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

Abstract

● 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.

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.

Graphical abstract

Keywords

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

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