Fe₃O₄-functionalised biochar for persulphate systems towards the removal of Remazol Brilliant Orange 3R: machine learning–based approach and toxicity analysis

This study focuses on the utilization of Fe₃O₄-functionalized rice straw biochar composite for the augmented activation of sulphate radicals at high temperature for the removal of Remazol Brilliant Orange 3R (RBO-3R). The process parameters were optimized using factorial modelling and were mathematically evaluated using Statistical Analysis System (SAS) programming and canonical-ridge analysis. The following optimized conditions for maximum decolourization of 365.78 mg/L RBO-3R dye were found: temperature of 80 °C, persulphate concentration of 5.22 mM, dye concentration of 500 mg/L and time of 30 min. A novel rice straw–based biochar (RC-BC) was then prepared through pyrolysis and impregnated with iron to synthesize ferrous-loaded biochar (Fe-BC). The surface morphology of Fe biochar was characterized using scanning electron microscopy-energy-dispersive X-ray (SEM–EDX), and their crystal structures were analysed using X-ray diffraction (XRD) analysis. The kinetic rate constants for the thermal-activated persulphate and Fe-BC and Fe-BC-incorporated thermal-activated persulphate system were 0.0475 min⁻¹, 0.0068 min⁻¹ and 0.0724 min⁻¹, respectively. The toxicity analysis of the degraded metabolites of gas chromatography mass spectrometry (GC–MS) using ProTox and EPI Suite models showed that the products had lower LD50 values, indicating their safer discharge into the environment. Despite this application, this functionalized rice straw biochar can be applied as soil amendments for heavy metal stabilisation, supports for enzyme immobilization, photocatalysts and adsorbents for removing environmental pollutants.