Revealing the vital role of dissolved O2 in Cu(II)-Cu(I)-Cu(III) cycle for promoting glyphosate degradation via percarbonate activation

Abstract

High-valent copper (Cu(III)) is a potential active species for the degradation of organic pollutants among the Fenton-like reactions. Cu(I), as the key intermediate for the generation of Cu (III), is often affected by the low reaction rate between Cu(II) and oxidants. Herein, glyphosate, as an universal herbicide, was efficiently eliminated by percarbonate (SPC) via addition of trace Cu(II) (50 μM). Batch experiments results showed that 97.6 % of glyphosate (0.10 mM) was degraded into orthophosphate (PO43-) by Cu(II)/SPC within 30 min over a wide pH scope (4 ∼ 10). Scavenging experiments and electron spin resonance (EPR) revealed that Cu(III) was the major active species in glyphosate degradation. The removal efficiency of glyphosate might be influenced by the phosphorus species under different pH conditions. Moreover, during the removal process of glyphosate, the in-situ generation of oxygen (O2) in Cu(II)/SPC system could be converted into superoxide radical (·O2–), which exhibited higher reaction rate with Cu(II) to produce Cu(I), and further transformed into Cu(III) for the removal of glyphosate. Overall, this work successfully structured a rapid way to the removal of glyphosate, and effectively alleviated the problem of low concentration of dissolved O2 in water caused by O2 consumption in Fenton reaction via the generation of in-situ O2.