Catalytic synergy of Au@CeO2–rGO nanohybrids for the reductive transformation of antibiotics and dyes

Abstract

Au@CeO₂–rGO nanohybrids (NHs) are synthesized using sucrose via a hydrothermal method. The interfacial interactions between gold encapsulated in CeO₂ and rGO are observed by Raman and X-ray photoelectron spectroscopy (XPS). The optical properties and crystallinity of the nanohybrids are determined by using UV-Vis and X-ray diffraction (XRD), respectively. Elemental mapping using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) clearly demonstrates the Au@CeO₂ core–shell sequence, in which the core of electron-dense Au NPs is encapsulated by the spherical CeO₂ shell; these Au@CeO₂ particles are then decorated on the reduced graphene oxide (rGO) nanosheets. As an application of the synthesized Au@CeO₂–rGO nanohybrids, the reductive transformation of organic contaminants present in wastewater is accomplished. Ampicillin (AMP) gives 6-methyl-3-phenylpyrazin-2-ol and ciprofloxacin (CIP) affords 1-cyclopropyl-6-fluoro-3-(hydroxymethyl)-7-(piperazin-1-yl)-2,3-dihydroquinolin-4(1H)-one. Moreover, rhodamine B (RhB) forms (2-(3,6-bis(diethylamino)-9H-xanthen-9-yl)phenyl)methanol and Congo red (CR) produces benzidine and 3,4-diaminonaphthalene-1-sulfonic acid. The elimination of the antibacterial activities of AMP and CIP using reductive degradation and transformation shows the possibility of decreasing exposure of bacteria to antibacterial chemicals. The transformed by-product of CR is considered to be a potential anti-AIDS agent.