Design of Photocatalytic Particle Assemblies Applicable to a Continuous Water Purification Process

Water purification process with photocatalysts exhibiting catalytic activities under light irradiation has received attention. Titanium oxide (TiO₂) has been widely studied as a practical photocatalyst because of its wide band gap, high chemical stability and high availability. Generally, photocatalysts are classified into dispersed-type and immobilized-type. The former ones are usually employed for the water purification due to their high specific surface area, but they need separation and recovery processes after photocatalytic reactions. In the latter case, TiO₂ particles immobilized on a substrate don’t require separation and recovery processes. However, the immobilized-type photocatalysts are less active than the dispersed-type ones because of their low specific surface area. Thus, an immobilized-type photocatalyst possessing high surface area is desired for a continuous process to treat a large amount of polluted water.

In the present work, we proposed a novel type of photocatalyst, the photocatalytic particles assembly composed of TiO₂ particles and an inverse opal silica (SiO₂) frame. TiO₂ particles are incorporated into the void spaces of the SiO₂ frame, and that enables the surface of TiO₂ particles to be exposed to continuous phase during water treatment. Aiming for a degradation of organic pollutants in continuous process, the photocatalytic activities of the fabricated particle assemblies were evaluated using a flow-type reactor. In this system, the photocatalytic reactions were successfully observed with a flow-type reactor, and the reaction rates were higher than those with a batch-type reactor. The particle assemblies also exhibited higher reaction rates than those of the typical immobilized-type photocatalyst due to its high contact efficiency. These results indicated that the photocatalyst proposed in this work can be a promising candidate for a continuous water purification process.

Reference:

Hikaru Namigata, Kanako Watanabe, Saya Okubo, and Daisuke Nagao. Polymer-coating of photocatalytic particles to prevent sintering in their calcination process. Colloids and Surfaces A, in press (2020)