skip to main content

Title: Membrane-supported metal organic framework based nanopacked bed for protection against toxic vapors and gases
Defense against small molecule toxic gases is an important aspect of protection against chemical and biological threat as well as chemical releases from industrial accidents. Current protective respirators/garments cannot effectively block small molecule toxic gases and vapors and retain moisture transmission capability without a heavy burden. Here, we developed a nanopacked bed of nanoparticles of UiO-66-NH₂ metal organic framework (MOF) by synthesizing them in the pores of microporous expanded polytetrafluoroethylene (ePTFE) membranes. The submicron scale size of membrane pores ensures a large surface area of MOF nanoparticles which can capture/adsorb and react with toxic gas molecules efficiently. It was demonstrated that the microporous ePTFE membrane with UiO-66-NH₂ MOF grown inside and around the membrane can defend against ammonia for a significant length of time while allowing passage of moisture and nitrogen. It was also demonstrated that the MOF-loaded ePTFE membrane could provide significant protection from Cl₂ intrusion as well as intrusion from 2-chloroethyl ethyl sulfide (CEES) (a simulant for sulfur mustard). Such MOF-filled membranes exhausted by NH₃ breakthrough experiments were regenerated conveniently by heating at 60 °C for one week under vacuum for further/repeated use; a single regenerated membrane could block NH₃ for 200–300 min. The moisture permeability of such more » a membrane/nanopacked bed was considerably above the breathability threshold value of 2000 g/m² -day. The results suggest that microporous membranes filled with reactive MOF nanoparticles could be designed as protective barriers against toxic gases/vapors, e.g., NH₃ and Cl₂ and yet be substantially permeable to H₂O and air. « less
; ; ; ;
Award ID(s):
Publication Date:
Journal Name:
Separation and purification technology
Page Range or eLocation-ID:
Sponsoring Org:
National Science Foundation
More Like this
  1. Traditional protective garments loaded with activated carbons to remove toxic gases are very bulky. Novel graphene oxide (GO) flake-based composite lamellar membrane structure is being developed as a potential component of a garment for protection against chemical warfare agents (CWAs) represented here by simulants, dimethyl methyl phosphonate (DMMP) (a sarin-simulant), and 2-chloroethyl ethyl sulfide (CEES) (a simulant for sulfur mustard), yet allowing a high-moisture transmission rate. GO flakes of dimensions 300−800 nm, 0.7−1.2 nm thickness and dispersed in an aqueous suspension were formed into a membrane by vacuum filtration on a porous poly(ether sulfone) (PES) or poly(ether ether ketone) (PEEK)more »support membrane for noncovalent π−π interactions with GO flakes. After physical compression of such a membrane, upright cup tests indicated that it can block toluene for 3−4 days and DMMP for 5 days while exhibiting excellent water vapor permeation. Further, they display very low permeances for small-molecule gases/vapors. The GO flakes underwent crosslinking later with ethylenediamine (EDA) introduced during the vacuum filtration followed by physical compression and heating. With a further spray coating of polyurethane (PU), these membranes could be bent without losing barrier properties vis-à-vis the CWA simulant DMMP for 5 days; a membrane not subjected to bending blocked DMMP for 15 days. For the PEEK-EDA-GO-PU compressed membranes after bending, the separation factors of H2O over other species for low gas flow rates in the dynamic moisture permeation cell (DMPC) are: αH2O−He is 42.3; αH2O−N2 is 110; and αH2O−ethane is 1800. At higher gas flow rates in the DMPC, the moisture transmission rate goes up considerably due to reduced boundary layer resistances and exceeds the threshold water vapor flux of 2000 g/(m2·day) that defines a breathable fabric. This membrane displayed considerable resistance to permeation by CEES as well. The PES-EDA-GO-PU-compressed membrane shows good mechanical property under tensile strength tests.« less
  2. With the increased bacteria-induced hospital-acquired infections (HAIs) caused by bio-contaminated surfaces, the requirement for a safer and more efficient antibacterial strategy in designing personal protective equipment (PPE) such as N95 respirators is rising with urgency. Herein, a self-decontaminating nanofibrous filter with a high particulate matter (PM) filtration efficiency was designed and fabricated via a facile electrospinning method. The fillers implemented in the electrospun nanofibers were constructed by grafting a layer of antibacterial polymeric quaternary ammonium compound (QAC), that is, poly[2-(dimethyl decyl ammonium) ethyl methacrylate] (PQDMAEMA), onto the surface of metal–organic framework (MOF, UiO-66-NH 2 as a model) to form themore »active composite UiO-PQDMAEMA. The UiO-PQDMAEMA filter demonstrates an excellent PM filtration efficiency (>95%) at the most penetrating particle size (MPPS) of 80 nm, which is comparable to that of the commercial N95 respirators. Besides, the UiO-PQDMAEMA filter is capable of efficiently killing both Gram-positive ( S. epidermidis ) and Gram-negative ( E. coli ) airborne bacteria. The strong electrostatic interactions between the anionic cell wall of the bacteria and positively charged nitrogen of UiO-PQDMAEMA are the main reasons for severe cell membrane disruption, which leads to the death of bacteria. The present work provides a new avenue for combating air contamination by using the QAC-modified MOF-based active filters.« less
  3. Isothermal membrane-based air dehumidification (IMAD) is much more energy-efficient and economical than traditional air-dehumidification technologies. There are, however, no practical IMAD process technologies currently available mainly due to limitations of current membranes. Ionic liquids (ILs) are a promising air-dehumidification membrane material. Current supported IL membranes suffer from poor stability, limiting their performances. Herein, we propose new stable IL membranes, encapsulated IL membranes (EILMs) by encapsulating 1-butyl-3-methylimidazolium bromide ([C 4 MIM][Br]) into ultrathin polycrystalline UiO-66-NH 2 metal–organic framework membranes via a ship-in-a-bottle method. The stability of IL membranes is significantly enhanced due to the IL entrapped in the pore cages ofmore »UiO-66-NH 2 . The EILMs show unprecedentedly high H 2 O permeance (∼2.36 × 10 −4 mol m −2 s −1 Pa −1 ), an order of magnitude greater than that of the most permeable air-dehumidification membranes reported so far. Furthermore, the encapsulated [C 4 MIM][Br] drastically increases the H 2 O/N 2 separation factor to ∼1560, satisfying the minimally required H 2 O/N 2 separation performance for commercially viable air-dehumidification.« less
  4. Organic solvent filtration is an important industrial process. It is widely used in pharmaceutical manufacturing, chemical processing industry, semiconductor industry, auto assembly etc. Most of the particle filtration studies reported in open literature dealt with aqueous suspension medium. The current work has initiated a study of cross-flow solvent filtration behavior of microporous ethylene chlorotrifluoroethylene (ECTFE) membranes using 12 nm silica nanoparticles suspended in an aqueous solution containing 25% ethanol. In the constant pressure mode of operation of cross-flow microfiltration (MF), permeate samples were collected at different time intervals. The permeate particle size distribution (PSD) results for different experiments were identical.more »Particle agglomerates having less than 100 nm size can pass through the membrane; some fouling was observed. The governing fouling mechanisms for tests operated using 3.8×10−3 kg/m3 (3.8 ppm) at 6.9×103 Pag and 1.4×104 Pag were pore blocking. For tests conducted using 3.8×10−3 kg/m3 (3.8 ppm) at 27.6×103 Pag (4 psig) and 1.9×10−3 kg/m3 (1.9 ppm) at 6.9×103, 13.8×103 and 27.6×103 Pag (1, 2 and 4 psig), the mechanism was membrane resistance control. Less particles got embedded in membrane pores in experiments operated using suspensions with lower or higher particle concentrations with a higher transmembrane pressure. This is in good agreement with the values of the shear rate in the pore flow and scanning electron microscope images of the membrane after MF. In the dead-end mode of operation of solvent filtration using methanol, ethanol and 2-propanol, the permeate flux behavior follows Jmethanol > Jethanol > J2-propanol at all testing pressures. The values of permeance (kg/m2-s-Pa) determined from the slope of the linear plot of filtration flux vs. the applied pressure difference across the membrane, were 3.9×10−4, 2.3×10−4 and 3.0×10−5 for methanol, ethanol and 2-propanol, respectively. Further exploration was made on solvent sorption results reported earlier. The critical temperature of selected solvents shows a better correlation with solvent sorption rather than the solubility parameter.« less
  5. Continued integration of technologies capable of achieving higher degrees of sustainability while meeting global material and energy demands is of singular importance in halting human-caused climate change. Gas separation membranes composed of metal–organic frameworks (MOFs) are considered promising candidates for such integration; owing to their modular, scalable nature and high degree of tunability they are seen essential to maintain separation functionality. However, prior to sustainable implementation, both an evaluation of MOF characteristics and an intensive examination of MOF–gas molecule interactions are necessary to fully understand the fundamental separation criteria as well as to define suitable ranges of gas separation conditions.more »Herein, we present our findings on the greenhouse gas separation capabilities of the hydrophilic, Al-based MIL-160 in the selective uptake of carbon dioxide (CO 2 ) from other relevant greenhouse gases, i.e. , methane (CH 4 ), sulfur dioxide (SO 2 ), nitrogen dioxide (NO 2 ), and nitric oxide (NO), including gravimetric solubility, permeability, and diffusivity calculations. We found that a MIL-160 membrane has excellent applicability in the separation of gases of varying electronegativities, with a diffusivity selectivity of 72.0, 9.53, and 13.8 for CH 4 , NO 2 , and NO, respectively, relative to CO 2 . Further, we demonstrate that the selectivity at which gas molecules diffuse through the MIL-160 membrane varies strongly with the simulation pressure, suggesting that such membrane system is potentially an ideal candidate for the development of pressure-swing adsorption processes that achieve gas separations efficiently while mitigating the emission of greenhouse gases.« less