Kinetic evaluation of heterocatalytic ozone-based activation of peroxymonosulfate using acid-treated graphene catalyst for the degradation of micropollutants

Abstract

In this study, acid-treated graphene (Gr⎯COOH) catalyst was synthesized using a microwave plasma reactor, and its performance in different combinations of ozone and ozone activated peroxymonosulfate (O3, O3+Gr⎯COOH, O3+PMS, and O3+PMS+Gr⎯COOH) was kinetically evaluated. The yields of SO4•⎯ and HO• were quantified based on ozone consumption. Among the different operating parameters, the effect of pH (4−8) was particularly considered. The results showed that heterocatalytic ozone-based activation of peroxymonosulfate performed efficiently at neutral and alkaline conditions. The first-order rate constants for O3 decomposition in O3+PMS+Gr⎯COOH (1.2×10−2s−1) was higher than O3+PMS (8.5×10−3s−1) and O3 (2×10−4s−1) by a factor of 1 and 2 respectively. The radical yields were positively associated with pH. Higher pH values showed a notable increase in radical yields (η), with the maximum value of ηTotal (0.88) and ηHO• (0.53) obtained at pH 8 while ηSO4•⎯ showed maxima (0.46) at pH 7. This implies that at higher pH i.e., 8, HO• was the dominant reactive specie, which could be due to the presence of higher concentration of HO− and transformation of SO4•⎯ into HO•. Furthermore, the synergistic effects of the oxidative processes were tested considering atrazine (ATZ, 1 µM) and nitrobenzene (NB, 1 µM) as probe compounds. The best performance was obtained with O3+PMS+Gr⎯COOH process, reaching 96% and 81% of ATZ and NB removal respectively. The suppressive effects of inorganic ions and natural organic matter (NOM) on the degradation efficiency of ATZ and NB were also lower for O3+PMS+Gr⎯COOH process. These results confirmed that acid-treated graphene (Gr⎯COOH) catalyst in combination with ozone activated peroxymonosulfate could be an efficient and promising alternative oxidative process.