Steam treatment of metal acetylacetonate and ethyl acetoacetate complexes at 90 °C for preparation of metal oxides

Steam treatment is a technique for synthesizing metal oxides via the exposure of metal complexes to water vapor at low temperatures (<120 °C). Although zinc and aluminum complexes have been transformed to wurtzite ZnO and pseudo-AlOOH through steam treatment, other synthesis of metal β-ketoesterate complexes involving steam treatment have not yet been investigated. Herein, we focus on the behavior of metal acetylacetonate (acac) and ethyl acetoacetate (etac) complexes (metal = Mg, Ca, Ba, Ti, Zr, Fe, Co, Ni, and Cu) after steam treatment at 90 °C. Ti(acac)2(OiPr)2, Ti(etac)2(OiPr)2, Fe(acac)3, Co(acac)2, Co(etac)2, and Cu(etac)2 were transformed to crystalline metal oxides upon the steam treatment under air atmosphere. Other metal complexes were transformed to noncrystalline metal oxides, metal hydroxides, metal carbonates, or no decomposition. Hydrolysis mechanism of steam treatment proceeds by water attacking metal species. The formed reactive hydroxy group was quickly reacted to other molecules, and metalloxane bonding was formed.