MXene quantum dots decorated g-C3N4/BiOI heterojunction photocatalyst for efficient NO deep oxidation and CO2 reduction.

[Display omitted] • A ternary g-C 3 N 4 /MQDs/BiOI photocatalyst is constructed. • g-C 3 N 4 /BiOI heterojunction improves charge separation and light absorption. • MQDs further promote charge transfer and increase active sites. • NO deep oxidation and CO 2 reduction abilities are substantially enhanced. • The ternary photocatalyst shows good cycling stability. The photocatalytic performance of g-C 3 N 4 is greatly limited by the severe charge recombination due to its s-triazine unit structure. Hence, enhancing the separation of photogenerated carriers is the pivotal factor for high-efficiency photocatalysis of g-C 3 N 4. In this work, we construct a MXene quantum dots (MQDs) decorated BiOI/g-C 3 N 4 p-n heterojunction photocatalyst. The interfacial charge separation and transfer are substantially promoted, due to the synergistic effect of the internal electric field (IEF) of BiOI/g-C 3 N 4 heterojunction and strong electron-withdrawing capability of MQDs. Furthermore, the introduction of BiOI with a low band gap and MQDs with large specific areas and rich surface terminals lead to enhanced light absorption and active sites. As a result, the ternary g-C 3 N 4 /MQDs/BiOI photocatalyst achieves a much higher NO removal rate of 42.23 % and discharges less NO 2 intermediate than the individual and binary ones. Meanwhile, the g-C 3 N 4 /MQDs/BiOI photocatalyst also exhibits the most effective CO 2 photoreduction, with a CO production rate of 57.8 μmol·g−1·h−1 and a CH 4 production rate of 3.6 μmol·g−1·h−1, surpassing all other photocatalysts in this study. In addition, the designed composite photocatalyst shows remarkable stability. The photocatalytic mechanisms are studied by the trapping experiment and in-situ Fourier Transform Infrared (FTIR) Spectra. This work paves a new avenue for enhancing charge separation and thus improving performances of g-C 3 N 4 -based photocatalysts by integrating a p-n heterojunction and a co-catalyst, which would accelerate commercial deployment of emerging photocatalysts. [ABSTRACT FROM AUTHOR]