Transformation of tetracycline in water during degradation by visible light driven Ag nanoparticles decorated α-NiMoO4 nanorods: Mechanism and pathways

Abstract The microwave hydrothermal and photo-reduction/deposition methods were employed to synthesize silver nanoparticles (Ag NPs) decorated α-Nickel molybdate (α-NiMoO4) nanorods. TEM image clearly shows the decoration of Ag NPs on α-NiMoO4 nanorods. The Ag NPs decorated α-NiMoO4 revealed eight folds increase in photocatalytic degradation of tetracycline (TC) compared to the α-NiMoO4 under visible light irradiation. The photocatalyst shows excellent stability even after 5th cycle of TC degradation as confirmed by XRD, XPS, and FESEM measurements. In addition, the photocatalyst shows anti-photo corrosion properties. TOC analysis and fluorescence spectroscopy analysis indicate the efficient degradation and mineralization of TC. The enhanced photocatalytic activities of photocatalyst could be attributed to increase in visible light absorption, SPR effect, and efficient separation of electron-hole pairs. The suppression of charge recombination confirmed by PL spectra, transient photocurrent response, EIS, and CV. ESR measurement and scavenger experiment suggest that OH plays a major role whereas O2 − and h+ show the minor role for TC degradation. In order to find out the transformation products in water and degradation pathways of TC, UPLC-PDA and HR-QTOF ESI/MS techniques were used. The five degradation pathways are designed for TC on the basis of demethylation, hydroxylation, dehydroxylation, oxidation, and deamination organic reactions. Moreover, the ESR measurement was used to prove the photocatalytic mechanism. So, this work could provide a fabrication of efficient photocatalyst for removal of pharmaceuticals pollutants from waste water as well as deeper insight into photocatalytic mechanism, transformation products, and degradation pathways of TC in water.