Undoped and Al-doped ZnO nanoparticles for photocatalytic application

Abstract

Photocatalysis is a valuable method for the degradation of polluting organic dyes present in the wastewater. Therefore, in this study, undoped and Al-doped ZnO nanoparticles were synthesised via a solvothermal route, characterised and tested as photocatalysts for the photodegradation of Rhodamine B under UV-Visible light illumination. The amount of dopant incorporated into the final solid was quantified by inductively coupled plasma-optical emission spectrometry (ICP-OES). It showed that the experimental Al content represents about 65% of the nominal value. Transmission electron microscopy (TEM) investigation performed on both undoped and Al-doped ZnO revealed the presence of quasi-spherical nanoparticles with a diameter ranging between 10 and 60 nm. The structural features of the catalysts were investigated employing X-ray Powder Diffraction (XRPD). The patterns of the nanomaterials matched with the hexagonal wurtzite crystal phase. A secondary crystalline phase was also detected. In the Fourier transform infrared (FT-IR) spectra, a pronounced absorption between 800 and 3000 cm-1 is observed for all the Al-doped ZnO semiconductors while it is absent for the undoped material. The appearance of this absorption in the MID infrared can be attributed to plasmon absorption in the case of Al-doped ZnO nanoparticles. Furthermore, solid-state 27Al Magic Angle Spinning (MAS) NMR can provide information on the local environment of the aluminium ions inserted into the ZnO structure. The NMR results display that Al is occupying both octahedral and tetrahedral sites, and that higher Al contents result in decreasing fractions of Al occupying tetrahedral sites. The preliminary photocatalytic tests evinced that both undoped and Al-doped ZnO materials are active under UV-C, UV-A and visible-light irradiation, demonstrating their ability to remove the organic dye in aqueous solution.