Evolution of TiO2 coating layers on lamellar sericite in the presence of La and the pigmentary properties

TiO₂-coated sericite powders were prepared by the chemical deposition method starting from lamellar sericite and TiCl₄ in the presence or absence of La³⁺ cations. After calcination at 900 °C for 1 h, the resultant TiO₂ nanoparticles on the sericite surfaces existed in anatase phase. The light scattering indexes of the TiO₂-coated lamellar sericite powders were dozens of times higher than that of the naked lamellar sericite powders. The presence of La³⁺ in the deposition solution was beneficial to the formation of the small-sized anatase TiO₂ nanoparticles, resulting in the formation of the dense and uniform island-like TiO₂ coating layers in a large range of the weight ratios of TiO₂ to sericite from 5% to 20%. The TiO₂-coated lamellar sericite powders prepared in the presence of La³⁺ had higher light scattering index than that prepared in the absence of La³⁺. XPS analysis shows that when La³⁺ cations were absent in the reaction solution, TiO₂ coating layers anchored at the sericite surface via the Ti-O-Si and Ti-O-Al bonds. The presence of La³⁺ cations caused the formation of Si-O-La and Al-O-La bonds at the sericite surface and Ti-O-La bond at the surface of TiO₂ coating layers. After coating TiO₂ on the sericite surface, the yellowness of the TiO₂-coated sericite powders obviously increased and the brightness slightly decreased.