Visible-Light-Driven Nitrogen Fixation Catalyzed by Bi₅O₇Br Nanostructures: Enhanced Performance by Oxygen Vacancies

Abstract

Photocatalytic nitrogen fixation represents a green alternative to the conventional Haber–Bosch process in the conversion of nitrogen to ammonia. In this study, a series of Bi5O7Br nanostructures were synthesized via a facile, low-temperature thermal treatment procedure, and their photocatalytic activity toward nitrogen fixation was evaluated and compared. Spectroscopic measurements showed that the tubular Bi5O7Br sample prepared at 40 °C (Bi5O7Br-40) exhibited the highest electron-transfer rate among the series, producing a large number of O2 .– radicals and oxygen vacancies under visible-light photoirradiation and reaching a rate of photocatalytic nitrogen fixation of 12.72 mM·g–1·h–1 after 30 min of photoirradiation. The reaction dynamics was also monitored by in situ infrared measurements with a synchrotron radiation light source, where the transient difference between signals in the dark and under photoirradiation was analyzed and the reaction pathway of nitrogen fixation was identified. This was further supported by results from density functional theory calculations. The reaction energy of nitrogen fixation was quantitatively estimated and compared by building oxygen-enriched and anoxic models, where the change in the oxygen vacancy concentration was found to play a critical role in determining the nitrogen fixation performance. Results from this study suggest that Bi5O7Br with rich oxygen vacancies can be used as a high-performance photocatalyst for nitrogen fixation.

Recent Progress of the Design and Engineering of Bismuth Oxyhalides for Photocatalytic Nitrogen Fixation

“…Importantly, such a performance can be further enhanced by an increase in surface OVs, as demonstrated in a more recent study by Li et al [60] It should be noted that it is the strong interaction between the Bi 6p electrons and N 2p electrons that facilitates the adsorption of N 2 molecules onto the surface of the Bi-based catalysts, especially those with OVs. OVs can accumulate photogenerated electrons on the catalyst surface, which is conducive to N 2 adsorption.…”

“…Reproduced with permission. [60] Copyright 2020, American Chemical Society. materials are found to be conducive for effective photocatalytic nitrogen fixation (Figure 3a).…”

Photocatalytic Plasmon‐Enhanced Nitrogen Reduction to Ammonia

“…Many studies have demonstrated that oxygen vacancies (OVs) on a semiconductor surface can promote N 2 conversion to NH 3 under visible-light illumination. [44][45][46][47][48][49][50] The two advantages of OVs were first proposed by Zhang and co-workers which included; [45] 1) enhanced adsorption and activation of inert gas molecules such as N 2 due to abundant localized electrons on surface OVs and 2) trapping of charge carriers to inhibit recombination and promote the transfer of these trapped charge carriers to the adsorbates. By attaching a plasmonic nanostructure to a semiconductor, we can not only absorb broader range of the solar spectrum but also the hot electrons generated in the metal plasmonic particle can be injected into the semiconductor to drive NRR ( Figure 2A).…”

Three-dimensional graphene encapsulated Ag–ZnFe2O4flower-like nanocomposites with enhanced photocatalytic degradation of enrofloxacin

“…Interestingly, the results of UV-vis spectra indicated that Ag-ZnFe 2 O 4 -rGO denoted a red shi with broad light absorbance range, which was benecial to the higher photocatalytic performance in photocatalytic degradation reaction. 50 The room-temperature photoluminescence (PL) emission spectra gave details about the recombination, migration, and shiing of photo-generated charge carriers. The higher PL intensity indicates higher recombination efficiency of photogenerated e À and h + .…”