Modulating Local Charge Distribution of Carbon Nitride for Promoting Exciton Dissociation and Charge-Induced Reactions.

ABSTRACT

The sustainable light can generate reduction and oxidation centers in situ through the generation of photoexcited electrons and holes in the presence of photocatalyst. However, the photoexcited electrons and holes have huge Coulombic attraction and high exciton binding energy due to the weak screening effect and dielectric properties in many low-dimensional conjugated polymers, such as carbon nitride. Reducing the exciton binding energy of carbon nitride and promoting the conversion of excitons into free charge carriers are necessary for improving the activity of photocatalytic reactions but still very challenging. Here, by introducing amino-cyano functional groups into carbon nitride, it is demonstrated that excitons can be effectively dissociated into electrons and holes by finely controlling the charge distribution of heptazine ring. It is found that carbon nitride with heptazine rings of positive charge distribution can greatly reduce the exciton binding energy to 24 from 71 meV. Compared with heptazine ring having negative charge distribution, heptazine ring with positive charge distribution can increase photocatalytic hydrogen production of carbon nitride by up to ten times. This work provides an easy way to promote the dissociation of excitons in carbon nitride by regulating the charge distribution.