Effect of Basicity on Persulfate Reactivity

The generation of reactive species in activated persulfate systems under different conditions of basicity was investigated using three probe compounds. Anisole was used to detect both sulfate radical and hydroxyl radical. Nitrobenzene was used to detect hydroxyl radical, and hexachloroethane was used as a reductant probe. Minimal probe compound degradation occurred in persulfate reactions conducted at pH≤10, demonstrating that a low flux of reactants is generated at acidic, neutral, and slightly basic pH regimes. In persulfate reactions at pH 12, sulfate and hydroxyl radical were generated but minimal reductants were produced. Scavenging studies showed that the dominant reactive species at basic pH was hydroxyl radical. The generation of reductants increased at high molar ratios of base to persulfate; however, hydroxyl radical generation rates increased only when molar ratios of base to persulfate were >3∶1. The results of this research demonstrate that the hydroxyl radical is the dominant reactive oxygen species in base-activated persulfate formulations and that overall reactivity increases with increasing base:persulfate ratios.