Zinc titanium glycolate acetate hydrate and its transformation to zinc titanate microrods: synthesis, characterization and photocatalytic properties

Abstract

A heterobimetallic complex, zinc titanium glycolate acetate hydrate (Zn₂Ti₃–GAH), tentatively formulated as Zn₂Ti₃(OCH₂CH₂O)₄(OCH₂CH₂OH)₅(CH₃COO)₃·2HOCH₂CH₂OH·H₂O, was synthesized by a room-temperature homogeneous precipitation in ethylene glycol solution. Its chemical composition, crystal structure, morphology, growth mechanism and thermal behaviors were characterized in detail. The precipitated Zn₂Ti₃–GAH was of a highly crystalline monoclinic phase and porous microrod morphology. As the single source precursor (SSP), Zn₂Ti₃–GAH was transformed into different phases of zinc titanate via thermal decomposition. With the remaining shape of the microrods, cubic phases of Zn₂Ti₃O₈ and rutile TiO₂ (r-TiO₂) supported hexagonal phases of ZnTiO₃ (h-ZnTiO₃) were obtained by calcination at 500 and 700 °C, respectively; while r-TiO₂ supported Zn₂TiO₄ were yielded in the form of dispersed particles or chains at higher temperature (950 °C). Benefiting from the SSP route and the confinement in the specific microrod domains of precursors, the heterostructures of r-TiO₂–ZnTiO₃ and r-TiO₂–Zn₂TiO₄ were formed during programmable calcination. The studies on photocatalysis by degrading methylene blue (MB) under ultraviolet (UV) irradiation indicated that the as-transformed zinc titanate exhibited enhanced activity. In particular, r-TiO₂ supported h-ZnTiO₃ displayed the photodegradation reaction rate constant of 0.00163 s⁻¹, which was comparable to that of commercially available Degussa P25 TiO₂. This probably related to the more effective charge separation in the r-TiO₂–ZnTiO₃ heterostructure packed in the microrods.