Photocatalytic Performance of Perovskite and Metal–Organic Framework Hybrid Material for the Reduction of N₂ to Ammonia

Abstract

The orthorhombic phase of KNbO 3 perovskite has been applied for nitrogen (N 2 ) photoreduction to ammonia (NH 3 ). However, this material suffers from a low surface area and low ammonia production efficiency under UV light irradiation. To eliminate these barriers, we used a metal−organic framework (MOF), named as TMU-5 ([Zn(OBA)(BPDH) 0.5 ] n •1.5DMF, where H 2 OBA = 4,4′-oxybis-(benzoic acid) and BPDH = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene), for the synthesis of the KNbO 3 @TMU-5 hybrid material. KNbO 3 @TMU-5 achieved a NH 3 production rate of 39.9 μmol•L −1 •h −1 •g −1 upon UV light irradiation, as compared to 20.5 μmol•L −1 •h −1 •g −1 recorded for KNbO 3 under similar experimental conditions. Using different characterization techniques especially gas adsorption, cyclic voltammetry, X-ray photoelectron spectroscopy, photocurrent measurements, and Fourier transform infrared spectroscopy, it has been found that the higher photoactivity of KNbO 3 @TMU-5 in ammonia production is due to its higher surface area, higher electron−hole separation efficiency, and higher density of negative charges on Nb sites. This work shows that hybridization of conventional semiconductors (SCs) with photoactive MOFs can improve the photoactivity of the SC@MOF hybrid material in different reactions, especially kinetically complex reactions like photoconversion of nitrogen to ammonia.

Fundamentals and Advances in Emerging Crystalline Porous Materials for Photocatalytic and Electrocatalytic Nitrogen Fixation

“…To address this issue, Boukherroub and co-workers coupled MOFs (TMU-5) with significant adsorption potential for N 2 gas molecules with KNbO 3 for photocatalytic N 2 fixation (Figure 5b). 113 TMU-5 not only acts as a MOF material with good porosity but also can achieve excellent photocatalytic performance by enhancing light absorption, charge separation, and reactant activation. The NH 3 formation rate of KNbO 3 @TMU-5 is 39.9 μmol L −1 h −1 g −1 , which is much higher than that of KNbO 3 under the same experimental conditions.…”

“…112 Copyright 2019 Elsevier B.V. (b) Combination of PXRD patterns of KNbO 3 @TMU-5 and the components. Reproduced with permission 113. Copyright 2022 American Chemical Society.…”

Recent progress of photocatalysts based on tungsten and related metals for nitrogen reduction to ammonia

“…Most ternary metal oxides first used for photocatalytic nitrogen fixation are titanate or Bi-based oxide systems (Chen et al, 2018;Huang et al, 2020). Higher conversion efficiency for mingled transition metal composite oxides such as Sb 2 MoO 6 (Mousavi et al, 2022), SrMoO 4 (Luo et al, 2019), LaCoO 3 (Haiguang Zhang et al, 2019), CoFe 2 O 4 (Zheng et al, 2020), Ni 3 V 2 O 8 (Vesali-Kermani et al, 2020b), KNbO 3 (Xing et al, 2019;Xing et al, 2020;Chamack et al, 2022), LiNbO 3 (Xiazhang Li et al, 2020), have been reported compared to corresponding monometallic oxides. Most mixed metal oxides are perovskite oxide compounds with wide bandgaps (Zejian .…”

“…All samples depended on KTa 0.75 Nb 0.25 O 3 to provide the photo/piezogenerated electrons for promoting spatial charge separation, which likely played a dominant role for nitrogen fixation. A pioneering study that coupled conventional KNbO 3 with photoactive MOFs was conducted by Chamack et al ( Chamack et al, 2022 ). Introduction of ([Zn(OBA) (BPDH) 0.5 ] n ·1.5DMF (TMU-5) enhanced the photocatalytic performance owing to the porosity, high surface area, and higher density of negative charges on Nb sites observed by N 2 adsorption/desorption isotherms and XPS scans, respectively ( Figures 9A,B ).…”

“…(C) NH 3 concentration versus cycling test on KNbO 3 @TMU-5. Reproduced from Chamack et al (2022) with permission from American Chemical Society.…”