Trace-Dissolved S(-II) Triggers the Fe(III)-Activated H₂O₂ Process for Organic Pollutant Degradation by Promoting the Fe(III)/Fe(II) Cycle: Kinetics, Toxicity, and Mechanisms

The practical application of the traditional Fenton system (Fe(II)/H 2 O 2 ) is seriously hampered by the sluggish Fe(III)/Fe(II) cycle and the stringent acidic reaction condition. In this work, we found that trace-dissolved S(-II) (DS(-II), 5 μM) could significantly accelerate the Fe(III)/Fe(II) cycle and trigger a rapid H 2 O 2 activation process in the Fe(III)/H 2 O 2 system. Thus, more hydroxyl radicals ( · OH) were generated for the rapid removal of various organic pollutants such as bisphenol A (BPA) and sulfamethoxazole (SMX) from water. Besides, the additive DS(-II) effectively broadened the application pH range of the Fenton or Fenton-like system. The constructed Fe(III)/DS(-II)/H 2 O 2 system showed extensive applicability to different water matrices and maintained high BPA removal in the actual water sources. Furthermore, the toxicity assessment revealed that the toxicity of the target contaminant was diminished. The harmless SO 4 2– was the final product of DS(-II) in the Fe(III)/DS(-II)/H 2 O 2 system, and the residual DS(-II) was less than the threshold limit value for fresh or saltwater (0.5 mg/L). This discovery is expected to promote the large-scale practical application of iron-based Fenton or Fenton-like systems in practical organic wastewater purification.