Effect of Copper Oxide Concentration on the Formation and Persistency of Environmentally Persistent Free Radicals (EPFRs) in Particulates
Lomnicki, Slawomir M
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ABSTRACT Environmentally persistent free radicals (EPFRs) are formed by the chemisorption of substituted aromatics on metal oxide surfaces in both combustion sources and superfund sites. The current study reports the dependency of EPFRs yields and their persistency on metal loading in particles (0.25, 0.5, 0.75, 1, 2, and 3% CuO/silica). The EPFRs were generated through exposure of particles to adsorbate vapors at 230 0C: phenol, 2-monochlorophenol (2-MCP) and dichlorobenzene (DCBz). Adsorption resulted in the formation of surface-bound phenoxyl- and semiquinoine-type radicals with characteristic EPR spectra displaying a g-value ranging from ~2.0037 - 2.006. The highest EPFRs yield was observed for CuO concentrations between 1-3% in relation to MCP and Phenol adsorption. However, radical density, which is expressed as the number of radicals per copper atom, was highest at 0.75 - 1% CuO loading. For 1,2-dichlorobenzene adsorption, radical concentration increased linearly with decreasing copper content. At the same time, a qualitative change in the radicals formed was observed - from semiquinone to chlorophenoxyl radicals. The two longest lifetimes, 25 h and 23 h, were observed for phenoxyl-type radicals on 0.5% CuO and chlorophenoxyl-type radicals on 0.75% CuO, respectively.