High CO2 Adsorption Selectivity Research Articles

Microwave-assisted synthesis of Mg-gallate for efficient CO2 capture

With the development of modern industry and increasing population around the world, the overuse of fossil fuels for energy supply has produced large amounts of CO2 in the atmosphere. Metal-organic frameworks (MOFs) with tailorable structures and developed porosity have emerged as promising candidates for CO2 adsorption and separation. However, the synthesis of MOFs by conventional hydrothermal method faces challenges like low crystallization rate and yield, which limits their industrial application for gas adsorption. In this work, a highly efficient microwave (MW)-assisted method was employed for the synthesis of Mg-gallate. The effects of MW conditions on the structure, morphology, and CO2 adsorption properties of Mg-gallate were systematically investigated. The highest CO2 adsorption performance (5.37 mmol g−1 at 298 K and 1 bar) was achieved on the Mg-gallate synthesized at 100 °C for 20 min under an MW power of 100 W. The obtained Mg-gallate also exhibited high adsorption selectivity of CO2 over N2 (1500) and superior recyclability. Furthermore, the Mg-gallate@PEI composite beads were designed by incorporating the MOF crystals into the polymeric matrix in order to satisfy the industrial application demands. The combined advantages of rapid MW synthesis, excellent adsorption performance, and shaping make the Mg-gallate a promising material for practical CO2 capture.

3,11-Diaminodibenzo[a,j]phenazine: Synthesis, Properties, and Applications to Tröger's Base-Forming Ladder Polymerization.

A new class of diamino-substituted π-extended phenazine compound was synthesized, and its photophysical properties were investigated. The U-shaped diaminophenazine displayed photoluminescence in solution with moderate quantum yield. The diamino aromatic compound was found applicable to the poly-condensation with formaldehyde to form Tröger's base ladder polymer. The obtained microporous ladder polymer features high CO2 adsorption selectivity against N2 , most likely due to the presence of basic nitrogen atoms in the phenazine rings.

Enhanced Adsorption Selectivity of Carbon Dioxide and Ethane on Porous Metal–Organic Framework Functionalized by a Sulfur-Rich Heterocycle

Porous metal-organic framework [Zn2(ttdc)2(bpy)] (1) based on thieno [3,2-b]thiophenedicarboxylate (ttdc) was synthesized and characterized. The structure contains intersected zig-zag channels with an average aperture of 4 × 6 Å and a 49% (v/v) guest-accessible pore volume. Gas adsorption studies confirmed the microporous nature of 1 with a specific surface area (BET model) of 952 m2·g-1 and a pore volume of 0.37 cm3·g-1. Extensive CO2, N2, O2, CO, CH4, C2H2, C2H4 and C2H6 gas adsorption experiments at 273 K and 298 K were carried out, which revealed the great adsorption selectivity of C2H6 over CH4 (IAST selectivity factor 14.8 at 298 K). The sulfur-rich ligands and double framework interpenetration in 1 result in a dense decoration of the inner surface by thiophene heterocyclic moieties, which are known to be effective secondary adsorption sites for carbon dioxide. As a result, remarkable CO2 adsorption selectivities were obtained for CO2/CH4 (11.7) and CO2/N2 (27.2 for CO2:N2 = 1:1, 56.4 for CO2:N2 = 15:85 gas mixtures). The computational DFT calculations revealed the decisive role of the sulfur-containing heterocycle moieties in the adsorption of CO2 and C2H6. High CO2 adsorption selectivity values and a relatively low isosteric heat of CO2 adsorption (31.4 kJ·mol-1) make the porous material 1 a promising candidate for practical separation of biogas as well as for CO2 sequestration from flue gas or natural gas.

Inorganic Pillar Center-Facilitated Counterdiffusion Synthesis for Highly H2 Perm-Selective KAUST-7 Membranes.

Fluorinated metal-organic framework materials (NbOFFIVE-1-Ni, also referred to as KAUST-7) have attracted widespread attention because of their high chemical stability and thermal stability, outstanding tolerance with water and H2S, and high CO2-adsorption selectivity over H2 and CH4. KAUST-7 was expected to be a new membrane material candidate for H2/CO2 separation because of the hindered permeation of CO2 resulting from the interaction between CO2 and (NbOF5)2- of the KAUST-7 framework. A highly H2 perm-selective KAUST-7 membrane was first achieved using a novel strategy of inorganic pillar center-facilitated counterdiffusion (IPCFCD) proposed by us. The IPCFCD method not only effectively avoided the corrosion of hydrofluoric acid to α-Al2O3 tubes in the process of preparing KAUST-7 membranes, but also better reduced grain boundary defects because of the faster nucleation rate and resultant high crystallinity. The KAUST-7 membrane exhibited a high H2/CO2 separation factor (SF) of 27.30 for the 1:1 H2/CO2 binary gas mixture with a high H2 permeance of 5.30 × 10-7 mol m-2 s-1 Pa-1 under ambient conditions and a slight decrease of the H2/CO2 SF with increasing operation temperature and presence of steam. This study highlighted the importance of pre-synthesizing inorganic pillar centers (NiNbOF5 intermediate) and the innovation of a membrane formation process for synthesizing polycrystalline KAUST-7 membranes. Most important of all, our study provided a novel approach to overcome the challenge in fabricating metal-organic framework membranes containing corrosive reactants for the corresponding supports.

Porphyrin-based covalent organic polymer by inverse electron demand Diels-Alder reaction

Inverse electron demand Diels-Alder (IEDDA) reaction has been employed as a powerful ligation in several fields. In the current work, a synthetic approach relying on IEDDA reaction is developed for preparation of a porphyrin based covalent organic polymer (PoTz-COP). A tetra-norbornene functional porphyrin is chosen as the core and a bis-tetrazine as the linker. The PoTz-COP is readily formed by just mixing the components without a catalyst and under mild conditions. Chemical structure, morphology (XRD, SEM-EDX), porosity (BET), thermal stability (TGA), optical and gas sorption (CO2 uptake) and selectivity (CO2/N2) properties via Myers and Prausnitz's ideal adsorbed solution theory (IAST) are investigated. PoTz-COP shows remarkably high adsorption selectivity of CO2 over N2 as found 80, 42, and 47 at 50/50 ratio; 84, 39 and 40 at 15/85 ratio; and 84, 39 and 38 at 05/95 ratio at temperatures of 273 K, 298 K and 320 K at 1.1 bar pressure respectively. The optical band gap is determined relatively narrow as 1.66 eV.

A new porous heterometallic metal‐organic framework for gas adsorption and luminescence sensing

AbstractA new heterometallic metal‐organic framework, namely [Zn2Sr(btc)2(H2O)3]n ⋅ x(solvent) (1 btc=1,3,5‐benzenetricarboxylate), has been solvothermally synthesized and structurally characterized. X‐ray structural analysis reveals that compound 1 exploits heterometallic trinuclear [Zn2Sr(COO)6] clusters as secondary building subunits, and displays a 3D framework with 1D channels along crystallographical c axis that can be simplified into a binodal (3,6)‐connected topological network. The activated sample of 1 a shows high CO2 adsorption capacity and high adsorption selectivity of CO2 over N2 at 298 K. Luminescent properties investigations indicate that 1 a can sensitively sensing of CS2 via luminescence quenching.

Facile syntheses of tetrahedral imidazolate framework for CO2 separation

Exploring the facile synthesis of metal-organic frameworks (MOFs) is necessary for their future industrial applications. In this work, the former reported a three dimensional (3D) tetrahedral imidazolate framework TIF-A1 with formula as Zn(int)(ad)•DMF (Hint ​= ​isonicotinic acid, Had ​= ​adenine) has been synthesized by various facile methods. Interestingly, TIF-A1 can be easily obtained by heating reactants at 120 ​°C in short time (30 ​min) with high yield (ca. 83%), which are furtherly used to realize the upscale synthesis (>800 ​g) of TIF-A1. More importantly, highly crystalline TIF-A1 showed high adsorption selectivity of CO2 over N2 (73) and CH4 (21) under ambient conditions.

Advanced mixed matrix membranes of Pebax embedded with amino acid ionic liquids@PIM core-shell composite nanoparticles for CO2 separation

Introducing the amino acid ionic liquids (AAILs) into polymeric membranes, have been a promising way to improve CO2 permeation-separation performance. A series of novel mixed matrix membranes (MMMs), based on Pebax 2533 and the AAILs@polymers of intrinsic microporosity (core-shell) composite nanoparticles (AAILs@PIM (core-shell) CNPs), were prepared. The composite nanoparticle was composed of the PIM as the dense shell and the AAILs as the core. The AAILs as the core provided high CO2 adsorption selectivity; and the AAILs covered by nanospheres avoided its loss. Moreover, the PIM shell and Pebax matrix also provided a good organic-organic interface in the MMMs. The chemical characterization of AAILs@PIM (core-shell) CNPs was performed by Fourier transform infrared spectroscopy. The morphology and structure of AAILs@PIM (core-shell) CNPs was investigated by transmission electron microscopy. The effect of incorporating the PIM HNPs on the chain segments of Pebax matrix was investigated by the differential scanning calorimeter. Gas transport property of the (AAILs@PIM (core-shell) CNPs)/Pebax MMMs was reported. Compared with the original Pebax membrane, the (AAILs@PIM (core-shell) CNPs)/Pebax MMMs displayed higher CO2/N2 selectivity at the cost of a reduction in CO2 permeability because of the hydrogen bond of the AAILs-CO2 complexes. It is also found that increasing the temperature can eliminate the hydrogen bond of the AAILs-CO2 complexes. Therefore, at high temperature, the (AAILs@PIM (core-shell) CNPs)/Pebax MMMs exhibit both higher CO2 permeability and higher CO2/N2 selectivity than the original Pebax membrane has. The outstanding CO2 permeation-separation performance shows great potential application to the flue gas treatment.

Insight into the separation mechanism of acetate anion-based ionic liquids on CO2 and N2: A multi-scale simulation study

Based on the favorable absorption performance of acetate anion-based ionic liquids (AcILs) for CO2, which has been confirmed in experiments, three representative AcILs, i.e., triethylbutylammonium acetate ([N2224][OAc]), 1-butyl-1-methylpyrrolidinium acetate ([PY14][OAc]) and tetrabutylphosphine acetate ([P4444][OAc]), were investigated for the separation of CO2/N2 from flue gas, and combined quantum chemistry (QC), molecular dynamics (MD) and Grand Canonical Monte Carlo (GCMC) methods, the separation mechanism of AcILs on CO2/N2 was revealed from a microscopic perspective. Herein, stable configurations for AcILs-gas molecules were determined by electrostatic potential (ESP) analysis and interaction energies calculation. The interaction nature of AcILs with gas molecules was characterized by atoms in molecules (AIM) theory, which indicated that both anions and cations interacted with gas molecules, and the interaction of AcILs with CO2 was stronger than those with N2 due to the formation of weak hydrogen bond (H-bond) between them. Meanwhile, MD results suggested that the interaction between AcILs and CO2 was dominated by [OAc]−, and cations also played important roles. The effect of diffusion on separation mechanism was also further illustrated, and large self-diffusion coefficients (Ds) of N2 over CO2 were identified. Moreover, the adsorption isotherms of CO2/N2 molecules in three AcILs at different pressures were calculated using GCMC method. The results showed that all AcILs exhibited high adsorption selectivity for CO2, and [N2224][OAc] had the strongest solubility among them, which were in accordance with the QC analyses results. Hopefully, this work could contribute to better understand the microscopic interaction mechanisms between AcILs and CO2/N2, give an intuitive explanation for their solubility differences, and ultimately provide theoretical guidance for the screening of CO2/N2 separation absorbents.

Heterometallic trinuclear cluster-based microporous metal-organic framework with high adsorption selectivity of CO2 over N2

A new metal-organic compound, [Zn2Ca(bdc)3(H2O)2]n•x(solvent) (1 H2bdc = terephthalic acid), has been successfully constructed via the solvothermal reactions of H2bdc, Zn(NO3)2·6H2O and Ca(NO3)2·4H2O. Two symmetry-related Zn(II) ions and one Ca(II) are bridged by six bis-monodentate carboxylate groups together to form a heterometallic trinuclear [Zn2Ca(COO)6] cluster subunit. The linear bdc2− ligands further connected these trinuclear clusters into a 3D porous framework with 6-connected pcu topology. Remarkably, this porous compound can be stable up to 256 ℃ verified by the thermogravimetric analysis and powder X-ray diffraction analysis. Gas adsorption property investigations demonstrated that it shows high adsorption selectivity for CO2 over N2 at ambient conditions.

An intriguing N-oxide-functionalized 3D flexible microporous MOF exhibiting highly selectivity for CO2 with a gate effect

The axial chiral ligand 2,2′-bipyridyl-3,3′-dicarboxylic acid-1,1′-dioxide (H2bdd) has been employed to synthesize a 3D flexible microporous metal-organic framework (MOF), {[Cu2(bdd)2(bpa)2(H2O)2]·6.5H2O}n (1) (bpa = 1,2-bis(4-pyridyl)ethane), which contains an N-oxide open donor site. A gas adsorption test shows that complex 1′ (dehydrated 1) has a high adsorption selectivity for CO2 rather than N2 and H2. In particular, its CO2 adsorption isotherms exhibit an uncommon gate effect adsorption. The CO2 adsorption enthalpies were calculated from the adsorption isotherms. Compared to a flexible framework with respiration, 1′ displays a low energy consumption for sorbent regeneration, indicating the potential application of complex 1 in gas separation.

Synthesis of hierarchical porous Zeolite-Y for enhanced CO2 capture

Abstract In the present study, a facile and one step approach has been developed for the synthesis of hierarchical porous zeolite-Y using bifunctional cationic polymer, polydiallyldimethyl ammonium chloride (PDDA) as a mesopore directing template. The effects of various synthesis parameters such as hydrothermal reaction temperature, time, amount of PDDA and NaOH were systematically investigated to produce crystalline and hierarchical zeolite-Y crystals (PDYs). All the synthesized zeolite-Y samples were characterized by XRD, FT-IR, SEM, EDAX, TEM, TGA, CO2-TPD and Nitrogen adsorption-desorption measurements. The characterization results showed that the zeolite-Y samples synthesized at optimized ratios of PDDA/Al2O3 and NaOH/Al2O3 exhibited higher crystallinity, higher BET surface area and larger total pore volume in comparison to the sample synthesized in the absence of the template (ZY). Interestingly, the hierarchical porous zeolite-Y samples (PDY-7) displayed substantial enhancement in CO2 adsorption capacity (5.40 mmol/g) at 298 K and 100 kPa as compared to the non-templated one (ZY) (4.5 mmol/g). The effective improvement in CO2 adsorption performance of PDY samples is attributed to the existence of interconnected micro-meso channel network, the higher total pore volume and higher concentration of acid-base sites (due to the lower Si/Al ratio). Owing to the higher CO2 adsorption capacity, the PDY samples also displayed high equilibrium selectivity for CO2 over N2 (∼250) as well as over CH4 (∼110) at 298 K. The enhanced CO2 adsorption capacity combined with the high CO2 adsorption selectivity renders the hierarchical zeolite-Y an excellent contender for the efficient CO2 capture.

A dynamic microporous magnet exhibiting room-temperature thermal hysteresis, variable magnetic ordering temperatures and highly selective adsorption for CO2

A dynamic microporous magnet exhibits a room-temperature hysteresis loop, variable magnetic ordering temperatures and high adsorption selectivity for CO2 over N2.

CO2 adsorption on polyethylenimine-modified ZSM-5 zeolite synthesized from rice husk ash

Mesoporous ZSM-5 zeolite as the adsorbent supporting material was synthesized from rice husk ash (RHA), and then impregnated with polyethylenimine (PEI) for amine functional modification. A series of adsorbents (ZSM-5-PEI-X) with different PEI loading ratios were characterized by XRD, FTIR, TGA/DTG, nitrogen adsorption-desorption, SEM and EDX techniques. The measurement of the adsorption capacity at different temperatures was indicated that ZSM-5-PEI-30 had the highest adsorption capacity at 120 °C (1.96 mmol/g). The experimental data were fitted by adsorption kinetic models and isotherm models, indicated that fractional-order model and the Dual-site langmuir model can be used to describe the adsorption mechanism and predict the adsorption performance. The high CO2 adsorption selectivity and regeneration stability suggested that this adsorbent is a potential candidate in the adsorption and separation of CO2 in industrial flue gas.

Microporous metal–organic framework with 1D helical chain building units: Synthesis, structure and gas sorption properties

The design, synthesis, and structural characterization of a new anionic metal-organic framework, namely, {(H2N(Me)2)[Cu(bidc)](H2O)3}n (1), with 1D helical metal chains is reported here. The title complex was synthesized by solvothermal reaction of Cu(NO3)2·3H2O and benzimidazole-5,6-dicarboxylic acid (H3bidc) in a mixed solvent of DMF, 1,4-dioxane, H2O and HNO3 (aq) at 120°C for three days, which reveals a 3D porous framework with 1D nanotubular channels running along the c axis. The pore characteristics and gas sorption properties of this compound were investigated at both cryogenic temperature and room temperature by experimentally measuring N2, CH4 and CO2 adsorption/desorption isotherms. The amount of the N2 and CO2 uptake is 146cm3/g at 77K and 52cm3/g at 273K, which is the highest among MOFs constructed from the H3bidc ligand. In addition the activated 1 shows high adsorption selectivity of CO2 over CH4 at room temperature.

Characterization of CPs/Ca-exchanged FAU- and LTA-type zeolite nanocomposites and their selectivity for CO2 and N2 adsorption

The objective of this study was to investigate the adsorption capacity and selectivity of CPs/Ca-exchanged FAU- and LTA-type zeolite composites for carbon dioxide (CO2), and nitrogen (N2). The adsorption isotherms of CO2 and N2 on the adsorbents were measured at 298, 323, and 348 K and with a pressure range of 0–5 bar by means of the volumetric adsorption method.Modification of zeolite using cation exchange technique was used to determine the effect of different cation on gas adsorption characteristics. Sodium cations originally present in NaX, NaY and NaA are exchanged with calcium cations. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), X-Ray Diffraction (XRD) and N2 adsorption/desorption isotherms were used to characterize the structure of the prepared zeolites. The addition of conducting polymers (CPs), polythiophene (PTh) and polypyrrole (PPy), to Ca-exchanged zeolites can improve the adsorption capacities of the material and at the same time increase the selectivity of the composite. CPs/Ca-zeolite nanocomposites were prepared by adding CPs to the CaX, CaY and CaA with different weight percentages p% (p = 5, 10 and 15%). CaX/PTh-15 can be used to separate CO2 from N2 due to its high adsorption selectivity for CO2 over N2.

A porous Cd(II) metal-organic framework with high adsorption selectivity for CO2 over CH4

Metal-organic frameworks (MOFs) have attracted a lot of attention in recent decades. We applied a semi-rigid four-carboxylic acid linker to assemble with Cd(II) ions to generate a novel microporous Cd(II) MOF material. Single crystal X-ray diffraction study reveals the different two dimension (2D) layers can be further packed together with an AB fashion by hydrogen bonds (O4H4⋯O7 = 1.863 Å) to construct a three dimension (3D) supermolecular architecture. The resulting sample can be synthesized under solvothermal reactions successfully, which exhibits high selectivity adsorption of CO2 over CH4 at room temperature. In addition, the obtained sample was characterized by thermal gravimetric analyses (TGA), Fourier-transform infrared spectra (FT-IR), elemental analysis (CHN) and powder X-ray diffraction (PXRD).

Porous pcu-type Zn(II) framework material with high adsorption selectivity for CO2 over N2

Reported here is a new Zn(II) compound, namely [Zn2(tdc)2(MA)]n (H2tdc = 2,5-thiophenedicarboxylic acid, MA = melamine), which has been constructed by the self-assembly reaction of Zn(NO3)2, H2tdc and MA under solvothermal conditions. Single crystal X-ray diffraction analysis reveals that this compound features a 3D porous framework with 6-connected pcu topology. Notably, this compound exhibits high CO2 sorption capacity and high sorption selectivity for CO2 over N2 at 298 K.

Matrix effect of mixed‐matrix membrane containing CO2‐selective MOFs

ABSTRACTFacilitated mixed‐matrix membranes (MMMs) containing Cu‐metal organic frameworks (Cu‐MOFs) with high CO2 selectivity on an asymmetric polysulfone support were fabricated and examined the effect of gas separation performance using different matrices. An amorphous poly(2‐ethyl‐2‐oxazoline) (POZ) and semicrystalline poly(amide‐6‐b‐ethylene oxide) (PEBAX®MH 1657) block copolymer were chosen as the polymeric matrix and the effect of the matrix on CO2 separation for MMMs containing Cu‐MOFs was investigated. The interaction of CO2 in different matrix was investigated theoretically using the density functional theory method, and it was found that the amide segment in PEBAX would contribute more to the CO2 solubility than ether segment. The morphological changes were investigated by differential scanning calorimetry, field emission scanning electron microscope and X‐ray diffractometer. The ideal selectivity of CO2/N2 was enhanced significantly with the addition of a Cu‐MOF, and the values are higher in the Cu‐MOF/PEBAX MMM compared with that in a POZ based asymmetric MMM. Improvement in the CO2/N2 selectivity of a Cu‐MOF/PEBAX MMM was achieved via facilitated transport by the CO2‐selective Cu‐MOFs due to both their high adsorption selectivity of CO2 over N2 and the decreased crystallinity of PEBAX due to the presence of the Cu‐MOFs, which would provide a synergic effect on the CO2 separation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 132, 42853.

High CO2 /CH4 Selectivity of a Flexible Copper(II) Porous Coordination Polymer under Humid Conditions.

The development of highly efficient CO2 separation materials is very important for environmental preservation and energy conservation. Crystalline porous coordination polymers (PCPs)/metal-organic frameworks are one of a number of promising types of porous materials for CO2 separation because of their controllable pore size, shape and surface function. Simultaneously, the unique structural flexibility of PCPs affords both high CO2 selectivity and inexpensive regeneration. However, this family of materials suffers from the coexistence of water that destroys the framework of PCPs and its adsorption in the pores is greater than that of CO2 , which results in a deterioration in CO2 -separation performance. Herein, a flexible and hydrophobic CuII PCP that is stable towards water has been designed and synthesised. This PCP has extremely high adsorption selectivity for CO2 over CH4 , derived from its structural flexibility. Furthermore, the obtained water-tolerant flexible PCP, under CO2 /CH4 mixed-gas conditions, exhibits highly selective CO2 adsorption over CH4 , even in the presence of water.