Synthesis of zinc oxide by microwave hydrothermal method for application to transesterification of soybean oil (biodiesel)

ZnO nanostructures were synthesized by microwave hydrothermal treatment using two different mineralization agents (NaOH and NH₄OH), and were evaluated as catalysts for biodiesel synthesis. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analysis. The XRD patterns indicated the formation of the hexagonal wurtzite phase in both samples. SEM analysis showed completely different morphologies based on the mineralization agent employed. The ZnO nanostructures synthesized with NaOH (ZONa5 and ZONa5P) presented plate-like agglomerates, resulting in a quasi-spherical morphology, whereas the materials synthesized with NH₄OH (ZONH5 and ZONH5P) presented a flower-like morphology. The ZONa5P sample showed an activity of 77.82% for the catalytic conversion of soybean oil into biodiesel by transesterification using methanol. - Highlights: • ZnO was synthesized by MH method in only 5 min. • The powders morphology is completely influenced by mineralization agent. • ZONa5P showed activity of 77.82% for the conversion of soybean oil into biodiesel.