Strategies to extend near-infrared light harvest of polymer carbon nitride photocatalysts

Graphitic carbon nitride (g-C3N4), as a significant metal-free photocatalyst, has elicited ripples of excitement due to its many extraordinary features, such as its mild bandgap, high thermal and chemical stability, inexpansive, and environmental friendly. However, the unsatisfactory solar light absorption, low surface area and the rapid recombination of photogenerated charges severely restrict the photocatalytic activity of bulk g-C3N4. Especially, g-C3N4 with a bandgap of 2.7 eV means an absorption threshold at about 450 nm that is still insufficient for efficient visible light capturing and leaves the near-infrared (NIR) light spectrum unexploited. In order to facilitate future material design for efficient g-C3N4 photocatalysts under solar light (UV ~5%, visible light ~43%, NIR light ~52%), we reviewed the recent progress of NIR-driven g-C3N4 based photocatalysts. Many strategies, including combination of narrow optical gap materials, bandgap engineering, upconversion materials, plasmonic materials, and photosensitizers, have been summarized to broaden the light absorption of g-C3N4 to NIR light region. Besides, the diverse photocatalytic applications of NIR driven g-C3N4 photocatalysts have been summarized, including water purification, water splitting, N2 photofixation, CO2 reduction, NO removal, H2O2 production, bacteria disinfection, photodynamic therapy and organic synthesis, etc. The mechanism and the roles of various strategies in the NIR photocatalytic process were highlighted in details. Moreover, the limitations and possible solutions for each method are discussed.