PMS activation using reduced graphene oxide under sonication: Efficient metal-free catalytic system for the degradation of rhodamine B, bisphenol A, and tetracycline

This study addresses the influence of ultrasound irradiation on the activation of peroxymonosulfate (PMS) using reduced graphene oxide (rGO) under metal-free conditions for the catalytic degradation of rhodamine B (RhB), bisphenol A (BPA) and tetracycline (TC). Our results revealed that the combination of PMS/rGO and ultra-sonication enhanced significantly the degradation rate, reaching full degradation in relatively short times with total organic carbon (TOC) removal exceeding 85% of the investigated pollutants. In contrast, under these experimental conditions, rGO/ultrasound and PMS/ultrasound achieved less than 20% degradation of the same pollutants. Electron paramagnetic resonance (EPR) studies along with quenching experiments suggested that hydroxyl radicals ((OH)-O-center dot) are the dominant reactive species in the degradation process. Furthermore, inductively coupled plasma atomic emission spectroscopy (ICP-AES) and EPR data revealed the presence of trace manganese (Mn) in rGO. To elucidate the role of Mn on the degradation process, rGO was subjected to hot acid treatment for 48 h to remove trace Mn. While the chemical composition of rGO was not significantly altered by this chemical treatment, the degradation efficiency decreased upon Mn dissolution. The result suggests that trace metal in rGO might account for the efficiency of PMS activation. Finally, plausible degradation pathways were proposed based on LC-MS analysis of the reaction intermediates.