Reactive Capture and Conversion of CO2 into Hydrogen over Bifunctional Structured Ce1-xCoxNiO3/Ca Perovskite-Type Oxide Monoliths.

Carbon capture, utilization, and storage (CCUS) technologies are pivotal for transitioning to a net-zero economy by 2050. In particular, conversion of captured CO2 to marketable chemicals and fuels appears to be a sustainable approach to not only curb greenhouse emissions but also transform wastes like CO2 into useful products through storage of renewable energy in chemical bonds. Bifunctional materials (BFMs) composed of adsorbents and catalysts have shown promise in reactive capture and conversion of CO2 at high temperatures. In this study, we extend the application of 3D printing technology to formulate a novel set of BFMs composed of CaO and Ce1-xCoxNiO3 perovskite-type oxide catalysts for the dual-purpose use of capturing CO2 and reforming CH4 for H2 production. Three honeycomb monoliths composed of equal amounts of adsorbent and catalyst constituents with varied Ce1-xCox ratios were 3D printed to assess the role of cobalt on catalytic properties and overall performance. The samples were vigorously characterized using X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2-TPR, in situ CO2 adsorption/desorption XRD, and NH3-TPD. Results showed that the Ce1-xCox ratios-x = 0.25, 0.50, and 0.75-did not affect crystallinity, texture, or metal dispersion. However, a higher cobalt content reduced reducibility, CO2 adsorption/desorption reversibility, and oxygen species availability. Assessing the structured BFM monoliths via combined CO2 capture and CH4 reforming in the temperature range 500-700 °C revealed that such differences in physiochemical properties lowered H2 and CO yields at higher cobalt loading, leading to best catalytic performance in Ce0.75Co0.25NiO3/Ca sample that achieved 77% CO2 conversion, 94% CH4 conversion, 61% H2 yield, and 2.30 H2/CO ratio at 700 °C. The stability of this BFM was assessed across five adsorption/reaction cycles, showing only marginal losses in the H2/CO yield. Thus, these findings successfully expand the use of 3D printing to unexplored perovskite-based BFMs and demonstrate an important proof-of-concept for their use in combined CO2 capture and utilization in H2 production processes.

Performance of MIL-101(Cr) and MIL-101(Cr)-Pore Expanded as Drug Carriers for Ibuprofen and 5-Fluorouracil Delivery.

Metal-organic frameworks (MOFs) have been extensively investigated as nanocarriers for drug delivery applications owing to their remarkable surface area and porosity, which allow for impregnation of large quantities of drugs with fast pharmacokinetics. In this work, we developed a pore-expanded version of MIL-101(Cr), MIL-101(Cr)-P, and assessed its potential as a carrier for ibuprofen and 5-fluorouracil drugs along with its regular MIL-101(Cr) analogue. The pore expansion strategy gave rise to a higher surface area and mesopore volume for MIL-101(Cr)-P relative to regular MIL-101(Cr). The characterization results revealed successful incorporation of 30, 50, and 80 wt % of both drugs within the MOF structure. Upon incorporation of species, the surface area and porosity of the two MOF carriers decreased drastically; however, the drug-loaded MOFs still retained some degree of porosity, even at high drug loadings. For both drugs, the delivery experiments conducted in phosphate-buffered saline (PBS) showed that MIL-101(Cr)-P possessed better pharmacokinetic behavior than MIL-101(Cr) by delivering higher amounts of drug at all three loadings and exhibiting much faster release rates. Such behavior was originated from large mesopores that were created during pore expansion, providing diffusional pathways for efficient delivery of the drugs. The highest rate constant obtained by fitting the release kinetics to the Higuchi model was found to be 0.44 h-1/2 for the release of 30 wt % 5-fluorouracil from MIL-101(Cr)-P. The findings of this study highlight the role of tuning physiochemical properties of MOFs in improving their pharmacokinetic behavior as drug carriers.

Cooperative and Bifunctional Adsorbent-Catalyst Materials for In-situ VOCs Capture-Conversion.

Volatile organic compounds (VOCs) are gases that are emitted into the air from products or processes and are major components of air pollution that significantly deteriorate air quality and seriously affect human health. Different types of metals, metal oxides, mixed-metal oxides, polymers, activated carbons, zeolites, metal-organic frameworks (MOFs) and mixed-matrixed materials have been developed and used as adsorbent or catalyst for diversified VOCs detection, removal, and destruction. In this comprehensive review, we first discuss the general classification of VOCs removal materials and processes and outline the historical development of bifunctional and cooperative adsorbent-catalyst materials for the removal of VOCs from air. Subsequently, particular attention is devoted to design of strategies for cooperative adsorbent-catalyst materials, along with detailed discussions on the latest advances on these bifunctional materials, reaction mechanisms, long-term stability, and regeneration for VOCs removal processes. Finally, challenges and future opportunities for the environmental implementation of these bifunctional materials are identified and outlined with the intent of providing insightful guidance on the design and fabrication of more efficient materials and systems for VOCs removal in the future.

Influence of Interfering Ions and Adsorption Temperature on Radioactive Iodine Removal Efficiency and Stability of Ni-MOF-74 and Zr-UiO-66.

Metal-organic frameworks (MOFs) often exhibit an exceptional adsorption-based separation performance for a variety of gases, ions, and liquids. While most radioactive iodine removal studies focus on the capture of radioactive iodine from off-gas streams, few studies have systematically investigated the effect of structure-property relationships of MOFs on iodine removal performance in the presence of interfering ions in liquid solutions. Herein, we investigated the iodide ion (I-) adsorption performance of two model MOFs (e.g., Ni-MOF-74 and Zr-UiO-66) in liquid phase as a function of iodine concentration (e.g., 0.125 to 0.25 and 0.50 mmol/L) and adsorption temperature (e.g., 25 to 40 and 60 °C), and in the presence of interfering ions such as Cl- and CO32- through batch-mode experiments. Under identical experimental conditions, Ni-MOF-74 outperformed Zr-UiO-66 in immobilizing iodine from the solution by achieving a maximum iodine removal efficiency of 97% at 60 °C. The results showed that the presence of other interfering ions marginally affects the iodine removal efficiency (e.g., capacity and rate of iodine capture) over both MOF adsorbents. The adsorption kinetics was found to be controlled by multiple transport processes encompassing external surface adsorption, intraparticle diffusion, and final equilibrium. Moreover, the leach test results revealed 8 and 12% iodine release from Ni-MOF-74 and Zr-UiO-66, respectively, at 25 °C after 48 h aging. This study establishes guiding principles for sustainable removal of iodine in the presence of Cl- and CO32- species in cyclohexane.

Drug Delivery on Mg-MOF-74: The Effect of Drug Solubility on Pharmacokinetics.

Biocompatible metal-organic frameworks (MOFs) have emerged as potential nanocarriers for drug delivery applications owing to their tunable physiochemical properties. Specifically, Mg-MOF-74 with soluble metal centers has been shown to promote rapid pharmacokinetics for some drugs. In this work, we studied how the solubility of drug impacts the pharmacokinetic release rate and delivery efficiency by impregnating various amounts of ibuprofen, 5-fluorouracil, and curcumin onto Mg-MOF-74. The characterization of the drug-loaded samples via X-ray diffraction (XRD), N2 physisorption, and Fourier transform infrared (FTIR) confirmed the successful encapsulation of 30, 50, and 80 wt % of the three drugs within the MOF structure. Assessment of the drug delivery performances of the MOF under its various loadings via HPLC tests revealed that the release rate is a direct function of drug solubility and molecular size. Of the three drugs considered under fixed loading condition, the 5-fluorouracil-loaded MOF samples exhibited the highest release rate constants which was attributed to the highest degree of solubility and smallest molecular size of 5-fluorouracil relative to ibuprofen and curcumin. It was also noted that the release kinetics decreases with drug loading, due to a pharmacokinetic shift in release mechanism from singular to binary modes of compound diffusion. The findings of this study highlight the effects of drug's physical and chemical properties on the pharmacokinetic rates from MOF nanocarriers.

Examining the Effect of a Chitosan Biopolymer on Alkali-Activated Inorganic Material for Aqueous Pb(II) and Zn(II) Sorption.

Biopolymers and alkali-activated materials have attracted a great deal of attention as adsorbents for the removal of heavy metal contaminants from aqueous solutions. Both materials are sustainable and feature unique properties, but biopolymers are relatively more expensive or difficult to prepare and exhibit low mechanical and surface properties, a narrow pH range, and thermal stability. In this study, hybrid adsorbents were prepared from both types of material, by alkali activation of low-cost fly ash precursors accompanied by incorporation of 0-2%mass chitosan biopolymer. Two types of alkaline activating solutions, NaOH and Na2SiO3, were employed to generate two sets of hybrid adsorbents with varying chitosan contents. The effect of the chitosan dosage on the aqueous Pb(II) and Zn(II) sorption efficiency was also investigated. The adsorbents exhibited 98-100% removal efficiencies for both metals, but the sorption of Zn(II) was generally higher than that of Pb(II). The addition of 0.1-2.0%mass chitosan resulted in very little improvement in the overall efficiency of the adsorbents. In contrast, 0.05%mass chitosan led to a decrease in the sorption efficiency; this was linked to the decrease in the adsorbents' ζ potential. The Na2SiO3-activated materials featured larger BET surface areas and better overall sorption performance, while the NaOH-activated materials showed the worst Pb(II) sorption performance and hence more noticeable improvement upon addition of chitosan. Mechanistic investigation shows that the sorption process follows second-order kinetics and is a chemisorption-driven process.

Combined Ibuprofen and Curcumin Delivery Using Mg-MOF-74 as a Single Nanocarrier.

Metal-organic frameworks (MOFs) have been extensively used as drug delivery platforms because of their considerable textural properties and physiochemical tunability. However, most medicinal treatments often administer multiple therapeutic pharmaceuticals simultaneously and combined drug delivery over a single MOF carrier has not been extensively developed. As such, in this study we implemented Mg-MOF-74, which is known to have rapid pharmacokinetic properties, for the combined delivery of ibuprofen and curcumin to demonstrate the proof-of-concept for dual-drug delivery over this previously unexplored MOF. To this end, 30 wt % total drug loading of two drugs was impregnated at various ratios (25:5 ibuprofen-curcumin, 20:5 ibuprofen-curcumin, 15:15 ibuprofen-curcumin, 10:20 ibuprofen-curcumin, and 5:25 ibuprofen-curcumin), and the drug delivery performance of the materials was assessed from 0 to 24 h in phosphate-buffered saline (PBS) solution using high-performance liquid chromatography (HPLC). The experiments revealed that all five ratios of ibuprofen-curcumin loadings can effectively deliver both compounds; however, elevating the curcumin loading beyond 10 wt % decreases the drug loading efficiency for ibuprofen and can also inhibit ibuprofen release. Nevertheless, because Mg-MOF-74 was able to successfully deliver both compounds, this study serves as a promising proof-of-concept for dual-drug delivery from a single MOF carrier. In this regard, the work demonstrated herein expands the use of MOFs for drug delivery applications and can be used to supplement drug administration via orally ingested tablets.

Screening of Adsorbent/Catalyst Composite Monoliths for Carbon Capture-Utilization and Ethylene Production.

Combining CO2 adsorption and utilization in oxidative dehydrogenation of ethane (ODHE) into a single bed is an exciting way of converting a harmful greenhouse gas into marketable commodity chemicals while reducing energy requirements from two-bed processes. However, novel materials should be developed for this purpose because most adsorbents are incapable of capturing CO2 at the temperatures required for ODHE reactions. Some progress has been made in this area; however, previously reported dual-functional materials (DFMs) have always been powdered-state composites and no efforts have been made toward forming these materials into practical contactors. In this study, we report the first-generation of structured DFM adsorbent/catalyst monoliths for combined CO2 capture and ODHE utilization. Specifically, we formulated M-CaO/ZSM-5 monoliths (M = In, Ce, Cr, or Mo oxides) by 3D-printing inks with CaCO3 (CaO precursor), insoluble metal oxides, and ZSM-5. The physiochemical properties of the monoliths were vigorously characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physisorption, elemental mapping, pyridine Fourier transform infrared spectroscopy (Py-FTIR), H2-temperature-programmed reduction (H2-TPR), and NH3-temperature-programmed desorption (NH3-TPD). Their performances for combined CO2 adsorption at 600 °C and ODHE reaction at 700 °C under 25 mL/min of 7% C2H6 were then investigated. The combined adsorption/catalysis experiments revealed the best performance in Cr-CaO/ZSM-5, which achieved 56% CO2 conversion, 91.2% C2H4 selectivity, and 33.8% C2H4 yield. This exceptional performance, which was improved from powdered-state DFMs, was attributed to the high acidity and numerous oxidation states of the Cr2O3 dopant which were verified by NH3-TPD and H2-TPR. Overall, this study reports the first-ever proof-of-concept for 3D-printed DFM adsorbent/catalyst materials and furthers the area of CO2 capture and ODHE utilization by providing a simple pathway to structure these composites.

Passive Control of Indoor Formaldehyde by Mixed-Metal Oxide Latex Paints.

This work reports the incorporation of mixed-metal oxides (MMOs) such as Si/Ti and Si/Zr into latex paints in the form of thin coatings for permanent trapping of indoor formaldehyde. The formaldehyde removal performance of the surface coatings was evaluated in a lab-scale indoor air chamber, and the results were compared with those of powder analogues. Due to the pore blockage by the latex, the incorporation led to 6-30% reduction in adsorption capacity and 50-70% drop in the adsorption rate for MMO-latex paints relative to their powder MMO analogues. Under the operating conditions of concentration, temperature, and relative humidity, the Si/Zr-latex paints outperformed the Si/Ti counterparts. It was also observed that performance could decrease over excessive loading, for example, Si/Zr-latex paint with 15/1 Si/Zr weight ratio showed a 20% lower adsorption capacity than that of the Si/Zr-latex paint with 25/1 Si/Zr ratio at 5 ppmv, 25 °C, and 70% RH. While high temperature greatly reduced the adsorption rate of the MMO-latex paints, high humidity slightly promoted the rate of formaldehyde capture. In 10 L, flow-through chamber tests, 25Si/Zr-latex paint reduced 5 ppmv formaldehyde by up to 60% at 25 °C and 70% RH with an adsorption rate of 0.34 ppmv/h. Overall, this study highlights the potential of MMO-latex paints with optimized formation for the efficient abatement of indoor aldehydes.

Recent Advances in 3D Printing of Structured Materials for Adsorption and Catalysis Applications.

Porous solids in the form of adsorbents and catalysts play a crucial role in various industrially important chemical, energy, and environmental processes. Formulating them into structured configurations is a key step toward their scale up and successful implementation at the industrial level. Additive manufacturing, also known as 3D printing, has emerged as an invaluable platform for shape engineering porous solids and fabricating scalable configurations for use in a wide variety of separation and reaction applications. However, formulating porous materials into self-standing configurations can dramatically affect their performance and consequently the efficiency of the process wherein they operate. Toward this end, various research groups around the world have investigated the formulation of porous adsorbents and catalysts into structured scaffolds with complex geometries that not only exhibit comparable or improved performance to that of their powder parents but also address the pressure drop and attrition issues of traditional configurations. In this comprehensive review, we summarize the recent advances and current challenges in the field of adsorption and catalysis to better guide the future directions in shape engineering solid materials with a better control on composition, structure, and properties of 3D-printed adsorbents and catalysts.

Curcumin Delivery on Metal-Organic Frameworks: The Effect of the Metal Center on Pharmacokinetics within the M-MOF-74 Family.

Metal-organic frameworks (MOFs) have gained considerable attention as drug delivery platforms over the past decade owing to their tunable physiochemical properties, biodiversity, and capability to encapsulate sizable active compound loadings. Nevertheless, many fundamental properties pertaining to MOFs' pharmacokinetic performances as drug carriers have been poorly investigated. One such property is the relationship between the MOF metal center solubility and drug release rate. In this study, we investigated this relationship within the M-MOF-74 family by impregnating 30 or 50 wt % curcumin on either Mg-, Ni-, Zn-, or Co-MOF-74. The drug delivery performance of the materials was assessed in phosphate buffered saline solution by high-performance liquid chromatography over a time period of 0-24 h. From these experiments, it was determined that the 30 wt % curcumin loading led to increased drug delivery and kinetics compared to the 50 wt % loading regardless of the metal center, as the lower drug concentration did not hinder diffusion from the MOF pores. As such, the optimal curcumin loading within the M-MOF-74 family was concluded to be greater than 30 wt % but less than 50 wt %. These experiments also revealed that using Mg-MOF-74 as a drug carrier produced a twofold enhancement in the release rate from 0.15 to 0.30 h1/2 compared to the other three metal centers, where Mg-MOF-74's improved pharmacokinetics were attributed to the increased group II Mg solubility compared to Ni, Co, or Zn transition metals. On the basis of these findings, it was concluded that to promote rapid pharmacokinetics, it is essential to use MOFs with more soluble metal centers to promote dissolution of the nanocarrier. While this study focused on M-MOF-74, we expect that this conclusion has implications to other crystallites as well.

Mixing Mg-MOF-74 with Zn-MOF-74: A Facile Pathway of Controlling the Pharmacokinetic Release Rate of Curcumin.

Recently, metal-organic frameworks (MOFs) have been widely employed as potential drug-delivery platforms; however, most studies have focused on the initial aspects of material development and have made little progress toward using MOFs as a means of controlling the pharmacokinetic rate of drug delivery. Nevertheless, it was recently determined that MOFs with highly soluble metal centers impart faster pharmacokinetic properties, so it stands to reason that combining two MOFs with different metal center solubilities could be used to control the pharmacokinetic release rate. To this end, in this study we varied the ratio of Mg-MOF-74 and Zn-MOF-74 between 80:20, 60:40, 40:60, and 20:80 wt % Mg:Zn to control the pharmacokinetic release rate of 30 wt % curcumin. The drug loading was characterized by using Fourier transform infrared spectroscopy and N2 physisorption, where it was confirmed that curcumin was impregnated successfully. More importantly, the drug delivery experiments in phosphate buffered saline from 0 to 24 h at 37.4 °C revealed that increasing the Mg-MOF-74 concentration enhanced both the raw amount of curcumin delivered and the pharmacokinetic rate of drug delivery. Specifically looking at the rate of drug delivery, drug diffusion constants of 0.17, 0.23, 0.24, and 0.26 h1/2 were calculated for the 20:80, 40:60, 60:40, and 80:20 Mg-Zn-MOF-74 samples, respectively, which indicated the profound relationship between the Mg-MOF-74 loading and the rate of curcumin delivery. In this regard, this study successfully demonstrated a potential pathway of controlling the pharmacokinetic rate of drug release from MOFs which can be considered a promising advancement in pharmacological medicine.

Investigating the microstructure of high-calcium fly ash-based alkali-activated material for aqueous Zn sorption.

The performance of adsorbents prepared by alkali activation of high calcium fly ash was investigated for removing aqueous Zn. Two formulations involving the use of NaOH and Na2SiO3 activating solutions were used to prepare the adsorbents that feature different microstructural characteristics. The Zn sorption data indicates a sorption process that is controlled by both chemisorption and intra-particle diffusion. The Na2SiO3-activated material displayed higher sorption rates compared to the NaOH-activated material. The sorption kinetics show strong dependence on the microstructures of the adsorbents, wherein the Na2SiO3-activated material featuring higher contents of amorphous phases (96 %mass) in the hydrated phase assemblage, with attendant improved porosity and surface area, performed better than the NaOH-activated material (86 %mass amorphous phases) which showed higher degree of crystallinity and coarse morphology. The Na2SiO3-activated material exhibited 100% Zn removal efficiency within the first 5 min in all studied initial adsorbate concentrations(corresponding to sorption capacity of up to 200 mg/g), while the NaOH-activated analogue tends to lag, reaching 99.99% Zn removal efficiency after about 240 min in most cases. The two formulations were also examined with thermodynamic modeling and the results agree with experimental data in indicating that the use of alkali-silicate activating solution is most suitable for converting high calcium fly ash into efficient adsorbent for removing aqueous heavy metals.

Direct Ink Writing of Metal Oxide/H-ZSM-5 Catalysts for n-Hexane Cracking: A New Method of Additive Manufacturing with High Metal Oxide Loading.

Previously, 3D printing of porous materials and metal oxides was limited to low loading metal loadings, as increasing the nitrate salt concentrations, which are used to generate the oxide component, gave rise to poor rheological properties beyond 10 wt %. In this study, we addressed this problem by directly printing insoluble oxides alongside H-ZSM-5 zeolite, which allowed for increased oxide loadings. Various metal oxides such as V2O5, ZrO2, Cr2O3, and Ga2O3 were doped onto H-ZSM-5 through the additive manufacturing method. Characterization and correlation between the X-ray diffraction, NH3-temperature-programmed desorption, O2-temperature programmed oxidation, temperature-programmed reduction, scanning electron microscopy-energy dispersive spectroscopy, and in situ CO2 DRIFTS experiments revealed that directly 3D printing metal oxides/H-ZSM-5 inks leads to significant modification in the surface properties and oxide bulk dispersion, thereby enhancing the composites' reducibility and giving rise to widely differing product distributions in n-hexane cracking reaction. The obtained metal oxide/zeolite structured materials were used as bifunctional structured catalysts for the selective formation of light olefins from hexane at 550-600 °C and GHSV = 9000 mL/gcatalst·h in a packed-bed reactor. Among the various compositions of metal oxides/H-ZSM-5 examined (i.e., 15 wt % Ga2O3, 15 wt % ZrO2, 15 wt % V2O5, 15 wt % Cr2O3, or 5 wt % Cr/10 wt % ZrO2/10 wt % V2O5/10 wt % Ga2O3 balanced with H-ZSM-5), the 15 wt % Cr/ZSM-5 monolith displayed the best n-hexane cracking performance, as it achieved 80-85% conversion of hexane with a 40% selectivity toward propylene, 30% selectivity toward ethylene, and 10% selectivity toward butene at 550 °C. The sample also showed zero benzene/toluene/xylene selectivity and no deactivation after 6 h. This study represents a proof-of-concept for tailoring customizable heterogeneous structured catalysts by directly 3D printing high loading of metal oxides/porous zeolite and is a breakthrough in material science.

Gel-Print-Grow: A New Way of 3D Printing Metal-Organic Frameworks.

3D printing offers an attractive means of forming structured metal-organic frameworks (MOFs), as this technique imparts digital geometric tuning to fit any process column. However, 3D-printed MOF structures are usually formed by suspending presynthesized particles into an ink for further processing. This leads to poor rheological properties as MOFs do not bind with inert binders. Herein, we address this problem by coordinating the MOF secondarily by 3D printing its gelated precursors. Specifically, we produced a printable sol-gel containing ∼70 wt % of HKUST-1 precursors and optimized the in situ growth conditions by varying the desolvation temperature and activation solvent. Analysis of the so-called gel-print-grow monoliths' properties as a function of the coordination variables revealed that desolvating at 120 °C produced fully formed MOF particles with comparable diffractive indices to the parent powder regardless of the activation solvent used. Assessment of the samples' textural properties revealed that washing in acetone or methanol produced the highest surface areas, pore volumes, and CO2 adsorption capacities, however, washing with methanol produced binder swelling and collapse of the printed structure, thereby indicating that washing with acetone was more effective overall. This study represents a promising way of 3D printing MOFs and a breakthrough in additive manufacturing, since the simple, high-throughput, framework detailed herein-whereby the synthesis temperature and washing solvent are varied to optimize MOF coordination-could easily be applied to other crystallites. As such, it is anticipated that this new and exciting method will provide new paths to shape engineer MOFs for applications in energy-intensive fields and beyond.

Optimizing ibuprofen concentration for rapid pharmacokinetics on biocompatible zinc-based MOF-74 and UTSA-74.

Metal-organic frameworks (MOFs) have potential as drug carriers on the basis of their surface areas and pore volumes that allow for high loading and fast release. This study investigated two biocompatible MOFs - Zn MOF-74 and UTSA-74 - for ibuprofen delivery. The effect of drug loading was studied by impregnating the MOFs with 30, 50, and 80 wt% ibuprofen. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and N2 physisorption. From SEM, the MOF structures were maintained at 30 wt% ibuprofen, however, became agglomerated at 50-80 wt% loading, as the drug deposited on the surface and adhered the particles to one another. In the physisorption measurements, the Zn MOF-74 samples decreased in surface area with ibuprofen loading, until they became zero at 80 wt%. In UTSA-74, the drug impregnation was less effective, as 35% of the original surface area was retained in the 80 wt% sample. On the basis of our drug release measurements, 50 wt% ibuprofen loading was found to be optimal on Zn MOF-74, as it gave rise to fast kinetics (k = 0.27 h-1/2) and high drug concentrations within the first 10 h. In UTSA-74, the fastest release rate was observed at 30 wt% loading (k = 0.22 h-1/2), as the poor impregnation efficiency blocked diffusion through the MOF pores at higher loading. Color changes of phosphate buffer saline (PBS) solutions at different time intervals also suggested that Zn MOF-74 decomposed during drug release, as it produced yellowing of the PBS solution. On the other hand, UTSA-74 did not discolor the PBS solution, and was concluded to not have dissolved during drug release. From these results, it was concluded that Zn MOF-74 was the superior drug carrier, as it could effectively deliver higher ibuprofen loadings and would dissolve in the process of drug release, thereby reducing its invasiveness in the human body.

Atomic Layer Deposited Ni/ZrO2-SiO2 for Combined Capture and Oxidation of VOCs.

This work reports on the development of novel Ni nanoparticle-deposited mixed-metal oxides ZrO2-SiO2 through atomic layer deposition (ALD) method and their application in combined capture and oxidation of benzene, as a model compound of aromatic VOCs. Concentrating ppm-level VOCs in situ, before their oxidation, offers a practical approach to reduce the catalyst inventory and capital cost associated with VOC emissions abatement. The benzene vapor adsorption isotherms were measured at 25 °C and in the pressure range of 0 to benzene saturation vapor pressure thereof (0.13 bar). In the combined capture-reaction tests, the materials were first exposed to ca. 86 100 ppmv benzene vapor at 25 °C, followed by desorption and catalytic oxidation while raising the bed temperature to 250 °C. The textural properties revealed that ALD of Ni or ZrO2 on SiO2 decreased surface area and pore volume, while sequential doping with ZrO2 and then Ni caused the otherwise. The benzene vapor adsorption isotherms followed the type-IV isotherm classification, revealing a combination of monolayer-multilayer and capillary condensation adsorption mechanisms in sequence. At saturation vapor pressure, an average equilibrium adsorption capacity of 15 mmol/g was obtained across the materials. However, the dynamic adsorption capacities were up to 50% less than the corresponding equilibrium uptake for the materials. Benzene desorption temperature was observed around 90 °C, and conversion of 85-95% and TOF of 1.28-16.42 mmolC6H6/molNi/s were obtained over the materials, with 3Ni/ZrO2-SiO2, prepared with 3 ALD cycles, exhibiting the maximum conversion and TOF indicating synergistic effects of Ni nanoparticles and ZrO2 support based on the number of ALD cycles. However, the yields of CO2 and H2O were about 5% and 40%, respectively. The small value of the CO2 yield was hypothesized to be due to simultaneous high-temperature adsorption of CO2 as the catalytic reaction progressed. The high adsorption affinity, low desorption temperature, and high catalytic activity of the materials investigated in this study made these materials as promising candidates for the abatement of BTX.

Amine-Based Latex Coatings for Indoor Air CO2 Control in Commercial Buildings.

High levels of indoor air CO2 in commercial buildings can lead to various health effects, commonly known as sick building syndrome. Passive control of indoor air CO2 through solid adsorbents incorporated into the paint offers a high potential to handle CO2 without utilizing much energy. This study focuses on incorporating silica-supported aminopolymers into a polyacrylic-based latex that could be used as a buffer material for the passive control of CO2 in enclosed environments. To maximize the effect of the pigment (adsorbent), paints were all prepared at critical pigment volume concentration (CPVC) levels. CO2 at 800 and 3000 ppm were used to asses both low and high level contaminations. The removal efficiency of the surface coatings was evaluated within typical time frames (10 h for adsorption and desorption). Our laboratory-scale chamber results indicated that the silica-tetraethylenepentamine-based paint with 70 wt % loading exhibits the best adsorption performance, comparable to that of the powder-based sorbent, with only a ∼20% decrease in the adsorption efficiency. Our results also revealed that the optimization of paint formulation is critical in passively controlling indoor air CO2. The findings of this study highlight the potential of amine-based adsorbents as pigments in high PVC paints for indoor CO2 control in commercial buildings.

All-Nanoporous Hybrid Membranes: Redefining Upper Limits on Molecular Separation Properties.

New membrane-based molecular separation processes are an essential part of the strategy for sustainable chemical production. A large literature on "hybrid" or "mixed-matrix" membranes exists, in which nanoparticles of a higher-performance porous material are dispersed in a polymeric matrix to boost performance. We demonstrate that the hybrid membrane concept can be redefined to achieve much higher performance if the membrane matrix and the dispersed phase are both nanoporous crystalline materials, with no polymeric phase. As the first example of such a system, we find that surface-treated nanoparticles of the zeolite MFI can be incorporated in situ during growth of a polycrystalline membrane of the MOF ZIF-8. The resulting all-nanoporous hybrid membrane shows propylene/propane separation characteristics that exceed known upper-bound performance limits defined for polymers, nanoporous materials, and polymer-based hybrid membranes. This serves as a starting point for a new generation of chemical separation membranes containing interconnected nanoporous crystalline phases.

UTSA-16 Growth within 3D-Printed Co-Kaolin Monoliths with High Selectivity for CO2/CH4, CO2/N2, and CO2/H2 Separation.

Honeycomb monoliths loaded with metal-organic frameworks (MOFs) are highly desirable adsorption contactors because of their low-pressure drop, rapid mass-transfer kinetics, and high-adsorption capacity. Moreover, three-dimensional (3D)-printing technology renders direct material modification a realistic and economic prospect. In this study, 3D printing was utilized to impregnate kaolin-based monolith with UTSA-16 metal formation precursor (Co), whereupon an internal growth was facilitated via a solvothermal synthesis approach. The cobalt weight loading in the kaolin support was varied systematically to optimize the MOF growth while retaining monolith mechanical integrity. The obtained UTSA-16 monolith with 90 wt % loading exhibited similar textural features and adsorption characteristics to its powder analogue while improving upon structural integrity. In comparison to previously developed 3D-printed UTSA-16 monoliths, the UTSA-16-kaolin monolith not only showed higher MOF loading but also higher compression stress, indicative of its robust structure. Furthermore, the 3D-printed UTSA-16-kaolin monolith displayed a comparable CO2 adsorption capacity to the UTSA-16 powder (3.1 vs 3.5 mmol/g at 25 °C and 1 bar), which was proportional to its loading. Selectivity values of 49, 238, and 3725 were obtained for CO2/CH4, CO2/N2, and CO2/H2, respectively, demonstrating good separation potential of the 3D-printed MOF monolith for various gas mixtures, as determined by both equilibrium and dynamic adsorption measurements. Overall, this study provides a novel route for the fabrication of UTSA-16-loaded monoliths, which demonstrate both high MOF loading and mechanical integrity that could be readily applied to various CO2 capture applications.