Engineering an ultrathin amorphous TiO2 layer for boosting the weatherability of TiO2 pigment with high lightening power

TiO₂ pigments are typically coated with inert layers to suppress the photocatalytic activity and improve the weatherability. However, the traditional inert layers have a lower refractive index compared to TiO₂, and therefore reduce the lightening power of TiO₂. In the present work, a uniform, amorphous, 2.9-nm-thick TiO₂ protective layer was deposited onto the surface of anatase TiO₂ pigments according to pulsed chemical vapor deposition at room temperature, with TiCl₄ as titanium precursor. Amorphous TiO₂ coating layers exhibited poor photocatalytic activity, leading to a boosted weatherability. Similarly, this coating method is also effective for TiO₂ coating with amorphous SiO₂ and SnO₂ layers. However, the lightening power of amorphous TiO₂ layer is higher than those of amorphous SiO₂ and SnO₂ layers. According to the measurements of photoluminescence lifetime, surface photocurrent density, charge-transfer resistance, and electron spin resonance spectroscopy, it is revealed that the amorphous layer can prevent the migration of photogenerated electrons and holes onto the surface, decreasing the densities of surface electron and hole, and thereby suppress the photocatalytic activity.