On February 14, 2023, Beijing time, Zhang Xiqi, an associate researcher from the team of academician Jiang Lei of the Institute of Physical and Chemical Technology of the Chinese Academy of Sciences, published a research result entitled “Regulating Interlayer Spacing of Aminated Graphene Oxide Membranes for Efficient Flow Reactions” in the journal Matter.
This achievement proposes a strategy to combine nano-confined effect with flow chemistry to achieve efficient confined flow reaction based on two-dimensional laminar flow membrane system, which provides a new idea for constructing a flow catalytic system with high conversion rate under mild conditions.
The first authors of the article are Pang Shuai, a doctoral student at the Institute of Physics and Chemistry of the Chinese Academy of Sciences, Professor Peng Daoling of South China Normal University, and Dr. Hao Yuwei of Beijing Institute of Graphic Arts, and the corresponding author is Zhang Xiqi, associate researcher of the Institute of Physics and Chemistry of the Chinese Academy of Sciences.
Flow chemistry has the advantages of low pollution, fastness, safety and simplicity. Flow reactions supported with heterogeneous solid catalysts in microreactors are currently the most common protocols. However, achieving fast and efficient flow reactions under relatively mild conditions remains a challenge. Functionalized graphene oxide membranes with continuously tunable two-dimensional nanochannels have shown great potential in the field of rapid molecular/ion transport. The interlayer nano-confinement channel is theoretically very suitable for the microspace of the flow reaction, and the nano-confinement effect in the channel also has an important impact on the chemical reaction activity.
To this end, Academician Jiang Lei’s team proposed a strategy to combine nano-confined effect with flow chemistry and realize efficient confined flow reaction based on two-dimensional laminar flow membrane system. In this work, the team prepared aminoated graphene oxide (GO-NH2) nanosheets, characterized and confirmed their structures using elemental analysis, infrared spectroscopy, X-ray spectroscopy, and atomic force microscopy, and then constructed a multilayer GO-NH2 membrane by vacuum filtration. By heat treatment (80-120 °C), the layer spacing (20.5-14.7 Å) of the GO-NH2 film is regulated. Taking the Knoevenagel condensation reaction as an example, the GO-NH2 membrane with different layer spacing was used as a membrane reactor, driven by the pressure difference, the reaction solution was directed to flow through the GO-NH2 membrane, and the reactants reacted between layers, and the product flowed out with the solvent (Figure 1a). By characterizing the compositional composition of the permeation mixture, the effect of layer spacing on the efficiency of the confined flow reaction was analyzed.
Figure 1: GO-NH2 membrane reactor for confined flow reactions.
The results show that the reaction conversion rate gradually increases as the layer spacing decreases (Figure 1b), and when the layer spacing decreases to 14.7 Å, a ~100% conversion rate (in-film residence time < 29 s) is achieved under mild conditions (22 °C). Mechanistic studies have shown that interlaminar confinement enhances the matching of reactant front orbital symmetry (Figure 1c). In contrast, the researchers used GO-NH2 powder as a heterogeneous catalyst to catalyze bulk reactions of the same magnitude and found that bulk phase should require a long reaction time (> 24 h) at 22°C to achieve ~100% conversion (Figure 2a-b). The researchers further demonstrated that the confinement flow reaction has obvious advantages in the proportional reaction by adjusting the differential pressure and residence time in the membrane, changing the reaction temperature and concentration, and expanding the substrate molecules. Compared with the bulk phase reaction, the characterization and DFT calculation of the membrane catalyst show that the delocalized π electrons in the graphite domain on the surface of the GO-NH2 nanosheet participate in the deprotonation process of reactant molecules, reducing the overall confinement reaction energy level (Figure 2c-d). At the same time, the molecules are transported rapidly in the confined channel, which reduces the disordered diffusion of molecules in solution, shortens the reaction time, and finally realizes the confined flow reaction with fast and high conversion rate. This work provides a new idea for constructing a flow catalytic system with high conversion rate under mild conditions, which is expected to be used in future tubular membrane reactors.
Figure 2: Comparison of bulk phase reaction and confined flow reaction and DFT calculation of the two reaction processes.
The above work was carefully guided by Academician Jiang Lei, and Professor Song Bo of University of Shanghai for Science and Technology provided important support in theoretical calculation. The research was supported by the National Key Basic Research and Development Program of China (2021YFA1200402, 2018YFA0208502), the National Natural Science Foundation of China (51973227, 21988102) and the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2020028). (Source: Science Network)
Related paper information:https://doi.org/10.1016/j.matt.2023.01.020
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