Evolution of TiO2 coating layers on lamellar sericite in the presence of La3+ 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.