Carbonitride Heterojunctions for Photocatalytic Reduction of Uranium(Ⅵ)

Abstract

The development and application of nuclear energy is often considered as a potential solution to meet the increasing energy demand. However, it is important to acknowledge that the utilization of nuclear energy resources and the treatment of nuclear waste pollution pose significant challenges that require careful consideration and management. Therefore, it is crucial to address the challenges of uranium pollution treatment and uranium resource recovery to ensure the sustainable development of nuclear energy. The technology of photocatalytic reduction has been found to have a synergistic adsorption reduction ability, which allows it to overcome the thermodynamic limitations of single adsorption removal. As a result, photocatalytic reduction technology is widely recognized as having great potential in the removal and recycling of uranium in nuclear waste liquid. One of the key factors for the effective application of this technology is the acquisition of a catalyst with high photocatalytic reduction ability. Nitride carbon materials are considered an ideal photocatalyst for photocatalytic reduction of U（Ⅵ） due to their excellent photochemical properties, excellent physicochemical adjustability, and good chemical stability. However, the pure g-C3N4 photocatalyst still suffers from its low separation efficiency of photogenerated charge carriers, which results in unsatisfactory photocatalytic activity. In recent years, research on modifying and applying carbon nitride has provided in-depth insights into the reduction of uranium through photocatalysis. Discussing the strategy of modifying C3N4, constructing heterojunction nanostructures, and utilizing them for the photocatalytic reduction of uranium, along with the mechanisms involved. This review summarizes the recent significant progress on the design of g-C3N4-based heterostructure photocatalysts and their special separation/transfer mechanisms of photogenerated charge carriers. On the one hand, according to the key steps of photocatalytic uranium reduction, modification strategies using g-C3N4 photocatalysts can be classified into the following groups: morphology modification, band-structure regulation, and heterostructure construction. Moreover, according to the different transfer mechanisms of photogenerated charge carriers between g-C3N4 and the coupled components, the g-C3N4-based heterostructure photocatalysts can be divided into the following categories: g-C3N4-based conventional Type-Ⅱ heterojunction, g-C3N4-based Z-scheme heterojunction, g-C3N4-based S-scheme heterojunction, and g-C3N4/metal heterostructure. We also focused on the structure-activity relationship between the modification of photocatalytic materials based on carbon nitride and their photocatalytic reduction performance for U（Ⅵ）, as well as the mechanism of their catalytic reduction removal. Finally, this section offers concluding remarks and prospects for exploring the challenges and opportunities faced by advanced carbon nitride-based photocatalytic materials in the removal of uranium pollution and the recovery of uranium resources. It also provides directions for future breakthroughs.

Keywords

• carbon nitride
• heterojunction
• photocatalysis
• uranium reduction
• nuclear wastewater