Potassium-doped carbon nitride: Highly efficient photoredox catalyst for selective oxygen reduction and arylboronic acid hydroxylation

Abstract

Photocatalytic two-electron oxygen reduction reaction for hydrogen peroxide production, a promising liquid energy carrier and an environmentally friendly oxidant, is regard as a promising process owing to its low-cost and environment-friendly advantages compared to the state-of-art anthraquinone oxidation for H2O2 production. Herein, a potassium-doped carbon nitride photocatalyst has been successfully synthesized by the copolymerization of self-assembly supramolecular cyanuric acid and melamine aggregates with introduction of potassium chloride (KCMCN), wherein its band structure was carefully tuned and a new channel for charge transfer was created. Notably, DFT calculations pointed out that a lower absorption energy of oxygen (Eads = 0.27 eV) over KCMCN was estimated than that of MCN (Eads = 1.02 eV) with the introduction of K into carbon nitride framework, which is beneficial for superior H2O2 evolution. The H2O2 yield of KCMCN (317.9 µmol·L−1·h−1) was about 10.7 times higher than bulk carbon nitride at low concentration of sacrificial agent (0.5% isopropanol aqueous solution) and the apparent quantum efficiency (AQE) of KCMCN reached to 7.5% at 420 nm. Furthermore, in-situ photoinduced superoxide radical anion (·O2−) species were generated from dioxygen in KCMCN, which were reacted with arylboronic acids to produce corresponding aryl alcohols through a hydroxylation process under visible light irradiation. This work opens up prospects for providing guidance for other organic synthesis based on the oxidative effect of H2O2 and exploring novel heterogeneous photocatalysts in the field of value-added products formation.