One-step fabrication of mesoporous sulfur-doped carbon nitride for highly selective photocatalytic transformation of native lignin to monophenolic compounds

摘要

Photocatalytic selective transform native lignin into valuable chemicals is an attractive but challenging task. Herein, we report a mesoporous sulfur-doped carbon nitride (MSCN-0.5) which is prepared by a facile one-step thermal condensation strategy. It is highly active and selective for the cleavage C alpha-C beta bond in beta-O -4 lignin model compound under visible light radiation at room temperature, achieving 99% substrate conversion and 98% C alpha -C beta bond cleavage selectivity. Mechanistic studies revealed that the C beta-H bond of lignin model compounds activated by holes and generate key C beta radical intermediates, further induced the C alpha -C beta bond cleavage by superoxide anion radicals (center dot O-2(-)) to produce aromatic oxy-genates. Waste Camellia oleifera shell (WCOS) was taken as a representative to further understand the reaction mechanisms on native lignin. 33.2 mg of monophenolic compounds (Vanillin accounted for 22% and Syringaldehyde for 34%) can be obtained by each gram of WCOS lignin, which is 2.5 times as that of the pristine carbon nitride. The present work offers useful guidance for designing metal-free heteroge-neous photocatalysts for C alpha -C beta bond cleavage to harvest monophenolic compounds.

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