Enhanced aging properties of HKUST-1 in hydrophobic mixed-matrix membranes for ammonia adsorption.

Metal-organic frameworks (MOFs) in their free powder form have exhibited superior capacities for many gases when compared to other materials, due to their tailorable functionality and high surface areas. Specifically, the MOF HKUST-1 binds small Lewis bases, such as ammonia, with its coordinatively unsaturated copper sites. We describe here the use of HKUST-1 in mixed-matrix membranes (MMMs) prepared from polyvinylidene difluoride (PVDF) for the removal of ammonia gas. These MMMs exhibit ammonia capacities similar to their hypothetical capacities based on the weight percent of HKUST-1 in each MMM. HKUST-1 in its powder form is unstable toward humid conditions; however, upon exposure to humid environments for prolonged periods of time, the HKUST-1 MMMs exhibit outstanding structural stability, and maintain their ammonia capacity. Overall, this study has achieved all of the critical and combined elements for real-world applications of MOFs: high MOF loadings, fully accessible MOF surfaces, enhanced MOF stabilization, recyclability, mechanical stability, and processability. This study is a critical step in advancing MOFs to a stable, usable, and enabling technology

Investigating the cheletropic reaction between sulfur dioxide and butadiene-containing linkers in UiO-66

UiO-66 and a muconic-acid-functionalized derivative of UiO-66 (UiO-66-MA) were synthesized via the solvothermal method to determine if the muconic acid could undergo a cheletropic reaction in the presence of sulfur dioxide inside the MOF. Both MOFs were exposed to a constant flow of sulfur dioxide, and UiO-66-MA was observed to take up three times more sulfur dioxide than unfunctionalized UiO-66. Despite the improved uptake of sulfur dioxide in UiO-66-MA, NMR and IR data indicate that no chemical change occurred to the muconic acid indicating that a cheletropic reaction did not occur. We thus propose that the increased adsorption is either due to an interaction between the sulfur dioxide and un-bound carboxylic acid from the muconic acid or a favourable interaction between the butadiene of muconic acid and sulfur dioxide.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Tailoring the Adsorption and Reaction Chemistry of the Metal–Organic Frameworks UiO-66, UiO-66-NH₂, and HKUST‑1 via the Incorporation of Molecular Guests

Metal–organic frameworks (MOFs) are versatile materials highly regarded for their porous nature. Depending on the synthetic method, various guest molecules may remain in the pores or can be systematically loaded for various reasons. Herein, we present a study that explores the effect of guest molecules on the adsorption and reactivity of the MOF in both the gas phase and solution. The differences between guest molecule interactions and the subsequent effects on their activity are described for each system. Interestingly, different effects are observed and described in detail for each class of guest molecules studied. We determine that there is a strong effect of alcohols with the secondary building unit of UiO MOFs, while Lewis bases have an effect on the reactivity of the −NH₂ group in UiO-66-NH₂ and adsorption by the coordinatively unsaturated copper sites in HKUST-1. These effects must be considered when determining synthesis and activation methods of MOFs toward various applications

Facile Synthesis and Direct Activation of Zirconium Based Metal–Organic Frameworks from Acetone

In recent years much emphasis has been placed on the synthesis of highly novel metal–organic frameworks (MOFs) with general disregard to development of sustainable synthesis techniques. A novel synthesis of UiO-66 and UiO-66-NH₂, two highly stable MOFs that have shown much promise in the area of catalysis and reactive removal of small molecules, from acetone is demonstrated here. Using this method, the MOFs can be activated by simple heating under vacuum without the need for solvent exchange, which can be a timely processing step that requires the use of large amounts of solvent. The activity of the series of MOFs synthesized at various temperatures was determined by the rate of hydrolysis of methyl paraoxon and the reactive capacity of UiO-66-NH₂ with chlorine gas. Direct correlations were observed between synthesis temperature, crystallinity, BET surface area, and activity of the MOFs

Enhanced aging properties of HKUST-1 in hydrophobic mixed-matrix membranes for ammonia adsorption.

Metal-organic frameworks (MOFs) in their free powder form have exhibited superior capacities for many gases when compared to other materials, due to their tailorable functionality and high surface areas. Specifically, the MOF HKUST-1 binds small Lewis bases, such as ammonia, with its coordinatively unsaturated copper sites. We describe here the use of HKUST-1 in mixed-matrix membranes (MMMs) prepared from polyvinylidene difluoride (PVDF) for the removal of ammonia gas. These MMMs exhibit ammonia capacities similar to their hypothetical capacities based on the weight percent of HKUST-1 in each MMM. HKUST-1 in its powder form is unstable toward humid conditions; however, upon exposure to humid environments for prolonged periods of time, the HKUST-1 MMMs exhibit outstanding structural stability, and maintain their ammonia capacity. Overall, this study has achieved all of the critical and combined elements for real-world applications of MOFs: high MOF loadings, fully accessible MOF surfaces, enhanced MOF stabilization, recyclability, mechanical stability, and processability. This study is a critical step in advancing MOFs to a stable, usable, and enabling technology

Engineering UiO-66-NH₂ for Toxic Gas Removal

The metal–organic framework UiO-66-NH₂ was synthesized in a scaled batch of approximately 100 g. The material was then pressed into small pellets at pressures ranging from 5000 to 100000 psi to determine the effects on porosity and crystal structure. Nitrogen isotherm data and powder X-ray diffraction data indicate that the structure remains intact up to 25000 psi, with only a slight decrease in surface area. The structure exhibits significant degradation at pressures above 25000 psi. Subsequently, the powder was pressed at 5000 psi and then crushed and sieved into 20 × 40 mesh granules for evaluation against ammonia and cyanogen chloride in a breakthrough system simulating individual protection filters and respirator cartridges. The MOF showed capacity similar to that of a broad-spectrum carbon for both ammonia and cyanogen chloride; however, the breakthrough times, especially for cyanogen chloride, were dramatically reduced, likely as a result of mass-transfer limitations from the completely microporous MOF

Enhanced Stability of Cu-BTC MOF via Perfluorohexane Plasma-Enhanced Chemical Vapor Deposition

Metal organic frameworks (MOFs) are a leading class of porous materials for a wide variety of applications, but many of them have been shown to be unstable toward water. Cu-BTC (1,3,5 benzenetricarboxylic acid, BTC) was treated with a plasma-enhanced chemical vapor deposition (PECVD) of perfluorohexane creating a hydrophobic form of Cu-BTC. It was found that the treated Cu-BTC could withstand high humidity and even submersion in water much better than unperturbed Cu-BTC. Through Monte Carlo simulations it was found that perfluorohexane sites itself in such a way within Cu-BTC as to prevent the formation of water clusters, hence preventing the decomposition of Cu-BTC by water. This PECVD of perfluorohexane could be exploited to widen the scope of practical applications of Cu-BTC and other MOFs

Direct Surface Growth Of UIO-66-NH₂ on Polyacrylonitrile Nanofibers for Efficient Toxic Chemical Removal

Direct solvothermal growth of the metal–organic framework (MOF) UiO-66-NH₂ on polymer surface was successfully demonstrated. By using acetone as the solvent for synthesis instead of <i>N</i>,<i>N</i>-dimethylformamide, polymers like polyacrylonitrile (PAN) can be used directly in the solvothermal synthesis step to grow MOF on the polymer surface. We use X-ray diffraction and FT-IR to confirm our method produces crystalline UiO-66-NH2 on the surface of electrospun PAN nanofibers. Characterization of this type of composite revealed up to 50 wt % MOF loading according to nitrogen isotherms. Since the MOFs are located on the surface of the polymer fibers, the composites are capable of high loadings of chlorine gas. Compared to electrospun composites made with preformed UiO-66-NH₂, the in situ method is a simple alternative that produces composites with higher MOF loading