Passivation bypassed Zero valent Iron based heterostructures for effective removal of persistent antibiotics by solar driven photo-Fenton process

Abstract

The natural passivation phenomena in nano zerovalent iron (nZVI) through formation of surface oxide layer is a bottleneck for exploring the complete potential of the material. This problem is addressed by the in-situ synthesis of nZVI/Cu bimetallic heterostructure and exploring its improved potential towards solar-driven photodegradation of persistent antibiotics and their mixture in contaminated water. Effect of passivation bypassing by Cu0 on the stability of nZVI as a photo-Fenton candidate is scrutinized through aging of the materials and their effect on degradation performance. Post-aging studies reveal a higher performance of nZVI/Cu as compared to bare nZVI. A systematic comparative study of photo-Fenton activity for nZVI and nZVI/Cu is estimated through degradation of toxic organic pollutants such as Tetracycline (TET) and Ciprofloxacin (CIP) and also a mixture of both antibiotics using High performance Liquid Chromatography (HPLC). The degradation efficiencies achieved with nZVI/Cu for TET and CIP were 99.99% and 98.59% with rate constant of 0.0631 min−1 and 0.032 min−1 respectively. Furthermore, nZVI/Cu showed a removal efficiency of 99.34% and 99.9% for TET and CIP in antibiotic mixture. Hydroxyl radicals are found to be the prominent active species from radical trapping experiments. The degradation pathway is traced with LC-MS/MS analysis to identify the intermediates and byproducts formed during degradation process. The reusability of nZVI/Cu catalyst is evaluated with five successive cycles of CIP and TET degradation. The inherent magnetic property of nZVI/Cu sample is employed for the effortless retrieval of catalyst. Finally, a plausible explanation for the photo-Fenton degradation mechanism of nZVI/Cu for the antibiotics is put forward.