The double role of p-toluenesulfonic acid in the formation of ZnO particles with different morphologies

The role of p-toluenesulfonic acid (p-TSA) as a catalyst and/or morphology-directing agent for the formation of ZnO particles with different sizes (20 to 250 nm) and shapes (from bullet-like to complex, cauliflower architectures) was studied. One-pot, low-temperature syntheses were performed using reaction mixtures containing zinc acetylacetonate hydrate (zinc oxide precursor), 1-butanol (medium and oxygen source) and different concentrations of p-TSA. The catalytic role of the p-TSA was pronounced when the p-TSA concentration was kept low, while an elevated acid concentration inhibits the reactivity of the ZnO precursor toward the alcoholysis, presumably due to the adhesion of the p-TSA on its surface. The abundance of ZnO surface chelation with the p-TSA controls the ZnO particle growth and shape as well as the self-assembly of ZnO nanocrystals into complex architectures. The particles' characterization and growth were assessed using TEM, HRTEM, FE-SEM, XRD and FTIR, while the reaction mechanism was proposed on the basis of C-13 and H-1 NMR experiments.