Modification strategies for visible-light photocatalysts and their performance-enhancing effects on photocatalytic degradation of volatile organic compounds

Photocatalytic oxidation is a potent approach for removing gaseous volatile organic compounds (VOCs) from air streams. Although a plethora of photocatalysts have been developed to degrade VOCs under ambient conditions, their practical feasibility has often been confined by their short lifetime (rapid deactivation) and/or wide bandgap (activation under ultraviolet radiation). In light of such limitations, the feasibility of various strategies (e.g., doping with metal/nonmetal ions, coupling with other semiconductors, surface engineering, morphology modification, and miscellaneous approaches) has been explored toward the visible-light photodegradation of both polar and nonpolar VOC (i.e., formaldehyde and toluene, respectively as the model compound) in terms of the key performance metrics such as quantum yield (QY) and space-time yield (STY) values. According to the STY-based evaluation (molecules/photon/g), the construction of composite photocatalysts such as Au@Co3O4 and ultra-small C-doped TiO2/carbon cloth substrate has been identified as the best mitigation strategy for formaldehyde (2.4E-02) and toluene (9.3E-01), respectively. Nonetheless, as the commercial feasibility of these photocatalysts is yet confined by high energy consumption and/or production cost, suggestions are put forth to help enhance their scalability as well as processing performance.