Thesis submitted in fulfilment of the requirements for the degree
DOCTOR TECHNOLOGIAE: ENGINEERING: CHEMICAL
in the
FACULTY OF ENGINEERING
at the
CAPE PENINSULA UNIVERSITY OF TECHNOLOGY
2014 / Several authors have reported on the use of alcohols – water /or mixed solvents to synthesise metal oxide
nanoparticles. However, no systematic study has been carried out to evaluate the effect of mixed solvent
on the particle characteristics, although considerable research has been reported, a gap still exists with
regard to the effect of the alcohols as solvents on the growth kinetics of nanoparticles. To address these
issues, four different alcohols, namely, methanol (MeOH), ethanol (EtOH), propanol (PrOH) and butanol
(BuOH) were used as solvents in the synthesis of β-FeOOH particles.
The effect of organic solvents on the growth kinetics of β-FeOOH nanorods has been evaluated for the
first time in this study. Two-stage growth of akaganeite nanorods has been observed in BuOH and PrOH.
The first growth stage follows a typical power law representing Ostwald ripening (OR) kinetic. The
second stage was found to be asymptotic and obeyed oriented attachment (OA) kinetic. The proof of the
OA kinetic also comes from the HRTEM images of the synthesised particles. Simultaneous occurrence of
the two mechanisms was observed in the growth of the particles synthesised in EtOH and MeOH. The
rate constants for OR kinetic, KOR, was found to be higher than the rate constant for OA kinetic, KOA, for
different solvents used.
Preamble
The use of a mixed solvent is a new approach in the synthesis and processing of materials. Various
researchers have stated that the surface tension of the solvent plays an important role in the formation of
uniform nanorods. However, the effect of surface tension was not correlated with the particle growth,
earlier, though the dielectric properties of the mixed solvents were only taken into account. Additionally,
no quantitative or qualitative relationship was presented between surface tension and particle growth in
the literature. In this work an attempt to correlate these two parameters (surface tension and particle
growth) with the concentration of the precursor and temperature was made, resulting in an exponential
relationship between KOR for the particle growth and surface tension of the alcohols. Furthermore, the
relationship between surface tension and particle growth was validated by an independent study using
statistically designed experiments to account for the influence of various process variables on the particle
growth. The findings in this study obtained from both theoretical and experimental work provides an
insight into the relationship between solvent surface tension and particle growth interactions, producing a
new piece of information that will further promote our understanding of the formation mechanisms of β-
FeOOH growth.
The transformation temperature of akaganeite (β-FeOOH) nanorods to hematite (α-Fe2O3) particles was
found to be solvent dependent. Thermogravimetric analysis and differential scanning calorimetry were
performed to evaluate the effect of alcohol on the thermodynamic stability of the particles. Alcohol as
solvent played a significant role in the dehydration property of the synthesised particles. The percentage
mass loss of the particles at 300°C decreases linearly with increasing carbon number in the linear alkyl
chain of the solvent.
The effect of alcohol type on the particle morphology was found to be more pronounced at higher FeCl3
concentrations (>0.5M). Splitting of β-FeOOH nanorods was observed at FeCl3 concentration of 0.7M in
BuOH. In PrOH, rectangular morphologies were obtained whereas nanoribbons resulted in surfactant-free
conditions. It was found that the nature of anions (chloride vs. nitrate and sulphate) in the precursor salt
also influenced the morphology.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/928 |
| Date | January 2014 |
| Creators | Chowdhury, Mahabubur Rahman |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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