Comment on 'Synergetic Transformations of Multiple Pollutants Driven by Cr(Ⅵ)-Sulfite Reactions'

摘要

A recent article by Jiang et al. entitled "Synergetic transformations of multiple pollutants driven by Cr(Ⅵ)-sulfite reactions" reports the efficient oxidation of contaminants (e.g., As(Ⅲ)) in the Cr(Ⅵ)-S(Ⅳ) system. They ascribed the oxidation in aqueous solutions at acid pH to SO_4~(·-) and ~·OH. They determined the contributions of SO_4~(·-) and ~·OH to As (Ⅲ) oxidation by using tert-butanol (TBA) as scavenger for the radical ~·OH. Although the performance of the Cr(Ⅵ)-S(Ⅳ) system is unquestionable, we disagree with the interpretation regarding the role of ~·OH in As(Ⅲ) oxidation. Two arguments may be presented against such interpretation of ~·OH formation and its role. First, qualitative characterization of ~·OH by electron spin resonance (ESR) spectroscopy or use of coumarin as chemical probe in the Cr(Ⅵ)-S(Ⅳ) system in the presence of SO_4~(·-) is not valid. Second, quantitative differentiation between SO_4~(·-) and ~·OH cannot be done because of simultaneous scavenging of SO_4~(·-) by TBA at excess concentrations.