Effects of Al3+ concentration on the optical, structural, photocatalytic and cytotoxic properties of Al-doped ZnO

ZnO-Al x% nanoparticles (NPs), with x = 0, 1, 3, 5 or 10 mol% Al3+, were synthesized by a modified sol-gel method. The effects of Al3+ content on the structure, morphology and optical properties of Al-doped ZnO were investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, photoacoustic absorption spectroscopy (PAS), photoluminescence spectroscopy (PL) and specific surface area determination. A single crystalline phase characteristic of ZnO with wurtzite structure was detected for all synthesized oxides. With increasing dopant content, the average crystallite size of the NPs decreased from 25 to 7 nm. ZnO-Al x% NPs exhibited enhanced optical properties with the absorption slightly shifted to the visible region and with the band gap energy (Eg) decreased from 3.12 (undoped ZnO) to 2.95 eV (ZnO-Al 3%). Undoped ZnO showed intense PL above 430 nm, which was considerably decreased with the insertion of Al3+. Despite the increase of the surface area with Al3+ doping of ZnO NPs, its catalytic activity in the decomposition reaction of Congo red showed a decrease with doping. Research has shown that ZnO NPs can selectively target and kill cancer cells and that its cytotoxicity is dependent of the concentration. The doping can be a method of shape the cytotoxicity of ZnO NPs and their optical and photocatalytic properties. In-vitro cytotoxicity studies showed that both undoped ZnO and Al-doped ZnO NPs synthesized were highly cytotoxic for fibroblast cells, suggesting that these nanomaterials could be promising anticancer agents.