Dorina Florentina Sava Gallis

Electrochemical activity of Fe-MIL-100 as a positive electrode for Na-ion batteries

Here we investigate the electrochemical activity of metal–organic frameworks (MOFs) as positive electrodes for Na-ion batteries in coin cell configurations. The performance of Fe-MIL-100 material is highly dependent on the choice of sodium salt source, and electrolyte system. The overall capacity fades over many cycles, however the high coulombic efficiency is maintained. This can be correlated with inaccessibility of active sites for Na intercalation, due to the increase of extra carbonaceous material inside the pores. Powder X-ray diffraction via synchrotron data and pair distribution function analyses of the as-made and cycled electrodes reveal the structure maintains the long-range order with progressive cycling. This finding suggests that careful consideration of all variables in battery components, and especially electrolyte selection can lead to greatly improved performances.

Na intercalation in Fe-MIL-100 for aqueous Na-ion batteries

Here we report for the first time the feasibility of using metal–organic frameworks (MOFs) as electrodes for aqueous Na-ion batteries. We show that Fe-MIL-100, a known redox-active MOF, is electrochemically active in a Na aqueous electrolyte, under various compositions. Emphasis was placed on investigating the electrode–electrolyte interface, with a focus on identifying the relationship between additives in the composition of the working electrode, particle size and overall performance. We found that the energy storage capacity is primarily dependent on the binder additive in the composite; the best activity for this MOF is obtained with Nafion as a binder, owing to its hydrophilic and ion conducting nature. Kynar-bound electrodes are clearly less effective, due to their hydrophobic character, which impedes wetting of the electrode. The binder-free systems show the poorest electrochemical activity. There is little difference in the overall performance as function of particle size (micro vs. nano), implying the storage capacities in this study are not limited by ionic and/or electronic conductivity. Excellent reversibility and high coulombic efficiency are achieved at higher potential ranges, observed after cycle 20. That is despite progressive capacity decay observed in the initial cycles. Importantly, structural analyses of cycled working electrodes confirm that the long range crystallinity remains mainly unaltered with cycling. These findings suggest that limited reversibility of the intercalated Na ions in the lower potential range, together with the gradual lack of available active sites in subsequent cycles is responsible for the rapid decay in capacity retention.

Efficient MOF-based degradation of organophosphorus compounds in non-aqueous environments

Decontamination of sensitive electronics exposed to chemical contaminants such as chemical warfare agents (CWA) is incompatible with existing water-based/corrosive methods. The development of new chemistries to tackle this challenge is of great interest. In this paper we investigate the effectiveness of metal–organic frameworks (MOFs) to degrade organophosphorus compounds in non-aqueous environments, via a combined experimental-molecular modeling study. Emphasis is placed on understanding the effect of framework characteristics (metal identity and linker functional group) on the methanolysis of these toxic chemicals, along with identifying reactivity trends for relevant sarin (GB) simulants. Several representative materials based on a hexanuclear metal cluster were judiciously selected, including the well-known catalytically active MOF, UiO-66. Complementary insights into the vibrational and structural properties of these materials were provided by periodic density functional theory (DFT) calculations. Findings indicate that Zr is a more effective metal center to support the degradation of organophosphorus compounds in methanol, as compared to Eu and Y. Detailed investigation into the reactivity of three relevant simulant candidates (diethyl chlorophosphate, DECP, dimethyl 4-nitrophenylphosphate, DMNP, and diisopropyl fluorophosphate, DFP), revealed that nitro- and fluorophosphates are better surrogates to mimic the reactivity of GB in methanol, as compared to chlorophosphate-based molecules. Importantly, experimental results on the MOF based degradation of GB in methanol are reported here for the first time. Additionally, this is the first study that systematically investigates the effectiveness of using MOFs for the solvolysis of organophosphorus compounds, providing valuable insights for materials design and simulant downselection.

Biocompatible MOFs with high absolute quantum yield for bioimaging in the second near infrared window

Here we detail a study highlighting the correlation between particle size and absolute quantum yield (QY) in novel mixed metal near-infrared (NIR) emitting metal–organic frameworks (MOFs) materials. The nanoscale analogue in this series presents a QY of 6.3%, the highest of any NIR emitting MOFs reported to date.

Enhancing Van der Waals Interactions of Functionalized UiO‐66 with Non‐polar Adsorbates: The Unique Effect of para Hydroxyl Groups

UiO-66 is a highly stable metal-organic framework (MOF) that has garnered interest for many adsorption applications. For small, nonpolar adsorbates, physisorption is dominated by weak Van der Waals interactions limiting the adsorption capacity. A common strategy to enhance the adsorption properties of isoreticular MOFs, such as UiO-66, is to add functional groups to the organic linker. Low and high pressure O2 isotherms were measured on UiO-66 MOFs functionalized with electron donating and withdrawing groups. It was found that the electron donating effects of -NH2 , -OH, and -OCF3 groups enhance the uptake of O2 . Interestingly, a significant enhancement in both the binding energy and adsorption capacity of O2 was observed for UiO-66-(OH)2 -p, which has two -OH groups para from one another. Density functional theory (DFT) simulations were used to calculate the binding energy of oxygen to each MOF, which trended with the adsorption capacity and agreed well with the heats of adsorption calculated from the Toth model fit to multi-temperature isotherms. DFT simulations also determined the highest energy binding site to be on top of the electron π-cloud of the aromatic ring of the ligand, with a direct trend of the binding energy with low pressure adsorption capacity. Uniquely, DFT found that oxygen molecules adsorbed to UiO-66-(OH)2 -p prefer to align parallel to the -OH groups on the aromatic ring. Similar effects for the electron donation of the functional groups were observed for the low pressure adsorption of N2 , CH4 , and CO2 .

Novel metal-organic frameworks for efficient stationary sources via oxyfuel combustion

Oxy-fuel combustion is a well-known approach to improve the heat transfer associated with stationary energy processes. Its overall penetration into industrial and power markets is constrained by the high cost of existing air separation technologies for generating oxygen. Cryogenic air separation is the most widely used technology for generating oxygen but is complex and expensive. Pressure swing adsorption is a competing technology that uses activated carbon, zeolites and polymer membranes for gas separations. However, it is expensive and limited to moderate purity O₂ . MOFs are cutting edge materials for gas separations at ambient pressure and room temperature, potentially revolutionizing the PSA process and providing dramatic process efficiency improvements through oxy-fuel combustion. This LDRD combined (1) MOF synthesis, (2) gas sorption testing, (3) MD simulations and crystallography of gas siting in pores for structure-property relationship, (4) combustion testing and (5) technoeconomic analysis to aid in real-world implementation.