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.