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Drake, Hannah F.

Publications and source records attributed to Drake, Hannah F..

16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Assembling Phenothiazine into a Porous Coordination Cage to Improve Its Photocatalytic Efficiency for Organic Transformations

Abstract Photo‐catalysis by small‐molecules is often limited by catalyst degradation and low electron‐transfer efficiency. Herein we report a stable N‐phenyl‐phenothiazine (PTH)‐derived porous coordination cage (PCC) as a highly efficient photocatalyst. By the incorporation of the photocatalytic PTH moiety into a PCC, aggregation‐induced quenching (AIQ) was shown to be reduced. An improvement in catalyst stability was discovered, ascribed to the synergistic effects of the PTH moieties. The catalyst, operating through a photolytic single‐electron transfer, was utilized for photo‐catalyzed dehalogenation and borylation. Evaluation of the catalytic mechanism in the borylation reaction showed that the improved performance results from the more efficient formation of the electron donor‐acceptor (EDA) complex with the cage. This discovery provides a potential strategy to improve the photophysical properties and stabilities of small‐molecule organic photocatalysts via supramolecular chemistry.

Chemistry↗
DOE OSTI2022

Photoinduced reversible phase transition in a phenothiazine-based metal-organic framework

Photoinduced phase transitions in metal-organic frameworks are provoked by structural changes of photoresponsive linkers within the framework under light irradiation. These transitions are rare but fundamentally important as they can bring about light-switchability on a variety of properties of the materials. In this work, phenothiazine as a photoresponsive unit with distinctive photochemical properties is incorporated into a Zn-based metal-organic framework, PCN-401. The structural characterization of PCN-401 revealed a reversible structural transition upon light irradiation. The mechanisms behind the photoinduced phase transition are studied systematically by spectrometric methods and structural stability characterization. Our mechanistic studies successfully showcased how the phenothiazine unit in the framework undergoes structural transformation under light irradiation and how the reversible phase transition leads to the property changes. The findings have emphasized the significance of phenothiazine in photoresponsive materials and can serve as inspiration for the design and understandings of next-generation photoresponsive metal-organic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Influence of Metal Identity on Light-Induced Switchable Adsorption in Azobenzene-Based Metal–Organic Frameworks

Energy-efficient capture and release of small gas molecules, particularly carbon dioxide (CO 2 ) and methane (CH 4 ), are of significant interest in academia and industry. Porous materials such as metal–organic frameworks (MOFs) have been extensively studied, as their ultrahigh porosities and tunability enable significant amounts of gas to be adsorbed while also allowing specific applications to be targeted. However, because of the microporous nature of MOFs, the gas adsorption performance is dominated by high uptake capacity at low pressures, limiting their application. Hence, methods involving stimuli-responsive materials, particularly light-induced switchable adsorption (LISA), offer a unique alternative to thermal methods. Here, we report the mechanism of a well-known LISA system, the azobenzene-based material PCN-250, for CO 2 and CH 4 adsorption. There is a noticeable difference in the LISA effect dependent on the metal cluster involved, with the most significant being PCN-250-Al, where the adsorption can change by 83.1% CH 4 and 56.1% CO 2 at 298 K and 1 bar and inducing volumetric storage changes of 36.2 and 33.9 cm 3 /cm 3 at 298 K between 5 and 85 bar (CH 4 ) and 2 and 9 bar (CO 2 ), respectively. Using UV light in both single-crystal X-ray diffraction and gas adsorption testing, we show that upon photoirradiation, the framework undergoes a “localized heating” phenomenon comparable to an increase of 130 K for PCN-250-Fe and improves the working capacity. Furthermore, this process functions because of the constrained nature of the ligand, preventing the typical trans-to-cis isomerization observed in free azobenzene. In addition, we observed that the degree of localized heating is highly dependent on the metal cluster involved, with the series of isostructural PCN-250 systems showing variable performance based upon the degree of interaction between the ligand and the metal center.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Light-induced switchable adsorption in azobenzene- and stilbene-based porous materials

Despite the long history of porous materials as adsorbates, fundamental limitations remain regarding the efficient capture and release of the gas molecules, with the working capacity of the material often overlooked. In microporous materials, the uptake is dominated by low-pressure adsorption, with much of this being at pressures below the minimum working threshold for many gas utilization processes. Thus, research has focused on several advances in porous materials, including photoresponsive organic units for light-induced switchable adsorption. This process utilizes light to trigger structural or electronic changes, alter the gas uptake, and change the working capacity. Additionally, while a relatively recent development, there is a significant body of research regarding the use of light to control gas storage performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Structural Manipulation of a Zirconocene-Based Porous Coordination Cage Using External and Host–Guest Stimuli

Porous coordination cages (PCCs) constructed from a zirconocene-based cluster have drawn great attention for their high stability and structural tunability. These features have enabled these cages to be utilized for a wide array of applications. Here this work demonstrates the structural flexibility and stimulus-responsive features of two interconvertible zirconocene-based PCCs. The subjects, PCC-20c (capsular) and PCC-20t (tetrahedral), are constructed from the same cluster and ligand but exhibit different shapes and properties. In the synthetic study of the cages, it is found that higher temperatures of synthesis yield PCC-20c in several different crystalline phases while lower temperatures of synthesis yield pure phase PCC-20t. Thermodynamic studies on the interconversion of the two cages show that the conversion from PCC-20t into PCC-20c is an entropically driven process and can be largely affected by the solvent environment. Additionally, the process of PCC-20t/c conversion can be mediated by the counter anions and light irradiation as evidenced by the change in equilibrium constants under these influences. The current studies are conducted to decipher how the PCC-20t/c phase can be controllably synthesized, interconverted, and their properties can be modified under the use of external stimuli: heat, light, and guest molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Stepwise Assembly of Turn‐on Fluorescence Sensors in Multicomponent Metal–Organic Frameworks for in Vitro Cyanide Detection

Abstract The controlled synthesis of multicomponent metal–organic frameworks (MOFs) allows for the precise placement of multiple cooperative functional groups within a framework, leading to emergent synergistic effects. Herein, we demonstrate that turn‐on fluorescence sensors can be assembled by combining a fluorophore and a recognition moiety within a complex cavity of a multicomponent MOF. An anthracene‐based fluorescent linker and a hemicyanine‐containing CN − ‐responsive linker were sequentially installed into the lattice of PCN‐700. The selective binding of CN − to hemicyanine inhibited the energy transfer between the two moieties, resulting in a fluorescence turn‐on effect. Taking advantage of the high tunability of the MOF platform, the ratio between anthracene and the hemicyanine moiety could be fine‐tuned in order to maximize the sensitivity of the overall framework. The optimized MOF‐sensor had a CN − ‐detection limit of 0.05 μ m , which is much lower than traditional CN − fluorescent sensors (about 0.2 μ m ).

Li, Jialuo↗
DOE OSTI2019

Improving Alkylamine Incorporation in Porous Polymer Networks through Dopant Incorporation

The industrial scale capture of CO 2 from flue gas streams is becoming an increasingly important environmental issue. However, many of the existing CO 2 capture systems either have regenerative energy demands that are too high or are cost prohibitive. A promising solution is the utilization of functionalized solid sorbents, such as porous polymer networks (PPNs). PPNs are attractive due to their inherent structural stability, flexibility, high surface areas, and ability to incorporate various functional groups within the chemical scaffold. Herein, a low cost, scalable alternative to common carbon capture systems using a series of robust mesoporous melamine-formaldehyde resins (mPMFs) loaded with active alkylamine sorbents is presented, which is dubbed as the PPN-150 family. The variants within this material class are differentiated based on the incorporation of functionalized dopants; small molecules added at low molar percent concentrations to impart additional functionality into the PPN in order to achieve low cost noncovalent tethering of alkylamines. The cyanuric acid doped PPN-151-DETA (DETA = diethylenetriamine) demonstrate unique features such as improved cycling capacity and heat of adsorption. To show its scalability, PPN-151-DETA is successfully synthesized at the 250 g scale without loss of the sorbent properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The thermally induced decarboxylation mechanism of a mixed-oxidation state carboxylate-based iron metal–organic framework

Investigations into a thermally generated decarboxylation mechanism for metal site activation and the generation of mesopores in a carboxylate iron-based MOF, PCN-250, have been conducted. PCN-250 exhibits an interesting oxidation state change during thermal treatment under inert atmospheres or vacuum conditions, transitioning from an Fe(III)3 cluster to a Fe(II)Fe(III) 2 cluster. To probe this redox event and discern a mechanism of activation, a combination of thermogravimetric analysis, gas sorption, scanning electron microscopy, 57 Fe Mössbauer spectroscopy, gas chromatography-mass spectrometry, and X-ray diffraction studies were conducted. The results suggest that the iron-site activation occurs due to ligand decarboxylation above 200 °C. This is also consistent with the generation of a missing cluster mesoporous defect in the framework. The resulting mesoporous PCN-250 maintains high thermal stability, preserving crystallinity after multiple consecutive high-temperature regeneration cycles. Additionally, the thermally reduced PCN-250 shows improvements in the total uptake capacity of methane and CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗