Environmental challenges especially air pollution (particulate matter (PM) and toxic gases) pose serious threats to public health globally. Metal–organic frameworks (MOFs) are crystalline materials ...with high porosity, tunable pore size, and rich functionalities, holding the promise for poisonous pollutants capture. Here, nanocrystals of four unique MOF structures are processed into nanofibrous filters (noted as MOFilter) with high MOF loadings (up to 60 wt %). The MOFilters show high PM removal efficiencies up to 88.33 ± 1.52% and 89.67 ± 1.33% for PM2.5 and PM10, respectively, in the hazy environment, and the performance remains largely unchanged over 48 h of continuous filtration. For the first time, the interactions between such porous crystalline material and particulate pollutants were explored. These thin MOFilters can further selectively capture and retain SO2 when exposed to a stream of SO2/N2 mixture, and their hierarchical nanostructures can easily permeate fresh air at high gas flow rate with the pressure drop <20 Pa.
Through layer-by-layer (LBL) deposition of a graphene oxide (GO) suspension on a semicontinuous ZIF-8 layer, we have developed a novel bicontinuous ZIF-8@GO membrane. Since only the gaps between the ...ZIF-8 crystals are sealed by the GO layer due to capillary forces and covalent bonds, the gas molecules can only permeate through the ZIF-8 micropore system (0.34 nm). Therefore, the ZIF-8@GO membranes show high hydrogen selectivity. At 250 °C and 1 bar, the mixture separation factors of H2/CO2, H2/N2, H2/CH4, and H2/C3H8 are 14.9, 90.5, 139.1, and 3816.6, with H2 permeances of about 1.3 × 10–7 mol·m–2·s–1·Pa–1, which is promising for hydrogen separation and purification by molecular sieving.
“Where do we go from here?” is the underlying question regarding the future (perhaps foreseeable) developments in computational chemistry. Although this young discipline has already permeated ...practically all of chemistry, it is likely to become even more powerful with the rapid development of computational hard‐ and software.
This study reports a new interlayer decoration method for fabricating thin film composite (TFC) forward osmosis (FO) membranes. Metal–organic framework (UiO-66) particles were dispersed at the ...aqueous–organic interface before interfacial polymerization. Both the TFC membrane without UiO-66 and the conventionally UiO-66 incorporated membrane prepared by interfacial polymerization were fabricated as the control for comparison. Compared with the two control membranes, the interlayer decoration method prepared TFC membrane under an optimized UiO-66 loading showed improved water permeability, salt rejection, and significantly reduced structural parameters. At a much lower UiO-66 loading, with only 5% of the amount used for the conventional incorporation method, the interlayer decorated TFC membrane exhibited significantly enhanced FO water flux and selectivity compared with the conventionally UiO-66 incorporated membrane. Such promising performance is mainly attributed to the unique interlayer UiO-66 decorated structure, in which water molecules can permeate through the channel apertures of UiO-66 nanoparticles, while other hydrated ions can be effectively rejected. This study demonstrates that interlayer decoration by UiO-66 between the polyamide layer and the porous support layer is a promising and economic way to develop new FO membranes with high permeability and selectivity.
In the field of nanofluidics, it has been an ultimate but seemingly distant goal to controllably fabricate capillaries with dimensions approaching the size of small ions and water molecules. We ...report ion transport through ultimately narrow slits that are fabricated by effectively removing a single atomic plane from a bulk crystal. The atomically flat angstrom-scale slits exhibit little surface charge, allowing elucidation of the role of steric effects. We find that ions with hydrated diameters larger than the slit size can still permeate through, albeit with reduced mobility. The confinement also leads to a notable asymmetry between anions and cations of the same diameter. Our results provide a platform for studying the effects of angstrom-scale confinement, which is important for the development of nanofluidics, molecular separation, and other nanoscale technologies.
Permeability (P m) across biological membranes is of fundamental importance and a key factor in drug absorption, distribution, and development. Although the majority of drugs will be charged at some ...point during oral delivery, our understanding of membrane permeation by charged species is limited. The canonical model assumes that only neutral molecules partition into and passively permeate across membranes, but there is mounting evidence that these processes are also facile for certain charged species. However, it is unknown whether such ionizable permeants dynamically neutralize at the membrane surface or permeate in their charged form. To probe protonation-coupled permeation in atomic detail, we herein apply continuous constant-pH molecular dynamics along with free energy sampling to study the permeation of a weak base propranolol (PPL), and evaluate the impact of including dynamic protonation on P m. The simulations reveal that PPL dynamically neutralizes at the lipid–tail interface, which dramatically influences the permeation free energy landscape and explains why the conventional model overestimates the assigned intrinsic permeability. We demonstrate how fixed-charge-state simulations can account for this effect, and propose a revised model that better describes pH-coupled partitioning and permeation. Our results demonstrate how dynamic changes in protonation state may play a critical role in the permeation of ionizable molecules, including pharmaceuticals and drug-like molecules, thus requiring a revision of the standard picture.
The seeming contradiction that K
channels conduct K
ions at maximal throughput rates while not permeating slightly smaller Na
ions has perplexed scientists for decades. Although numerous models have ...addressed selective permeation in K
channels, the combination of conduction efficiency and ion selectivity has not yet been linked through a unified functional model. Here, we investigate the mechanism of ion selectivity through atomistic simulations totalling more than 400 μs in length, which include over 7,000 permeation events. Together with free-energy calculations, our simulations show that both rapid permeation of K
and ion selectivity are ultimately based on a single principle: the direct knock-on of completely desolvated ions in the channels' selectivity filter. Herein, the strong interactions between multiple 'naked' ions in the four filter binding sites give rise to a natural exclusion of any competing ions. Our results are in excellent agreement with experimental selectivity data, measured ion interaction energies and recent two-dimensional infrared spectra of filter ion configurations.
•The removal efficiencies for CAP in water by PS activated by Fe2+ and ZVI were studied.•CAP was effectively removed by the ZVI–PS system at a broad pH range of 3–10.•CAP removal was significantly ...influenced by operational parameters.•The ZVI–PS system shows potential prospects in wastewater or even concentrated wastewater treatment.•An oxidation pathway was proposed for CAP removal by the ZVI–PS system.
This study evaluated the removal of chloramphenicol (CAP) by persulfate (PS) activated by Fe2+ and zerovalent iron (ZVI). Results showed that the Fe2+–PS system ineffectively degraded CAP. However, CAP oxidation accelerated as the number of Fe2+ portions added increased. Comparing with Fe2+, up to 96.1% of CAP was degraded when ZVI was employed as an alternative source of Fe2+. The ZVI–PS system was effective in a broader initial pH range from 3 to 10, and low pH promoted CAP degradation. In addition, the results of scavenging tests suggested that HO, SO4− and O2− contributed to the overall degradation performance, but HO predominated at all pH levels used. The rate of CAP removal slightly increased upon the addition of 1mM Cl−, but adding Cl− at concentrations higher than 1mM apparently inhibited CAP degradation. HCO3−, NO3−, NO2−, H2PO4−, HPO42−, and HA significantly inhibited CAP decomposition. Up to 92.8%, 94.7%, and 75.7% of CAP were removed from the filtrate, permeate, and retentate phases of wastewater, respectively. This result indicated that the ZVI–PS system can significantly remove CAP from wastewater and even concentrated wastewater. The intermediate products during oxidation were identified, and the degradation pathways of CAP were tentatively proposed.
A graphene oxide (GO) membrane is supported on a ceramic hollow fiber prepared by a vacuum suction method. This GO membrane exhibited excellent water permeation for dimethyl carbonate/water mixtures ...through a pervaporation process. At 25 °C and 2.6 wt % feed water content, the permeate water content reached 95.2 wt % with a high permeation flux (1702 g m−2 h−1).
On a roll: A graphene oxide (GO) membrane (see picture, dark gray) was prepared on a ceramic hollow fiber (light gray) by a vacuum suction method. The resulting GO membrane exhibits excellent selective water permeation of aqueous dimethyl carbonate solution (water: purple; Me2CO3: red; scale bar: 1.5 μm).
One-atom-thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. We show that monolayers of graphene and boron nitride can be used to ...separate hydrogen ion isotopes. Using electrical measurements and mass spectrometry, we found that deuterons permeate through these crystals much slower than protons, resulting in a separation factor of ≈10 at room temperature. The isotope effect is attributed to a difference of ≈60 milli–electron volts between zero-point energies of incident protons and deuterons, which translates into the equivalent difference in the activation barriers posed by two-dimensional crystals. In addition to providing insight into the proton transport mechanism, the demonstrated approach offers a competitive and scalable way for hydrogen isotope enrichment.
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