Evolution of TiO 2 coating layers on lamellar sericite in the presence of La 3+ and the pigmentary properties

Abstract

TiO 2-coated sericite powders were prepared by the chemical deposition method starting from lamellar sericite and TiCl 4 in the presence or absence of La 3+ cations. After calcination at 900 °C for 1 h, the resultant TiO 2 nanoparticles on the sericite surfaces existed in anatase phase. The light scattering indexes of the TiO 2-coated lamellar sericite powders were dozens of times higher than that of the naked lamellar sericite powders. The presence of La 3+ in the deposition solution was beneficial to the formation of the small-sized anatase TiO 2 nanoparticles, resulting in the formation of the dense and uniform island-like TiO 2 coating layers in a large range of the weight ratios of TiO 2 to sericite from 5% to 20%. The TiO 2-coated lamellar sericite powders prepared in the presence of La 3+ had higher light scattering index than that prepared in the absence of La 3+. XPS analysis shows that when La 3+ cations were absent in the reaction solution, TiO 2 coating layers anchored at the sericite surface via the Ti–O–Si and Ti–O–Al bonds. The presence of La 3+ 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 TiO 2 coating layers. After coating TiO 2 on the sericite surface, the yellowness of the TiO 2-coated sericite powders obviously increased and the brightness slightly decreased.