TiO2-based photocatalytic oxidation process for indoor air VOCs removal: A comprehensive review

The unavoidable existence of volatile organic compounds (VOCs) in indoor environments, as the major indoor air pollutants, significantly affects indoor air quality, and consequently threatens human health and comfort. Among air purification technologies, the TiO2-based photocatalytic oxidation process (PCO) has indicated significant promise as an eco-friendly, cost-effective, and sustainable purification technology to degrade indoor VOCs, even at low concentrations. Nevertheless, despite the benefits, some limitations, and drawbacks, including inefficient utilization of visible light, high charge recombination rate, low adsorption capacity toward pollutants, hazardous by-product formation, and rapid deactivation have prevented the commercialization of this technology. Therefore, many studies have been directed toward developing modification methods, i.e., metal/non-metal doping, co-doping, coupling with other semiconductors, and integrating with adsorbents to overcome the above-mentioned limitations. This review briefly introduces the fundamentals of the TiO2-based PCO process and summarizes the limitations and barriers of this technology and the recent studies on the modification of TiO2 photocatalysts, aimed at enhancing an efficient photodegradation of indoor VOCs. Finally, the outlook and required future research for designing an efficient TiO2-based photocatalyst are suggested accordingly.