Nano-hybrids of needle-like MnO2 on graphene oxide coupled with peroxymonosulfate for enhanced degradation of norfloxacin: A comparative study and probable degradation pathway

Abstract

In this work, 1D MnO₂ nano-needles were prepared and grown on the graphene oxide (GO) nano-sheets successfully. The morphology and structure of materials were explored. The MnO₂ nano-needles with a length of 200-400 nm were distributed uniformly on the GO nano-sheets. As a result of GO substrate, the MnO₂/GO nano-hybrids (MnO₂/GO) have the much larger surface area and more surface oxygen-containing functional groups than MnO₂ nano-needles, which are beneficial for enrichment and degradation of the norfloxacin (NOR). Results showed that more than 80% NOR was degraded within 20 min at the dose of 10 mM PMS and 0.8 g/L catalysts. Moreover, the optimal pH in MnO₂/PMS and MnO₂/GO/PMS system were both acidic condition. Furthermore, the mechanism of PMS activation by MnO₂/GO was investigated through radical identification using quenching experiments and EPR techniques. According to this, the HSO₅^- of PMS reacted with Mn (IV)/Mn(III) to form a redox loop, and GO played an important role in the degradation process. Finally, the transformation intermediates of NOR were identified and four probable degradation pathways were speculated. This work would provide a potential contribution towards NOR removal in the environmental remediation.

Keywords: Graphene; Norfloxacin; Sulfate radicals; Water treatment; α-MnO(2) nano-needles.