Oxygen Vacancy Engineering Promoted Photocatalytic Ammonia Synthesis on Ultrathin Two-Dimensional Bismuth Oxybromide Nanosheets

Abstract

The catalytic conversion of nitrogen to ammonia is one of the most important processes in nature and chemical industry. However, the traditional Haber-Bosch process of ammonia synthesis consumes substantial energy and emits a large amount of carbon dioxide. Solar-driven nitrogen fixation holds great promise for the reduction of energy consumption and environmental pollution. On the basis of both experimental results and density functional theory calculations, here we report that the oxygen vacancy engineering on ultrathin BiOBr nanosheets can greatly enhance the performance for photocatalytic nitrogen fixation. Through the addition of polymetric surfactant (polyvinylpyrrolidone, PVP) in the synthesis process, V O-BiOBr nanosheets with desirable oxygen vacancies and dominant exposed {001} facets were successfully prepared, which effectively promote the adsorption of inert nitrogen molecules at ambient condition and facilitate the separation of photoexcited electrons and holes. The oxygen defects narrow the bandgap of V O-BiOBr photocatalyst and lower the energy requirement of exciton generation. In the case of the specific surface areas are almost equal, the V O-BiOBr nanosheets display a highly improved photocatalytic ammonia production rate (54.70 μmol·g–1·h–1), which is nearly 10 times higher than that of the BiOBr nanoplates without oxygen vacancies (5.75 μmol·g–1·h–1). The oxygen vacancy engineering on semiconductive nanomaterials provides a promising way for rational design of catalysts to boost the rate of ammonia synthesis under mild conditions.

Synthesis of Large‐Area Atomically Thin BiOI Crystals with Highly Sensitive and Controllable Photodetection

“…Additionally, a down‐shift of banding energies was observed in Bi 4f (0.7 eV), O 1s (0.8 eV), and I 3d (0.8 eV). Such phenomenon of BiOI is similar with that of BiOBr, which also displays a down‐shift of banding energies in Bi 4f, O 1s, and Br 3d caused by oxygen vacancies . Our result is consistent with the previous reports for SiO 2 , BiOCl, and TiO 2 , which demonstrated the V O formation under UVIR.…”

Thin‐Layered Photocatalysts

“…Because, their ultrathin thickness can not only shorten the charge migration distance, but also provide abundant surface active sites for the N 2 fixation and activation ( Table 3 ). [ 32,33,132,138,206–216 ] Benefitting from their abundant surface atoms, surface engineering is widely used in obtaining efficient thin‐layered photocatalysts for nitrogen fixation. Zhang's group fabricated a series of ultrathin M II M III ‐LDHs (M II = Mg, Ni, Zn, and Cu, M III = Al and Cr) through coprecipitation method.…”

Identification of preferentially exposed crystal facets by X-ray diffraction

“…In this work, bismuth oxyhalides (BiOX, where X ¼ Cl, Br, or I) were synthesized as examples for the demonstration of facet identication by XRD. Typically, BiOCl, 10,12 BiOBr, 13,14 and BiOI 15,16 nanoplates with exposed (001) facets are synthesized by hydrothermal methods under different conditions; whereas, we show a precipitation approach that is applicable to the synthesis of all BiOX with plate-like structures. The presence of Bi, O, and X in the samples was evidenced by energy-dispersive X-ray spectroscopy (EDX, Fig.…”