Applying bronzite mineral as a novel and effective magnetic catalyst for photo-Fenton reaction: Experimental design and machine learning

Abstract

This study investigates bronzite, an iron-rich orthopyroxene mineral, as a natural and cost-effective catalyst for the photo-Fenton degradation of amaranth dye in water. Bronzite powder's high Fe content, visible-light absorption (band gap of 2.48 eV), and magnetic recoverability were confirmed by XRD, FTIR, SEM/EDS, BET, DRS, and magnetic analysis. The optimal conditions for attaining 98.3% dye degradation and 64% TOC removal under visible-light irradiation were found to be pH 3, catalyst dosage of 1 g L⁻¹ , and 100 µg L⁻¹ H₂O₂ using a central composite rotational design (CCRD). Photogenerated holes (h⁺) are the predominant reactive species, whereas •OH and e⁻ have minor contributions, according to scavenger tests. The degradation profiles under various operating circumstances were accurately represented (R²>0.95) by a kinetic model linking adsorption–desorption and surface oxidation. Reaction intermediates were successfully predicted by machine learning (Random Forest), which supported a degradation route that began with azo bond cleavage and progressively oxidized aromatic fragments. Over the course of five reuse cycles, the catalyst remained highly active and showed no discernible ecotoxicity to Artemia salina. These findings show that bronzite is a stable, reusable, and eco-friendly natural catalyst with potential use in the photo-Fenton treatment of wastewater tainted with dyes.