Ethylenediamine loading into a manganese-based metal-organic framework enhances water stability and carbon dioxide uptake of the framework.

Aisha Asghar,Timothy L Easun,Naseem Iqbal,Luke Kidwell,Tayyaba Noor,Leena Aftab,Benson M Kariuki

doi:10.1098/rsos.191934

Abstract

Metal–organic frameworks (MOFs) based on 2,5-dihydroxyterepthalic acid (DOBDC) as the linker show very high CO2 uptake capacities at low to moderate CO2 pressures; however, these MOFs often require expensive solvent for synthesis and are difficult to regenerate. We have synthesized a Mn-DOBDC MOF and modified it to introduce amine groups into the structure by functionalizing its metal coordination sites with ethylenediamine (EDA). Repeat framework synthesis was then also successfully performed using recycled dimethylformamide (DMF) solvent. Characterization by elemental analysis, FTIR and thermogravimetric studies suggest that EDA molecules are successfully substituting the original metal-bound DMF. This modification not only enhances the material's carbon dioxide sorption capacity, increasing stability to repeated CO2 sorption cycles, but also improves the framework's stability to moisture. Moreover, this is one of the first amine-modified MOFs that can demonstrably be synthesized using recycled solvent, potentially reducing the future costs of production at larger scales.

Highlights

Among the greenhouse gases highlighted under the Kyoto Protocol, carbon dioxide is a significant contributor to climate change [1]
We have recently reported the modification of a copperbased Metal−organic frameworks (MOFs) during synthesis by doping with hexamethylenetetramine, resulting in the enhancement of carbon dioxide sorption over the unmodified framework [31]
The Mn-DOBDC MOF crystallizes in a monoclinic cell with a = 9.6916(5) Å, b = 11.8690(6) Å and c = 15.3430(9) Å, and α = 90°, β = 102.788(6)° and γ = 90°, with broadly rhomboidal pores occupied by (a)

Summary

Introduction

Among the greenhouse gases highlighted under the Kyoto Protocol, carbon dioxide is a significant contributor to climate change [1]. Significant effort has been made to develop materials that can capture and remove carbon dioxide from process streams and flue gases. These materials include porous adsorbents, which are solid-state alternatives to the well-known amine scrubbing technologies for CO2 capture and sequestration; they have potentially lower energetic costs, greater environmental sustainability and regenerability [2]. Metal−organic frameworks (MOFs) are a class of nanomaterials comprising metal coordination sites bridged by organic ligands [3,4,5]. These organic/inorganic three-dimensional hybrid networks often have well-defined structures, are commonly highly crystalline and can have very high surface areas. Water-stable MOFs are being reported including examples such as UiO-66, MIL-101, NOTT-400 and NOTT-401 [20,21,22]

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Conclusion