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

In this contribution, the synthesis and characterization of a 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 with infrared spectroscopy studies and X-ray diffraction analyses, its morphology was seen under SEM, pointing to the presence of nanometric spherical aggregates of hexagonal nanocrystals (d≈23 nm) and the photoluminescence spectrum yields a broad band in the yellow region (578 nm). All these properties were compared to those of ZnO nanoparticles synthesised in nitrate-urea Deep Eutectic Solvent, in which case the nanoparticles adopt a bidimensional morphology, the XRD spectrum demonstrates a preferential orientation, and the fluorescence peak is moved in the orange wavelength range. Therefore, we show that the use of urea changes the system from ionic liquid to DES and promotes a switch of template effect from 0D to 2D.