Application of Cobalt/Peracetic Acid to Degrade Sulfamethoxazole at Neutral Condition: Efficiency and Mechanisms

Abstract

An advanced oxidation process of combining cobalt and peracetic acid (Co/PAA) was developed to degrade sulfamethoxazole (SMX) in this study. The formed acetylperoxy radical (CH3CO3 •) through the activation of PAA by Co (Co2+) was the dominant radical responsible for SMX degradation, and acetoxyl radical (CH3CO2 •) might also have played a role. The efficient redox cycle of Co3+/Co2+ allows good removal efficiency of SMX even at quite low dosage of Co (<1 μM). The presence of H2O2 in the Co/PAA process has a negative effect on the degradation of SMX due to the competition for reactive radicals. The SMX degradation in the Co/PAA process is pH dependent, and the optimum reaction pH is near-neutral. Humic acid and HCO3 – can inhibit SMX degradation in the Co/PAA process, while the presence of Cl– plays a little role in the degradation of SMX in this system. Although transformation products of SMX in the Co/PAA system show higher acute toxicity, the low Co dose and SMX concentration in aquatic solution can efficiently weaken the acute toxicity. After reaction in the Co/PAA process, numerous carbon sources that could be provided for bacteria and algae growth can be produced, suggesting that the proposed Co/PAA process has good potential when combined with the biotreatment processes.

Activation of Peracetic Acid with Lanthanum Cobaltite Perovskite for Sulfamethoxazole Degradation under a Neutral pH: The Contribution of Organic Radicals

“…As shown in Figure 4 a, the presence of excess TBA (500 mM) slightly inhibited the degradation of SMX in PAA/ LaCoO 3 system, indicating that • OH played a negligible role in LaCoO 3 /PAA system for SMX degradation. Moreover, MeOH is regarded as a common scavenger for • OH (k = 6.0 × 10 8 M −1 s −1 ), and has been recently reported as a scavenger for organic radicals (R-O • ) in the activated PAA [ 31 ]. Therefore, the addition of excess MeOH could be used to evaluate the contributions of R-O • under the premise of TBA quenching results.…”

“…PAA was first adsorbed on the surface of LaCoO 3 , and then activated by the Co on the B site of perovskite to generate organic radicals, e.g., CH 3 COO • , which could act as an oxidant for SMX degradation. Meanwhile, Co(II) was oxidized to Co(III) after PAA activation (Equation (7)) [ 31 , 49 , 50 ]. The decomposition of CH 3 COO • can generate CO 2 and CH 3 • , which could further react with oxygen to generate CH 3 OO • .…”

“…Meanwhile, this result also indicated that PAA was more easily activated by LaCoO 3 than H 2 O 2 . Indeed, the peroxide bond energy in PAA was reported to be 159 kJ mol −1 , which is lower than that in H 2 O 2 (213 kJ mol −1 ) [31]. Hence, the dissociation of peroxide bond in PAA to generate reactive species is thermally feasible and even likely more easily than H 2 O 2 .…”

“…After the introduction of intensive energy (e.g., heat and UV) or catalysts, the peroxide bond in PAA can be activated to produce reactive species (e.g., HO • and R-O • ) [19,[27][28][29]. Compared with the inorganic peroxides, e.g., H 2 O 2 (213 kJ mol −1 ), PAA has a weaker -O-O-bond (159 kJ mol −1 for PAA [26,30]), which can be easily activated for intensive radical generation to attack target contaminants, such as pharmaceuticals [19,31], phenols [27,32], and dyes [33]. Therefore, PAA shows a great potential to be an ideal alternative to H 2 O 2 in AOPs and the development of efficient and environmentally friendly methods to activate PAA is of great significance.…”

“…Among them, transition metal ions have been reported as the most viable activators. For example, iron and cobalt ions showed a great performance for the activation of PAA to degrade organic contaminants [31,34]. However, one of the serious hindrances to this homogeneous processes was the poor reusability and potential toxicity of some metal ions [35].…”