Degradation of metronidazole by nanoscale zero-valent metal prepared from steel pickling waste liquor

Abstract

In this study, steel pickling waste liquor was employed to obtain reactive nanoscale zero-valent metal (nZVM) with the purpose of engineering application. The degradation of metronidazole reacted with as-prepared nZVM in water was investigated to explore the feasibility of using the nZVM to treat antibiotics in wastewater. The synthesized nZVM was characterized by Brunauer–Emmett–Teller (BET) surface analyzer, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectrometer (EDS). The results showed that the nZVM (20–40nm) with crystalline structure had a BET surface area of 35m2/g. XPS and EDS only detected Fe, C and O on the surface, suggesting Ni and Zn distributed inside the core of nanoscale alloy. Degradation of metronidazole followed the pseudo-first-order kinetics, and the observed reaction rate constant (kobs) could be improved with increasing nZVM dosage, as well as with diminishing initial metronidazole concentration and pH. A high reaction rate was observed at reduction potential, indicating that electrons and hydrogen species produced by nZVM were driving forces of reaction. The surface area-normalized rate coefficient (kSA) for nZVM (0.254Lmin−1m−2) was 375.2 times larger than that for commercial iron powder (6.67×10−4Lmin−1m−2). Several possible pathways of degradation of metronidazole were proposed according to the results of UV–vis spectra and HPLC chromatograms.