Alkali Etching of Layered Double Hydroxide Nanosheets for Enhanced Photocatalytic N₂ Reduction to NH₃

Abstract

Layered double hydroxide (LDH) nanosheets show good activity in a wide range of photoreactions, with this activity being generally attributable to an abundance of surface oxygen vacancies or coordinatively unsaturated metal cations in the nanosheets which serve as active sites for reactant adsorption and activation. Recently, LDH nanosheets have been shown to be very effective for photocatalytic N2 reduction to NH3 using water as the reducing agent. Herein, it is demonstrated that a simple pretreatment of ZnCr‐LDH, ZnAl‐LDH, and NiAl‐LDH nanosheets with aqueous NaOH can greatly enhance the concentration of oxygen vacancies and low coordination metal centers in the nanosheets, thus significantly enhancing their photocatalytic activity for N2 reduction to NH3 under UV–vis irradiation (without the need for added sacrificial agents or cocatalysts). The facile alkali etching strategy introduced here is expected to be widely adopted in the future development of high‐performance LDH photocatalysts for ammonia production and other challenging chemical transformations (e.g., CO2 reduction and water splitting).

Polymeric Carbon Nitride‐Derived Photocatalysts for Water Splitting and Nitrogen Fixation

“…Most research reports on the selectivity and conversion rate of photocatalytic N 2 reduction are relatively low, and the output of ammonia is usually low. [214,215] Therefore, in the experiment of photocatalytic N 2 reduction to produce NH 3 , the ammonia produced is not necessarily produced by dinitrogen reduction, and it may also come from other pollutants, such as ammonia, nitrogen oxides, and nitrates contained in air, nitrogen flow, and catalyst itself. Therefore, it is necessary to perform a series of control experiments to ensure that the N in the production of NH 3 comes from N 2 , rather than accidental pollution.…”

“…In addition, the detection of product NH 3 also requires careful selection of appropriate detection methods. Commonly used ammonium detection methods include: ion chromatography, [214,220] colorimetry (indophenol blue method and Nessler's reagent), [221][222][223][224] 1 H NMR spectroscopy, [225] and ammonia ion selective electrodes. [226] For aqueous ammonia solutions, these methods have shown higher accuracy in a wide range of ammonia concentrations.…”

Single-Atom Photocatalysts for Emerging Reactions

“… 3 − 11 Among various solar energy conversion techniques, photocatalysis is deemed as a promising, environmentally benign, and cost-effective strategy to generate both fuels and high-value chemicals. 12 − 18 During the past decades, numerous studies have been focused on several well-known reactions (e.g., H 2 production, 19 − 26 N 2 fixation 27 − 30 and CO 2 conversion 31 − 34 ) achieved via photocatalysis. Recently, a range of emerging photocatalytic reactions generating fuels and/or valuable chemicals has been attracting increasing attention.…”

Research Progress in Organic Synthesis by Means of Photoelectrocatalysis

“…This efficient charge transfer inhibits the recombination of charge carriers, which is beneficial to improve catalytic performance. It is reported that there are large number of surface oxygen vacancies or coordinated unsaturated metal cations in LDH, which can serve as active sites for the adsorption and activation of reactants, thus offering good catalytic activity [116–118] . Scientists may develop abundant materials; for example, hematite can realize non‐directional aromatic C−H amination.…”