A Mechanism Investigation of how the Alloying Effect Improves the Photocatalytic Nitrate Reduction Activity of Bismuth Oxyhalide Nanosheets

Abstract

Alloyed bismuth oxyhalides have been widely used in photocatalytic water treatment processes due to their superior photocatalytic activity. However, there is no report on the removal of NO3− for alloyed bismuth oxyhalides, and the mechanism of the effect of alloying on NO3− reduction activity is still unclear. In this work, we prepared a series of BiOClnBr1‐n (0≤n≤1) with different Cl/Br ratios but with controlled similar morphologies, and explored their catalytic activities on reducing NO3− under visible light irradiation. Density functional theory investigations revealed that the formation energy for an oxygen (O) vacancy on the surface of BiOClnBr1‐n alloys is clearly reduced in comparison with the monohalide, illustrating that more O vacancies can be produced on the surface of BiOClnBr1‐n alloys. A high concentration of O vacancies not only promotes the adsorption of NO3− but also enhances the separation efficiency of the photogenerated electron‐hole (e–h) pairs, with both being beneficial to enhance the photocatalytic activity of BiOClnBr1‐n alloys for NO3− reduction. These new discoveries not only promote the design and development of new photocatalysts with excellent NO3− reduction properties, but also help to understand the relationship between alloying effects and semiconductor photocatalytic properties.

Present State and Future Outlook of Ammonia Production through Photocatalytic Nitrate Reduction

“…À reduction research has been directed toward converting NO 3 À into inert N 2 gas, especially for environmental water treatment processes. [24][25][26][27][28][29][30][31][32] In the NO 3 À reduction process, the initial deoxygenation step (*NO 3 À ! *NO 2 ), which involves 2e À transfer, [20] is commonly considered the rate-determining step for the overall reaction because the transfer of electrons into the high-energy state of the lowest unoccupied molecular orbital (LUMO) of NO 3…”

“…Consequently, the N 2 formation pathway is more likely to occur compared to NH 3 production, and as a result, a significant portion of previous photocatalytic NO 3 − reduction research has been directed toward converting NO 3 − into inert N 2 gas, especially for environmental water treatment processes. [ 24‐32 ]…”

Reaction mechanism and selectivity regulation of photocatalytic nitrate reduction for wastewater purification: progress and challenges

“…NO 2 À + H + # HNO 2 (18) Nitrite exists in the form of ions or acid in the solution according to the acid-base equilibria (eqn (18)), which is closely related to the pH value. 71 The two forms of nitrite are reduced sequentially under the combined action of light and CO 2 c À (ref. 72) as the Fig.…”

A review on bismuth oxyhalide based materials for photocatalysis

“…8). 50,95 For manufacture of fertilizers as well as chemicals, synthesis of ammonia (NH3) is very important in agriculture and industry. The Haber-Bosch approach dominates commercial ammonia synthesis, which involves stringent reaction conditions (over 300 °C and 100 atm).…”