Highly nitrogen-doped porous carbon transformed from graphitic carbon nitride for efficient metal-free catalysis.

• N-doped porous carbon was prepared via transformation from graphitic carbon nitride. • N-doped porous carbon (NC 1.0) possesses ultrahigh N content up to 33.75 at%. • NC 1.0 exhibits excellent reactivity and stability for peroxymonosulfate activation. • DFT calculations reveal PMS activation involving PMS reduction and oxidation. • Singlet oxygen (1O 2) is the main reactive oxygen species in the NC 1.0 /PMS system. Nitrogen-doped carbon materials are proposed as promising metal-free catalysts for persulfate-mediated catalytic oxidation process, yet the nitrogen content in the final carbon products is typically low. Moreover, controversies remain in the unambiguous identification of active sites in nitrogen-doped carbons for persulfate activation. Here we report the facile synthesis of nitrogen-doped carbon material via one-step pyrolysis of urea and D-mannitol, which simultaneously combine ultrahigh nitrogen content (up to 33.75 at%) with apparent porous structure via transformation from graphitic carbon nitride. With this strategy, the highly nitrogen-doped porous carbon (NC 1.0) exhibits excellent catalytic activity toward peroxymonosulfate (PMS) activation for oxidation of organic pollutants. Both experiments and density functional theory (DFT) calculations, for the first time, revealed that the electron-rich graphitic N and electron-deficient carbon atom adjacent to graphitic N in NC 1.0 served as active sites for PMS reduction and oxidation toward the generation of hydroxyl radical (OH) and singlet oxygen (1O 2), respectively, in which PMS oxidation was the main reaction in the course of PMS activation rendering 1O 2 the dominant reactive oxygen species (ROS) in the NC 1.0 /PMS system. More importantly, NC 1.0 presents robust stability in PMS activation, superior to most reported nitrogen-doped carbon-based catalysts, offering great promise for practical environmental remediation. [ABSTRACT FROM AUTHOR]