Identification of Active Radical Species in Alkaline Persulfate Oxidation

A proposed mechanism for alkaline activation of persulfate involves generation of sulfate (SO4-center dot), hydroxyl (HO center dot), and superoxide radicals (O-2(-)center dot). The present study investigated the feasibility of chloroform (CF) degradation using alkaline activated persulfate and identified the active radical species using a radical inhibition technique. 2-propanol (PrOH) (preferentially reacted with HO center dot), phenol (preferentially reacted with both HO center dot and SO4-center dot), and carbon tetrachloride (CT) (preferentially reacted with O-2(-)center dot) were used to inhibit the degradation of CF, and the extent of inhibited degradation was used to indicate the predominant radical species. Additions of PrOH and phenol appeared to significantly scavenge SO4-center dot and HO center dot and resulted in inhibited CF degradation. Here, the authors demonstrated that SO4-center dot and HO center dot were predominant radicals in the alkaline activated persulfate system. The presence of O-2(-)center dot scavengers (i.e., CT) resulted in a partial inhibition of CF degradation and, hence, one can speculate that O-2(-)center dot is a minor radical species.