Templating effect travelling on the edge between an ionic liquid and a DES: the case of fluorescent ZnO nanostructures in choline nitrate

In this study, the synthesis and characterization of novel fluorescent ZnO nanopowder are reported. The reaction medium used for the oxide precipitation procedure was choline nitrate, a compound that is a liquid molten salt at room temperature. The purity of the obtained ZnO was assessed through infrared spectroscopy studies and X-ray diffraction analyses; its morphology was observed under SEM, indicating the presence of nanometric spherical aggregates of hexagonal nanocrystals (d ≈ 23 nm), and the photoluminescence spectrum yielded a broad band in the yellow region (578 nm). All these properties were compared with those of ZnO nanoparticles synthesised in a nitrate-urea deep eutectic solvent, wherein the nanoparticles adopted bidimensional morphology; the XRD spectrum demonstrated a preferential orientation, and the fluorescence peak moved in the orange wavelength range. Thus, we show that the use of urea changes the system from an ionic liquid to a DES and promotes a switch in the template effect from 0D to 2D.