Riki Drout

The expansion of manufacturing and commercial agriculture alongside rapid globalization have resulted in the widespread contamination of freshwater supplies with chemical toxins including persistent organic pollutants. Effective mitigation of such pollution is paramount to the safeguarding of human health, animal and aquatic life, and the environment. Currently, adsorption is the most economically viable water purification strategy. Owing to their crystallinity and modular nature, metal–organic… Show more

The expansion of manufacturing and commercial agriculture alongside rapid globalization have resulted in the widespread contamination of freshwater supplies with chemical toxins including persistent organic pollutants. Effective mitigation of such pollution is paramount to the safeguarding of human health, animal and aquatic life, and the environment. Currently, adsorption is the most economically viable water purification strategy. Owing to their crystallinity and modular nature, metal–organic frameworks (MOFs) are an excellent platform material for systematically investigating the physical and chemical properties which govern adsorption processes. X-ray diffraction techniques provide atomically precise descriptions of toxin-MOF interactions, while liquid-phase adsorption isotherms readily allow for the determination of uptake capacity and kinetics; however, determination of the thermodynamics of toxin-MOF interactions in aqueous media remains tedious. Herein, we add isothermal titration calorimetry (ITC) to our arsenal of techniques for characterizing adsorption mechanisms in MOFs. With this method, we are able to directly quantify the full thermodynamic profile of a chemical process (Ka, ΔG, ΔH, TΔS), providing critical details to support the rational design of next-generation sorbents. We demonstrate the suitability of ITC through our exploration of the parameter space of organophosphorus agrochemical adsorption in zirconium-based MOFs. Show less

The performance of metal–organic frameworks (MOFs) under mechanical stress is an important consideration in the design, synthesis, and application of MOF materials in both fundamental and industrial settings. We herein demonstrate that the bulk modulus (K = −V dP/dV) of a 4,8-connected Zr-based MOF, NU-901, comprised of Zr6O8 nodes and tetratopic pyrene linkers, increases systematically upon postsynthetic installation of a structural organic linker, 2,6-naphthalenedicarboxylic acid (NDC), via… Show more

The performance of metal–organic frameworks (MOFs) under mechanical stress is an important consideration in the design, synthesis, and application of MOF materials in both fundamental and industrial settings. We herein demonstrate that the bulk modulus (K = −V dP/dV) of a 4,8-connected Zr-based MOF, NU-901, comprised of Zr6O8 nodes and tetratopic pyrene linkers, increases systematically upon postsynthetic installation of a structural organic linker, 2,6-naphthalenedicarboxylic acid (NDC), via solvent assisted linker incorporation. We calculated the bulk modulus, a measure of resistance to hydrostatic compression, of these modified NU-901 samples through in situ variable powder X-ray diffraction pressure measurements collected using a synchrotron source. As the amount of NDC incorporation into the NU-901 framework increased, the lattice strength of the framework also increased. This strategy of postsynthetic modification at the molecular level serves as a promising blueprint to tune the bulk mechanical properties of other MOFs by increasing the connnectivity of the secondary building unit. Furthermore, we envision this method may allow for structural reinforcement of other frameworks along one preferential axis or direction dependent on the desired application. Show less

Krypton and xenon are important gases in many applications, including, but not limited to, electronics, lighting, and medicine. Separation of these two gases by cryogenic distillation is highly energy-intensive; however, adsorption-based separation processes provide an alternative strategy for isolating gases in high purity. The absence of strong interactions between these molecules and porous adsorbents has impeded the advancement of adsorptive separation of krypton and xenon. Herein, we… Show more

Krypton and xenon are important gases in many applications, including, but not limited to, electronics, lighting, and medicine. Separation of these two gases by cryogenic distillation is highly energy-intensive; however, adsorption-based separation processes provide an alternative strategy for isolating gases in high purity. The absence of strong interactions between these molecules and porous adsorbents has impeded the advancement of adsorptive separation of krypton and xenon. Herein, we capitalized on the modular nature of metal–organic frameworks (MOFs) to design a porous material which relies on gas confinement to separate krypton/xenon (Kr/Xe) mixtures. We solvothermally synthesized a new zirconium-based MOF, NU-403, which comprises a three-dimensional linker, bicyclo[2.2.2]octane-1,4-dicarboxylic acid. Comprehensive gas adsorption measurements revealed that the linker dimensionality and MOF pore aperture dramatically affect the separation of xenon from krypton owing to the confinement of gas molecules inside the framework. Moreover, Kr/Xe selectivity increased significantly after postsynthetic defect healing, which further enhanced gas–framework interactions, demonstrating an effective strategy for enhancing krypton and xenon separation. Show less

Recent efforts have examined metal-organic frameworks (MOFs) as sorbents for removing pollutants and trace chemicals, such as pharmaceuticals, from aqueous media. To date, few studies have investigated the energetics of interactions between toxic species and MOF-based sorbents. To this end, we elected to use isothermal titration calorimetry (ITC) to quantify the thermodynamic parameters associated with the adsorption of uremic toxins, namely p-cresyl sulfate and indoxyl sulfate, onto… Show more

Recent efforts have examined metal-organic frameworks (MOFs) as sorbents for removing pollutants and trace chemicals, such as pharmaceuticals, from aqueous media. To date, few studies have investigated the energetics of interactions between toxic species and MOF-based sorbents. To this end, we elected to use isothermal titration calorimetry (ITC) to quantify the thermodynamic parameters associated with the adsorption of uremic toxins, namely p-cresyl sulfate and indoxyl sulfate, onto zirconium-based MOFs. NU-1000, a mesoporous MOF comprising a pyrene-based linker, possesses two distinct adsorption sites that display dramatically different enthalpic and entropic parameters. ITC measurements further reveal that a concerted interaction that embodies both favorable enthalpic and entropic contributions is critical for designing a high-capacity MOF-based adsorbent. Show less

The rapid expansion of manufacturing and the industrialization of agriculture during the 20th century pervaded surface and groundwater sources with organic contaminants including agrochemicals, dyes, and pharmaceuticals. Efficient purification of these water sources is critical to safeguard human health and Earth’s ecosystems. Of the numerous strategies investigated for water purification, adsorption has received the most attention; however, the ability to design a sorbent with high uptake… Show more

The rapid expansion of manufacturing and the industrialization of agriculture during the 20th century pervaded surface and groundwater sources with organic contaminants including agrochemicals, dyes, and pharmaceuticals. Efficient purification of these water sources is critical to safeguard human health and Earth’s ecosystems. Of the numerous strategies investigated for water purification, adsorption has received the most attention; however, the ability to design a sorbent with high uptake capacity and selectivity for a single pollutant continues to elude researchers. The precise synthetic control over chemical functionality offered by metal–organic frameworks (MOFs) make them ideal scaffolds for the systematic investigation of selectivity-enhancing binding interactions. Herein, we review the recent reports on the use of water-stable zirconium-based MOFs (Zr-MOFs) to extract organic pollutants from water and briefly discuss the field’s future directions. Show less

A new bismuth metal–organic framework (MOF), bismuth-NU-901 (Bi-NU-901), featuring the scu topology and a pore with a diameter of ∼11 Å, was solvothermally synthesized, and its use as an X-ray computed tomography (CT) contrast agent was tested. X-ray CT is a common diagnostic method used in the medical field. Inside the body, contrast media enhance the distinction between tissues and organs of similar density. Bi-NU-901 consists of eight connected Bi6 nodes and tetratopic… Show more

A new bismuth metal–organic framework (MOF), bismuth-NU-901 (Bi-NU-901), featuring the scu topology and a pore with a diameter of ∼11 Å, was solvothermally synthesized, and its use as an X-ray computed tomography (CT) contrast agent was tested. X-ray CT is a common diagnostic method used in the medical field. Inside the body, contrast media enhance the distinction between tissues and organs of similar density. Bi-NU-901 consists of eight connected Bi6 nodes and tetratopic 1,3,5,8-(p-benzoate)pyrene linkers (TBAPy). Numerous material characterization studies including powder X-ray diffraction (PXRD), scanning transmission electron microscopy (STEM), and DFT pore size distribution support the scu structure. Additionally, given the framework’s high density of nontoxic heavy atoms, Bi-NU-901 was evaluated as an X-ray computed tomography (CT) agent. Importantly, in vitro studies revealed this new bismuth MOF demonstrates ∼7 times better contrast intensity compared to a zirconium MOF featuring the same topology and ∼14 times better contrast than a commercially available CT contrast agent. These results suggest bismuth MOFs may be promising CT contrast agents. Show less

The global catalyst industry is valued at nearly 20 billion USD and demand continues to rise. Enzymes, biological macromolecules, are highly selective and efficient catalysts; however, their commercial implementation has been hindered due to their poor chemical and thermal stability and low reusability. Numerous strategies have been investigated to stabilize enzymes and improve their processability. Recently, metal–organic frameworks (MOFs) have been investigated as enzyme immobilization… Show more

The global catalyst industry is valued at nearly 20 billion USD and demand continues to rise. Enzymes, biological macromolecules, are highly selective and efficient catalysts; however, their commercial implementation has been hindered due to their poor chemical and thermal stability and low reusability. Numerous strategies have been investigated to stabilize enzymes and improve their processability. Recently, metal–organic frameworks (MOFs) have been investigated as enzyme immobilization supports. Herein, we highlight the immobilization of enzymes in MOF cages and pores for catalysis applications and discuss the future of this enzyme encapsulation strategy. Show less

The United States Environmental Protection Agency (EPA) recognizes atrazine, a commonly used herbicide, as an endocrine disrupting compound. Excessive use of this agrochemical results in contamination of surface and ground water supplies via agricultural runoff. Efficient removal of atrazine from contaminated water supplies is paramount. Here, the mechanism governing atrazine adsorption in Zr6-based metal–organic frameworks (MOFs) has been thoroughly investigated by studying the effects of MOF… Show more

The United States Environmental Protection Agency (EPA) recognizes atrazine, a commonly used herbicide, as an endocrine disrupting compound. Excessive use of this agrochemical results in contamination of surface and ground water supplies via agricultural runoff. Efficient removal of atrazine from contaminated water supplies is paramount. Here, the mechanism governing atrazine adsorption in Zr6-based metal–organic frameworks (MOFs) has been thoroughly investigated by studying the effects of MOF linkers and topology on atrazine uptake capacity and uptake kinetics. We found that the mesopores of NU-1000 facilitated rapid atrazine uptake saturating in <5 min and that the pyrene-based linkers offered sufficient sites for π–π interactions with atrazine as demonstrated by the near 100% uptake. Without the presence of a pyrene-based linker, NU-1008, a MOF similar to NU-1000 with respect to surface area and pore size, removed <20% of the exposed atrazine. These results suggest that the atrazine uptake capacity demonstrated by NU-1000 stems from the presence of a pyrene core in the MOF linker, affirming that π–π stacking is responsible for driving atrazine adsorption. Furthermore, NU-1000 displays an exceptional atrazine removal capacity through three cycles of adsorption–desorption. Powder X-ray diffraction and Brunauer–Emmett–Teller surface area analysis confirmed the retention of MOF crystallinity and porosity throughout the adsorption–desorption cycles. Show less

Practical applications involving the magnetic bistability of single-molecule magnets (SMMs) for next-generation computer technologies require nanostructuring, organization, and protection of nanoscale materials in two- or three-dimensional networks, to enable read-and-write processes. Owing to their porous nature and structural long-range order, metal–organic frameworks (MOFs) have been proposed as hosts to facilitate these efforts. Although probing the channels of MOF composites using indirect… Show more

Practical applications involving the magnetic bistability of single-molecule magnets (SMMs) for next-generation computer technologies require nanostructuring, organization, and protection of nanoscale materials in two- or three-dimensional networks, to enable read-and-write processes. Owing to their porous nature and structural long-range order, metal–organic frameworks (MOFs) have been proposed as hosts to facilitate these efforts. Although probing the channels of MOF composites using indirect methods is well established, the use of direct methods to elucidate fundamental structural information is still lacking. Herein we report the direct imaging of SMMs encapsulated in a mesoporous MOF matrix using high-resolution transmission electron microscopy. These images deliver, for the first time, direct and unambiguous evidence to support the adsorption of molecular guests within the porous host. Bulk magnetic measurements further support the successful nanostructuring of SMMs. The preparation of the first magnetic composite thin films of this kind furthers the development of molecular spintronics. Show less

Two-dimensional metal–organic frameworks (2D-MOFs) have shown promise in gas storage and separation applications due to their structural isomerism in response to external stimuli such as temperature, mechanical pressure, and/or guest molecules. Here, we report the guest-dependent phase transitions of a uranyl-based 2D-MOF, NU-1302, observed as single-crystal-to-single-crystal transformations. Different stacking configurations of the same structure were observed in DMF and ethanol, and after… Show more

Two-dimensional metal–organic frameworks (2D-MOFs) have shown promise in gas storage and separation applications due to their structural isomerism in response to external stimuli such as temperature, mechanical pressure, and/or guest molecules. Here, we report the guest-dependent phase transitions of a uranyl-based 2D-MOF, NU-1302, observed as single-crystal-to-single-crystal transformations. Different stacking configurations of the same structure were observed in DMF and ethanol, and after supercritical CO2 activation. The structural isomerism upon exposure to different solvents and when solvent-free demonstrated the ability of this system to respond to guests by shifting neighboring 2D sheets, resulting in the expansion or contraction of one-dimensional channels. Show less

A representative mesoporous metal–organic-framework (MOF) material, NU-1000, has been rendered electronically conductive via a robust inorganic approach that permits retention of MOF crystallinity and porosity. The approach is based on condensed-phase grafting of molecular tin species onto the MOF nodes via irreversible reaction with hydroxyl and aqua ligands presented at the node surface, a self-limiting process termed solvothermal installation (of metal ions) in MOFs (SIM, a solution-phase… Show more

A representative mesoporous metal–organic-framework (MOF) material, NU-1000, has been rendered electronically conductive via a robust inorganic approach that permits retention of MOF crystallinity and porosity. The approach is based on condensed-phase grafting of molecular tin species onto the MOF nodes via irreversible reaction with hydroxyl and aqua ligands presented at the node surface, a self-limiting process termed solvothermal installation (of metal ions) in MOFs (SIM, a solution-phase analog of atomic layer deposition in MOFs). Treatment of the modified MOF with aerated steam at 120 °C converts the grafted tin molecules to tetratin(IV)oxy clusters, with the clusters being sited between insulating pairs of zirconia-like nodes (the zirconium component being key to endowing the parent material with requisite chemical and thermal stability). By introducing new O–H presenting ligands on the modified-MOF node, the high-temperature steam step additionally serves to reset the material to reactive form, thus enabling a second self-limiting tin-grafting step to be run (and after further steam treatment, enabling a third)... Show less

Abstract: Strict monitoring and control of selenium concentrations in freshwater supplies is critical to safeguarding human health and aquatic life. A handful of previously investigated sorbents exhibit noteworthy gravimetric (mg/g) Se uptake capacities; however, often display insufficient volumetric (mg/cm^3) capacities, thereby requiring large volumes of material for commercial implementation. In pursuit of mitigating this material inefficiency, we investigated the selenite (SeO32−) and… Show more

Abstract: Strict monitoring and control of selenium concentrations in freshwater supplies is critical to safeguarding human health and aquatic life. A handful of previously investigated sorbents exhibit noteworthy gravimetric (mg/g) Se uptake capacities; however, often display insufficient volumetric (mg/cm^3) capacities, thereby requiring large volumes of material for commercial implementation. In pursuit of mitigating this material inefficiency, we investigated the selenite (SeO32−) and selenate (SeO42−) affinity of MOF-808, a Zr-based metal–organic framework with a high density of potential Se oxyanion binding sites. MOF-808 recorded exceptional volumetric and gravimetric Se oxyanion capacities of 133 mg/g (127 mg/cm^3) and 118 mg/g (112 mg/cm^3) for aqueous selenite and selenate, respectively. Single-crystal X-ray diffraction studies revealed that selenite and selenate can bind at the MOF node via two distinct binding motifs, an η2μ2 motif in which the oxyanion coordinates to two different metal atoms in a single node, and a μ2 motif in which the oxyanion interacts with only a single metal atom. Furthermore, powder X-ray diffraction (PXRD) patterns and N2 adsorption/desorption isotherms confirm the retention of bulk crystallinity and porosity after the uptake of Se oxyanions. Show less

Diabetes affects millions of people worldwide and the number of diagnoses continues to climb annually. While several effective medications and therapeutic methods have been developed to treat type 1 (T1DM) and type 2 (T2DM) diabetes mellitus, direct insulin injection remains the only effective treatment for insulin resistant (IR) diabetes patients. Here, we immobilize insulin in a crystalline mesoporous metal–organic framework (MOF), NU-1000, and obtain a high loading of~ 40 wt% in only 30 min.… Show more

Diabetes affects millions of people worldwide and the number of diagnoses continues to climb annually. While several effective medications and therapeutic methods have been developed to treat type 1 (T1DM) and type 2 (T2DM) diabetes mellitus, direct insulin injection remains the only effective treatment for insulin resistant (IR) diabetes patients. Here, we immobilize insulin in a crystalline mesoporous metal–organic framework (MOF), NU-1000, and obtain a high loading of~ 40 wt% in only 30 min. The acid-stable MOF capsules are found to effectively prevent insulin from degrading in the presence of stomach acid and the digestive enzyme, pepsin. Furthermore, the encapsulated insulin can be released from NU-1000 under simulated physiological conditions. Show less

At the Hanford Site in southeastern Washington state, the U.S. Department of Energy intends to treat 56 million gallons of legacy nuclear waste by encasing it in borosilicate glass via vitrification. This process ineffectively captures radioactive pertechnetate (TcO4–) because of the ion’s volatility, thereby requiring a different remediation method for this long-lived (t1/2 = 2.1 × 105 years), environmentally mobile species. Currently available sorbents lack the desired combination of high… Show more

At the Hanford Site in southeastern Washington state, the U.S. Department of Energy intends to treat 56 million gallons of legacy nuclear waste by encasing it in borosilicate glass via vitrification. This process ineffectively captures radioactive pertechnetate (TcO4–) because of the ion’s volatility, thereby requiring a different remediation method for this long-lived (t1/2 = 2.1 × 105 years), environmentally mobile species. Currently available sorbents lack the desired combination of high uptake capacity, fast kinetics, and selectivity. Here, we evaluate the ability of the chemically and thermally robust Zr6-based metal–organic framework (MOF), NU-1000, to capture perrhenate (ReO4–), a pertechnetate simulant, and pertechnetate. Our material exhibits an excellent perrhenate uptake capacity of 210 mg/g, reaches saturation within 5 min, and maintains perrhenate uptake in the presence of competing anions. Additionally, experiments with pertechnetate confirm perrhenate is a suitable surrogate. Single-crystal X-ray diffraction indicates both chelating and nonchelating perrhenate binding motifs are present in both the small pore and the mesopore of NU-1000. Postadsorption diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) further elucidates the uptake mechanism and powder X-ray diffraction (PXRD) and Brunauer–Emmett–Teller (BET) surface area analysis confirm the retention of crystallinity and porosity of NU-1000 throughout adsorption. Show less