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Enhancement of CO₂ binding and mechanical properties upon diamine functionalization of M₂(dobpdc) metal-organic frameworks.

ABSTRACT: The family of diamine-appended metal-organic frameworks exemplified by compounds of the type mmen-M₂(dobpdc) (mmen = N,N'-dimethylethylenediamine; M = Mg, Mn, Fe, Co, Zn; dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are adsorbents with significant potential for carbon capture, due to their high working capacities and strong selectivity for CO₂ that stem from a cooperative adsorption mechanism. Herein, we use first-principles density functional theory (DFT) calculations to quantitatively investigate the role of mmen ligands in dictating the framework properties. Our van der Waals-corrected DFT calculations indicate that electrostatic interactions between ammonium carbamate units significantly enhance the CO₂ binding strength relative to the unfunctionalized frameworks. Additionally, our computed energetics show that mmen-M₂(dobpdc) materials can selectively adsorb CO₂ under humid conditions, in agreement with experimental observations. The calculations further predict an increase of 112% and 124% in the orientationally-averaged Young's modulus E and shear modulus G, respectively, for mmen-Zn₂(dobpdc) compared to Zn₂(dobpdc), revealing a dramatic enhancement of mechanical properties associated with diamine functionalization. Taken together, our calculations demonstrate how functionalization with mmen ligands can enhance framework gas adsorption and mechanical properties.

SUBMITTER: Lee JH

PROVIDER: S-EPMC6001253 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Enhancement of CO2 binding and mechanical properties upon diamine functionalization of M2(dobpdc) metal-organic frameworks.

Lee Jung-Hoon JH Siegelman Rebecca L RL Maserati Lorenzo L Rangel Tonatiuh T Helms Brett A BA Long Jeffrey R JR Neaton Jeffrey B JB

Chemical science 20180523 23

The family of diamine-appended metal-organic frameworks exemplified by compounds of the type mmen-M2(dobpdc) (mmen = N,N'-dimethylethylenediamine; M = Mg, Mn, Fe, Co, Zn; dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are adsorbents with significant potential for carbon capture, due to their high working capacities and strong selectivity for CO2 that stem from a cooperative adsorption mechanism. Herein, we use first-principles density functiona ...[more]

PMID: 29997874

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Project description:Carbon capture and sequestration is a key element of global initiatives to minimize anthropogenic greenhouse gas emissions. Although many investigations of new candidate CO2 capture materials focus on equilibrium adsorption properties, it is also critical to consider adsorption/desorption kinetics when evaluating adsorbent performance. Diamine-appended variants of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising materials for CO2 capture because of their cooperative chemisorption mechanism and associated step-shaped equilibrium isotherms, which enable large working capacities to be accessed with small temperature swings. However, the adsorption/desorption kinetics of these unique materials remain understudied. More generally, despite the necessity of kinetics characterization to advance adsorbents toward commercial separations, detailed kinetic studies of metal-organic framework-based gas separations remain rare. Here, we systematically investigate the CO2 adsorption kinetics of diamine-appended Mg2(dobpdc) variants using a thermogravimetric analysis (TGA) assay. In particular, we examine the effects of diamine structure, temperature, and partial pressure on CO2 adsorption and desorption kinetics. Importantly, most diamine-appended Mg2(dobpdc) variants exhibit an induction period prior to reaching the maximum rate of CO2 adsorption, which we attribute to their unique cooperative chemisorption mechanism. In addition, these materials exhibit inverse Arrhenius behavior, displaying faster adsorption kinetics and shorter induction periods at lower temperatures. Using the Avrami model for nucleation and growth kinetics, we determine rate constants for CO2 adsorption and quantitatively compare rate constants among different diamine-appended variants. Overall, these results provide guidelines for optimizing adsorbent design to facilitate CO2 capture from diverse target streams and highlight kinetic phenomena relevant for other materials in which cooperative chemisorption mechanisms are operative.

Dataset Information

Enhancement of CO₂ binding and mechanical properties upon diamine functionalization of M₂(dobpdc) metal-organic frameworks.

Publications

Enhancement of CO<sub>2</sub> binding and mechanical properties upon diamine functionalization of M<sub>2</sub>(dobpdc) metal-organic frameworks.

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