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.