Nitrogen-doped porous biochar with p-π conjugated structure for efficient visible-light photocatalytic amine oxidation integrated with CO2 reduction

Developing low-cost and efficient metal-free carbon-based photocatalysts is of great significance but remains a challenge for light-driven selective organic synthesis integrated with CO 2 reduction. Herein, the N/O functional groups and high specific surface areas of porous biochars are dexterously designed by one-pot pyrolysis of waste coconut shell with combining tripolycyanamide and K 2 CO 3 co-modification, and demonstrate the high performance of the obtained porous biomass-derived biochar photocatalysts with photogenerated holes and electrons on the synergistic coupling amine dehydrogenation oxidation and reaction of CO 2 reduction to HCOOH, which can swiftly convert 86.0 % of benzylamine into N-benzylidenebenzylamine with a selectivity of 99.9 % under visible-light radiation. This coconut shell-derived biochar exhibits a wide generality for various aromatic amines, accompanied by the advantages of good recyclability and stability. Structure analysis and theoretical calculations reveal that the construction of the orbital interaction between the p-orbital on nitrogen and π-orbitals of polyaromatics with the terminal carboxylic acid groups greatly boosts the photogenerated charge-carrier separation, and reduce the possibility of recombination of photogenerated electrons and holes along with the layered graphitic structure. Meanwhile, the polyaromatic carboxylic acid groups and graphitic-N moieties serve as active sites with the π-π electron-donor-acceptor interactions for the adsorption/activation of amines and CO 2 , which promotes the synergistic oxidation-reduction process.