Enhanced exciton dissociation and charge transfer via grafting conjugated thiophene onto carbon nitride for improved photocatalytic H2O2 production from air and water

The efficiency of photocatalytic H 2 O 2 synthesis by polymer carbon nitride (CN) is impeded by insufficient exciton dissociation and charge carrier transport, and sluggish redox reaction dynamics. However, no report has systematically clarified these specific impacts based on precise intramolecular donor-acceptor (D-A) structural models of CN. Herein, three newly designed CN-based polymers are firstly reported for the first time by introducing different numbers of thiophene groups (n = 1, 2, 3) as electron donors. The introduction of different conjugated thiophene enables modulation of the conjugations within the CN plane, thereby achieving different photocatalytic activity for H 2 O 2 production in pure water under air. The optimal photocatalyst (named as CN-DTD) exhibits the highest H 2 O 2 evolution rate of 14200 μM g −1  h −1 without additional sacrificial agents, which is 6.3-fold of bulk CN (2267 μM g −1  h −1 ), and exceeding numerous reported CN-based materials. Comprehensive experimental characterizations and theoretical calculations disclose that increasing the number of thiophene groups, from 2.43 D to 3.67 D, contributes to a larger dipole moment, generating a robust internal electric field that not only weakens exciton effect and promotes subsequent intramolecular charge transfer, but also enhances O 2 adsorption and activation while lowering the activation energy barrier of ∗OOH, thereby accelerating H 2 O 2 formation. This work provides new insights for designing molecular-level catalysts for the green synthesis of H 2 O 2 .