Photocatalytic air cleaners and materials technologies – Abilities and limitations

• PCO technology-based air cleaners and building materials for air quality improvement were reviewed.
• PCO principles were discussed from mass transfer, adsorption, and photochemical reactions.
• Both experimental and modeling work was described for each scenario.
• Research limitations were summarized and future research directions were proposed.

Heterogeneous photocatalytic oxidation (PCO) is one of the most active research areas in environmental purification. Recently, research on PCO technologies-based air cleaners and building materials has been intensively conducted for indoor/outdoor air treatment. The innovative technology is dedicated to decompose gaseous pollutants using photocatalysts under illumination of UV or solar light without extra energy added. Comprehensive knowledge on the properties and performance of PCO for treatment of air using batch reactors or continuous reactors has been established. This critical review has been carried out with aims to examine the state-of-the-art of PCO technologies in the field of air purification and their application prospects. First, PCO fundamental principles, including mass transfer, adsorption, and surface reaction, are reviewed, providing rational explanations for research results. Second, the experimental work in various scales and other related research, such as modeling methods, coating techniques, and testing methods, are discussed and evaluated separately for PCO air cleaners and building materials. Based on these insights, the corresponding technological problems and future research directions for promotion of commercial applications in two aspects are also described in detail.