Shape controlled Hafnium oxide nanoparticles grafted with organic acid molecules synthesized in supercritical water

Abstract Shape controlled Hafnium oxide nanoparticles were synthesized under supercritical water with and without organic acid surface modifiers to produce grafted nanocrystals. The obtained nanoparticles displayed novel and unique controlled shaped morphologies spherical, semispherical, rod-like cylinders and eruciforms by using either propionic acid, citric acid, 3,4-dihydroxybenzoic acid or gallic acid as demonstrated by transmission electron microscopy. X-ray diffraction analysis showed that monoclinic Hafnium oxide nanocrystals were synthesized in this manner. During the single step synthesis, organic acid molecules directly interact with the nanocrystal surface through carboxylate bonding. Chemical bonding between organic acids and the nanoparticles was evaluated by Fourier transform infrared spectroscopy validating the integrity of the grafted molecules which modify the interaction of the nanoparticles with the media. The grafting density was quantified from the weight loss measured using thermogravimetric analysis, our results show that citric acid and 3,4-dihydroxybenzoic acid have a remarkable interaction accounting for 41.64 % and 100 % respectively of surface coverage of the nanoparticles. The novelty in this experimental research can be emphasized in the unique size and shape control as well as the effective modification of the surface of the Hafnium oxide nanocrystals all of this in a simple single step synthesis under supercritical water.