Designing and Understanding Biphasic TiO₂ Composites for a Long-Lasting Photocatalytic Air Purification

Dual- and single-phase TiO2 photocatalysts were prepared and evaluated for their durable performance in air purification through repeated cycles of toluene degradation under ambient air condition. The prepared anatase–brookite heterostructures (AB-350 and AB-450 with 84% anatase and 16% brookite) were compared with commercial P25 (biphasic anatase–rutile), P25-derived monophasic anatase (P25-A), and rutile (P25-R). Only the biphasic AB hybrids maintained the long-lasting photocatalytic activity for toluene mineralization to CO2, while the other titania forms exhibited gradual deactivation over repeated uses. The AB photocatalysts exhibited the largest number of trapped electrons, the longest lifetime of trapped charge carriers, the minimized accumulation of carbonaceous intermediates, and the highest concentration of surface water molecules during irradiation. The sustained performance of the AB photocatalyst is attributed to two key factors: (1) an optimal level of trapping sites that facilitates charge separation and complete oxidation of organics and (2) surface properties that maintain a high density of surface water during prolonged irradiation. These combined features enabled the sustained production of •OH, preventing the accumulation of toluene degradation intermediate residues on the photocatalyst surface. With its excellent long-term activity in the photodegradation of volatile aromatic compound, the AB heterostructure is proposed as a promising candidate for practical air purification applications.