Effect of copper oxide concentration on the formation and persistency of environmentally persistent free radicals (EPFRs) in particulates.
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 EPFR yields and their persistency on metal loading in particles (0.25, 0.5, 0.75, 1, 2, and 5% CuO/silica). The EPFRs were generated through exposure of particles to three adsorbate vapors at 230 °C: 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 to 2.006. The highest EPFR yield was observed for CuO concentrations between 1 and 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 and 23 h, were observed for phenoxyl-type radicals on 0.5% CuO and chlorophenoxyl-type radicals on 0.75% CuO, respectively.
Department of Chemistry and LSU Superfund Research Center, Louisiana State University , Baton Rouge, Louisiana United States of America.
Lucy W
LW
Kiruri
Lavrent
L
Khachatryan
Barry
B
Dellinger
Slawo
S
Lomnicki
D000327:Adsorption; D002722:Chlorobenzenes / Q000302:isolation & purification; D002733:Chlorophenols / Q000302:isolation & purification; D003300:Copper / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy; D004785:Environmental Pollutants / Q000032:analysis*; D005609:Free Radicals / Q000032:analysis*; D052638:Particulate Matter / Q000737:chemistry*; D019800:Phenol / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013696:Temperature
D002722:Chlorobenzenes; D002733:Chlorophenols; D004785:Environmental Pollutants; D005609:Free Radicals; D052638:Particulate Matter; D019800:Phenol; C004726:2-dichlorobenzene; D012822:Silicon Dioxide; D003300:Copper; C030683:2-chlorophenol; C000520:cuprous oxide