Synthesis of ZnO@γ-Fe₂O₃ core–shell nanocomposites by a facile thermal decomposition approach and their application in photocatalytic degradation of congo red

ZnO@γ-Fe₂O₃ core–shell nanocomposites were synthesized by a facile thermal decomposition approach. ZnO nanorods were first synthesized by calcination of zinc acetate at 300 °C, in air. γ-Fe₂O₃ nanoparticles were then deposited on the surface of ZnO nanorods by the thermal decomposition of iron acetylacetonate at 200 °C in diphenyl ether. The structure, composition, optical and magnetic properties of the nanocomposites were studied using an array of techniques. XRD results suggest the presence of γ-Fe₂O₃ nanoparticles and ZnO, and FE-SEM images indicate formation of shell of iron oxide on the ZnO nanorods. Transmission electron microscopy studies clearly show that ZnO possesses rod morphology (length = 1.1 ± 0.1 μm, diameter = 40.1 ± 7 nm) and TEM images of the ZnO@γ-Fe₂O₃ nanocomposites show uniform shell of γ-Fe₂O₃ coated on the ZnO nanorods and thickness of the γ-Fe₂O₃ shell varies from 10 to 20 nm. Diffuse reflectance spectra of ZnO@γ-Fe₂O₃ nanocomposites reveal extended optical absorption in the visible range (400–600 nm) and photoluminescence spectra indicate that the ZnO@γ-Fe₂O₃ nanocomposites exhibit enhanced defect emission. The ZnO@γ-Fe₂O₃ core–shell nanocomposites show superparamagnetic behaviour at room temperature. The core–shell nanocomposites exhibit enhanced visible-light driven photocatalytic degradation of congo red in an aqueous solution as compared to pure ZnO nanorods and γ-Fe₂O₃ nanoparticles. The enhanced photocatalytic activity is attributed to good visible-light absorption and effective charge separation at the interface of ZnO@γ-Fe₂O₃ core–shell nanocomposites.