Sieving Performance Research Articles

A Novel Strategy to Fabricate Cation-Cross-linked Graphene Oxide Membrane with High Aqueous Stability and High Separation Performance.

Graphene oxide (GO) membranes have shown enormous promise in desalination and molecular/ionic sieving. However, the instability of GO membranes in aqueous solutions seriously hinders their practical applications. Herein, we report a novel and simple strategy to fabricate stable GO membranes in water-based environments through the insertion of various metal cations from metal foils (e.g., copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) foils) and natural deposition. Based on the cation-π, coordination, and electrostatic interaction between metal cations and GO nanosheets, the aqueous stability and mechanical strength of the membranes are significantly improved. The permeation rates for acetone, toluene, and p-xylene molecules across the GO membrane cross-linked by copper ions with a deposition time of 24 h are 0.966, 0.074, and 0.100 mol m-2 h-1, respectively. Moreover, this membrane displays excellent separation performance, and the separation factor of K+/Mg2+ is up to 68.8 in mono-/multivalent metal cation sieving, which indicate the effective molecular/ionic sieving performance. Meanwhile, the ionic sieving of the GO membrane cross-linked by copper ions has excellent repeatability and long-term stability. The versatility of this natural deposition strategy to fabricate GO membranes cross-linked by metal cations is investigated by using Fe foil, Zn foil, and Ni foil as well as other porous substrates such as polyvinylidene fluoride (PVDF), polyethersulfone (PES), and nylon membranes and filter paper. This fabrication strategy also enables low-cost preparation of large-area GO membranes. Therefore, GO membranes cross-linked by metal cations and prepared by this simple metal cation incorporation strategy have large potential application for molecular/ionic sieving in various solution systems.

Cross-linked Graphene Oxide Framework Membranes with Robust Nano-Channels for Enhanced Sieving Ability.

It remains challenging for graphene oxide (GO) membranes to achieve highly efficient performance and sufficient stability for aqueous molecule/ion precise separations. Herein, a molecular-level rational structure design protocol was proposed to develop ceramic-based graphene oxide framework (GOF) membranes with significantly enhanced sieving performance and stability for efficient removal of salts and micropollutants. Via a molecular cross-linking strategy, interlayered nanochannels between GO nanosheets can be rationally designed, featuring precisely tailorable channel size, promising surface chemistries and remarkably robust stability suitable for aqueous separation. Due to a significantly decreased nanochannel size, cross-linking of TU (thiourea) molecule significantly improved monovalent salt rejection (95.6% for NaCl), outperforming existing state-of-the-art GO-based, commercial organic nanofiltration and emerging two-dimensional MoS2 membranes, while moderately decreasing water permeability. In comparison, the GOF membranes cross-linked with MPD (m-phenylenediamine) exhibited a simultaneous increase in permeability and rejection for both salts and micropollutants (21.0% and 53.3% enhancement for chloramphenicol (CAP) solution), breaking their conventional trade-off issue. Cross-linking mechanism indicates that more robust nanochannels were formed by stronger covalent bonds via dehydration condensation between amine (TU/MPD) and carboxyl groups (GO), and nucleophilic addition between amine (TU/MPD) and epoxy groups (GO). Molecule/ion separation mechanism involved size sieving (steric hindrance), electrostatic interaction, Donnan effect, and partial dehydration effect. This work provides a novel protocol for rationally designing size and surface chemistry of highly robust GO nanochannels at a subnanometer level to construct water-stable functional GOF membranes with enhanced sieving performance for water treatment applications.

Performance optimization of the elliptically vibrating screen with a hybrid MACO-GBDT algorithm

As a typical screening apparatus, the elliptically vibrating screen was extensively employed for the size classification of granular materials. Unremitting efforts have been paid on the improvement of sieving performance, but the optimization problem was still perplexing the researchers due to the complexity of sieving process. In the present paper, the sieving process of elliptically vibrating screen was numerically simulated based on the Discrete Element Method (DEM). The production quality and the processing capacity of vibrating screen were measured by the screening efficiency and the screening time, respectively. The sieving parameters including the length of semi-major axis, the length ratio of two semi-axes, the vibration frequency, the inclination angle, the vibration direction angle and the motion direction of screen deck were investigated. Firstly, the Gradient Boosting Decision Trees (GBDT) algorithm was adopted in the modelling task of screening data. The trained prediction models with sufficient generalization performance were obtained, and the relative importance of six parameters for both the screening indexes was revealed. After that, a hybrid MACO-GBDT algorithm based on the Ant Colony Optimization (ACO) was proposed for optimizing the sieving performance of vibrating screen. Both the single objective optimization of screening efficiency and the stepwise optimization of screening results were conducted. Ultimately, the reliability of the MACO-GBDT algorithm were examined by the numerical experiments. The optimization strategy provided in this work would be helpful for the parameter design and the performance improvement of vibrating screens.

Gas-sieving zeolitic membranes fabricated by condensation of precursor nanosheets.

The synthesis of molecular-sieving zeolitic membranes by the assembly of building blocks, avoiding the hydrothermal treatment, is highly desired to improve reproducibility and scalability. Here we report exfoliation of the sodalite precursor RUB-15 into crystalline 0.8-nm-thick nanosheets, that host hydrogen-sieving six-membered rings (6-MRs) of SiO4 tetrahedra. Thin films, fabricated by the filtration of a suspension of exfoliated nanosheets, possess two transport pathways: 6-MR apertures and intersheet gaps. The latter were found to dominate the gas transport and yielded a molecular cutoff of 3.6 Å with a H2/N2 selectivity above 20. The gaps were successfully removed by the condensation of the terminal silanol groups of RUB-15 to yield H2/CO2 selectivities up to 100. The high selectivity was exclusively from the transport across 6-MR, which was confirmed by a good agreement between the experimentally determined apparent activation energy of H2 and that computed by ab initio calculations. The scalable fabrication and the attractive sieving performance at 250-300 °C make these membranes promising for precombustion carbon capture.

Numerical Investigation on the Sieving Performance of Elliptical Vibrating Screen

Screening techniques have been widely deployed in industrial production for the size-separation of granular materials such as coal. The elliptical vibrating screen has been regarded as an excellent screening apparatus in terms of its high screening efficiency and large processing capacity. However, its fundamental mechanisms and operational principles remain poorly understood. In this paper, the sieving process of an elliptical vibrating screen was numerically simulated based on the discrete element method (DEM), and an approach coupling the DEM and the finite element method (DEM–FEM) was introduced to further explore the collision impact of materials on the screen deck. The screening time, screening efficiency, maximum stress and maximum deformation were examined for the evaluation of sieving performance. The effects of six parameters—length of the semi-major axis, length ratio between two semi-axes, vibration frequency, inclination angle, vibration direction angle and vibration direction—on different sieving results were systematically investigated in univariate and multivariate experiments. Additionally, the relationships among the four performance indexes were discussed and the relational functions were obtained. The conclusions and methodologies presented in this work could be of great significance for the design and improvement of elliptical vibrating screens.

Effect of gradual widening of d/w-ratio on optical performance of photon sieves produced by two maskless lithography techniques: lift-off and chemical etching

The two important parameters, to evaluate the performance of the photon sieves quantitatively, are the intensity and resolution at the focus plane. Both high-intensity and super-resolution depend on the ratio of the diameter (d) of each pinhole to the width (w) of the related Fresnel zone: the d/w ratio. The size deviations in the produced pinholes may adversely affect the optical performance of the photon sieves. The mispositioned and imperfectly-shaped pinholes cause the super-resolution at the focus to be disrupted. The photon sieves are produced by using two sub-methods of maskless lithography: lift-off and wet chemical etching. Although designed to be constant of 1, the d/w ratio was measured to widen gradually for both chemical-etched and lift-off samples. It is revealed the optical performance of the photon sieves may be enhanced as a result of gradual increase of the d/w ratio, compared to the structure of constant d/w ratio.

Ultrathin and ultradense aligned carbon nanotube membranes for water purification with enhanced rejection performance

Carbon nanotube (CNT) membranes are promising for high-performance self-assembly membranes in water purification, and their molecular sieving performance depends on the effective pore size of the membranes. For the first time, to enhance the separation selectivity of water purification membranes, we prepared the SACNT membrane with smaller pore sizes, more compact pores with 15 nm thickness and an average 0.88 nm CNT spacing in the observed area for water purification. We found that the aligned CNT membranes exhibited salt rejection 2 times higher than that of membranes prepared by disordered CNTs. It can be explained by the sieving effect. In addition, the adsorption interactions between the CNTs and aromatic rings in dyes also contributed to the improved rejection performance, which was confirmed by the molecular dynamics simulation. Our study represents a significant exploration of enhanced properties for aligned CNT membrane fabricated by a simple method, paving the way for high-performance membrane for water purification.

An Investigation on the Sound Absorption Performance of Granular Molecular Sieves under Room Temperature and Pressure.

The sound absorption of granular silica-aluminate molecular sieve pellets was investigated in this paper. The absorption coefficients of molecular sieve pellets with different pore sizes, pellet sizes, and layer thicknesses were measured through impedance tubes under room temperature and pressure conditions. The effects of pore size, pellet size, layer thickness were compared and explained. The comparisons show that at room temperature and pressure, the sound absorption of molecular sieve pellets is not a result of the crystalline structure, but rather it mainly changes with the pellet size and layer thickness. In addition, the five non-acoustical parameters of molecular sieve pellets were obtained by an inverse characterization method based on impedance tube measurements. The measurement by impedance tubes is in good agreement with the calculation of Johnson-Champoux-Allard (JCA) model, proving that the JCA model can be effectively used to predict the sound absorption of molecular sieve pellets.

Ideal two-dimensional molecular sieves for gas separation: Metal trihalides MX3 with precise atomic pores

Membrane technology has been widely applied in gas separation field. In this work, a series of two-dimensional (2D) metal trihalides MX3 (AsI3, ScI3, SbI3, YI3, BiI3, ScCl3, ScBr3 and YBr3) are expected to be served as realistic 2D molecular sieves in gas separation applications due to their intrinsically and uniformly well-defined atomic pores. The gas separation performance of these 2D MX3 molecular sieves has been systematically explored by using first-principles calculations. Different from the conventional membranes, the atomic pores of 2D MX3 molecular sieves behave like breathing mode via flexible change of M-X bond during the gas molecules transport process. These 2D MX3 molecular sieves exhibit excellent H2/CO and O2/N2 separation performance, which surpasses the state-of-the-art upper bound. Remarkably, the O2/N2 selectivity of YBr3, SbI3, YI3 and BiI3 molecular sieves is within the range of 102-103 under superior permeance, which exceeds that of common membranes (~101) to a large extent. The extremely high selectivity and superior permeance indicate that these 2D MX3 molecular sieves possess great potentials in gas separation applications.

Effective ion sieving with Ti3C2Tx MXene membranes for production of drinking water from seawater

Traditional ways of producing drinking water from groundwater, water recycling and water conservation are not sufficient. Seawater desalination would close the gap but the main technology used is thermally driven multi-flash distillation, which is energy consuming and not sustainable. Stacking two-dimensional (2D) nanomaterials into lamellar membranes is a promising technique in the pursuit of both high selectivity and permeance in water desalination. However, 2D membranes tend to swell in water, and increasing their stability in aqueous solution is still challenging. Here, we report non-swelling, MXene membranes prepared by the intercalation of Al3+ ions. Swelling is prevented by strong interactions between Al3+ and oxygen functional groups terminating at the MXene surface. These membranes show excellent non-swelling stability in aqueous solutions up to 400 h and possess high rejection of NaCl (~89.5–99.6%) with fast water fluxes (~1.1–8.5 l m−2 h−1). Such membranes can be easily fabricated by simple filtration and ion-intercalating methods, which holds promise for their scalability. Two-dimensional lamellar membranes for water purification are promising but suffer from swelling that reduces their ion sieving performance in water. This study reports easy-to-fabricate, non-swelling MXene membranes prepared by the intercalation of Al3+ ions that could be scalable.

The roles of oxygen-containing functional groups in modulating water purification performance of graphene oxide-based membrane

Due to the excellent mechanical properties and tunable inter-layer distance spacing (D-spacing), graphene oxide based nanofiltration membranes (GONMs) have attracted tremendous attention for wastewater treatment and seawater desalination. However, GONMs with different reduction degrees or originate from different graphite resources present totally distinct purification performance. The principal consideration of the differences between those GONMs is the oxygen-containing functional groups (carboxyl (–COOH), hydroxyl (–OH) and epoxy (–COC-)). While, it is still not fully understood what role do different oxygen-contained functional groups play. Herein, in order to reveal this knowledge gap, we fabricated and systematically studied three oxygen-containing functional groups dominant (C-GO, H-GO and E-GO) GO membranes. Zeta potential was measured to analysis the surface properties of C-GO, H-GO and E-GO nanosheets. Furthermore, XRD was used to observe the D-spacing of GONMs. The results showed that the oxygen-contained functional groups with different hydrophilicity and electricity modulated the D-spacing of GONMs effectively, which resulted in different water permeance and sieving performance of the GONMs. Besides, C-GONMs with abundant negative charges exhibited excellent antifouling capacity for Trypan blue (dye) owing to the electrostatic interaction effect. Such differences between GONMs with three kinds of oxygen-contained functional groups pave a powerful platform to better understand and design the GO based separation membrane.

Comparative evaluation of the operation of a combine harvester with an additional sieve with adjustable holes for sunflower harvesting

The cost of production of sunflower is determined by the number of operations for its cultivation as well as the manufacturing charges for them. The extraneous matter content of the hopper sunflower heap is the factor that can increase the cost of sunflower production. In connection with that, it is advisable to reach the minimum values of the extraneous matter content in the hopper heap during sunflower harvesting. The article substantiates the design of the sieve with additional holes which is installed as an additional cleaning stage in the combine harvester. Adjustable sieve holes have a shape similar to the longitudinal shape of oilseeds. The area of the sieve hole can be adjusted depending on the type or variety of sunflower, which will significantly reduce the extraneous matter content in the hopper heap. To analyze the sieve performance, a check sample was made which was installed as an additional cleaning stage on the “Niva” SK-5-M-1 and “Vector 410” grain combine harvesters. The analysis is presented of the extraneous matter content in the hopper heap with the use of an additional sieve with a different area of adjustable holes and without it.

Feedstock particle size distribution and water content dynamic in a pellet mill production process and comparative sieving performance of horizontal 3.15-mm mesh and 3.15-mm hole sieves

Pellet feedstock particle size distribution is the main factor affecting pellet quality. Feedstock samples were obtained from different places in the production process of a commercial pellet mill. Particle size distribution and water content of the sieved particle fractions were analyzed. The results showed an alternation of particle size distribution and water content of the feedstock induced by the processing in the mill. Storage had a balancing effect on the water content distribution between the different particle size classes. Further experiments evaluated the reason for the underrepresentation of the 2.8–3.15-mm fraction in the feedstock. It was found that the major sieving factor for non-spherical wood particles was their width rather than their length, though the aspect ratio was important for the sorting between the 2.8–3.15-mm and the 2.0–2.8-mm sieve fractions. The significant differences between the particle width in the sieve fractions and the distribution of the particle aspect ratio improved when using a 3.15-mm mesh sieve instead of the 3.15-mm hole sieve. This indicates the better sieving performance of the 3.15-mm mesh sieve, which should be considered by pellet manufacturers and researchers investigating pellet feedstock.

Polymer Composite Membrane with Penetrating ZIF‐7 Sheets Displays High Hydrogen Permselectivity

AbstractOriented and penetrating molecular sieving membranes display enhanced separation performance. A polyimide (PI) solution containing highly dispersed ZIF‐7(III) sheets in CHCl3 was deposited on a glass side and subjected to flat‐scraping with a membrane fabricator. In this way we developed a novel oriented and penetrating ZIF‐7@PI mixed matrix membrane (MMM) with 50 wt. % ZIF‐7 loading. Because the height of the ZIF‐7 sheets (5 μm) is higher than the film thickness, every ZIF‐7 sheet penetrates both surfaces of the polyimide film. Since the ZIF‐7 channels are the dominant pathway for gas permeation, the ZIF‐7@PI MMM displays a high molecular sieve performance for the separation of H2 (0.29 nm) from larger gas molecules. At 100 °C and 2 bar, the mixture separation factors of H2/CO2 and H2/CH4 are 91.5 and 128.4, with a high H2 permeance of about 3.0×10−7 mol m−2 s−1 Pa−1, which is promising for hydrogen separation by molecular sieving.

Polymer Composite Membrane with Penetrating ZIF-7 Sheets Displays High Hydrogen Permselectivity.

Oriented and penetrating molecular sieving membranes display enhanced separation performance. A polyimide (PI) solution containing highly dispersed ZIF-7(III) sheets in CHCl3 was deposited on a glass side and subjected to flat-scraping with a membrane fabricator. In this way we developed a novel oriented and penetrating ZIF-7@PI mixed matrix membrane (MMM) with 50 wt. % ZIF-7 loading. Because the height of the ZIF-7 sheets (5 μm) is higher than the film thickness, every ZIF-7 sheet penetrates both surfaces of the polyimide film. Since the ZIF-7 channels are the dominant pathway for gas permeation, the ZIF-7@PI MMM displays a high molecular sieve performance for the separation of H2 (0.29 nm) from larger gas molecules. At 100 °C and 2 bar, the mixture separation factors of H2 /CO2 and H2 /CH4 are 91.5 and 128.4, with a high H2 permeance of about 3.0×10-7 mol m-2 s-1 Pa-1 , which is promising for hydrogen separation by molecular sieving.

Toward Understanding of the Effect of Nucleation Temperature on Porous Structure of Micro-Mesoporous Composite Molecular Sieves and Related Crystallization Mechanism

Although micro-mesoporous composite molecular sieves have received significant attention due to their desirable properties, they still lack systematic studies on their crystallization process to achieve controllable synthesis of composite molecular sieves. In this study, a series of Y/SBA-15 micro-mesoporous composite molecular sieves with different porous structures were synthesized by tuning nucleation temperature, based on epitaxial growth on the outer surface of the Y-type crystal particle. All composite molecular sieves were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Moreover, the effect of nucleation temperature on the structure of composite molecular sieves was investigated, while the crystallization mechanism was also explored. Furthermore, the performance of the molecular sieves on isomerization of n-pentane was investigated, the results suggested that the isomerization selectivity was positively correlated with regularity degree of the mesoporous porous structure, where the highest isomerization reached 95.81%. This work suggests that nucleation temperature plays a key role in structures of micro-mesoporous composite molecular sieves, providing a solid basis for the further development of functional composite molecular sieves.

A MOF membrane with ultrathin ZIF-8 layer bonded on ZIF-8 in-situ embedded PSf substrate

Metal–organic framework (MOF) membranes exhibit enormous potential for molecular mixtures’ sieving with high permeance, as well as high selectivity. Current MOF composite membranes suffer from unduly thick MOF layer and poor adhesion to the porous support. By a simple multiple seeded growth method, the ultrathin (less than 200 nm) and defect-free MOF layer is prepared on a ZIF-8 in-situ embedded PSf substrate. On the one hand, the nano-sized ZIF-8 crystals embedded on substrate surface act as anchors linking the ZIF-8 layer with the substrate. On the other hand, these ZIF-8 crystals also act as seeds to promote the formation of the ZIF-8 layer and reduce the crystallization time, leading to a thin and continuous ZIF-8 layer. The obtained ultrathin ZIF-8 membrane shows superior gas molecular sieving performance, with a high gas permeance of 24.5 × 10−7 mol/m2/s/Pa for H2 and selectivity of 4.5, 23.2, and 31.5 for H2/CO2, H2/N2, and H2/CH4, respectively. In addition, neither the permeance or the selectivity shows a noticeable change after 3% elongation, which indicates high mechanical integrity of the MOF layer on the ZIF-8 in-situ embedded PSf substrate. We believe that the utilization of MOF in-situ embedded polymer substrate offers a universal and simple strategy strengthening and thinning the MOF layer of its composite membranes.

Direct femtosecond laser fabricated photon sieve

Photon sieves, a collection of randomly positioned apertures, focus electromagnetic radiation diffractively and find applications in x-ray optics to astronomy to bio-medical imaging. Femtosecond laser direct writing is an emerging rapid, reliable, and versatile technique for creating diffraction-limited features in dielectrics and metals. Using this technique, we produce localized spots with a modified refractive index within bulk glass and thus fabricate phase photon sieves for optical wavelengths. The distribution of spots was based on numerical simulations. A comparison of the performance of the phase photon sieves and zone-plates created showed a superior performance of the former in terms of tighter focusing and reduction of secondary maxima, thus offering better spatial resolution and imaging capabilities.

Enhancement of Water Adsorption–desorption Performance of Aluminophosphate Molecular Sieves (AlPO-5) Substituted with Several Metals

Enhancement of Water Adsorption–desorption Performance of Aluminophosphate Molecular Sieves (AlPO-5) Substituted with Several Metals

Electrochemically-derived graphene oxide membranes with high stability and superior ionic sieving.

Crosslinker-free electrochemically-derived graphene oxide membranes are found to be extraordinarily stable in aqueous solutions and exhibit superior ionic sieving performance because of their unique chemical structure.