Youn Sang Bae

Development and Evaluation of Porous Materials for Carbon Dioxide Separation and Capture

The development of new microporous materials for adsorption separation processes is a rapidly growing field because of potential applications such as carbon capture and sequestration (CCS) and purification of clean-burning natural gas. In particular, new metal-organic frameworks (MOFs) and other porous coordination polymers are being generated at a rapid and growing pace. Herein, we address the question of how this large number of materials can be quickly evaluated for their practical application in carbon dioxide separation processes. Five adsorbent evaluation criteria from the chemical engineering literature are described and used to assess over 40 MOFs for their potential in CO(2) separation processes for natural gas purification, landfill gas separation, and capture of CO(2) from power-plant flue gas. Comparisons with other materials such as zeolites are made, and the relationships between MOF properties and CO(2) separation potential are investigated from the large data set. In addition, strategies for tailoring and designing MOFs to enhance CO(2) adsorption are briefly reviewed.

Using molecular simulation to characterise metal–organic frameworks for adsorption applications

Molecular simulation is a powerful tool to predict adsorption and to gain insight into the corresponding molecular level phenomena. In this tutorial review, we provide an overview of how molecular simulation can be used to characterise metal-organic frameworks for adsorption applications. Particular attention is drawn to how these insights can be combined to develop design principles for specific applications.

Carborane-based metal–organic frameworks as highly selective sorbents for CO2 over methane

Separation of CO(2)/CH(4) mixtures was studied in carborane-based metal-organic framework materials with and without coordinatively unsaturated metal sites; high selectivities for CO(2) over CH(4) ( approximately 17) are obtained, especially in the material with open metal sites.

High propene/propane selectivity in isostructural metal-organic frameworks with high densities of open metal sites

Crystalline metal–organic frameworks (MOFs) have attracted great attention in the past decade due to their modular, tailorable structures, as well as their potential in applications such as gas storage and separations. Open metal sites in some MOFs provide special adsorption sites, which are favorable for H2 storage, [4] CO2 capture, [5] and CO2 separations. Propene is an important commercial petrochemical, produced on a large scale. Its production requires separation from propane/propene mixtures, but this is intrinsically difficult due to the similar physical and chemical properties of these molecules. Energy-intensive, costly cryogenic distillation has been used for over 70 years for this separation. In general, adsorptive separation is an energyand cost-effective alternative to distillation, and a few MOFs have shown potential for propene/propane separations through either an equilibrium-based, a kinetic-based or a gate-opening mechanism. Notably, open metal sites have been shown to play important roles in the two existing reports on the equilibrium separation of propene/propane mixtures. From a combined experimental and simulation study, Lamia et al. reported that open Cu sites in HKUST-1 interact preferentially with propene, due to specific interactions between the electron-rich p-bonding orbital in propene and the vacant sorbital of the open metal sites. Yoon et al. experimentally demonstrated that the existence of unsaturated Fe and Fe sites in MIL-100(Fe) substantially increases the strength of interaction with unsaturated propene molecules (the heat of adsorption was up to 70 kJmol 1 at low coverage), which leads to high selectivity for propene over propane (ca. 29). However, this high selectivity was observed at very low pressure (0.0025 bar), and it decreased markedly with increasing pressure presumably due to satuaration of the open metal sites. Herein, we report the adsorption selectivities of propene over propane for a series of isostructural frameworks MMOF-74 (M=Co, Mn, and Mg) with high concentrations of open metal sites. Adsorption experiments, ideal adsorbed solution theory (IAST) predictions, breakthrough experiments, first-principles calculations, and grand canonical Monte Carlo (GCMC) simulations reveal that Co-MOF-74 exhibits the highest thermodynamic propene/propane selectivity (ca. 46) ever reported for MOFs, due to strong pcomplexation between the open Co sites and the propene molecules. Remarkably, these high selectivities occur at ambient pressure and temperature, conditions favorable for industrial adsorptive separations. An unusual increase of the C3H6/C3H8 selectivity with increasing pressure is observed due to emergent behavior of the system that arises from the appropriate pore size relative to the size of the propene molecules. The series of M-MOF-74 materials is also denoted CPO-27-M or M/DOBDC (DOBDC = 2,5-dioxido1,4-benzene-dicarboxylate) in the literature. These materials have 1D hexagonal channels of 11–12 diameter with high densities of open metal sites (Figure 1) that can potentially interact with propene. Here, single-component adsorption isotherms for propene and propane were measured exper-

Kinetic separation of propene and propane in metal-organic frameworks: Controlling diffusion rates in plate-shaped crystals via tuning of pore apertures and crystallite aspect ratios

A series of isostructural, noncatenated, zinc-pillared-paddlewheel metal-organic framework materials has been synthesized from 1,2,4,5-tetrakis(carboxyphenyl)benzene and trans-1,2-dipyridylethene struts. Substantial kinetic selectivity in the adsorption of propene over propane can be observed, depending on the pore apertures and the rectangular-plate morphology of the crystals.

Chemical reduction of a diimide based porous polymer for selective uptake of carbon dioxide versus methane

A diimide based porous organic polymer (POP) post-synthetically reduced with lithium metal demonstrates a drastic increase in selectivity for carbon dioxide over methane.

Separation of gas mixtures using Co(II) carborane-based porous coordination polymers

Separations of CO(2)/CH(4), CO(2)/N(2), and O(2)/N(2) mixtures were studied in three porous coordination polymers made of the same carborane ligand and Co(ii) nodes. High selectivities for CO(2) over CH(4) ( approximately 47) and CO(2) over N(2) ( approximately 95) were obtained, especially in the material with coordinated pyridine. Unusual selectivity for O(2) over N(2) (as high as 6.5) was demonstrated in the materials with open Co(ii) sites.

Selective and Regenerative Carbon Dioxide Capture by Highly Polarizing Porous Carbon Nitride

Energy-efficient CO2 capture is a stringent demand for green and sustainable energy supply. Strong adsorption is desirable for high capacity and selective capture at ambient conditions but unfavorable for regeneration of adsorbents by a simple pressure control process. Here we present highly regenerative and selective CO2 capture by carbon nitride functionalized porous reduced graphene oxide aerogel surface. The resultant structure demonstrates large CO2 adsorption capacity at ambient conditions (0.43 mmol·g(-1)) and high CO2 selectivity against N2 yet retains regenerability to desorb 98% CO2 by simple pressure swing. First-principles thermodynamics calculations revealed that microporous edges of graphitic carbon nitride offer the optimal CO2 adsorption by induced dipole interaction and allows excellent CO2 selectivity as well as facile regenerability. This work identifies a customized route to reversible gas capture using metal-free, two-dimensional carbonaceous materials, which can be extended to other useful applications.

Enhanced Performance of Mixed-Matrix Membranes through a Graft Copolymer-Directed Interface and Interaction Tuning Approach

Herein, a high performance mixed-matrix membrane (MMM) is reported with simultaneously large improvements in the CO2 permeability by 880 % from 70.2 to 687.7 Barrer (1 Barrer=1×10(-10)  cm(3)  cm cm(-2)  s(-1)  cmHg(-1) ) and CO2 /N2 selectivity by 14.4 % from 30.5 to 34.9. These findings represent one of the most dramatic improvements ever reported for MMMs. These improvements are obtained through an interface and interaction tuning approach based on an amphiphilic grafted copolymer. Poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer plays a key role as a soft organic matrix to provide good permeation properties, uniform distribution of zeolite imidazole frameworks-8 (ZIF-8), and better interfacial contact with inorganic compounds. In particular, the CO2 /C3 H8 and CO2 /C3 H6 selectivities reached 10.5 and 42.7, respectively, for PVC-g-POEM/ZIF (40 %) MMMs; this indicates that it could be a promising membrane material for the purification of C3 hydrocarbons.

Selective nitrogen capture by porous hybrid materials containing accessible transition metal ion sites

Selective dinitrogen binding to transition metal ions mainly covers two strategic domains: biological nitrogen fixation catalysed by metalloenzyme nitrogenases, and adsorptive purification of natural gas and air. Many transition metal-dinitrogen complexes have been envisaged for biomimetic nitrogen fixation to produce ammonia. Inspired by this concept, here we report mesoporous metal-organic framework materials containing accessible Cr(III) sites, able to thermodynamically capture N2 over CH4 and O2. This fundamental study integrating advanced experimental and computational tools confirmed that the separation mechanism for both N2/CH4 and N2/O2 gas mixtures is driven by the presence of these unsaturated Cr(III) sites that allows a much stronger binding of N2 over the two other gases. Besides the potential breakthrough in adsorption-based technologies, this proof of concept could open new horizons to address several challenges in chemistry, including the design of heterogeneous biomimetic catalysts through nitrogen fixation.