Selectively constructing nitrogen vacancy in carbon nitrides for efficient syngas production with visible light

Photocatalytic reduction of CO2 and H2O is believed to be a green and sustainable approach for syngas production. However, this reaction typically suffers from moderate efficiency and uncontrollable H2/CO ratio. Herein, we report a general acetonitrile treatment approach to create nitrogen vacancies (NVs) on the surface of polymeric carbon nitride (PCN) photocatalyst. The type and distribution of NVs are analyzed by X-ray photoelectron spectroscopy, positron annihilation spectroscopy, solid-state nuclear magnetic resonance and element analysis. Results confirm that the NVs are mainly stemmed from the selectively breaking of surface N-(C)3 sites of PCN. In-situ diffuse reflectance infrared Fourier transform spectroscopy and DFT calculations determine that the NVs can improve the activation and reduction of CO2, while considerably lowering the formation barrier of COOH* intermediates. Besides, the NVs modification can accelerate the separation and transfer kinetics of photogenerated charge carriers of PCN. As a result, the NVs-PCN exhibits excellent photocatalytic activity. The syngas production rate of the NVs-PCN is almost 10 times higher than that of the pristine PCN under visible light. Importantly, the syngas H2/CO ratio can be tuned between 0.24:1 and 6.8:1 by merely adjusting the concentrations of NVs. Furthermore, we found that this NVs engineering can also promote the visible-light harvesting of PCN, hence realizing efficient syngas production under visible light, even under low-energy red light irradiation (610 nm). Also, this defect implantation strategy can be further extended to synthesize other NVs-functionalized PCN for syngas production with high efficiency.

Automated summary

The study presented a strategy of using acetonitrile treatment to create nitrogen vacancies on the surface of PCN photocatalyst, greatly improving the efficiency of syngas production. This method not only accelerates the transfer kinetics of photogenerated charge carriers, but also allows for tuning the H2/CO ratio of syngas, achieving efficient syngas production under visible light.