Nitrogen-rich carbon nitride with heptazine phase controlled by pyrolysis temperature towards photocatalytic U(VI) reduction

Photocatalytic process is a new and efficient technology, which has great potential in the U(VI) reduction process. Nitrogen is volatile at high temperatures, so its synthesis reaction is significantly influenced by pyrolysis temperature. Herein, a series of nitrogen-rich carbon nitride with different nitrogen content and different catalytic properties were prepared by changing the pyrolysis temperature from 450 °C to 650 °C. With the increase of pyrolysis temperature, the nitrogen content decreases continuously, and the triazine ring, tetrazine ring and azo bond generated by low temperature pyrolysis are gradually replaced by heptazine ring and nitrogen single bond. The nitrogen-rich carbon nitride synthesized at 550 °C has the best reducing activity for U(VI) reduction, which is attributed to the good cavity structure, narrow light absorption band gap and high electron transport channel. These results can provide guidance for regulating the electron transport structure of the nitrogen-rich carbon nitride to achieve enhanced photocatalytic activity.