Synthesis of carbon nitride in potassium hydroxide molten salt for efficient uranium extraction from radioactive wastewater

Highlights

● Develop a one-step unary KOH molten salt carbon nitride synthesis method.

● Enhance light absorption and separation efficiency of electron-hole pair of K-CN-80.

● Improve photocatalytic activity and kinetics of U(VI) extraction onto K-CN-80.

● Separated U(VI) from wastewater as metastudtite by the photocatalytic extraction.

Abstract

Photocatalysis-assisted removal of uranium has been proven as an effective method for the elimination of radioactive pollution from wastewater. In this work, carbon nitride materials were synthesized in potassium hydroxide (KOH) molten salt and applied to photocatalytic uranyl extraction. Obtained materials were confirmed to possess the triazine-s-heptazine structure by NMR, XPS and UV-Vis characterization, and exhibited a wider visible light absorption than graphitic carbon nitride (g-C₃N₄). The photocatalytic activity of the carbon nitride materials was tailored by varying the precursor mass fractions. The carbon nitride obtained at 80% melamine as precursor (K-CN-80) exhibited the highest photocatalytic extraction ability and its photocatalytic reaction rate is 6.6 times faster than that of g-C₃N₄. The influence of sacrificial agents was studied and the results showed that triethanolamine inhibited U(VI) photoreduction, but methanol can accelerate U(VI) photoreduction by consuming photogenerated holes. This unary KOH molten salt synthesis method has exceptional potential applications in the preparation of carbon nitrides, and the obtained products showed potential in extracting U(VI) from aqueous solutions for use in nuclear fuel industry and for U(VI) environmental pollution cleanup.

Keywords

Uranium / Carbon nitride / Molten salt / Photocatalysis / Radioactive wastewater

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Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Nos. 22376059 and 21976104), the Young Elite Scientists Sponsorship Program of China Association for Science and Technology (No. 2021QNRC001), the Brain Pool program funded by the Ministry of Science and ICT through the National Research Foundation of Korea (No. NRF-2022H1D3A2A02051548).

Conflict of Interests

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-024-1859-5 and is accessible for authorized users.

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