Hydrous alumina/silica double-layer surface coating of TiO2 pigment

The hydrous alumina/silica double-layer surface coating of TiO2 pigment was prepared by precipitation method under two different conditions. High-resolution transmission electron microscopy (HRTEM), Energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectrum (FTIR) as well as ζ-potential analysis were used to characterize the morphology, structure and surface electrokinetic behavior, respectively. The results show that hydrous alumina is continuously coated on the surface of silica-coated TiO2 particle with a compact layer at 60 °C, pH 4.0. There is a chemical interaction between the hydrous alumina layer and silica layer. An AlOSi bond was formed and a thin film of aluminosilicate was existed. A flocculent hydrous alumina layer was formed at 60 °C, pH 8.0. The XPS spectra of O1s show that the peak of 531.2 eV is assigned to AlO(OH) for the loose and flocculent morphology. The theoretical calculations reveal that the coated Al2O3·H2O on SiO layer combined with (−1 1 1) lattice plant of rutile TiO2 is more stable than the coated AlO(OH) and the discrepancy of total energy between them is about −1.303 eV, i.e., the sample obtained at 60 °C, pH 4.0 has a more stable thermodynamic property. In addition, the adsorption of H+ ion on AlO(OH) surface is easier than that on Al2O3·H2O surface, as the discrepancy of total energy between them decrease to −0.721 eV.

The structure of (a) 4AlO(OH)/4SiO2/12TiO2; (b) Al2O3·H2O/4SiO2/12TiO2; (c) 2H+/4AlO(OH)/4SiO2/12TiO2; (d) 2H+/2Al2O3·H2O/4SiO2/12TiO2.Figure optionsDownload as PowerPoint slideHighlights
► Hydrous alumina/silica layer by layer surface coating of TiO2 pigment was prepared.
► There is a chemical interaction between the hydrous alumina layer and silica layer.
► Possible structure of coated layers were investigated by computer simulation.
► The coated Al2O3·H2O on SiO layer is more stable than the coated AlO(OH) on it.