Bismuth Semimetal-Boosted Electron Transfer, Nitrogen Adsorption, and Nitrogen Photoreduction Activity of Bi/g-C₃N₄ Nanosheets

Abstract

Nitrogen photoreduction is a promising ammonia production technology since it can be carried out at the atmospheric pressure by merely utilizing the abundant solar energy. However, the low conversion efficiency is still a big challenge for practical applications. In this work, Bi-decorated g-C 3 N 4 nanosheets are successfully prepared by an in situ solvothermal method. The ultraviolet−visible diffuse reflection spectrum shows that Bi decoration conspicuously enhances the visible light absorption because of the surface plasmon resonance effect of the Bi semimetal. Moreover, the photoluminescence spectrum demonstrates that Bi decoration greatly improves the charge separation efficiency because the high work function of Bi (4.5 eV) favors electron transfer from the conduction band of g-C 3 N 4 to the Bi surface. Meanwhile, nitrogen sorption isotherms show that Bi decoration obviously increases the Brunauer−Emmett−Teller surface area (4.3 m 2 g −1 for g-C 3 N 4 vs 7.7−8.4 m 2 g −1 for Bi/g-C 3 N 4 ), which is beneficial for N 2 adsorption. Additionally, the density functional theory calculation shows that the adsorption energy (E ad ) of N 2 on Bi/g-C 3 N 4 (−2.3 eV) is 6.2 times higher than that on g-C 3 N 4 (−0.3 eV), which indicates that N 2 is easier to adsorb on Bi/g-C 3 N 4 thermodynamically. It is assumed that the decorated Bi can also provide new active sites that significantly improve the adsorption and activation of N 2 . Therefore, Bi/g-C 3 N 4 exhibits a high nitrogen photoreduction activity under visible light irradiation (λ > 420 nm): the ammonia yield over 30-Bi/g-C 3 N 4 (3075 μmol L −1 g −1 ) is 1.8 times higher than that over g-C 3 N 4 (1076 μmol L −1 g −1 ) and the ammonia production rate over 30-Bi/g-C 3 N 4 (1025 μmol L −1 g −1 h −1 ) is 1.8 times higher than that over g-C 3 N 4 (359 μmol L −1 g −1 h −1 ). The improved activity is mainly attributed to the Bi decoration on the g-C 3 N 4 surface, which improves the adsorption and activation of N 2 , the electron−hole separation efficiency, and the light-harvesting ability. This work demonstrates that similar to precious metals, Bi semimetal can also greatly improve the nitrogen photoreduction activity. Most importantly, Bi semimetal is more abundant and cheaper than precious metals, and it could be more promising for practical applications.

Flux-assisted synthesis of bismuth nanoparticle decorated carbon nitride for efficient photocatalytic degradation of endocrine disrupting compound

“…It was reported that the bismuth oxide thin layer was easily formed on the surface of metallic bismuth to prevent further oxidation of bismuth metal. 35 This phenomenon provided a reasonable explanation for the existence of two pairs of characteristic peaks in different positions in BiCCN-15 and BiCN-15, indicating that bismuth metal has been successfully decorated on the catalyst surface.…”

“…Thus, metallic-Bi-decorated carbon nitride materials have great potential in the degradation of wastewater. However, the synthesis process of Bi metal is complex and generally requires a reductant to reduce Bi(NO 3 ) 3 , 35,36 which is not conducive to environmental protection. Therefore, an environmentally-friendly and simple method for preparing C 3 N 4 photocatalysts decorated with metallic Bi nanoparticles needs to be developed.…”

Advanced Strategies for Improving the Photocatalytic Nitrogen Fixation Performance: A Short Review

“…Therefore, morphological control of catalysts is an ideal method to increase the active catalytic sites, which is helpful to improve the photocatalytic nitrogen fixation performance. For example, nanosheets, nanotubes, and mesoporous structures were prepared for g-C 3 N 4 catalysts; , two-dimensional (2D) nanosheets and three-dimensional (3D) microspheres were prepared for BiOCl-based photocatalysts . It was found that the adjustment of the morphology and size of the catalyst can effectively promote the separation and interfacial transport of photogenerated electrons and holes, which can weaken the bond energy of the NN triple bond to a certain extent, thus achieving the purpose of nitrogen activation.…”

Interspersed Bi Promoting Hot Electron Transfer of Covalent Organic Frameworks Boosts Nitrogen Reduction to ammonia

“…[28] In addition, the other peaks at 158.1 and 163.3 eV were indexed to Bi 3+ (Figure 3d), probably because the metallic Bi could be oxidized by O 2 in the air to form Bi 2 O 3 on the surface of Bi. [28,34] It's worth noting that the deposition of Bi onto the surface of COF-TaTp, N 1s, and O 1s peaks of 5% Bi/COF-TaTp were shifted to higher and lower binding energies respectively. These results suggested that strong interaction occurred between the Bi and N, O of COF-TaTp.…”