In this study, a reproducible spectrophotometric method was established and
applied to measure reductive capacity of various nanomaterials. Reductive capacity had
been implicated in the toxicity of nanomaterials, but a standardized measurement
method had been lacking until this work.
The reductive capacity of nanoparticles was defined as the mass of iron reduced
from Fe3 to Fe2 by unit mass of nanoparticles, in an aqueous solution that initially
contained ferric ions. To measure the reductive capacity, the nanomaterials were
incubated in a ferric aqueous solution for 16 hours at 37 degrees C, and the reductive capacity of
the nanoparticles was determined by measuring the amount of Fe3 reduced to Fe2 using
a spectrophotometric method. The reagents 1,10-phenanthroline and hydroquinone were
used as a Fe2 indicator and a reducing agent respectively for the assay.
To standardize this method, various experiments were carried out. For the initial
ferric solution, various Fe salts were tested, and Iron(III) sulfate was chosen as Fe salt
for the standard method. The measured reductive capacity of nanoparticles was found to
vary with the measurement conditions; the measured reductive capacity increased with increasing the Fe/nanoparticle ratio; the measured reductive capacity increased with
incubation time and leveled off after 8 hours of incubation. For hydrophobic materials,
the surfactant Tween-20 was added so that the particles could be wetted and suspended
in the ferric aqueous solution. After incubation, the particles were removed from the
solution by either filtration or centrifugation before applying the spectrophotometric
method. In addition, optimal pH and minimum time to reach ultimate color intensity
were also found.
Carbon-based nanomaterials, standard reference material and metal oxides were
measured for their reductive capacities with this method and characterized by
transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS),
x-ray diffraction (XRD), BET measurement and Raman spectroscopy. For some
nanoparticles, the reductive capacity was measured for both the pristine form and the
form treated by oxidization or grinding.
All carbon-based nanomaterials, except for pristine C60, have a significant
reductive capacity while reductive capacity of metal oxides is very low. And it was
found that reductive capacity can be increased by surface functional groups or structural
defects and reduced by oxidization or heating (graphitization). The reductive capacity of
a material can play an important role in its toxicology by synergistic toxic effects in the
presence of transition metal ions through the Fenton reaction. Moreover, even without
transition metal ions, the ability of a material to donate electrons can be involved in
toxicity mechanisms via generation of reactive oxygen species.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-08-8204 |
| Date | 2010 August 1900 |
| Creators | Hwang, Wonjoong |
| Contributors | Guo, Bing |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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