Metal-free 2D/2D C3N5/GO nanosheets with customized energy-level structure for radioactive nuclear wastewater treatment

How to efficiently treat radioactive uranium-containing nuclear wastewater is one of the significant challenges to ensure the safety of nuclear technology and to avoid environmental pollution. Here we firstly prepare the metal-free 2D/2D C3N5/GO nanosheets, and customize a type-II heterojunction based on the band bending theory to achieve enhanced uranium extraction capacity via synergistic adsorption photoreduction engineering. The structure of C3N5 is explained by electron energy loss spectroscopy and synchrotron-based near-edge X-ray absorption fine structure. And C3N5 with larger pi-conjugated structure expands the light response range to 747 nm, which is about 1.67 times that of C3N4. Further, we also use density functional theory to prove the existence of alternating energy levels so that photogenerated electrons could be continuously injected into the surface of GO to ensure the effective separation of electron-hole pairs and increase the material activity. The results show that the removal ratio of uranium by 2D/2D C3N5/GO heterojunction is achieved as high as 96.1% even at a low uranium concentration of 10 ppm, and reached 93.4% after exposure to gamma-ray. This work will lay a foundation for customizing the energy band structure of nonmetal-based 2D/2D nanohybrids and enriching uranium-containing wastewater through adsorption photoreduction engineering in the future.

Automated summary

Researchers prepared metal-free 2D/2D C3N5/GO nanosheets and customized a type-II heterojunction based on band bending theory to enhance uranium extraction capacity. The structure of C3N5 was explained through electron energy loss spectroscopy and synchrotron-based X-ray absorption fine structure, showing a expanded light response range compared to C3N4. Density functional theory was used to demonstrate the presence of alternating energy levels for continuous injection of photogenerated electrons into the surface of GO, resulting in effective electron-hole pair separation and increased material activity. The 2D/2D C3N5/GO heterojunction achieved a high uranium removal ratio of 96.1% even at low concentration and 93.4% after gamma-ray exposure, laying a foundation for future customization of nonmetal-based 2D/2D nanohybrids for uranium-containing wastewater enrichment.