In this study, the inference that the heavy metal-resistant
bacteria, Paenibacillus castaneae, has the propensity to synthesize metal NPs was
validated.
NP formation was achieved after the exposure of bacterial cell biomass or cell-free
extracts (CFE) to excess metal ion precursors in solution. These include lead nitrate
and calcium sulphate dehydrate, gold (III) chloride trihydrate and silver nitrate,
respectively. All reactions were incubated at 37 °C for 72 h at 200 rpm and observed
for a colour change. UV–visible (UV-Vis) spectral scans (200 nm – 900 nm) were
measured on a Jasco V-630 UV-Vis spectrophotometer. For scanning electron
microscopy (SEM), samples were fixed, dehydrated and loaded onto carbon-coated
aluminium stubs. The stubs were then sputter-coated with either Au/Pd or Cr and
analysed on the FEI Nova Nanolab 600 FEG-SEM/FIB. Size distribution analysis
was done using transmission electron microscopy (TEM) using the FEI Tecnai T12
TEM and Image J software. Powder X-ray diffraction measurements were carried
out on a Rigaku Miniflex-II X-ray diffractrometer.
Colour changes indicative of the synthesis of PbS, Au and Ag NPs were observed
as a white precipitate (PbS), purple (Au) and yellow-brown (Ag) colour,
respectively. This was confirmed by absorbance peaks at 325 nm and 550 nm (PbS),
595 nm (Au) and 440 nm (Ag) from UV-Vis analyses. Exposure of P. castaneae
biomass and CFE to PbS ions in solution resulted in the production of nanospheres,
irregularly-shaped NPs, nanorods, nanowires as well as large nanoflowers.
Exposure of P. castaneae biomass to Au3+ ions in solution produced Au
nanospheres, nanotriangles, nanohexagons, nanopentagons and nanopolyhedrons.
Ag/AgCl NP production occurred using both the P. castaneae biomass and CFE,
and resulted in the synthesis of nanospheres only.
This is the first report of the biosynthesis of such a diverse set of anisotropic NPs
by P. castaneae. It is also the first instance in which anisotropic PbS nanorods and
nanowires, 3-D Au nanoprisms as well as “rough” Ag/AgCl nanospheres were
bacterially produced. This study serves as an eco-friendly approach for the
synthesis of NPs that is a simple yet amenable method for the large-scale
commercial production of nanoparticles with technical relevance. This in turn
expands the limited knowledge surrounding the biological synthesis of heavy metal
NMs. / MT 2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/23489 |
| Date | January 2017 |
| Creators | Hiebner, Dishon Wayne |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xiii, 130 leaves), application/pdf |
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