Accelerating reduction of ferric iron by tourmaline for efficient H₂O₂ activation in removing aqueous organic pollutants

The efficient generation of active ferrous ions is essential for the continuous degradation of organic pollutants in the Fenton system; however, this process is significantly hindered by the sluggish reduction of ferric ions. In this study, commercial tourmaline (Tr), a natural silicate mineral, was employed to overcome this kinetic limitation. The Tr/Fe³⁺/H₂O₂ (Tr + Fe³⁺ + H₂O₂) system achieved an accelerated redox cycle of Fe³⁺/Fe²⁺, rapid decomposition of H₂O₂, and enhanced removal of 2,4,6-trichlorophenol (TCP) within 30 min. Compared to the Fe³⁺/H₂O₂ system, the Tr/Fe³⁺/H₂O₂ system improved the degradation efficiency by 43-fold, even with low concentrations of H₂O₂ (0.5 mM) and Fe³⁺ (0.05 mM). Moreover, the system generated free hydroxyl radicals (•OH), super oxygen (O₂^•-), and singlet oxygen (¹O₂), which contributed to the effective removal of various pollutants, including organic dyes, pharmaceuticals, and phenolic compounds. In-situ FTIR and XPS analyses revealed that the iron cycle was facilitated by surface Si-OH sites through the formation of Si-O-Fe bonds. Tourmaline also exhibited excellent recyclability and sustained reactivity in five consecutive experimental runs. Overall, this study presents a promising strategy to address the rate-limiting step of Fe³⁺/Fe²⁺ conversion and promotes the application of natural minerals in iron-based advanced oxidation processes (AOPs).