7 research outputs found
Formation of environmentally persistent free radicals (EPFRs) on ZnO at room temperature: Implications for the fundamental model of EPFR generation.
Environmentally persistent free radicals (EPFRs) have significant environmental and public health impacts. In this study, we demonstrate that EPFRs formed on ZnO nanoparticles provide two significant surprises. First, EPR spectroscopy shows that phenoxy radicals form readily on ZnO nanoparticles at room temperature, yielding EPR signals similar to those previously measured after 250°C exposures. Vibrational spectroscopy supports the conclusion that phenoxy-derived species chemisorb to ZnO nanoparticles under both exposure temperatures. Second, DFT calculations indicate that electrons are transferred from ZnO to the adsorbed organic (oxidizing the Zn), the opposite direction proposed by previous descriptions of EPFR formation on metal oxides
Environmentally Persistent Free Radicals (EPFRs). 3. Free versus Bound Hydroxyl Radicals in EPFR Aqueous Solutions
Additional experimental evidence is presented for in vitro generation of hydroxyl radicals because of redox cycling of environmentally persistent free radicals (EPFRs) produced after adsorption of 2-monochlorophenol at 230 °C (2-MCP-230) on copper oxide supported by silica, 5% Cu(II)O/silica (3.9% Cu). A chemical spin trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed. Experiments in spiked O17 water have shown that ∼15% of hydroxyl radicals formed as a result of redox cycling. This amount of hydroxyl radicals arises from an exogenous Fenton reaction and may stay either partially trapped on the surface of particulate matter (physisorbed or chemisorbed) or transferred into solution as free OH. Computational work confirms the highly stable nature of the DMPO–OH adduct, as an intermediate produced by interaction of DMPO with physisorbed/chemisorbed OH (at the interface of solid catalyst/solution). All reaction pathways have been supported by ab initio calculations
Environmentally Persistent Free Radicals (EPFRs). 3. Free versus Bound Hydroxyl Radicals in EPFR Aqueous Solutions
Additional experimental evidence
is presented for <i>in vitro</i> generation of hydroxyl
radicals because of redox cycling of environmentally
persistent free radicals (EPFRs) produced after adsorption of 2-monochlorophenol
at 230 °C (2-MCP-230) on copper oxide supported by silica, 5%
CuÂ(II)ÂO/silica (3.9% Cu). A chemical spin trapping agent, 5,5-dimethyl-1-pyrroline-<i>N</i>-oxide (DMPO), in conjunction with electron paramagnetic
resonance (EPR) spectroscopy was employed. Experiments in spiked O<sup>17</sup> water have shown that ∼15% of hydroxyl radicals formed
as a result of redox cycling. This amount of hydroxyl radicals arises
from an exogenous Fenton reaction and may stay either partially trapped
on the surface of particulate matter (physisorbed or chemisorbed)
or transferred into solution as free OH. Computational work confirms
the highly stable nature of the DMPO–OH adduct, as an intermediate
produced by interaction of DMPO with physisorbed/chemisorbed OH (at
the interface of solid catalyst/solution). All reaction pathways have
been supported by <i>ab initio</i> calculations