Tuning the VB of COF to improve the efficiency of photoreduction of CO2 with water

Porous covalent organic framework (COF), as an emerging material, has the characteristics of high stability, large proportion series, easy synthesis, modification, and adjustable amplitude. It has the potential to become a good-performance catalyst. Bromine, as a halogen, has attracted intensive interests in modification of photocatalyst for photocatalytic reaction. It is feasible to enhance activity and selectivity of the material by facile functionalization of the reticular parent structure electron-withdrawing groups. In addition, the conjugation effect of bromine, further delocalizing the electrons of COF, which is beneficial to the progress of photocatalytic reaction. The report on modification of COF by bromine functional group to improve its catalytic performance has not been found so far. Here, TAPP and 2,5-dibromo-1,4-benzenedialdehyde instead of terephthalaldehyde were chosen to synthesize porphyrin-based COF (TAPBB-COF) by solvothermal method. As expected, VB of TAPBB-COF has been adjusted to a more suitable position. In the end, the CO production of TAPBB-COF under full-wavelength light for 12 hours was 295.2 mumol.g-1, which was three times that of COF-366, and has good recycle stability and selectivity (95.6%). Theoretical calculations indicated that the nitrogen of the porphyrin ring and the Schiff base, and the bromine in TAPBB-COF contribute greatly to the activation of H2O and the conversion of CO2 in the photoreaction.