Rapid dephosphorylation of glyphosate by Cu-catalyzed sulfite oxidation involving sulfate and hydroxyl radicals

Glyphosate is a broad-spectrum toxic herbicide that has entered the environment. Advanced oxidation processes efficiently remove various persistent organic contaminants. In particular, generation of sulfate radicals based on catalytic sulfite oxidation is promising, but previously used Fe(II/III) catalysts have reduced activity at pH above 4 due to precipitative deactivation. Therefore, here we tested Cu catalysis because Cu(II) remains an homogeneous ionic species over a wide pH range. We used Cu(II) to activate sulfite for oxidative glyphosate dephosphorylation at various pH, Cu, and sulfite concentrations. Results show that alkaline pH and high Cu(II) concentrations induce higher glyphosate dephosphorylation efficiency, though the effect of sulfite concentration exhibits a volcanic pattern due to self-scavenging. The Cu(II)/sulfite system achieved 81% dephosphorylation of 6 µM glyphosate with 0.025 mM Cu(II) and 0.25 mM sulfite at pH 9. The strong oxidation capability of the Cu(II)/sulfite system is explained by the synergistic action of SO 4 ·− and HO·, which accounted for 53% and 47% of glyphosate dephosphorylation, respectively. Overall, we show that Cu(II) is a superior catalyst for sulfite oxidation, with potential industrial application of Cu(II)/sulfite in wastewater treatment.