Hwang, Wonjoong (2010-08). Standardization and Application of Spectrophotometric Method for Reductive Capacity Measurement of Nanomaterials. Master's Thesis. Thesis uri icon

abstract

  • 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.
  • 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.

publication date

  • August 2010