Reuse of Crude Glycerol for the Synthesis of Zinc Oxide (ZnO) Nanoparticles by Glycerol–Urea (GU) Route

The global continuing growth of biodiesel production has triggered the search for an economically viable destination for glycerol which is one of the main by-products of the process. Herein, crude glycerol was evaluated as a solvent in the synthesis of zinc oxide nanoparticles (ZnO NPs) by the glycerol–urea (GU) route, a new and less aggressive synthetic route for ZnO NPs. Five of the most common glycerol contaminants were individually or simultaneously added to pure glycerol. The influence of these contaminants on the shape and size of the nanoparticles was studied. Thereafter, the synthesis of ZnO NPs by the GU route was repeated with real crude glycerol from the transesterification reaction. The obtained ZnO NPs were characterized regarding their chemical composition by X-ray diffractometry (XRD) and UV–Vis spectroscopy. The size, morphology, and size distribution were characterized by transmission electron microscopy. The results showed that the glycerol contaminants did not change the size and morphology of the ZnO NPs obtained by the GU route. ZnO NPs obtained in the presence of different contaminants had average diameters smaller than 25 nm. Nevertheless, a high degree of agglomeration, possibly due to the presence of several organic groups adhered to the surface of the NPs was observed. Therefore, the use of crude glycerol in the synthesis of ZnO NPs by the GU route was shown to be an efficient application of this byproduct, enabling the production of an important precursor for the catalysis of the transesterification reaction, and closing the biodiesel production chain.