Sulfite Activation by Glucose-Derived Carbon Catalysts for As(III) Oxidation: The Role of Ketonic Functional Groups and Conductivity

In this study, a series of glucose-derived carbon catalysts were developed and applied for the activation of sulfite for the oxidation of As(III). The process of sulfite activation with the carbon catalysts is based on the production of oxysulfur free radicals such as SO3•-, SO5•-, and SO4•-. The factors responsible for the sulfite activation performance of carbon catalysts are conductivity and ketonic functional groups. A complex is formed between the sulfite and carbon catalysts, and the electron transfer that takes place within the complex leads to the generation of semiquinone and oxysulfur radicals, and finally, the oxysulfur radicals are converted into SO4•- by means of O2, which results in the As(III) oxidation. The efficiency of the sulfite/carbon system is enhanced under normoxia conditions due to the reversible transformation cycle occurring among C═O/C-O•/C-OH triads. The present study is of great environmental significance as sulfite is a source of SO4•- generated, and the activation is achieved by a metal-free carbon material, which makes the process viable and environmentally friendly.