Metal-free oxidized carbon nitride for efficient sunlight-driven photocleavage of lignin ?-O-4 bond

Benefitting from mild reaction conditions and good reusability, photocatalysis has industrial potential for highvalue utilization of lignin waste. Commonly used metal sulfide photocatalysts present the risk of contamination of aromatic products by heavy metal ions due to photocorrosion. Here, a metal-free oxidized g-C3N4 photocatalyst was developed to selectively cleave the beta-O-4 bond of lignin. Simple high-temperature oxidation treatment reduced carbon nitride size and scavenged the terminal NH2 groups, resulting in higher oxygen adsorption capacity and valence band potential. In the photoelectric effect, oxidized g-C3N4 exhibited lower carrier migration resistance and a longer photogenerated electron lifetime. The high oxygen adsorption and specific surface area led to a 160 % increase in superoxide radicals. Two routes for the photocatalytic cleavage beta-O-4 bond in g-C3N4 are proposed. The catalytic activity of oxidized g-C3N4 is 8.5 times higher than that of untreated g-C3N4, the selective photocleavage reactivity attributed mainly to more & BULL;OOH radicals and higher valence band potential. This work will provide a green and efficient strategy for the high-value conversion of lignin.