VOCs adsorption by modified MCM-41 and a new way to recycle adsorbents

MCM-41 was modified by ion exchange of nickel and the adsorptive property was examined using ethylene and n-butane as the representatives of VOCs. The adsorption capacity for n-butane barely changed after modification. The isosteric heat of n-butane adsorption at different coverage was calculated through Clausius–Clapeyron equation and it increased only a little. After modification the maximum adsorption amount for ethylene was 0.59 g g _adsorbent ^?1 at 308 K up to 10⁵ Pa. The adsorption capacity was much higher than former reported adsorbents. A possible mechanism was proposed. After thermal treatment, Ni⁺ ion formed and became the active center of ethylene polymerization. Carbon chain lengths of the final products were limited to the sizes of molecular sieves. Catalytic polymerization and adsorption was considered as a new route for ethylene adsorption. We also declared a new way to recycle the adsorbents by washing with organic solution.     

The Planar CoB18− Cluster as a Motif for Metallo‐Borophenes

Monolayer‐boron (borophene) has been predicted with various atomic arrangements consisting of a triangular boron lattice with hexagonal vacancies. Its viability was confirmed by the observation of a planar hexagonal B₃₆ cluster with a central six‐membered ring. Here we report a planar boron cluster doped with a transition‐metal atom in the boron network (CoB₁₈^?), suggesting the prospect of forming stable hetero‐borophenes. The CoB₁₈^? cluster was characterized by photoelectron spectroscopy and quantum chemistry calculations, showing that its most stable structure is planar with the Co atom as an integral part of a triangular boron lattice. Chemical bonding analyses show that the planar CoB₁₈^? is aromatic with ten π‐electrons and the Co atom has strong covalent interactions with the surrounding boron atoms. The current result suggests that transition metals can be doped into the planes of borophenes to create metallo‐borophenes, opening vast opportunities to design hetero‐borophenes with tunable chemical, magnetic, and optical properties.     

Enhancement of greenhouse gas adsorption on the new α-type reconstructed structure of two-dimensional borophene via biaxial strain engineering

The adsorption of CO, CO₂, and N₂O on a newly found α-type reconstructed form of borophene was investigated via density functional theory calculations. It is revealed that the new α-type reconstructed borophene structure consists of several large holes, and has the same order of stability as the predicted α₁-borophene in Wu et al. On the pristine reconstructed borophene case, CO and CO₂ adsorb moderately and weakly, respectively. Interestingly, N₂O spontaneously dissociated on the α-type reconstructed borophene. Upon the application of biaxial strain, especially at 10%, the adsorption of CO and CO₂ on the reconstructed borophene becomes significantly enhanced, and this is attributed to changes in the density of states near the Fermi level of the reconstructed borophene.     

Ultrastable Crystalline Semiconducting Hydrogenated Borophene

Borophene sheets have been synthesized in recent experiments, but the metallic nature and structural instability of the sheets seriously prevent emerging applications. Hydrogenated borophene has been predicted as an ideal material for nanoelectronic applications due to its high stability as well as excellent electronic and mechanical properties. However, the fabrication of hydrogenated borophene is still a great challenge. Here, we demonstrate that hydrogenated borophenes in large quantities can be prepared without any metal substrates by a stepwise in‐situ thermal decomposition of sodium borohydride under hydrogen as the carrier gas. The borophenes with good crystallinity exhibit superior stability in strong acid or base solvents. The structure of the grown borophene is in good agreement with the predicted semiconducting α‐boron sheet. A fabricated borophene‐based memory device shows a high ON/OFF‐current ratio of 3×10³ and a low operating voltage of less than 0.35 V as well as good stability.     

The Role of Holes in Borophenes: An Ab Initio Study of Their Structure and Stability with and without Metal Templates

An electron‐counting strategy starting from magnesium boride was used to show the inevitability of hexagonal holes in 2D borophene. The number (hole density, HD) and distribution of the hexagonal holes determine the binding energy per boron atom in monolayer borophenes. The relationship between binding energy and HD changes dramatically when the borophene is placed on a Ag(111) surface. The distribution of holes in borophenes on Ag(111) surfaces depends on the temperature. DFT calculations show that aside from the previously reported S1 and S2 borophene phases, other polymorphs may also be competitive. Plots of the electron density distribution of the boron sheets suggest that the observed STM image of an S2 phase corresponds to a sheet with a HD of 2/15 instead of a sheet with a HD of 1/5. The hole density and the hole distribution echo the distribution of vacancies and extra occupancies in complex β‐rhombohedral boron.     

Quantum-chemical modeling of ethylene and acetylene adsorption on gold clusters

The interaction of ethylene and acetylene molecules with planar (2D) and nonplanar (3D) gold clusters Au _n (n = 10, 12, 20) was studied by the density functional theory (DFT) method. The coordination of hydrocarbons at the vertices, edges, and fragments of the Au₃ cluster was shown to form π, di-σ, and μ type complexes, respectively. The standard Gibbs energy and the C-C bond length of the hydrocarbon change during its adsorption in the series μ > di-σ > π complexes. The highest selectivity in adsorption of acetylene relative to that of ethylene was achieved on Au₁₂ (3D) and Au₂₀ (2D) clusters.     

Designed Single Atom Bifunctional Electrocatalysts for Overall Water Splitting: 3d Transition Metal Atoms Doped Borophene Nanosheets

Single atom catalysts (SAC) for water splitting hold the promise of producing H₂ in a highly efficient and economical way. As the performance of SACs depends on the interaction between the adsorbate atom and supporting substrate, developing more efficient SACs with suitable substrates is of significance. In this work, inspired by the successful fabrications of borophene in experiments, we systematically study the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) activities of a series of 3d transition metal-based SACs supported by various borophene monolayers (BMs=α_sheet, α₁_sheet, and β₁_sheet borophene), TM/BMs, using density functional theory calculations and kinetic simulations. All of the TM/BMs systems exhibit superior HER performance compared to Pt with close to zero thermoneutral Gibbs free energy (ΔG_H*) of H adsorption. Furthermore, three Ni-deposited systems, namely, Ni/α_BM, Ni/α₁_BM and Ni/β₁_BM, were identified to be superior OER catalysts with remarkably reduced overpotentials. Based on these results, Ni/BMs can be expected to serve as stunning bifunctional electrocatalysts for water splitting. This work provides a guideline for developing efficient bifunctional electrocatalysts.     

Effect of the chemical and structural modification of CMK-3 mesoporous carbon molecular sieve on hydrogen adsorption

The effect of the conditions of postsynthetic modification of CMK-3 carbon mesoporous molecular sieves on their structural and adsorption properties was studied. The specific surface, volume, pore size, and hydrogen adsorption are markedly enhanced upon activation of CMK-3 by thermal, steam, and chemical treatment using H₂, CO₂, H₂O₂, and HNO₃. Analysis of the occupancy density of the mesopore surface indicated increased hydrogen adsorption capacity of the hydrogen-activated carbon surface of CMK-3. Hydrogen adsorption is increased from 1.20 to 2.23 mass % at 1 atm and 77 K by steam treatment. This effect may be employed to create efficient carbon MMS adsorbents, including composite adsorbents, for the accumulation and storage of hydrogen at high pressure (adsorption >6 mass %).     

Simple fabrication of a phosphorus-doped hierarchical porous carbon via soft-template method for efficient CO2capture

Hierarchical porous carbons are widely used as adsorbents, catalyst supports, electrode materials, and other applications because of their high specific surface area (SSA), varied pore structure, adjustable porosity, and excellent physicochemical stability. Introducing heteroatoms such as N, P, or S, with electronegativities different from that of carbon, into the carbon skeleton can change the chemical properties of the surface and the density of the electron cloud around the carbon matrix, thus altering interactions of CO₂molecules with the surface and improving CO₂adsorption capacity. Therefore, doping heteroatoms in carbon materials has attracted a great amount of attention. In this paper, the template method was used with F108 (polyethylene glycol–polypropylene glycolpolyethylene glycol) as the template, resorcinol and formaldehyde solutions as the carbon sources, phosphoric acid as the phosphorus source, and KOH as the activator to prepare phosphorus-doped hierarchical porous carbons. Through a series of characterization and CO₂adsorption experiments, the influence of the amount of KOH and template agent on the pore structure of carbon materials was studied. We conclude that these phosphorus-doped hierarchical porous carbon materials are promising CO₂adsorbents.     

Universal Scaling of Intrinsic Resistivity in Two‐Dimensional Metallic Borophene

Two‐dimensional boron sheets (borophenes) have been successfully synthesized in experiments and are expected to exhibit intriguing transport properties. A comprehensive first‐principles study is reported of the intrinsic electrical resistivity of emerging borophene structures. The resistivity is highly dependent on different polymorphs and electron densities of borophene. Interestingly, a universal behavior of the intrinsic resistivity is well‐described using the Bloch–Grüneisen model. In contrast to graphene and conventional metals, the intrinsic resistivity of borophenes can be easily tuned by adjusting carrier densities, while the Bloch–Grüneisen temperature is nearly fixed at 100 K. This work suggests that monolayer boron can serve as intriguing platform for realizing tunable two‐dimensional electronic devices.     

Composite materials based on zeolite 4A for adsorption heat pumps

Some additives and binders were chosen for the preparation of 4A-zeolite-based composites with high equivalent thermal conductivity for heat pumps application. Additives (SiC, Si₃N₄, graphite) and binders (PTFE, Al(OH)₃) were tested for their effectiveness in terms of equivalent thermal conductivity and maximum water adsorption capacity of the composites. The influence of the equivalent thermal conductivity of the composite adsorbents on the specific power of the heat pump was also calculated. Results show a significant improvement in the equivalent thermal conductivity of the composite samples which are prepared using aluminum hydroxide as binder, over that of zeolite pellet beds. Such composite materials could be used to build adsorption heat pumps with higher specific power and, consequently, with lower investment cost.     

Comparative study of adsorbents performance in ethylene/ethane separation

Some potential adsorbents for ethylene/ethane separation are ethylene selective while the others are ethane selective. Among different adsorbents, i.e., zeolites and metal organic frameworks (MOFs), a comparative study is critical to find the more suitable adsorbent for the separation. In this paper, binary ethylene/ethane adsorption performances of zeolites and MOFs, i.e., equilibrium selectivities and adsorption capacities are investigated utilizing ideal adsorbed solution theory (IAST). IAST model is applied at different gas compositions (0.1–0.9 ethylene mole fractions) and pressures up to 100 kPa. The results revealed that the most selective adsorbent toward ethylene is 5A zeolite while MOFs have higher equilibrium adsorption capacities. Among zeolites and MOFs, 5A and Fe₂(dobdc) have the highest selectivity (27.4 and 13.6) and capacity (≈2.8 and 5.8 mmol ethylene/g) at 100 kPa and 298 K for a 50/50 mixture. Among ethane selective adsorbents, Silicalite-1 zeolite and UTSA-33a (MOF) have the highest selectivity and capacity (≈2.9 and ≈1.5 mmol ethane/g) at 100 kPa and 298 K for a 50/50 mixture, respectively. Investigation showed that adsorption capacity of ethylene selective adsorbents is higher than that of ethane selective ones.     

Distribution coefficients in the water-dodecane system and heats of adsorption of ethylene glycol monoalkyl ethers on hydrophilic and hydrophobic carriers

The distribution coefficients in the water-dodecane system and the heats of adsorption of ethylene glycol monoalkyl ethers on hydrophilic (Silochrom S-80) and hydrophobic (Apiezon L on Chromaton) carriers were determined by gas chromatography. At low concentrations and 25°C, ethers with C₁-C₄ alkyl radials predominantly occurred in the aqueous phase, whereas the amyl ether of ethylene glycol was better soluble in the organic phase. Ethers adsorbed formed monomolecular and polymolecular coatings on the hydrophobic and hydrophilic adsorbents, respectively. The heats of adsorption of ethers on the hydrophilic adsorbent were higher than the heats of adsorption on the hydrophobic adsorbent by factors of from 1.93 to 2.20.     

Analyzing the adsorption of blood plasma components by means of fullerene-containing silica gels and NMR spectroscopy in solids

The results from studying the adsorption of blood plasma components (e.g., protein, triglycerides, cholesterol, and lipoproteins of low and high density) using silica gels modified with fullerene molecules (in the form of C₆₀ or the hydroxylated form of C₆₀(OH) _x ) and subjected to hydration (or, alternatively, dehydration) are presented. The conditions for preparing adsorbents that allow us to control the adsorption capacity of silica gel and the selectivity of adsorption toward the components of blood plasma, are revealed. The nature and strength of the interactions of the introduced components (fullerene molecules and water) with functional groups on the silica surface are studied by means of solid state NMR spectroscopy (NMR-SS). Conclusions regarding the nature of the centers that control adsorption are drawn on the basis of NMR-SS spectra in combination with direct measurements of adsorption. The interaction of the oxygen of the hydroxyl group of silica gel with fullerene, leading to the formation of electron-donor complexes of C₆₀-H, C₆₀-OH, or C₆₀-OSi type, is demonstrated by the observed changes in the NMR-SS spectra of silica gels in the presence of fullerene.     

Purification of phloridzin from Lithocarpus polystachyus Rehd leaves using polymeric adsorbents functionalized with glucosamine and β-cyclodextrin

A high-efficient purification method of flavonoids from Lithocarpus polystachyus Rehd leaves is reported. Two adsorbents functionalized with glucosamine (GA) and β-cyclodextrin (β-CD) were synthesized and characterized by the Fourier transform infrared (FTIR) spectra. Also, adsorption properties and purification effect of flavonoids on different adsorbents were investigated. Two typical commercial adsorbents, AB-8 and D101, were employed as the reference materials. The adsorption capacity was enhanced remarkably by the introduction of GA and β-CD groups to the adsorbents. Moreover, the isotherms were well fitted by the Freundlich model. After a one-step column chromatographic separation, the purity of phloridzin increased significantly from 14.65 % to 79.48 % for PS-CD, to 66.56 % for PS-GA, 44.68 % for D101, and to 52.84 % for AB-8. This study provides a novel alternative matrix for the purification of phloridzin from Lithocarpus polystachyus Rehd leaves extracts.     

Adsorption characteristics of malachite green dye onto novel kappa-carrageenan-g-polyacrylic acid/TiO2–NH2 hydrogel nanocomposite

Batch adsorption experiments were carried out for the removal of malachite green (MG) cationic dye from aqueous solution using novel hydrogel nanocomposite that was prepared by graft copolymerization of acrylic acid (AA) onto kappa-carrageenan (κC) biopolymer in the presence of a crosslinking agent, a free radical initiator and aminosilica-functionalized TiO₂ nanoparticles (κC-g-PAA/TiO₂–NH₂). The factors influencing adsorption capacity of the adsorbents such as initial pH value (pH₀) of the dye solutions, TiO₂–NH₂ content (wt%), initial concentration of the dye, amount of adsorbents, and temperature were investigated. The adsorption capacity of hydrogel nanocomposite for MG was compared with hydrogel. The adsorption behaviors of both adsorbents showed that the adsorption kinetics and isotherms were in good agreement with a pseudo-second-order equation and the Langmuir equation. The high adsorption capacity (q _m= 666–833 (mg/g)) and the favorable heterogeneity factor (n = 1.2–1.5) calculated from isotherm equations show the efficiency of the novel adsorbents.     

The adsorption and decomposition of ethylene on Ni(100)

The adsorption behavior of ethylene on Ni(100) at a variety of temperatures has been studied using temperature programmed desorption, and X-ray and UV photoemission. The adsorption of ethylene at 98 K results in molecular adsorption with a saturation C/Ni ratio of 0.76. Heating this surface to any temperature between 213 and 683 K reduces the C/Ni ratio to 0.5. Exposure to ethylene at 300 K leads to decomposition producing surface carbide, adsorbed hydrogen atoms and an adsorbed C_xH_2x species. A comparison with other work on Ni(111) indicates that ethylene adsorption processes are structure sensitive.     

Volatile organic compounds sensing properties of tetrakis(alkylthio)-substituted lutetium(III) bisphthalocyanines thin films

The effect of volatile organic compounds (VOCs) such as acetone, methanol, ethanol, chloroform, carbon tetrachloride, dichloromethane, and hexane on electrical conductivity of thin films of bis[tetrakis(alkylthio)phthalocyaninato]lutetium(III) double decker complexes [(C_nH_2n+1S)₄Pc]₂Lu(III) was investigated. The [(C_nH_2n+1S)₄Pc]₂Lu(III) molecules substituted with different alkylthia chains (n = 6, 8, 10, 12, and 16) were coated on interdigital transducers using a jet spray technique. A change (increase or decrease) in the conductivity of the [(C_nH_2n+1S)₄Pc]₂Lu(III) films was observed depending on the concentration of the VOCs, which was ranging from 500 to 5000 ppm. The decrease in the conductivity of the sensors for the dissolvent of the compounds (chloroform, carbon tetrachloride, dichloromethane and hexane) could be related to swelling of the films. On the other hand, the increase in the conductivity of the sensors for the other VOCs (acetone, methanol and ethanol) could be resulted from that the VOCs act as electron donors and/or acceptors in the films. A linear relationship between the sensor response and concentration of the VOC vapors is obtained. The sensitivities of the [(C_nH_2n+1S)₄Pc]₂Lu(III) films were in the range of 2.10⁻⁴-3.10⁻³%/ppm.     

High selective purification of flavonoids from natural plants based on polymeric adsorbent with hydrogen-bonding interaction

The efficient purification method of high purity flavonoids from natural plants was reported. A series of polymeric adsorbents with novel structure were synthesized based on the copolymerization of methyl acrylate (MA) and ethylene glycol dimethacrylate (EDGMA). Functional groups, such as ester, amino or amide group, were introduced into the adsorbent matrix, respectively, to produce the hydrogen-bonding interaction and enhance the adsorption selectivity towards flavone compounds. The influences of matrix structure and functional groups of synthesized adsorbents on the adsorption selectivity were investigated. The resins were applied to purify flavonoids in natural plants. It was illuminated that the adsorbent No. 3B with 15% EGDMA content and amide groups performed optimal selectivity to flavone compounds in Scutellaria barbata D.Don, from which the purity of flavonoids in extracts was obtained more than 50%, obviously higher than that from commercial adsorbents. The result of adsorption thermodynamics experiment showed that the isosteric adsorption enthalpy of No. 3B was in the range of 25–30 kJ/mol, which testified that the adsorption mechanism was related to hydrogen-bonding interaction. The method showed its universality via good effects on the purification of total flavonoids from Ginkgo biloba L., Radix puerariae and Hypericum perforatum L.     

A Series of Mesoporous Metal-Organic Frameworks with Tunable Windows Sizes and Exceptionally High Ethane over Ethylene Adsorption Selectivity

The NIIC-20 (NIIC stands for Nikolaev Institute of Inorganic Chemistry) is a family of five isostructural metal-organic frameworks (MOFs) based on dodecanuclear wheel-shaped carboxylate building blocks {Zn₁₂(RCOO)₁₂(glycol)₆} (glycol is deprotonated diatomic alcohol: ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol or glycerol), quantitatively crystallized from readily available starting chemicals. The crystal structures contain large mesoporous cages of 25 Å connected through {Zn₁₂} rings, of which inner diameter and chemical nature depend solely on the chosen glycol. The NIIC-20 compounds feature high surface area and rarely observed inversed adsorption affinity for saturated hydrocarbon (ethane) over the unsaturated ones (ethylene, acetylene). The corresponding IAST (Ideal Adsorbed Solution Theory) adsorption selectivity factors reach as much as 15.4 for C₂H₆/C₂H₄ and 10.9 for C₂H₆/C₂H₂ gas mixtures at ambient conditions, exceeding those for any other porous MOF reported so far. The remarkable combination of high adsorption uptakes and high adsorption selectivities makes the NIIC-20 series a new benchmark of porous materials designed for ethylene separation applications.