Key Takeaways & Executive Findings
- •• • MCOF-E achieves an aniline production rate of 4.90 mM h−1 in nitrobenzene hydrogenation, with ~100% conversion and >99% selectivity, outperforming MCOF-Z and other contrast materials, demonstrating superior photocatalytic efficiency. • • The E/Z linkage modes in MCOF-E and MCOF-Z result in distinct stacking structures, leading to differences in light absorption and charge transfer, which are critical for optimizing photocatalytic performance. • • Density functional theory calculations reveal that MCOF-E has a narrower band gap than MCOF-Z, facilitating more efficient generation of photo-induced carriers and accelerating reaction kinetics. • • The isomerization approach in MCOFs provides a novel strategy to tune photocatalytic properties, offering a pathway for rational design of high-performance materials for solar-driven chemical transformations.
Abstract
The tuning of ligand linkage modes in porous crystalline materials to create isomers with varied properties is significant, yet remains rare in structural design and photocatalytic applications. Here, we investigate isomeric metal-covalent organic frameworks (MCOFs), MCOF-E and MCOF-Z, and reveal that specific construction struts lead to E/Z ligand linkage modes with distinct stacking structures, stimulated by temperature. These isomeric MCOFs exhibit different light absorption, charge transfer, and photocatalytic performance. Notably, MCOF-E achieves an aniline generation efficiency of 4.90 mM h−1 in nitrobenzene hydrogenation, with high conversion (~100%) and selectivity (>99%), outperforming MCOF-Z and other counterparts. Theoretical calculations indicate that MCOF-E possesses a narrower band gap than MCOF-Z, facilitating more efficient generation of photo-induced carriers, which accelerates reaction kinetics and significantly improves nitrobenzene hydrogenation efficiency. This work provides insight into the structure-function relationships of MCOFs and demonstrates the potential of isomerization as a strategy to optimize photocatalytic performance.
1. Introduction
Photocatalytic hydrogenation of nitroaromatics to anilines is a pivotal industrial process, yet conventional thermal routes demand high pressures and temperatures, incurring energy penalties and byproduct formation. Metal-covalent organic frameworks (MCOFs) have emerged as promising photocatalysts due to their crystallinity, porosity, and tunable electronic structures, but their performance is often limited by inefficient charge separation and narrow light absorption. Isomerization—the rearrangement of molecular structure without altering composition—offers a means to fine-tune these properties, but its application in MCOFs has been largely unexplored.
This work addresses that gap by synthesizing two isomeric MCOFs, MCOF-E and MCOF-Z, which differ solely in the E/Z linkage mode of their organic struts. Temperature-controlled synthesis yields distinct stacking architectures, leading to divergent optoelectronic properties. The superior photocatalytic activity of MCOF-E, with an aniline production rate of 4.90 mM h−1 and >99% selectivity, underscores the impact of isomerism on catalytic efficiency. By correlating structural isomerism with band gap and charge dynamics, this study provides a blueprint for designing high-performance MCOF photocatalysts.
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Jia-Nan Chang, Qi Li, Fei Yu, Bing-Yu Song, Zhi-Feng Xin, Yifa Chen, Ya-Qian Lan (2026). Steering E/Z Linkage Modes in Isomeric Metal-Covalent Organic Frameworks for Photocatalytic Hydrogenation. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3846-9
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Frequently Asked Questions
What is the specific role of temperature in steering the E/Z linkage modes, and how does it affect the stacking structure and photocatalytic performance?
Temperature acts as a kinetic control parameter during synthesis, favoring the formation of either the E or Z isomer. The resulting stacking structures differ in interlayer distances and electronic coupling, which directly influence light absorption and charge transfer. MCOF-E, formed at a specific temperature, exhibits a narrower band gap and enhanced carrier generation, leading to a 4.90 mM h−1 aniline production rate with ~100% conversion and >99% selectivity.
How does the band gap difference between MCOF-E and MCOF-Z quantitatively correlate with their photocatalytic efficiency?
DFT calculations show that MCOF-E has a narrower band gap than MCOF-Z, which enhances its ability to absorb visible light and generate photo-induced electron-hole pairs. This increased carrier concentration accelerates the reduction kinetics of nitrobenzene, as evidenced by the higher aniline production rate (4.90 mM h−1) compared to MCOF-Z.
What are the long-term stability and recyclability of MCOF-E under photocatalytic conditions?
The study does not explicitly report long-term stability or recyclability data. However, MCOFs are known for their covalent bonding, which typically imparts superior chemical and thermal stability compared to MOFs. Further investigations would be required to assess performance over multiple cycles and under prolonged irradiation.
How does the photocatalytic performance of MCOF-E compare with other state-of-the-art photocatalysts for nitrobenzene hydrogenation?
MCOF-E achieves an aniline production rate of 4.90 mM h−1 with >99% selectivity, which is higher than MCOF-Z and other contrast counterparts mentioned in the study. This performance is competitive with or superior to many reported photocatalysts, though direct comparisons require standardized conditions.
What is the scalability potential of the synthesis method for MCOF-E, and are there any bottlenecks for industrial adoption?
The synthesis involves temperature-controlled crystallization, which is scalable in principle. However, the use of specific organic ligands and metal clusters may present cost and availability challenges. Further optimization of reaction conditions and precursor costs would be necessary for large-scale production.
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