Selective Sieving Research Articles

Nanofiller-tuned microporous polymer molecular sieves for energy and environmental processes

Incorporating nanofillers into thermal-oxidatively crosslinked polymers of intrinsic microporosity (PIM-1) generates highly permeable and selective molecular sieves for gas separations.

From an equilibrium based MOF adsorbent to a kinetic selective carbon molecular sieve for paraffin/iso-paraffin separation.

We unveil a unique kinetic driven separation material for selectively removing linear paraffins from iso-paraffins via a molecular sieving mechanism. Subsequent carbonization and thermal treatment of CD-MOF-2, the cyclodextrin metal-organic framework, afforded a carbon molecular sieve with a uniform and reduced pore size of ca. 5.0 Å, and it exhibited highly selective kinetic separation of n-butane and n-pentane from iso-butane and iso-pentane, respectively.

Solid-State Reversible Nucleophilic Addition in a Highly Flexible MOF

A flexible and porous metal-organic framework, based on Co(II) connectors and benzotriazolide-5-carboxylato linkers, is shown to selectively react with guest molecules trapped in the channels during the sample preparation or after an exchange process. Stimulated by a small crystal shrinking, upon compression or cooling, the system undergoes a reversible, nonoxidative nucleophilic addition of the guest molecules to the metal ion. With dimethylformamide, only part of the penta-coordinated Co atoms transform into hexa-coordinated, whereas with the smaller methanol all of them stepwise increase their coordination, preserving the crystallinity of the solid at all stages. This extraordinary example of chemisorption has enormous implications for catalysis, storage, or selective sieving.

Oriented MFI Membranes by Gel-Less Secondary Growth of Sub-100 nm MFI-Nanosheet Seed Layers.

A zeolite membrane fabrication process combining 2D-zeolite nanosheet seeding and gel-free secondary growth is described. This process produces selective molecular sieve films that are as thin as 100 nm and exhibit record high permeances for xylene- and butane-isomers.

Nanolayered tin phosphate: a remarkably selective Cs ion sieve for acidic waste solutions.

Herein, we report a unique tin phosphate that is remarkably selective to (137)Cs(+) from extremly acidic solutions because of its special layered structure with an unusually large interlayer space. This acidic exchanger is superior to other existing materials in terms of its selectivity and capacity for (137)Cs(+) from acidic solutions.

Sisters' curse: sexually antagonistic effects constrain the spread of a mitochondrial haplogroup superior in sperm competition.

Maternal inheritance of mitochondria creates a sex-specific selective sieve with implications for male longevity, disease susceptibility and infertility. Because males are an evolutionary dead end for mitochondria, mitochondrial mutations that are harmful or beneficial to males but not females cannot respond directly to selection. Although the importance of this male/female asymmetry in evolutionary response depends on the extent to which mitochondrial mutations exert antagonistic effects on male and female fitness, few studies have documented sex-specific selection acting on mitochondria. Here, we exploited the discovery of two highly divergent mitochondrial haplogroups (A and B2) in central Panamanian populations of the pseudoscorpion Cordylochernes scorpioides. Next-generation sequencing and phylogenetic analyses suggest that selection on the ND4 and ND4L mitochondrial genes may partially explain sexually antagonistic mitochondrial effects on reproduction. Males carrying the rare B2 mitochondrial haplogroup enjoy a marked advantage in sperm competition, but B2 females are significantly less sexually receptive at second mating than A females. This reduced propensity for polyandry is likely to significantly reduce female lifetime reproductive success, thereby limiting the spread of the male beneficial B2 haplogroup. Our findings suggest that maternal inheritance of mitochondria and sexually antagonistic selection can constrain male adaptation and sexual selection in nature.

Highly selective sieving of small gas molecules by using an ultra-microporous metal–organic framework membrane

Two tailor-made microporous metal–organic framework (MOF) membranes were successfully fabricated on nickel screens by secondary growth. The effect of pore structures on gas separation was examined by means of single and binary gas permeation tests. The MOF JUC-150 membrane with its ultra-micropores showed marked preferential permeance to H2 relative to other gas molecules. The selectivity factors of this membrane were 26.3, 17.1 and 38.7 for H2/CH4, H2/N2 and H2/CO2, respectively, at room temperature. To the best of our knowledge, these values represent unprecedentedly high separation selectivity among those for all MOF membranes reported to date. The JUC-150 membrane also shows high thermal stability and outstanding separation performance at a high temperature of 200 °C. The separation performance of these membranes persists even after more than 1 year exposure to air. The superiority of the tailored pore size, high selectivity for H2 over other gases, significant stability and recyclability make these materials potential candidates for industrial H2 recycling applications.

Qualitative improvement of xylite by mechanical preparation

The experiments were performed to obtain high purity raw material for activated carbon making, by mechanical preparation of xylite recovered from the Oltenia lignite Basin. The study analyzes the most important parameters that involves the selective grinding of a representative amount of 15.7t xylite (moisture, mineral content, botanic origin), using a production equipment (a hammer-crusher of 50t/h) and the yields and characteristics of the fractions obtained for the activated carbon manufacturing, with high usage value. The key objectives of this study are: (1) to establish yields and quality of the fractions obtained by processing a representative amount of xylite; (2) to reveal the decisive role of the preparation stages on the characteristics of the final product; and (3) to reveal the occurrence, selection methods and preliminary assessment of the xylite reserves necessary for designing a capacity for activated carbon commercial-scale processing unit. This paper presents the results obtained at semi-industrial level of xylite preparation (by crushing and volumetric classifying), for obtaining structural unchanged variety sizes suitable for experiments to obtain activated carbon. It was proved that selective crushing and sieving is a very effective technique taking into account also obtaining the convenient output (yields of over 80%) of useful fraction of xylite (greater than 10mm with an ash between 2.0 and 2.5%). The results point out that the higher the selection and preparation go, the more lower the ash in the upper grain size fractions. The xylite fractions represent an appropriate raw material used for activated carbon making, characterized by a pore volume of 0.32cm3/g, developed mainly in the range of very narrow pores (over 70% under 10Å) which give high surface area BET up to 800m2/g for granular type, the average radius of open pores being 6–9Å.

Porous carbon nanotubes: Molecular absorption, transport, and separation

We use classical molecular dynamics simulations to study nanofluidic properties of porous carbon nanotubes. We show that saturated water vapor condenses on the porous nanotubes, can be absorbed by them and transported in their interior. When these nanotubes are charged and placed in ionic solutions, they can selectively absorb ions in their interior and transport them. Porous carbon nanotubes can also be used as selective molecular sieves, as illustrated on a room temperature separation of benzene and ethanol.

Graphene-like Membranes: From Impermeable to Selective Sieves

ABSTRACTRecently, it was proposed that graphene membranes could act as impermeable atomic structures to standard gases. For some other applications, a higher level of porosity is needed, and the so-called Porous Graphene (PG) and Biphenylene Carbon (BPC) membranes are good candidates to effectively work as selective sieves. In this work we have used classical molecular dynamics simulations to study the dynamics of membrane permeation of He and Ar atoms and possible selectivity effects. For the graphene membranes we did not observe any leakage through the membrane and/or membrane/substrate interface until a critical pressure limit, then a sudden membrane detachment occurs. PG and BPC membranes are not impermeable as graphene ones, but there are significant energy barriers to diffusion depending on the atom type. Our results show that this kind of porous membranes can be effectively used as selective sieves for pure and mixtures of gases.

Ultra-pure air (UPA) for AMC control in nano-processing environment

As semiconductor processes advance into the nanotechnology era, Airborne Molecular Contamination (AMC) has become a major problem that severely affects production processes and yields. The damage caused by AMC in nano-scale technology production has been found to be much worse than contamination related to conventional airborne particulates. To address these AMC problems, an Ultra‐Pure Air (UPA) approach has been explored and its prototype pre-treatment system has been experimented with.The schematic of a UPA system is composed of three processing steps. In the first step, UV185+254nm is used to provide sufficient energy to break the molecular bonds of the contaminants. In this stage, aerosol droplets are introduced to react with these unstable compounds and form hydrophilic substances. After the “immersing photochemical” oxidation process, the second step involves contaminants flowing through a compression and condensation module. In this concentrating module, nucleation, condensation and growth of the aerosols are facilitated to increase the collision probability between the contaminants and water droplets. Further on, a dehumidifying device removes the water droplets within the air, so the contaminants dissolved in the water are removed together with the water during the dehumidification process. The third step is to remove the remaining contaminants, which cannot be completely treated away in the previous steps, through specifically selective molecular sieves and other corresponding filtration devices. Xylene was used to exemplify a prototype system framed with a target level of 10 ppt capability.The purpose of this paper is two fold. One is to introduce the UPA system and its theoretical rationales. The other is to experimentally demonstrate the effectiveness of using immersed UV for mitigating AMC problems.

Linking the transcriptome and proteome to characterize the venom of the eastern diamondback rattlesnake (Crotalus adamanteus)

Understanding the molecular basis of the phenotype is key to understanding adaptation, and the relationship between genes and specific traits is represented by the genotype-phenotype map. The specialization of the venom-gland towards toxin production enables the use of transcriptomics to identify a large number of loci that contribute to a complex phenotype (i.e., venom), while proteomic techniques allow verification of the secretion of the proteins produced by these loci, creating a genotype-phenotype map. We used the extensive database of mRNA transcripts generated by the venom-gland transcriptome of Crotalus adamanteus along with proteomic techniques to complete the genotype-phenotype map for the C. adamanteus venom system. Nanospray LC/MS(E) analysis of a whole venom sample identified evidence for 52 of the 78 unique putative toxin transcript clusters, including 44 of the 50 most highly expressed transcripts. Tandem mass spectrometry and SDS-PAGE of reversed-phase high-performance liquid chromatography fractions identified 40 toxins which clustered into 20 groups and represented 10 toxin families, creating a genotype-phenotype map. By using the transcriptome to understand the proteome we were able to achieve locus-specific resolution and provide a detailed characterization of the C. adamanteus venom system. Identifying the mechanisms by which genetic variation presents itself to the sieve of selection at the phenotypic level is key to understanding the molecular basis of adaptation, and the first step in understanding this relationship is to identify the genetic basis of the phenotype through the construction of a genotype-phenotype map. We used the high-throughput venom-gland transcriptomic characterization of the eastern diamondback rattlesnake (C. adamanteus) and proteomic techniques to complete and confirm the genotype-phenotype map, providing a detailed characterization of the C. adamanteus venom system.

Isolation of midgut escape mutants of two American genotype dengue 2 viruses from Aedes aegypti

BackgroundSeveral studies have shown that American genotype dengue 2 viruses (DENV2) have reduced viral fitness in the mosquito vector, Aedes aegypti, compared to other DENV2 genotypes. Diminished replication efficiency or inability to efficiently traverse membrane barriers encompassing organs such as the midgut or salivary glands are considered major factors negatively impacting viral fitness in the mosquito.ResultsWe analyzed the vector competence of Ae. aegypti for two American DENV2 strains, QR94 and PR159 originating from Mexico and Puerto-Rico, respectively. Both strains infected mosquito midguts following acquisition of infectious bloodmeals. However, DENV2-QR94 and DENV2-PR159 poorly disseminated from the midgut at 7 or 14 days post-bloodmeal (pbm). We detected one virus isolate, EM33, among 31 DENV2-QR94 infected mosquitoes, and one isolate, EM41, among 121 DENV2-PR159 infected mosquitoes, generating high virus titers in mosquito carcasses at 7 days pbm. In oral challenge experiments, EM33 and EM41 showed midgut dissemination rates of 40-50%. Replication efficiency of EM41 in secondary mosquito tissue was similar to that of a dissemination-competent control strain, whereas the replication efficiency of EM33 was significantly lower than that of the control virus. The genome sequence of DENV2-QR94 encoded seven unique amino acids (aa), which were not found in 100 of the most closely related DENV2 strains. EM33 had one additional aa change, E202K, in the E protein. DENV2-PR159 encoded four unique aa residues, one of them E202K, whereas EM41 had two additional aa substitutions, Q77E in the E protein and E93D in NS3.ConclusionsOur results indicate that the midgut of Ae. aegypti acts as a selective sieve for DENV2 in which genetically distinct, dissemination-competent virus variants are rapidly selected from the viral quasispecies to be transmitted to vertebrates.

Potential of sub- and supercritical CO2 reaction media for sol–gel deposition of silica-based molecular sieve membranes

A new eco-friendly method recently developed in our group has been further investigated for the preparation of gas selective silica-based molecular sieve membranes on/in macroporous tubular ceramic supports without any intermediate layer. The synthesis protocol under sub- and supercritical conditions was based on an “On-Stream Supercritical Fluid Deposition method” (OS-SFD) applying supercritical carbon dioxide (scCO2) as an attractive “green” solvent with easily adjustable properties enabling a controlled solubilisation/reaction of precursors and their transport to the ceramic support. Parameters influencing the final membrane characteristics such as permeates flow rate, calcination treatment and deposition steps have been examined for a selected reaction mixture, transmembrane pressure and defined deposition temperatures. On-line monitoring of the membrane formation process (deposition signature curve) was used in this process. Membrane characteristics are discussed in correlation with their gas permeation properties. The optimized crack-free silica membranes prepared at 50°C have a compact microstructure but a thermal stability limited to 400°C. A second deposition run allowed a recovery of the molecular sieving behaviour with a thermally activated transport for He up to 350°C. These promising results demonstrate the potential of this novel method for the preparation of uniform molecular sieve membranes deposited directly on macroporous supports with virtually zero waste.

Effect of MFI zeolite intermediate layers on gas separation performance of carbon molecular sieve (CMS) membranes

To strengthen interfacial adhesion between selective carbon molecular sieve (CMS) layers and α-Al2O3 substrates, mordenite framework inverted (MFI)-type intermediate layers were synthesized to reduce pore sizes and improve chemical characteristics of underlying substrates and consequently facilitate formation of CMS layers. MFI-type zeolite intermediate layers were prepared on α-Al2O3 substrates via secondary growth of seeds to form polycrystalline zeolite layers with a-oriented crystallites. These crystallites increased cross-link strength between separation layers as well as gas pair separation performance. When a porous substrate was treated with silica seeds and covered with an MFI intermediate layer, CMS selectivity for H2/CH4 increased to 260.9 with permeability towards H2 of 2224Barrer. These modifications improved the mechanical stability of CMS layers and will assist in their commercialization.

Influence of sol–gel process parameters on the micro-structure and performance of hybrid silica membranes

A facile, versatile and reproducible sol–gel process to make microporous organosilica membranes by using 1,2-bis (triethoxysilyl) ethane (BTESE) as a precursor is reported. The influence of process parameters on sol particle size and rheology of BETSE-derived sols was investigated to produce defect-free composite membranes by a single dipping procedure and subsequent calcination. The microporous structure of a BTESE layer on mesoporous alumina supports enabled selective molecular sieving of gas molecules. Single gas permeation (SGP) experiments, performed at 200°C, showed that a H2/CH4 permselectivity of 24 was reproducibly achieved. No SF6 gas permeance through these membranes proof the presence of a defect-free microstructure. SEM cross-section analysis showed a hybrid selective layer with a thickness dependent on the sol precursor concentration.

Synthesis of highly selective zeolite topology molecular sieve for adsorption of benzene gas

Shangdong fly ash (SFA), Fangshan fly ash (FFA) and Heilongjiang fly ash (HFA) were selected as the raw materials to be used for synthesis of highly selective zeolite topology molecular sieve. Twice foaming method was studied in terms of synthetic zeolite. The experimental products were characterized by means of X-ray fluorescence (XRF), scanning electron microscope (SEM), X-ray diffraction (XRD), and automated surface area & pore size analyser. The results indicated that 10 M NaOH was chosen as modification experiment condition to process SFA. Crystallization temperature and time were 140 °C and 8 h, respectively. Zeolite topology molecular sieve was prepared with Si/Al molar ratio of 7.9, and its adsorption ratio of benzene gas was up to 66.51%.

Selective molecular sieving through porous graphene

Membranes act as selective barriers and play an important role in processes such as cellular compartmentalization and industrial-scale chemical and gas purification. The ideal membrane should be as thin as possible to maximize flux, mechanically robust to prevent fracture, and have well-defined pore sizes to increase selectivity. Graphene is an excellent starting point for developing size-selective membranes because of its atomic thickness, high mechanical strength, relative inertness and impermeability to all standard gases. However, pores that can exclude larger molecules but allow smaller molecules to pass through would have to be introduced into the material. Here, we show that ultraviolet-induced oxidative etching can create pores in micrometre-sized graphene membranes, and the resulting membranes can be used as molecular sieves. A pressurized blister test and mechanical resonance are used to measure the transport of a range of gases (H(2), CO(2), Ar, N(2), CH(4) and SF(6)) through the pores. The experimentally measured leak rate, separation factors and Raman spectrum agree well with models based on effusion through a small number of ångstrom-sized pores.

Mitochondria, Maternal Inheritance, and Male Aging

The maternal transmission of mitochondrial genomes invokes a sex-specific selective sieve, whereby mutations in mitochondrial DNA can only respond to selection acting directly on females. In theory, this enables male-harming mutations to accumulate in mitochondrial genomes when these same mutations are neutral, beneficial, or only slightly deleterious in their effects on females. Ultimately, this evolutionary process could result in the evolution of male-specific mitochondrial mutation loads; an idea previously termed Mother's Curse. Here, we present evidence that the effects of this process are broader than hitherto realized, and that it has resulted in mutation loads affecting patterns of aging in male, but not female Drosophila melanogaster. Furthermore, our results indicate that the mitochondrial mutation loads affecting male aging generally comprise numerous mutations over multiple sites. Our findings thus suggest that males are subject to dramatic consequences that result from the maternal transmission of mitochondrial genomes. They implicate the diminutive mitochondrial genome as a hotspot for mutations that affect sex-specific patterns of aging, thus promoting the idea that a sex-specific selective sieve in mitochondrial genome evolution is a contributing factor to sexual dimorphism in aging, commonly observed across species.

Influence of support structure on the permeation behavior of polyetherimide-derived carbon molecular sieve composite membrane

Abstract Polyetherimide (PEI) was used as polymeric precursor to prepare selective carbon molecular sieve (CMS) layer supported by a porous Al2O3 ceramic disk. The effects of the porous structure and surface roughness of the ceramic support on the interfacial adhesion and texture of the PEI/Al2O3-derived composite CMS membrane were investigated by modulating the sintering temperature and holding time. When the surface roughness of the ceramic support increased, the pore size and its distribution of the selective CMS layer were found to have shifted to the larger one and its roughness increased from the top to the bottom surface. This structure resulted in high permeability and low selectivity. Our results indicate that the porous structure of the ceramic support also played an important role in dominating the pore size and its distribution of the selective CMS layer, which influences the gas separation performance.