Hydrothermal assisted enhancing crystallinity of COF towards effective photocatalytic oxidation of benzylamines

Abstract

Photocatalysis is an environmentally friendly strategy for synthesis of high-value chemicals. However, covalent organic frameworks (COFs), as organic semiconductors, typically exhibit limited electrical conductivity, which significantly affects the photocatalytic efficiency of COF. In this work, a simple hydrothermal treatment method was presented to enhance the conductivity of aza-COF prepared by acid-catalyzed imine condensation of BTA⋅4HCl and HKH⋅8H₂O. The crystallinity and carbonization degree of the aza-COF were explored by adjusting the hydrothermal temperatures from 80 to 160 °C. Remarkably, the COF-3 prepared by 120 °C hydrothermal temperature displays the highest photocatalytic conversion rate of benzylamine of 97 % with the high selectivity of 99 % in 4 h, outperforming the pristine aza-COF by 40 %. From various test results analysis, COF-3 exhibits the strongest transient photocurrent response, smallest electrochemical impedance, narrowest bandgap energy, attributed to its enhanced crystallinity, which improves conductivity. Furthermore, the photocatalysis mechanism was elucidated through quenching experiments, which determined the reactive oxygen species.