Amino Acid-Assisted Synthesis of ZnO Hierarchical Architectures and Their Novel Photocatalytic Activities

A facile and bioinspired synthesis of ZnO hierarchical architectures, including prismlike and flowerlike structures and crytalline and noncrystalline hollow microspheres, has been developed using the amino acid histidine as the directing and assembling agent. The histidine molecules play different roles in the formation of ZnO hierarchical architectures due to the competitive coordination between histidine and OH− to Zn2+ when the reactant molar ratios are adjusted. The resulting architectures are characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectoscopy, and thermogravimetric analysis (TGA). Morphology- and phase-dependent photoluminescence of the ZnO architectures has been shown. In particularly, a novel photocatalytic activity of the ZnO hierarchical architectures for the reaction of the formaldehyde and carbon dioxide has been demonstrated, probably through mechanisms involving an oxidative coupling reaction and hydrolyzation process.