Behavior of zinc- and aluminum β-ketoesterate complexes during steaming treatment

Steaming treatment is a low-temperature technique used in the synthesis of metal oxides. However, little is known about the influence of the metal species and ligands on the outcomes of this process. In this work, we aim to investigate the effects of the metal species (zinc and aluminum) and β-ketoesterato ligands on the synthesis of metal oxides via steaming treatment. Zn(β-ketoesterate)2 (meac: methyl acetoacetate, iprac: isopropyl acetoacetate, tbuac: tert-butyl acetoacetate) was decomposed by steaming treatment at 70 °C for 24 h. Fourier-transform infrared and X-ray diffraction analysis of the steamed Zn(β-ketoesterate)2 indicated its transformation to wurtzite ZnO. The crystallite size of steamed Zn(meac)2 and Zn(iprac)2 was ~29 nm. However, the crystallite size of steamed Zn(tbuac)2 was much smaller, and impurities were detected in the product. Al(β-ketoesterate)3 (meac, iprac, tbuac, and ethyl acetoacetate) was subjected to the same steaming treatment. Steamed Al(meac)3 was plausibly transformed into amorphous Al2O3. Steamed Al(etac)3 formed a pseudo-boehmite structure (γ-AlOOH). Comparatively, steamed Al(iprac)3 comprised a mixture of various compounds, whereas Al(tbuac)3 could not be decomposed by steaming treatment. Based on these results, steaming treatment is dependent on the ionic radius and size of the β-ketoesterato ligand. To synthesize aluminum-doped zinc oxide (AZO), a mixture of Zn(etac)2 and 5 mol% Al(etac)3 (Zn+5% Al-mix) was subjected to steaming treatment. The steamed Zn+5% Al-mix yielded wurtzite structure. From the Tauc plot, the calculated band-gap energy of the steamed Zn+5% Al-mix powder was 3.32 eV, suggesting the formation of AZO. Therefore, steaming treatment can be applied to the preparation of doped-metal oxides.