Highly
tunable metal–organic framework (MOF) materials, including,
for example, UiO-66-NH2, are known to be effective catalysts
to degrade chemical warfare agents (CWAs) with half-lives near 1 min.
Therefore, many researchers have been actively working on producing
supported MOF materials to improve application effectiveness by using
relatively slow solvothermal synthesis or repetitious stepwise layer-by-layer
methods. Herein, we demonstrate a facile route to rapidly assemble
presynthesized UiO-66-NH2 crystals onto nonwoven polypropylene
(PP) fibrous mats at ambient temperature. Crystal assembly is chemically
directed using β-cyclodextrin (β-CD) and cetyltrimethylammonium
bromide (CTAB) as surfactant assembly agents, where the agents quickly
(within 5 min) self-assemble on the crystal surface and promote physically
robust chemical surface attachment while simultaneously impeding solution-phase
crystal agglomeration. Furthermore, we find that when the PP is preconditioned
using conformal metal oxide thin films, including Al2O3, TiO2, or ZnO formed via atomic layer deposition
(ALD), the hydrophilic metal oxide surface further helps improve assembly
uniformity and MOF mass loading, producing MOF crystal loading as
high as 40 wt % and an overall BET surface area exceeding 200 m2/g(MOF+Fiber). Using these surface-assembled MOFs,
we observe catalytic degradation of dimethyl 4-nitrophenyl phosphate
(DMNP), a CWA simulant, with a half-life of less than 5 min.
Metal-organic frameworks (MOFs) chemically bound to polymeric microfibrous textiles show promising performance for many future applications. In particular, Zr-based UiO-66-family MOF-textiles have been shown to catalytically degrade highly toxic chemical warfare agents (CWAs), where favorable MOF/polymer bonding and adhesion are attained by placing a nanoscale metal-oxide layer on the polymer fiber preceding MOF growth. To date, however, the nucleation mechanism of Zr-based MOFs on different metal oxides and how product performance is affected are not well understood. Herein, we provide new insight into how different inorganic nucleation films (i.e., AlO, ZnO, or TiO) conformally coated on polypropylene (PP) nonwoven textiles via atomic layer deposition (ALD) influence the quality, overall surface area, and the fractional yield of UiO-66-NH MOF crystals solvothermally grown on fiber substrates. Of the materials explored, we find that TiO ALD layers lead to the most effective overall MOF/fiber adhesion, uniformity, and a rapid catalytic degradation rate for a CWA simulant, dimethyl p-nitrophenyl phosphate (DMNP) with t = 15 min, 580-fold faster than the catalytic performance of untreated PP textiles. Interestingly, compared to ALD TiO and AlO, ALD ZnO induces a larger MOF yield in solution and mass loading on PP fibrous mats. However, this larger MOF yield is ascribed to chemical instability of the ZnO layer under MOF formation condition, leading to Zn ions that promote further homogeneous MOF growth. Insights presented here improve understanding of compatibility between active MOF materials and substrate surfaces, which we believe will help advanced MOF composite materials for a variety of useful functions.
The threat associated with chemical warfare agents (CWAs) motivates the development of new materials to provide enhanced protection with a reduced burden. Metal-organic frame-works (MOFs) have recently been shown as highly effective catalysts for detoxifying CWAs, but challenges still remain for integrating MOFs into functional filter media and/or protective garments. Herein, we report a series of MOF-nanofiber kebab structures for fast degradation of CWAs. We found TiO coatings deposited via atomic layer deposition (ALD) onto polyamide-6 nanofibers enable the formation of conformal Zr-based MOF thin films including UiO-66, UiO-66-NH , and UiO-67. Cross-sectional TEM images show that these MOF crystals nucleate and grow directly on and around the nanofibers, with strong attachment to the substrates. These MOF-functionalized nanofibers exhibit excellent reactivity for detoxifying CWAs. The half-lives of a CWA simulant compound and nerve agent soman (GD) are as short as 7.3 min and 2.3 min, respectively. These results therefore provide the earliest report of MOF-nanofiber textile composites capable of ultra-fast degradation of CWAs.
Rapid room-temperature synthesis of metal-organic frameworks (MOFs) is highly desired for industrial implementation and commercialization. Here we find that a (Zn,Cu) hydroxy double salt (HDS) intermediate formed in situ from ZnO particles or thin films enables rapid growth (<1 min) of HKUST-1 (Cu3(BTC)2) at room temperature. The space-time-yield reaches >3 × 10(4) kg·m(-3)·d(-1), at least 1 order of magnitude greater than any prior report. The high anion exchange rate of (Zn,Cu) hydroxy nitrate HDS drives the ultrafast MOF formation. Similarly, we obtained Cu-BDC, ZIF-8, and IRMOF-3 structures from HDSs, demonstrating synthetic generality. Using ZnO thin films deposited via atomic layer deposition, MOF patterns are obtained on pre-patterned surfaces, and dense HKUST-1 coatings are grown onto various form factors, including polymer spheres, silicon wafers, and fibers. Breakthrough tests show that the MOF-functionalized fibers have high adsorption capacity for toxic gases. This rapid synthesis route is also promising for new MOF-based composite materials and applications.
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