Oxidation of organic micropollutant surrogate functional groups with peracetic acid activated by aqueous Co(II), Cu(II), or Ag(I) and geopolymer-supported Co(II)

Abstract

Peracetic acid (PAA) in combination with transition metals has recently gained increasing attention for organic micropollutant abatement. In this study, aqueous Co(II), Cu(II), and Ag(I) were compared for their capacity to activate PAA. Co(II) outperformed Cu(II) or Ag(I) and the optimum conditions were 0.05 mM of Co(II), 0.4 mM of PAA, and pH 3. However, due to a wider applicability in water treatment, pH 7 (i.e., bicarbonate buffer) was selected for detailed investigations. The abatement of different micropollutant surrogates could be described with a second-order rate equation (observed second-order rate constants, k_obs were in the range of 42-132 M^-1 s^-1). For the para-substituted phenols, there was a correlation between the observed second-order rate constants of the corresponding phenolates and the Hammett constants (R² = 0.949). In all oxidation experiments, the reaction rate decreased significantly after 1-2 min, which coincided with the depletion of PAA but also with the deactivation of the Co(II) catalyst by oxidation to Co(III) and subsequent precipitation. It was demonstrated that Co(II) immobilized on a geopolymer-foam performed approximately similarly as aqueous Co(II) but without deactivation due to Co(III) precipitation. This provides a potential option for the further development of heterogeneous catalytic Co(II)/PAA advanced oxidation processes utilizing geopolymers as a catalyst support material.

Keywords: Advanced oxidation process; Geopolymer; Oxidant-reactive functional groups; Peracetic acid; Transition metal catalysts; Water treatment.