The oxygen reduction reaction mechanisms catalyzed by B, N doped α- and γ-graphyne were investigated in detail by DFT methods, in which doped graphynes with different configurations could exhibit different oxygen reduction reaction activities. The B or N single-doped α-B1G and α-N2G and co-doped α-B1N2G and α-B1N3G show relatively low catalytic activities, owing to their unfavorable reversible potential in oxygen reduction steps, while the co-doped α-B1N4G with separated B, N and single-doped γ-NG show relatively high activities. With the further increasing of the N content, the onset potential is largely enhanced to 0.413 V for α-B1(N4)3G. The origin of activity of α-B1(N4)3G and γ-NG is attributed to the higher energy levels of the highest occupied molecular orbital and/or more positive charge (spin) density distributions.

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In this study, the ultra-thin iron phosphate Fe7(PO4)6 nanosheets (FP1) with fine-controlled morphology, has been designed as a new two-dimensional (2D) material for uranium adsorption. Due to its unique high accessible 2D structure, atom-dispersed phosphate/iron anchor groups and high specific surface area (27.77 m2·g−1), FP1 shows an extreme-high U(VI) adsorption capacity (704.23 mg·g−1 at 298 K, pH = 5.0 ± 0.1), which is about 27 times of conventional 3D Fe7(PO4)6 (24.51 mg·g−1-sample FP2) and higher than most 2D absorbent materials, showing a great value in the treatment of radioactive wastewater. According to the adsorption results, the sorption between U(VI) and FP1 is spontaneous and endothermic, and can be conformed to single molecular layer adsorption. Based on the analyses of FESEM, EDS, Mapping, FT-IR and XRD after adsorption, the possibile adsorption mechanism can be described as a Monolayer Surface Complexation and Stacking mode (MSCS-Mode). Additionally, the research not only provide a novel preparing method for 2D phosphate materials but also pave a new pathway to study other two-dimensional adsorption materials.

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