27 research outputs found
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
Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia
Tailoring the Adsorption and Reaction Chemistry of the MetalâOrganic Frameworks UiO-66, UiO-66-NH<sub>2</sub>, and HKUSTâ1 via the Incorporation of Molecular Guests
Metalâorganic
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 âNH<sub>2</sub> group in
UiO-66-NH<sub>2</sub> 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 MetalâOrganic Frameworks from Acetone
In recent years much emphasis has
been placed on the synthesis
of highly novel metalâorganic frameworks (MOFs) with general
disregard to development of sustainable synthesis techniques. A novel
synthesis of UiO-66 and UiO-66-NH<sub>2</sub>, 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-NH<sub>2</sub> with chlorine gas. Direct correlations were
observed between synthesis temperature, crystallinity, BET surface
area, and activity of the MOFs
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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-NH<sub>2</sub> for Toxic Gas Removal
The metalâorganic
framework UiO-66-NH<sub>2</sub> 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 Ă 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-NH<sub>2</sub> on Polyacrylonitrile Nanofibers for Efficient Toxic Chemical Removal
Direct solvothermal
growth of the metalâorganic framework
(MOF) UiO-66-NH<sub>2</sub> 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-NH<sub>2</sub>, the in situ method is a simple alternative that produces composites
with higher MOF loading
MOFabric: Electrospun Nanofiber Mats from PVDF/UiO-66-NH<sub>2</sub> for Chemical Protection and Decontamination
Textiles
capable of capture and detoxification of toxic chemicals,
such as chemical-warfare agents (CWAs), are of high interest. Some
metalâorganic frameworks (MOFs) exhibit superior reactivity
toward CWAs. However, it remains a challenge to integrate powder MOFs
into engineered materials like textiles, while retaining functionalities
like crystallinity, adsorptivity, and reactivity. Here, we present
a simple method of electrospinning UiO-66-NH<sub>2</sub>, a zirconium
MOF, with polyvinylidene fluoride (PVDF). The electrospun composite,
which we refer to as âMOFabricâ, exhibits comparable
crystal patterns, surface area, chlorine uptake, and simulant hydrolysis
to powder UiO-66-NH<sub>2</sub>. The MOFabric is also capable of breaking
down GD (<i>O</i>-pinacolyl methylphosphonofluoridae) faster
than powder UiO-66-NH<sub>2.</sub> Half-life of GD monitored by solid-state
NMR for MOFabric is 131 min versus 315 min on powder UiO-66-NH<sub>2</sub>