Atomic layer deposition ultrathin amorphous TiO2 film in a fluidized bed reactor for improving the weatherability of TiO2 pigment

Abstract

Normally, a transparent inert film is coated on the surface of TiO₂ particles to enhance the weatherability of the pigment. Liquid-phase coating process is mainly used in industry, which difficult to get really uniform films. This work combining nanoparticle fluidization technology with atomic layer deposition (ALD) technology to achieve precise surface modification of a large number of micro-nano particles. First, we explored the fluidization characteristics of TiO₂ nanoparticles in a home-made atmospheric fluidized bed ALD reactor (FB-ALD) to ensure the uniform fluidization of a large number of nanoparticles. Then TiCl₄ and H₂O were used as precursors to deposit amorphous TiO₂ films on the surface of TiO₂ nanoparticles at 80 °C under atmospheric pressure, and the growth per cycle was about 0.109 nm per cycle. After 30 ALD cycles, the film thickness was about 3.1 nm, which could almost fully suppress the photocatalytic activity of TiO₂. Compared with other traditional coating materials, amorphous TiO₂ has higher light refractive index, and realizes the suppression of the photocatalytic activity of TiO₂ without introducing other substances, demonstrating greater application potential in TiO₂ pigment coating field. The process is a gas-phase coating method, which is efficient, no waste water, and easy to scale up. This work shown the excellent property of interface engineering in improving pigment weatherability and can also provide guidance for the nanoparticle surface modification.