Natural iron-rich tourmalines as effective catalysts for the heterogeneous and homogeneous activation of HCO3−/H2O2 to achieve the degradation of typical dyes

Abstract

The catalytic activation of HCO₃⁻/H₂O₂ to generate reactive oxygen species could treat neutral or weak alkaline organic wastewater effectively. Based on the activation principle of HCO₃⁻/H₂O₂ and the advantages of natural tourmaline, four types of common tourmaline powders were investigated as catalysts to activate HCO₃⁻/H₂O₂ for the degradation of typical anionic (methyl orange: MO) and cationic (methylene blue: MB; rhodamine B: RhB) dyes in aqueous solution. Compared to magnesium-rich tourmaline, lithium-rich tourmaline and low Fe content tourmaline, higher activity was observed for high Fe content tourmaline (high-Fe TM) in the catalytic activation of HCO₃⁻/H₂O₂ to achieve dye degradation. Furthermore, high-Fe TM exhibited acceptable stability for activating HCO₃⁻/H₂O₂ for the degradation of dyes, and the co-existing ions in municipal tap water, temperature and pH had a weak influence on the catalytic activity of high-Fe TM. The degradation of dyes in the high-Fe TM/HCO₃⁻/H₂O₂ system was found to be initiated by typical reactive oxygen species, which are mainly originated from the catalytic activation of HCO₃⁻/H₂O₂ with high-Fe TM. Specifically, the Fe-based sites of high-Fe TM and the Fe ions dissolved with high-Fe TM co-activated HCO₃⁻/H₂O₂ through heterogeneous and homogeneous catalysis, respectively. The degradation of RhB was driven by ˙OH and ˙O₂⁻, and the degradation of MB and MO was initiated by ¹O₂.