Erik Albenze

Fabrication of MMMs with improved gas separation properties using externally-functionalized MOF particles

Mixed matrix membranes (MMM) have the potential to overcome the limitations of traditional polymeric membranes for gas separation by improving both the permeability and selectivity. The most difficult challenge is accessing defect free and optimized MMM membranes. Defects are generally due to incompatible interfaces between the polymer and the filler particle. Herein, we present a new approach to modify and optimize the surface of UiO-66-NH2 based MOF particles to improve its interaction with Matrimid® polymer. A series of surface modified UiO-66-NH2 particles were synthesized and characterized using 1H NMR spectroscopy, mass spectrometry, XPS, and powder X-ray diffraction. MMMs containing surface optimized MOF particles exhibit improved thermal and mechanical properties. Most importantly, the MMMs show significantly enhanced gas separation properties; CO2 permeability was increased by ∼200% and CO2/N2 ideal selectivity was increased by ∼25%. These results confirm the success of the proposed technique to mitigate defective MOF/Matrimid® interfaces.

Contribution of the Acetate Anion to CO2 Solubility in Ionic Liquids: Theoretical Method Development and Experimental Study

A new theoretical method was developed to compute the Henrys law constant for gas absorption in a solvent through strong nonphysical interactions. The new method was created by expanding the test particle insertion method typically applied to physisorbing systems to account for the strong intermolecular interactions present in chemisorbing systems. By using an ab initio (AI)-based Boltzmann-averaged potential to model the interaction between CO2 and the tetra-n-butylphosphonium acetate ([P4444][CH3COO]) ionic liquid, the total Henryss law constant at 298 K was computed to be 0.011 to 0.039 bar, reasonably comparable to the experimental value of 0.18 bar measured in this work. Three different AI potentials were used to verify the applicability of this approach. In contrast, when a classical force field (FF) was used to describe the interaction between CO2 and [P4444][CH3COO], the Henrys law constant was computed to be 27 bar, significantly larger than the experimental value. The classical FF underestimates the CO2-[P4444][CH3COO] interaction compared with the AI calculations, which in turn leads to the smaller simulated CO2 solubility. Simulations further indicate that the CO2 interaction with the [CH3COO](-) anion is much stronger than with the [P4444](+) cation. This result strongly suggests that the large CO2 solubility in [P4444][CH3COO] is due to the strong CO2-[CH3COO](-) interaction.

Probing the effect of electron donation on CO2 absorbing 1,2,3-triazolide ionic liquids

Development of the next generation materials for effective separation of gases is required to address various issues in energy and environmental applications. Ionic liquids (ILs) are among the most promising material types. To overcome the many hurdles in making a new class of materials technologically applicable, it is necessary to identify, access, and scale up a range of representative substances. In this work, CO2 reactive triazolide ILs were synthesized and characterized with the aim of developing a deeper understanding of how structural changes affect the overall properties of these substances. It was found that substituents on the anion play a crucial role in dictating the physical properties for CO2 capture. Depending upon the anion substituent, CO2 capacities between 0.07 and 0.4 mol CO2 per mol IL were observed. It was found that less sterically-hindered anions and anions containing electron donating groups were more reactive towards CO2. Detailed spectroscopic, CO2 absorption, rheological, and simulation studies were carried out to understand the nature and influence of these substituents. The effect of water content was also evaluated, and it was found that water had an unexpected impact on the properties of these materials, resulting in an increased viscosity, but little change in the CO2 reactivity.

Toward a Materials Genome Approach for Ionic Liquids: Synthesis Guided by Ab Initio Property Maps

The Materials Genome Approach (MGA) aims to accelerate development of new materials by incorporating computational and data-driven approaches to reduce the cost of identification of optimal structures for a given application. Here, we use the MGA to guide the synthesis of triazolium-based ionic liquids (ILs). Our approach involves an IL property-mapping tool, which merges combinatorial structure enumeration, descriptor-based structure representation and sampling, and property prediction using molecular simulations. The simulated properties such as density, diffusivity, and gas solubility obtained for a selected set of representative ILs were used to build neural network models and map properties for all enumerated species. Herein, a family of ILs based on ca. 200,000 triazolium-based cations paired with the bis(trifluoromethanesulfonyl)amide anion was investigated using our MGA. Fourteen representative ILs spreading the entire range of predicted properties were subsequently synthesized and then characterized confirming the predicted density, diffusivity, and CO2 Henrys Law coefficient. Moreover, the property (CO2, CH4, and N2 solubility) trends associated with exchange of the bis(trifluoromethanesulfonyl)amide anion with one of 32 other anions were explored and quantified.

Ionic liquid regioisomers: structure effect on the thermal and physical properties

A systematic study was performed on two triazolium ionic liquid isomers which included examination of thermal, physical, and electrochemical properties. It was found that a minor change in structure significantly influences physical and thermal properties of ionic liquids.