Natural South African iron-rich sand as a functional catalyst in hybrid photocatalytic wet peroxide oxidation technology for the degradation of methyl orange dye pollutant

Abstract

Advanced oxidation processes (AOPs) are increasingly utilized for remediating hazardous pollutants like dyes, with a growing focus on sustainable, natural catalysts. Thus, this study investigated South African iron-rich sand (SAIRS) as a natural catalyst for light-mediated wet peroxide oxidation of methyl orange (MO) dye in wastewater. The SAIRS was characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and Brunauer–Emmett–Teller (BET), revealing an iron-rich composition (63.53% Fe₂O₃, 45 wt.% Fe, predominantly haematite) and micro-mesoporous structure (31.2 m²/g, 1–9 nm pores), enhancing its catalytic activity. Optimization of process parameters (irradiation source, SAIRS loading, pH, H₂O₂ concentration) identified optimal conditions of 3500 mg/L catalyst dose, 6 mM H₂O₂, and pH 2.5, achieving 94% MO degradation within 90 min under visible light. SAIRS exhibited versatility, with visible light (photocatalysis) and ultraviolet B (UVB) (photoreduction) outperforming UVA (70% degradation). At pH 2.5, minimal iron leaching (<0.5 mg/L) ensured environmental safety. Pseudo-first-order kinetics (R² = 0.99, k₁ = 0.045 min⁻¹) indicated mass transfer as the rate-limiting step, with oxidation dominating. SAIRS's natural abundance, low cost (50% cheaper than synthetic Fe₂O₃), and low waste generation (80% less sludge than traditional Fenton systems) position it as an eco-sustainable catalyst for industrial dye effluent remediation, supporting SDGs 6 and 14.