Modulating Electronic Structure of Carbon Nitride Oligomer Through Benzene-Ring Bridging and Oxygen Doping for Boosting H2O2 Photosynthesis

Photocatalytic oxygen reduction to hydrogen peroxide (H2O2) offers a promising route for sustainable chemical synthesis, yet the efficiency of carbon nitride-based photocatalysts is often limited by narrow light absorption and rapid charge recombination. Low-molecular-weight carbon nitride exhibits a favorable reduction potential but suffers from poor visible-light utilization, while π-conjugation extension and heteroatom doping are effective yet rarely combined within a single oligomeric framework. In this work, we report a low-temperature (400 °C) one-step copolymerization approach employing urea and terephthalonitrile to construct an oxygen-doped, benzene-bridged carbon nitride oligomer (O-B-CNO). Comprehensive characterization confirms the successful integration of both benzene rings and oxygen dopants into the oligomer backbone, with the former enhancing structural stability and the latter introducing active sites. The extended conjugation and oxygen incorporation synergistically modulate the electronic structure, leading to a narrowed bandgap, improved visible-light harvesting, and suppressed charge recombination. As a result, O-B-CNO delivers a photocatalytic H2O2 yield of approximately 3000 μM under visible-light irradiation, a 10-fold enhancement over the pristine oligomer, with optimal activity at neutral pH via the two-electron oxygen reduction pathway. The enhanced performance stems from the complementary functions of the two modifications: benzene rings promote electron delocalization and charge transport, while oxygen dopants serve as selective active centers for oxygen reduction. This work demonstrates a viable molecular engineering strategy for developing efficient carbon nitride photocatalysts for H2O2 production.