Increasing the Visible Light Absorption of Graphitic Carbon Nitride (Melon) Photocatalysts by Homogeneous Self-Modification with Nitrogen Vacancies

摘要

Photocatalysis is considered to be one of the more promising technologies to produce renewable fuels and remove pollutants. Efficient photocatalysts operating under solar light have been actively pursued, and many attractive visible light photocatalysts have been explored.'1' Melon (graphitic carbon nitride with a certain amount of hydrogen, which has been widely described as "g-C_3N_4" in the literature) with a bandgap of ca. 2.7 eV as a metal-free photocatalyst has attracted increasing attention largely due to its easy availability, ability of absorbing visible light with wavelength up to around 450 nm, low-cost and good stability. Concerning the full utilization of the visible light region from 400 to 700 nm in the solar spectrum, the ideal bandgap of a photocatalyst is considered to be ca. 2 eV. There is an inherent driving force to narrow the bandgap of photocatalysts towards this value. Introducing heteroatoms as a general strategy of tuning the bandgap of semiconductors has been attempted to narrow the bandgap of melon in order to extend its light absorption range. Several heteroatoms (i.e., boron, sulfur, oxygen, iodine, phosphorus, and iron) have been introduced into the framework of melon. A survey of doped melon shows that, although the light absorption range was greatly extended with the incorporation of appropriate heteroatoms, the effective bandgap narrowing of melon was achieved only in a few studies. Here, we reported an alternative way of narrowing the bandgap of melon from pristine 2.78 to 2.03 eV by homogeneous self-modification with nitrogen vacancies. The resultant melon with a strong visible light absorption and extremely low radiative recombination of photo-excited charge carriers shows significantly improved photocatalytic activity. These results could have important implications for modifying the electronic structures of other functional materials by a homogeneous self-modification strategy for various applications.