Biochar/steel slag composite derived from solid waste for rhodamine b degradation via singlet oxygen-dominated process driven by visible light-activated peroxymonosulfate

Abstract

A novel biochar/steel slag composite (SSBC) was developed via co-pyrolysis of steel slag and orange peel for visible-light-assisted peroxymonosulfate (PMS) activation to degrade Rhodamine B (RhB). The optimized SSBC-800 exhibited a high specific surface area (191.79 m² g⁻¹) and abundant functional groups, achieving complete degradation of 20 mg/L RhB within 10 min with 52% TOC removal. The system maintained high efficiency across pH 3–11 and demonstrated strong tolerance to common anions. Mechanistic studies revealed that singlet oxygen (¹O₂) contributed over 90% to the degradation, originating from synergistic electron transfer between quinone groups on biochar and the photo-accelerated Fe³⁺/Fe²⁺ cycle from steel slag. And minor contributions from photogenerated holes (h⁺) and radicals (such as SO₄•^⁻ and •OH). Effective RhB removal under natural sunlight highlights its practical potential. This work provides a sustainable non-radical oxidation pathway for dye wastewater treatment and a novel approach for solid waste valorization.