The luminescent properties and toxicity controllability investigation of novel ZnO quantum dots with Schiff base complexes modification

Abstract

The Schiff base complexes modified ZnO quantum dots (ZnO-SBC QDs) are successfully synthesized via the reflux and chemical co-precipitation route. For control experiments, we also synthesized the ZnO QDs and amino-modified ZnO QDs (ZnO-NH2 QDs). The structures and morphologies of the samples were characterized via X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), FTIR spectroscopy (IR), Fluorescence Spectrometer (FL) and so on. The XRD pattern shows that the three types of QDs possess hexagonal wurtzite structures. The TEM investigation reveals that the as-prepared products have hexagonal morphologies. The plane fringe with 0.26 nm crystalline plane spacing of three types of quantum dots is assigned to the ZnO {002} planes via HR-TEM, which match with the lattice parameter of the hexagonal wurtzite structure of ZnO and also coincide with the data obtained by XRD. By analyzing the fluorescence emission and excitation spectra of ZnO QDs, ZnO-NH2 QDs, ZnO-SBC QDs and Schiff base complexes, we find that the ZnO-SBC QDs still have a perfect fluorescence emission which makes it interesting candidates for luminescence applications such as biochemical sensors and fluorescent labels to mark the cells and DNA. This novel ZnO-SBC QDs under UV irradiation is capable of generating reactive oxygen species by UV irradiation and may be used for the photodynamic therapy. The surface modification with Schiff base complexes makes it difficult to release Zn2+, therefore the toxicity is much more controllable.