Sieving Effect Research Articles

The Molecular Sieve Effect in the Adsorption of Gold Cyanide on Carbon Adsorbents

The Molecular Sieve Effect in the Adsorption of Gold Cyanide on Carbon Adsorbents

Large-Area Fabrication of Ultrathin Metal-Organic Framework Membranes.

Metal-organic framework (MOF)-based membranes, featuring potential molecular sieving effects and therefore capable of surmounting the ubiquitous trade-off between membrane selectivity and permeability, hold great promise for multitudinous chemical separations. Nevertheless, it remains highly challenging for the large-area fabrication of ultrathin MOF membranes with variable thickness, great homogeneity, and preferential orientation. Herein, this work reports the facile fabrication of ultrathin (down to 20nm) NUS-8 membranes in large-area (>200 cm2 ) yet with great homogeneity and texture along (00l) direction due to the superior solution processability of the as-synthesized NUS-8 nanosheets. The resultant NUS-8 membranes with good adhesion properties and certain flexibility exhibit excellent rejections (>98% for Mg2+ and Al3+ , and dyes with molecular weights larger than 585.5 g mol-1 ) toward aqueous separation of various metal ions and dyes at modest permeance (1-3.2 L m-2 h-1 bar-1 ) due to the well-aligned structures. Such separation performance outstands among polymetric membranes, thin-film composite membranes, mixed matrix membranes, and other MOF membranes reported in the literature. The separation mechanism is reasonably discussed based on the experimental and theoretical results. This study opens up novel perspectives for preparing ultrathin and large-area MOF membranes using the solution processability of MOFs.

Direct Separation of UO2 2+ by Coordination Sieve Effect via Spherical Coordination Traps.

Molecule sieve effect (MSE) can enable direct separation of target, thus overcoming two major scientific and industrial separation problems in traditional separation, coadsorption, and desorption. Inspired by this, herein, the concept of coordination sieve effect (CSE) for direct separation of UO2 2+ , different from the previously established two-step separation method, adsorption plus desorption is reported. The used adsorbent, polyhedron-based hydrogen-bond framework (P-HOF-1), made from a metal-organic framework (MOF) precursor through a two-step postmodification approach, afforded high uptake capacity (close to theoretical value) towards monovalent Cs+ , divalent Sr2+ , trivalent Eu3+ , and tetravalent Th4+ ions, but completely excluded UO2 2+ ion, suggesting excellent CSE. Direct separation of UO2 2+ can be achieved from a mixed solution containing Cs+ , Sr2+ , Eu3+ , Th4+ , and UO2 2+ ions, giving >99.9% removal efficiency for Cs+ , Sr2+ , Eu3+ , and Th4+ ions, but <1.2% removal efficiency for UO2 2+ , affording benchmark reverse selectivity (SM/U ) of >83 and direct generation of high purity UO2 2+ (>99.9%). The mechanism for such direct separation via CSE, as unveiled by both single crystal X-ray diffraction and density-functional theory (DFT) calculation, is due to the spherical coordination trap in P-HOF-1 that can exactly accommodate the spherical coordination ions of Cs+ , Sr2+ , Eu3+ , and Th4+ , but excludes the planar coordination UO2 2+ ion.

Study of the influence of thermobaric conditions on the rheological characteristics of plugging solutions for insulation works

Since most of the fields in the Absheron peninsula of the Republic of Azerbaijan are at the final stage of development, an inevitable reduction in hydrocarbon production is expected. An increase in the proportion of formation water in well production, the presence of intra-reservoir, annulus and other cross-flows in this region, in most cases, is associated with inefficient isolation work.&#x0D; The development of effective recipes for cement slurries with controlled rheological properties is relevant. Natural zeolite was used as an additive to control the rheological properties of cement slurries. A feature of zeolites is the presence of a system of regular channels and communicating cavities capable of holding ions, atoms and molecules of substances, whose size corresponds to the size of free space.&#x0D; Zeolite (clinoptilolite) has the following properties: adsorption ‒ the ability to absorb and release various substances; ion exchange ‒ the ability to exchange cations; catalytic ‒ the ability to speed up chemical reactions. In addition, clinoptilolite has a molecular sieve effect that transmits (filtration) and absorbs molecules of various substances selectively. In the course of experiments, the effects of zeolite dispersions on the physicochemical parameters of cement stone were studied. When regulating the rheological properties of cement slurries with zeolite additives, it is necessary to determine the effect of thermobaric factors on the values of these properties. In studies to assess the effect of temperature on the rheological properties of zeolite-cement mortars, they were carried out for the temperature range of 25÷75 ℃

Application of Radial Type Multifiber Media Filtration Process for Combined Sewer Overflow Treatment

Fiber media filtration for combined sewer overflow (CSO) treatment was evaluated in this work. Pilot-scale experiments of CSO treatment involve seven layers that form radial-type fiber media filters. The fiber media filter was characterized using analysis techniques and exhibited extremely high hydrophobicity and negative charge. The results obtained for a sewer treatment plant at Tancheon in Seoul revealed potential for suspended solid, total organic carbon, and biochemical oxygen demand removal with efficiencies of 89.6%, 56%, and 42%, respectively. The results are consistent with the sieving effects and electrostatic repulsion between fiber media and pollutants. Head loss was induced by organic pollutants and was 10.5 cm after 20 h of operation. To mitigate the head loss induced by organic pollutants on the fiber media filter, sodium hypochlorite (NaClO) was used as a chemical backwashing agent. An NaClO concentration of 2000 mg/L with a soaking time of 24 h yielded an optimal head loss recovery of 96.2% of the initial head loss obtained for the virgin fiber media filter without media filter degradation. The result of the present study will provide practical insight and act as a technical guide for CSO treatment plant engineers.

Analytical solution of three-dimensional particle transport in porous media considering a dual deposition mode

Based on the classical one-dimensional particle transport model, a three-dimensional particle transport model with a dual deposition mode considering sieving and adsorption effects was established. Through Laplace and Fourier transforms, general solutions for particle transport in saturated semi-infinite porous media under one-dimensional seepage and three-dimensional dispersion conditions were derived. According to the basic solution in the case of a point source injection on the surface of a semi-infinite body, the analytical expression in the case of a circular surface source injection was obtained by the integration method. The analytical solution is verified using two well-established numerical simulation solvers. The influence of parameters such as the hydrodynamic dispersion coefficient, sieving coefficient, adsorption coefficient, and desorption coefficient, on the mechanism of the particle transport process was analyzed under the conditions of constant concentration and circulating concentration injection of the circular surface source. The results showed that the hydrodynamic dispersion effect accelerated the transport of particles, shortened the breakthrough time, and increased the peak concentration. Moreover, a larger sieving coefficient and particle adsorption coefficient meant a smaller particle release coefficient, and more particles deposited on the solid matrix with a smaller peak particle concentration in the pores.

Au-doped ZnO@ZIF-7 core-shell nanorod arrays for highly sensitive and selective NO2 detection

The exploration of novel NO2 sensors with high performance is of great importance for air quality monitoring and human health. In this work, Au-doped ZnO@ZIF-7 core-shell nanorod arrays were fabricated for high-performance NO2 detection. Due to the spill-over effects of Au nanoparticles, gas enriching and molecular sieving effects provided by ZIF-7 membranes, the ZnO-Au@ZIF-7 sensor affords highly sensitive and selective detection of NO2. The heterostructured ZnO-Au@ZIF-7 allows for ppb-level detection of NO2 (Response = 1.7–5 ppb) with excellent repeatability and provides improved selectivity, anti-humidity capacity, and long-term stability compared with bare ZnO, Au-doped ZnO or ZnO@ZIF-7 core-shell nanorod arrays. According to the calculation of density functional theory (DFT), the ZnO-Au@ZIF-7 sensor renders higher adsorption energy towards NO2 molecules compared with the aforementioned other materials, which also explains its outstanding sensing performances. We believe our approach that combines noble metals doped semiconductor metal oxides (SMOs) and MOF filtration membranes can be further extended to numerous new heterostructured SMO@MOF materials, which opens venues to the development of advanced chemiresistive gas sensors.

Fractionation of a Three‐Particle Mixture by Brownian Sieving Hydrodynamic Chromatography

AbstractParticles ranging in size from a few nanometers (exosomes or viruses) to a few micrometers (bacteria or red blood cells) can be sorted using a size‐based separation process. One of the simplest techniques is provided by hydrodynamic chromatography (HDC) which typically requires long channels to achieve adequate resolution. A new separation mechanism based on a Brownian sieving effect coupled with HDC has recently been proposed to overcome these limitations. An efficiency improvement of up to 2000 % has been predicted for a two‐size mixture. The aim of this work is to study and optimize a modified geometry useful for obtaining the simultaneous separation of a three‐size diluted suspension. The results suggest a significant performance improvement, up to 3000 %, over the standard HDC.

Advanced hybrid polybenzimidazole membrane enabled by a “linker” of metal-organic framework for high-performance vanadium flow battery

High current density vanadium flow batteries (VFBs) are important for the wide range of applications of renewable energy. The balance between proton conductivity and vanadium permeability of proton exchange membrane has been a huge challenge for the development of high-power density VFBs. Herein, a post-synthetic modification of Zr-MOFs (PSM) is introduced into PBI matrix to break the trade-off between vanadium permeability and ion selectivity, and remarkably improves the power density of VFBs. As a “linker” between the PBI backbone, the PSM creates more proton transport sites in the hybrid membrane, which significantly increases the proton conductivity. Meanwhile, the “acid-base” pairs are formed between PSM and PBI matrix, further promoting the proton transfer in the hybrid membrane. More importantly, the denser structure of hybrid membrane blocks the vanadium ion permeation based on the Donnan exclusion and size sieving effect, respectively. In consequence, the ion selectivity of the PBI/PSM hybrid membrane is substantially improved, almost four times that of the pure PBI membrane. Benefiting from such rational design, the VFB equipped with the PBI/PSM hybrid membrane exhibits an excellent energy efficiency of 75.4% at 500 mA cm−2, and at 300 mA cm−2, the energy efficiency can reach 81.2%, and the efficiency stability can maintain 600 cycles in charge and discharge. Consequently, the use of “linker” offers a very prospective strategy for the development of high-performance proton exchange membrane.

Electro-enhanced rapid separation of nanosized oil droplets from emulsions via the superhydrophilic micro-sized pore membrane

Waste oil-in-water emulsion is a special and unmanageable oily wastewater produced by several industries. Based on the sieving effect, the use of a membrane is a promising method to separate emulsion, whereas low flux remains a fundamental challenge. In this study, the coupling of an electric field with superhydrophilic fibrous membranes helped separate micro-/nano- paraffin in water emulsions (247–1887 nm) stabilized by SDS (100–500 mg/L) with a general applicability. The micro-sized pore membrane (0.634 μm) achieved outstanding rejection of nano-sized oil droplets (247 nm) using an electric field. It promoted flux from 1,202 to 18,388 LMH/bar by 1,429 % which was more than that in other literature by 1–2 orders of magnitude and improved oil removal from 97.61 % to 99.88 %. The reduction of equivalent pore size of membrane by the double layer force and the promotion of coalescence of oil droplets driven by the Laplace force rooted in the fibrous spindle of the membrane achieved enhanced selectivity. Electrophoretic force and double layer force mitigated the formation of the filter cake and irreversible fouling, respectively, to promote permeability and antifouling. This research provides a method for the simultaneous promotion of flux and improvement in effluent quality using an electric field, which breaks the limit of the trade-off effect.

2D Mesoporous Zincophilic Sieve for High-Rate Sulfur-Based Aqueous Zinc Batteries.

Sulfur-based aqueous zinc batteries (SZBs) attract increasing interest due to their integrated high capacity, competitive energy density, and low cost. However, the hardly reported anodic polarization seriously deteriorates the lifespan and energy density of SZBs at a high current density. Here, we develop an integrated acid-assisted confined self-assembly method (ACSA) to elaborate a two-dimensional (2D) mesoporous zincophilic sieve (2DZS) as the kinetic interface. The as-prepared 2DZS interface presents a unique 2D nanosheet morphology with abundant zincophilic sites, hydrophobic properties, and small-sized mesopores. Therefore, the 2DZS interface plays a bifunctional role in reducing the nucleation and plateau overpotential: (a) accelerating the Zn2+ diffusion kinetics through the opened zincophilic channels and (b) inhibiting the kinetic competition of hydrogen evolution and dendrite growth via the significant solvation-sheath sieving effect. Therefore, the anodic polarization is reduced to 48 mV at 20 mA cm-2, and the full-battery polarization is reduced to 42% of an unmodified SZB. As a result, an ultrahigh energy density of 866 Wh kgsulfur-1 at 1 A g-1 and a long lifespan of 10,000 cycles at a high rate of 8 A g-1 are achieved.

Enhancing selective adsorption of CO2 through encapsulating FeTPPs into Cu-BTC

Efficient capture and separation of CO2 from flue gas and natural gas are highly promising to reduce carbon emissions and promote fuel calorific value. Here, a novel adsorbent (FeTPPs@Cu-BTC) for CO2 separation was synthesized by encapsulating 5, 10, 15, 20-tetrakis (4-sulfonatophenyl) porphyrinato iron (III) chloride (FeTPPs) into the cages of Cu-BTC through an in-situ packaging strategy. Such strategy efficiently overcomes the shortcoming of pore clogging and leaching induced by incorporating guest molecules through the wet impregnation method. Meanwhile, more tunable micropores and extra affinity sites for CO2 adsorption were created after encapsulation of FeTPPs, which preferably enhanced the CO2 uptakes of FeTPPs@Cu-BTC under low pressures and promoted the separation performances for CO2/N2 (15:85, v/v) and CO2/CH4 (50:50, v/v) mixtures. The corresponding selectivity of FeTPPs@Cu-BTC calculated by ideal adsorbed solution theory (IAST) respectively increase to 57.7 and 14.0 from 36.0 and 10.8 of the pristine Cu-BTC at 273 K and 100 kPa, which also exceeds most reported adsorbents. Grand Canonical Monte Carlo (GCMC) simulations further elucidated that extra interaction with CO2 and ‘sieve effect’ for N2 or CH4 after FeTPPs encapsulation immediately boost CO2 uptakes and separation performance of FeTPPs@Cu-BTC. This study provides a new design idea for the development of new adsorbent materials.

Mechanism Analysis of PFHxS Purification in Water Using Nanofiltration under the Coexistence of Sodium Alginate and Ca2+ Based on DFT

Perfluorohexanesulfonic acid (PFHxS) is considered a persistent and harmful substance to ecosystems and human health and should thus be necessarily removed. In this paper, the influence of working pressure, temperature, pH value, initial concentration, and the coexistence of sodium alginate (SA) and calcium ions on removing PFHxS using nanofiltration were hereby studied through a self-made hyaluronic acid-interlayered thin-film composite nanofiltration membrane (HA-TFCiNFM). When the substances SA or/and calcium ions (Ca2+) co-existed, the retention rate of the HA-TFCiNFM to PFHxS exceeded that in the single PFHxS system and increased with SA and Ca2+ concentrations. By filtering a single PFHxS, PFHxS/SA, and PFHxS/SA/Ca2+ water sample system, it was observed that the HA-TFCiNFM had the highest membrane fouling degree in the PFHxS/SA/Ca2+ system. The mechanisms of membrane separation and fouling when SA and Ca2+ co-existed were explored based on density functional theory (DFT). Building on DFT, the PFHxS structure was constructed, and when Ca2+ co-existed, Ca2+ complexed two PFHxS molecules to increase the complex compound size, making the sieving effect notable. When SA co-existed, although PFHxS and SA could not react with each other, the presence of SA would block the membrane pore and enhance the negative charge on the membrane surface, thereby strengthening the sieving and Donnan effects. When the substances Ca2+ and SA co-existed, Ca2+ complexed a PFHxS molecule and a SA molecule to form a larger complex compound so that the sieving effect could be enhanced. From the molecular perspective, the intermolecular interaction relationship between pollutants and the HA-TFCiNFM was explored based on DFT, and weak interactions, such as hydrogen bonding and van der Waals interactions, were clarified as the main mechanisms to control the membrane fouling. These results provide insight into the purification mechanism of PFHxS in water using nanofiltration and highlight the usefulness of DFT in exploring membrane separation and fouling mechanisms.

A High-Permeance Organic Solvent Nanofiltration Membrane via Polymerization of Ether Oxide-Based Polymeric Chains for Sustainable Dye Separation

The widely used dyes in the pharmaceutical, chemical, and medical industries have brought about an intensive concern for the sustainable development of the environment. Membrane separation offers a versatile method for classified recycling and the reuse of residual components. In this work, polyimide membranes were synthesized via the polymerization of 4,4′-(hexafluor-isopropylidene) diphthalic anhydride and 1,4-bis (4-aminophenoxy) benzene diamine. The organic solvent nanofiltration membrane was prepared by casting onto a glass plate and precipitating in the non-solvent phase. The properties of the membranes were recorded by FTIR, 1HNMR, TGA, and GPC. The molecular simulations were carried out to analyze the affinity between the membrane and different solvents. The membrane was used in the removal of Rose Bengal, methyl blue, Victoria blue B, and crystal violet from methanol. The effects of the feed liquid concentration, operating pressure, swelling degree, organic solvent resistance, and long-term running on the membrane performance were studied. Results showed that membranes prepared in this work demonstrated high solvent permeation and dye rejection due to the sieving effect and solvent affinity. For methyl blue, the solvent performance achieved a permeability of 2.18 L∙m−2∙h−1∙bar−1 corresponding to a rejection ratio of 94.2%. Furthermore, the membrane exhibited good stability over 60 h of continued testing. These results recommend a potential strategy in the development of a suitable monomer to prepare a polyimide membrane for dye separation.

Tritium separation from radioactive wastewater by hydrogen isotope-selective exchange of hydrogen-bonded fluorine

The separation of tritium (3H) from radioactive wastewater is a persistent challenging problem in the nuclear industry from an environmental perspective. This study provides new insight into the tritium separation by investigating hydrogen isotope-selective exchange reaction on hydrogen-bonded fluorine (F····H····O) site. In this study, fluorinated mesoporous silica, F-MCM-41_NCs were prepared as a novel tritium sorbent that showed a significantly enhanced tritium isotope separation factor (α) compared to the pristine MCM-41 (α = 1.2). The optimal α of 3.3 is achieved using 0.5F-MCM-41_NC prepared with 0.5 g of NH4F per gram of MCM-41. This optimal α is attributed to an excellent compromise between the amount and the stability of (NH4)2SiF6 on the pore channel with the integrity of the MCM-41 framework. Experimental, theoretical, and analytical characterization results consistently support chemical affinity quantum sieving effect at F····H····O hydrogen-bonding sites via the hydrogen isotope-selective exchange reaction as the dominant tritiumseparation mechanism.

Optimized Sieving Effect for Ethanol/Water Separation by Ultramicroporous MOFs.

High-purity ethanol is a promising renewable energy resource, however separating ethanol from trace amount of water is extremely challenging. Herein, two ultramicroporous MOFs (UTSA-280 and Co-squarate) were used as adsorbents. A prominent water adsorption and a negligible ethanol adsorption identify perfect sieving effect on both MOFs. Co-squarate exhibits a surprising water adsorption capacity at low pressure that surpassing the reported MOFs. Single crystal X-ray diffraction and theoretical calculations reveal that such prominent performance of Co-squarate derives from the optimized sieving effect through pore structure adjustment. Co-squarate with larger rhombohedral channel is suitable for zigzag water location, resulting in reinforced guest-guest and guest-framework interactions. Ultrapure ethanol (99.9 %) can be obtained directly by ethanol/water mixed vapor breaking through the columns packed with Co-squarate, contributing to a potential for fuel-grade ethanol purification.

Optimized Sieving Effect for Ethanol/Water Separation by Ultramicroporous MOFs

AbstractHigh‐purity ethanol is a promising renewable energy resource, however separating ethanol from trace amount of water is extremely challenging. Herein, two ultramicroporous MOFs (UTSA‐280 and Co‐squarate) were used as adsorbents. A prominent water adsorption and a negligible ethanol adsorption identify perfect sieving effect on both MOFs. Co‐squarate exhibits a surprising water adsorption capacity at low pressure that surpassing the reported MOFs. Single crystal X‐ray diffraction and theoretical calculations reveal that such prominent performance of Co‐squarate derives from the optimized sieving effect through pore structure adjustment. Co‐squarate with larger rhombohedral channel is suitable for zigzag water location, resulting in reinforced guest‐guest and guest‐framework interactions. Ultrapure ethanol (99.9 %) can be obtained directly by ethanol/water mixed vapor breaking through the columns packed with Co‐squarate, contributing to a potential for fuel‐grade ethanol purification.

H2/D2 Separation Using UTSA-16@CAU-10-H@γ-AlOOH Composites as the Stationary Phase in Gas Chromatography via the Additive Effects of Kinetic Sieving and Chemical Affinity Quantum Sieving.

In this work, CAU-10-H@γ-AlOOH is prepared, and then UTSA-16 is loaded on CAU-10-H@γ-AlOOH to obtain UTSA-16@CAU-10-H@γ-AlOOH. Using the as-prepared composites as stationary materials by cryogenic gas chromatography at 77 K, while CAU-10-H@γ-AlOOH achieves the complete separation of ortho-H2 (o-H2) and D2 with a resolution R of 1.66 and a separation time t of 9.52 min, UTSA-16@CAU-10-H@γ-AlOOH achieves higher efficiency separation of hydrogen isotopes in a shorter separation time (4.56 min) with R = 1.7. Molecular simulation results show that CAU-10-H has both chemical affinity quantum sieving and kinetic sieving effects for H2/D2 at 77 K, and UTSA-16 can only exert the kinetic sieving effect. UTSA-16's load on CAU-10-H@γ-AlOOH weakens the adsorption of hydrogen isotopes, and the presence of Co2+ in UTSA-16 promotes the conversion of para-H2 to ortho-H2. In gas chromatography, H2 was preferentially desorbed from the system due to strong D2 adsorption caused by the chemical affinity quantum sieving effect and faster H2 diffusion caused by the kinetic sieving effect. These additive effects achieved efficient hydrogen isotope separation at 77 K.

Two-dimensional confined channels with high-density hydrophilic microregions for enhanced selective water transport

Two-dimensional (2D) membranes represented by graphene oxide (GO) exhibit great potential in developing high-performance separation membranes. However, insufficient interlayer chemical microenvironment and unstable laminar structure are still huge challenge to achieve high-efficiency water-selective transport. Herein, we construct high-density hydrophilic microregions in GO membrane through introducing sodium polystyrene sulfonate (PSSNa) with abundant ionized sulfonate groups to provide good hydrophilic chemical microenvironment, further facilitating fast water-selective permeation. Meanwhile, the obtained well-stacked lamina structure driven by self-assembly between PSSNa and GO nanosheets conduce to achieve superior separation of water-butanol mixture through strict size sieving effect. Consequently, the as-prepared PSSNa/GO membrane on polyethersulfone (PES) substrate exhibit excellent separation performance with flux of 5.28 kg m −2 h −1 and excellent separation factor of 3487 for water/butanol at 343 K, representing the state-of-the-art selective separation membranes. This strategy provides new insight to finely construct better chemical microenvironment in 2D confined channels for precise and high-efficiency aqueous molecular separation process.

Metal-Organic Frameworks-Based Optical Nanosensors for Analytical and Bioanalytical Applications

Metal-organic frameworks (MOFs)-based optical nanoprobes for luminescence and surface-enhanced Raman spectroscopy (SERS) applications have been receiving tremendous attention. Every element in the MOF structure, including the metal nodes, the organic linkers, and the guest molecules, can be used as a source to build single/multi-emission signals for the intended analytical purposes. For SERS applications, the MOF can not only be used directly as a SERS substrate, but can also improve the stability and reproducibility of the metal-based substrates. Additionally, the porosity and large specific surface area give MOF a sieving effect and target molecule enrichment ability, both of which are helpful for improving detection selectivity and sensitivity. This mini-review summarizes the advances of MOF-based optical detection methods, including luminescence and SERS, and also provides perspectives on future efforts.