Photocatalytic reduction of the uranium(Ⅵ) by ultra-thin porous g-C3N4 nanosheets synthesized via microwave-assisted

Graphitic carbon nitride (g-C 3 N 4 ) has garnered significant attention in the realm of photocatalytic reduction of U(Ⅵ) from aqueous solutions owing to its favorable bandgap and visible light responsiveness. Nevertheless, conventionally prepared bulk g-C 3 N 4 suffers from limitations such as a small specific surface area and high recombination of photo-generated charges, consequently impeding the efficiency of photocatalytic reactions and hampering practical applications. To address these shortcomings, this study presents a novel approach wherein ultra-thin porous g-C 3 N 4 nanosheets were successfully synthesized through the microwave-assisted calcination of urea in a single step. The resulting g-C 3 N 4 nanosheets exhibit a multi-hollow mesh structure with a significantly enlarged specific surface area, the specific surface area and pore size of MCN 90 are 170 m²/g and 17 nm, respectively, which are 2.3 times and 8 times that of the bulk g-C 3 N 4 . Photocatalytic experiments revealed that these ultra-thin porous nanosheets demonstrate superior performance in the reduction of U(Ⅵ) to U(Ⅳ), achieving a reduction rate of 100 % within 20 minutes for the optimal sample, as opposed to 78 % in 40 minutes for bulk g-C 3 N 4 . This enhanced photocatalytic activity can be primarily attributed to the unique ultra-thin porous nanosheet structure, which facilitates increased specific surface areas, improve photoelectric properties, and substantially shortened electron migration distances which reduce the recombination efficiency of photogenerated electrons and holes pairs. Consequently, these findings not only offer insights into the optimization of g-C 3 N 4 for U(Ⅵ) reduction but also provide a valuable reference for the preparation of other two-dimensional ultra-thin porous materials aimed at similar applications.