Synthesis of ZnOAl2O3 core-shell nanocomposite materials by fast and facile microwave irradiation method and investigation of their optical properties

- ZnO NPs were coated with Al2O3 by first, facile microwave irradiation method.
- Different surface morphology of ZnO after Al2O3 coating was confirmed by SEM.
- Uniform distributions of Zn, O, and Al atoms were justified by SEM-EDX.
- Formation of Al2O3 layer on ZnO was observed by TEM analysis.
- The XPS results affirmed that elements on the ZnO surface were Al and O.

Alumina (Al2O3) coated ZnO core-shell structures were synthesized by a novel, fast, and facile route utilizing microwave (MW) irradiation to control photocatalytic property of ZnO. The phase analysis and the core-shell structure development were corroborated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR). The XPS results affirmed that elements on the coated surface were Al and O. Zeta potential analysis predicted the presence of Al2O3 layer on ZnO due to almost similar zeta potential curve for pure Al2O3 and Al2O3 coated ZnO nanoparticles. There was no significant change in band gap energy of ZnO after amorphous Al2O3 coating as obtained from derived data of the reflectance spectra but gradual decreasing of reflectance in the visible range, measured by UV-vis spectroscopy, of the prepared core-shell nanoparticle may be due to the coating of amorphous Al2O3 on ZnO. The photocatalytic efficiency of ZnO was reduced after amorphous Al2O3 layer as confirmed by the photodegradation of methylene blue under UV irradiation.

Schematic diagram of the formation of Al2O3 coated ZnO NPs. Ammonia solution catalyzed the hydrolysis reaction and polymerization of aluminium triisopropoxide resulted in the formation of alumina shell on the surface of ZnO NPs (drawing not to scale).53