Mechanistic studies of surface catalyzed H2O2 decomposition and contaminant degradation in the presence of sand

This study examined the mechanism and kinetics of surface catalyzed hydrogen peroxide decomposition and degradation of contaminants in the presence of sand collected from an aquifer and a riverbed. Batch experiments were conducted using variable sand concentrations (0.2 to 1.0 g-sand/ml solution) and phenol and quinoline as model contaminants. Inhibition and probe studies were conducted to ascertain the role of several oxygen radicals (e.g. ˙OH, ˙HO2/O2−) on contaminant degradation. Phenol degradation products were consistent with reaction with hydroxyl radical. Concordant with this, phenol degradation was greatly inhibited in the presence of the widely accepted hydroxyl radical scavenger butanol. Additional inhibition studies with superoxide dismutase (SOD) support the conclusion that superoxide anion participates in the formation of hydroxyl radical. It is postulated that the relatively long-lived superoxide anion is capable of leaving the vicinity of the sand surface into bulk solution, where it may react with hydrogen peroxide to form hydroxyl radical and contribute to contaminant degradation. A mechanism is formulated and evaluated which accounts for these observations, as well as hydrogen peroxide decomposition kinetics and the complex decay behavior of phenol and quinoline in the presence of sand.