title: Monodisperse TiO2Spheres with High Charge Density and Their Self-Assembly.
abstract: Titanium dioxide (TiO2) spheres are potential candidates to fabricate three-dimensional (3D) photonic crystals owing to their high refractive index and low absorption in the visible and near-infrared regions. Here, TiO2spheres with both high surface charge density and uniform size, which are necessary for the self-assembly of TiO2spheres, have been prepared by means of sol-gel methods in ethanol in the presence of thioglycolic acid as ligand. Thioglycolic acid, which contains two functional groups, not only acts as coordinating ligand for stabilizing and controlling the growth of TiO2spheres but also endows the resulting TiO2spheres with high charge density as based on ζ-potential analysis when the pH of the TiO2aqueous dispersion was 6.5 or higher. The SEM images illustrate that the diameter of the prepared TiO2spheres can be tuned from 100 to 300 nm by simply controlling the concentration of H2O. FTIR spectra confirm that thioglycolic acid bonded to the surface of TiO2spheres through carboxylic groups. As anticipated, the obtained TiO2spheres could self-assemble to form a 3D opal photonic crystal structure by means of a simple gravity sedimentation method. Then the TiO2spheres in the 3D opal photonic crystal structure were able to transform into a pure anatase phase by annealing at different temperatures.
authors.affiliation: Department State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, P.R. China.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Xia
authors.affiliation: Department State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, P.R. China.
authors.forename: Suli
authors.initials: S
authors.lastname: Wu
authors.affiliation: Department State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, P.R. China.
authors.forename: Xin
authors.initials: X
authors.lastname: Su
authors.affiliation: Department State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, P.R. China.
authors.forename: Shufen
authors.initials: S
authors.lastname: Zhang
keywords: crystal growth; ligand effects; self-assembly; sol-gel processes; titanium