Selective Adsorption Of CO2 Research Articles

Core–shell adsorbents by electrospun MOF‐polymer composites with improved adsorption properties: Theory and experiments

AbstractA new class of core–shell adsorbents has been created by electrospun metal–organic framework (MOF) particles embedded in polymer nanofibers, which have provided many unique properties compared to the existing MOF coating technologies. For the first time, we demonstrate the improved adsorption selectivity of CO2over N2using electrospun polymer/ZIF‐8 adsorbents in experiments. Furthermore, an analytical model based on the assumption that the diffusivity in core is 10 times higher than that in shell is developed to describe the theory of improved selectivity for core–shell adsorbents that is validated against a more accurate finite element model developed in COMSOL. Our model shows three regimes including exclusive shell uptake, linear core uptake, and asymptotic core uptake. These regimes are related to material properties and uptake times, which could be used as design criteria to balance core stability, maximum selectivity, and maximum uptake. An advanced HAADF STEM tomography (MovieS1) shows that the shell thickness in the case of polymer/ZIF‐8 is on the order of 10 nm, allowing the regime of maximum selectivity to be realized. Kinetically limited adsorption tests at 45°C demonstrate that these composite fibers can perform in a regime of selectivity and uptake for the separation of CO2and N2that is unobtainable by either the MOF or fiber independently, showing a great potential for postcombustion CO2capture.

Crosslinked microporous polyimides with polar substituent group for efficient CO2 capture

Abstract Microporous polyimides have been extensively investigated for CO2 capture and separation applications. Here, the crosslinked structure and the polar CO2-philic trifluoromethyl group are introduced into the hyperbranched polyimides to construct the microporous polyimide networks for efficient CO2 capture. The HBPI-CL networks exhibit significant increased micropores (pore size less than 1 nm) surface area and volume ranging from 79 to 89 m2g-1 and 0.03–0.05 cm3 g−1. It is intriguingly found that the CF3TAPA-HBPI-CL have more abundant ultramicropores and exhibit higher CO2 uptake capacity and CO2/N2 selectivity (8.56 wt% and 33.3) than those of TAPA-HBPI-CL (7.47 wt% and 20.4) without the polar CO2-philic trifluoromethyl group at 273 K/1 bar. This work reveals that the introduction of polar CO2-philic trifluoromethyl group into crosslinked polyimides is an effective method to improve the CO2 adsorption capacity and selectivity of microporous polyimide, which can be also applied to other microporous polymers.

Ethylenediamine-functionalized metal organic frameworks MIL-100(Cr) for efficient CO2/N2O separation

To date, separating CO2 and N2O mixtures is still a great challenge due to their identical molecular masses and sizes. It is noteworthy that CO2 is acid gas, while N2O is not, we infered that they can be separated through acid-base coordination. Herein, we report the use of an ethylenediamine–functionalized metal organic framework ED-MIL-100Cr-0.2/0.4/0.6 towards the construction of a new alkaline adsorption site for the CO2 binding. The experimental results show that ED-MIL-100Cr-0.4 with the highest adsorption heat of CO2 up to ~80 KJ/mol and N2O being 25 KJ/mol, and it has the highest equilibrium adsorption selectivity (28.0, IAST method) of CO2 v N2O reported to date. It was also confirmed that ED-MIL-100Cr-0.4 had the best performance in the separation of CO2 and N2O mixtures by the breakthrough test. Finally, the cycling experiments revealed its good renderability, making its potentially useful in industrial CO2/N2O separation.

Devising Chemically Robust and Cationic Ni(II)-MOF with Nitrogen-Rich Micropores for Moisture-Tolerant CO2 Capture: Highly Regenerative and Ultrafast Colorimetric Sensor for TNP and Multiple Oxo-Anions in Water with Theoretical Revelation.

Metal-organic frameworks (MOFs) show distinctive superiority for carbon dioxide (CO2) capture and luminescent sensing of toxic pollutants over other materials, where combination of both of these properties together with improvement of hydrolytic stability and pore functionality is critical to environmental remediation applications. The Ni(II) framework [Ni2(μ2-OH)(azdc)(tpim)](NO3)·6DMA·6MeOH (CSMCRI-3) (tpim = 4,4',4″-(1H-imidazole-2,4,5-triyl)tripyridine, H2azdc = azobenzene-4,4'-dicarboxylic acid, DMA = dimethylacetamide, CSMCRI = Central Salt & Marine Chemicals Research Institute), encompassing cationic [Ni2(μ2-OH)(CO2)2] SBUs, is solvothermally synthesized from nitrogen-rich and highly fluorescent organic struts. The noninterpenetrated structure, containing free nitrogen atom affixed microporous channels, is stable in diverse organic solvents and weakly basic and acidic aqueous solutions. The activated MOF (3a) exhibits strong CO2-framework interaction and extremely selective CO2 adsorption over N2 (292.5) and CH4 (11.7). Importantly, water vapor exposure does not affect the surface area and/or multiple CO2 uptake-release cycles, signifying potential of the porous structure for long-term use under humid conditions. Aqueous-phase sensing studies illustrate extremely specific and ultrafast detection of explosive 2,4,6-trinitrophenol (TNP) via remarkable fluorescence quenching (KSV = 1.3 × 105 M-1), with a 0.25 ppm limit of detection (LOD). Furthermore, 3a serves as unique luminescent probe for highly discriminative and quick responsive detection of three noxious oxo-anions (Cr2O72-, CrO42-, MnO4-) in water via noteworthy turn-off responses and extreme low LODs (Cr2O72- 0.9; CrO42- 0.29; MnO4- 0.25 ppm). It is imperative to stress the outstanding reusability of the MOF toward multicyclic sensing of all four major water contaminants, alongside visible colorimetric changes upon individual analyte detection. Mechanistic insights in light of the electron transfer route together with density functional theory calculations portray the influence of pore functionalization in framework-analyte interactions, including alternation in energy levels, where varying degrees of contribution of energy transfer explicitly authenticates high quenching of the material.

Solvents-Dependent Formation of Three MOFs from the Fe3O Cluster and 3,3',5,5'-Diphenyltetracarboxylic Acid and Their Selective CO2 Adsorption.

On the basis of the [Fe3(μ3-O)(COO)6] cluster and 3,3',5,5'-diphenyltetracarboxylic acid (H4BPTC), three novel metal-organic frameworks (MOFs), NJU-Bai25, NJU-Bai26, and NJU-Bai27 (NJU-Bai for Bai's group at Nanjing University ) with different (4,4,4,6)-, (4,4,4,4,4,6)-, and (4,4,6)-connected nets were obtained in different solvent systems, in which due to the steric hindrance of the coordinated solvents the conformations of BPTC gradually change from the planar to the torsional; thus, the pore sizes of those MOFs were also gradually narrowed. Interestingly, the MOFs show high thermal/chemical stabilities and selective CO2 adsorption: NJU-Bai27 exhibits larger CO2 uptake (5.0 and 13.8 wt %) at 298 K under 0.15 and 1 bar, whereas NJU-Bai26 has a higher selectivity for CO2/N2 (366).

Experimental Study of High Purity CO2 Concentration from Syngas by a Dual-bed Six-step Pressure Swing Adsorption Process

With the industry development, the concentration of greenhouse gas increases year by year. Consequently, how to reduce the emission of greenhouse gas has become an important issue all over the world. This research is the experimental study of concentrating high purity CO2 from syngas after oxy-fuel combustion by a dual-bed six-step pressure swing adsorption (PSA) process. The composition of feed gas used in the process was simulated as 95% CO2, with N2 balanced. We chose UOP 13X zeolite as the adsorbent according to the adsorption capacity and selectivity of CO2 over N2 comparing to other adsorbents studied. The breakthrough and desorption curves were discussed by changing different feed flow rate and temperature. Next the carbon dioxide was purified by a dual-bed six-step PSA process. After exploring the effects of variables on performance of PSA process, we found the best operating conditions for obtaining high purity carbon dioxide among our experiments. The best operating conditions are feed pressure 3.45 atm, countercurrent depressurization pressure 0.48 atm and purge to feed ratio 0.105. The experimental results of best conditions are 99.94% purity and 42.84% recovery of carbon dioxide at bottom product, energy consumption 0.304 GJ/tonne CO2 and productivity 0.136 kg CO2/kg adsorbenth.

Graphene-containing microporous composites for selective CO2 adsorption

Abstract Activated carbons obtained from polymers, Cu-containing metal-organic framework (MOF) and their composites with graphene oxide were synthesized using facile methods and tested for the selective adsorption of CO2 over N2 at ambient conditions. The prepared materials have been characterized by scanning electron microscopy, X-ray diffraction analysis and N2 adsorption. The Cu-containing metal-organic framework showed high CO2 uptakes up to 9.59 mmol g−1 and 5.33 mmol g−1 under 1 bar at 0 °C and 25 °C, respectively. The MOF composite with ~10 wt % of graphene oxide exhibited the best CO2 adsorption selectivity over N2 among all samples studied. Although, most graphene-containing composites feature lower CO2 adsorption capacities, they show an enhanced CO2/N2 selectivity in comparison to the bare samples. This paper contains a comparative study of the CO2/N2 selectivity calculated by using different methods. Additionally, CH4 adsorption, CO2/CH4 selectivity and isosteric heat of CO2 adsorption were evaluated for the selected sorbents. This study indicates that graphene-containing composites are potential materials for large-scale selective CO2 capture at ambient conditions.

Selective CO2 adsorption and H2 storage in two porous amine-pillared graphene oxide frameworks

Two porous graphene oxide frameworks (GOFs) have been synthesized by a reaction of graphene oxide (GO) and benzylamine (GOF-1) or p-xylylenediamine (GOF-2) through a solvothermal process. The structures and porosity of these two GOFs were characterized and they exhibited different adsorption behaviours. GOFs both showed enhanced porosity and surface area than the parent graphene oxide, which was ascribed to the tunable interlayer spacing. The GOFs possess good H2 storage capacity (0.46 wt% for GOF-1 and 0.57 wt% for GOF-2 at 77 K and 1 bar) though with rather small surface area (86.4 m2/g for GOF-1 and 102.7 m2/g for GOF-2). The CO2 adsorption capacity and selectivity over N2 of GOFs has also been investigated by ideal adsorbed solution theory (IAST) method, and GOF-2 exhibited CO2/N2 selectivity of 40.7 which was higher than that of GOF-1. It emphasized a tunable synthesis of multifunctional materials for H2 storage and CO2 separation from flue gases by decorating 2-dimensional GO nanosheets.

Covalent Organic Frameworks for the Capture, Fixation, or Reduction of CO2

Covalent organic frameworks (COFs) are porous crystalline organic polymers which have been the subject of immense research interest in the past ten years. COF materials are designed by the organization of two distinct organic molecules bonded in a repeating fashion to form a porous crystal that has made them ideal of gas adsorption and storage. Chemists have strategically designed COFs for the purpose of heterogeneous catalysis of gaseous reactants. Presented in this critical review are efforts towards developing COFs for the sequestration of CO2 from the atmosphere. Researchers have determined the CO2 adsorption capabilities of several COFs is competitive with the highest surface area materials. Engineering the pore environment of COFs with chemical moieties that interact with CO2 have increased the CO2 adsorption performance. The installation of CO2 binding moieties in the COF has made possible the selective adsorption of CO2 over other gases such as N2. The high degree of control of internal pore composition in COFs is coupled with High CO2 adsorption to develop heterogeneous catalysts for the conversion of CO2 to value added products. Two notable examples of this catalysis are the conversion of fixation of CO2 to epoxides for the synthesis of cyclic carbonates and the reduction of CO2 to CO for combustion. Recent examples of COFs for the capture of CO2 will be discussed followed by COF catalysts which use CO2 as a feedstock for the production of value-added products.

Selective adsorption of Co(II)/Mn(II) by zeolites from purified terephthalic acid wastewater containing dissolved aromatic organic compounds and metal ions

Selective separation and recovery of Co(II)/Mn(II) from purified terephthalic acid (PTA) production wastewater is very important to reduce the Co(II)/Mn(II) catalysts consumption and control the pollutant discharge. This work employed zeolites NaA, NaX, and HZSM-5 with different pore sizes and Na(I) contents to selectively separate and recover Co(II)/Mn(II) from PTA wastewater and to understand the adsorption mechanism. It is found that only NaA can exclusively adsorb Co(II)/Mn(II) through ion-exchange without adsorbing any aromatic organic compound (AOC); oppositely, HZSM-5 shows the highest adsorption capacity for AOCs but almost no adsorption for Co(II)/Mn(II); and NaX exhibits moderate adsorption capacities for both Co(II)/Mn(II) and AOCs. Moreover, pH can significantly impact the adsorption of both Co(II)/Mn(II) and AOCs due to the competitive adsorption between H(I) and Co(II)/Mn(II) and the electrostatic repulsion between AOCs and zeolites. The adsorption kinetics, isotherms, and thermodynamics were also investigated to lay a good basis for process development. Importantly, bench-scale experiments for simulating the industrial operation were carried out, and the results show that the adsorption capacity of the NaA particles for Co(II)/Mn(II) from the industrial PTA wastewater is 9.1/8.6 mg/g, respectively, without adsorbing any AOC. Therefore, an efficient strategy to selectively separate and recover Co(II)/Mn(II) from PTA wastewater was successfully developed.

Thermodynamic Modeling of the Selective Adsorption of Carbon Dioxide over Methane in the Mechanically Constrained Breathing MIL‐53(Cr)

AbstractThe coadsorption of CO2/CH4 in the breathing MIL‐53(Cr) under the application of an additional mechanical pressure is investigated through the use of an extended thermodynamic mean‐field model. The focus is on the breathing behavior, negative gas adsorption (NGA), and selective adsorption of CO2 as well as to what degree the application of mechanical pressure influences this behavior. To this end, phase diagrams, coadsorption isotherms are constructed and the CO2/CH4 selectivity is computed in terms of the vapor pressure of methane and carbon dioxide as well as the mechanical pressure. As a result, it is found that NGA can be induced by coadsorption of CO2/CH4 gas mixtures with certain molar compositions. Finally, a specific adsorption/desorption cycle, which includes the application of an additional mechanical pressure, is proposed to allow for an increased CO2/CH4 selectivity as well as for an expected less energy demanding CO2 desorption step.

Metal-organic framework MIL-101 loaded with polymethacrylamide with or without further reduction: Effective and selective CO2 adsorption with amino or amide functionality

In order to improve the performances of a typical/highly porous metal-organic framework (MOF, MIL-101 structure) in CO2 adsorption/capture, methacrylamide was polymerized (to polymethacrylamide or PM) inside of MIL-101 (to get PM@MOF) and further reduced with lithium aluminum hydride. The obtained adsorbents (R-PM24@MOF or PM24@MOF) had highly enhanced performances, compared with the pristine MOF, in CO2 capture both in the adsorption capacity (especially at low pressure of 0.15 atm) and adsorption selectivity (against N2), suggesting the polyamides loading (and subsequent reduction) on MOFs is an effective mean to derive competitive adsorbent for CO2 adsorption/capture. For example, the developed adsorbent (R-PM24@MOF) showed 1.4 mmol/g of adsorbed CO2 (at 0.15 atm and 298 K) and adsorption selectivity (CO2/N2) of 143 at 298 K (CO2/N2 = 0.75/0.15, at 1 atm); which are ~3 and ~10 times to that of pristine MIL-101, respectively. The remarkably enhanced performances could be explained with the introduced functional groups and reduced porosity (for decreased N2 adsorption). Moreover, the adsorbent could be easily recycled, suggesting the potential application in selective adsorption of CO2 from off gas of post-combustions.

Triggered Gate Opening and Breathing Effects during Selective CO2 Adsorption by Merlinoite Zeolite.

Zeolites with flexible structures that adapt to coordinate extraframework cations when dehydrated show a rich variety of gas adsorption behavior and can be tuned to optimize kinetics and selectivity. Merlinoite zeolite (topology type MER) with Si/Al = 3.8 has been prepared in Na, K, and Cs forms and its structural response to dehydration measured: the unit cell volumes decrease by 9.8%, 7.7%, and 7.1% for Na-, K-, and Cs-MER, respectively. Na-MER adopts Immm symmetry, while K- and Cs-MER display P42/nmc symmetry, the difference attributed to the preferred locations of the smaller and larger cations. Their performance in CO2 adsorption has been measured by single-component isotherms and by mixed gas (CO2/CH4/He) breakthrough experiments. The differing behavior of the cation forms can be related to structural changes during CO2 uptake measured by variable-pressure PXRD. All show a "breathing" transition from narrow to wide pore forms. Na- and Cs-MER show non-Type I isotherms and kinetically-limited CO2 adsorption and delivery of pure CH4 in CO2/CH4 separation. However, K-MER shows good uptake of CO2 (3.5 mmol g-1 at 1 bar and 298 K), rapid adsorption and desorption kinetics, and promising CO2/CH4 separation. Furthermore, the narrow-to-wide pore transition occurs rapidly and at very low pCO2 via a "triggered" opening. This has the consequence that whereas no CH4 is adsorbed from a pure stream, addition of low levels of CO2 can result in pore opening and uptake of both CO2 and CH4, although in a continuous stream the CH4 is replaced selectively by CO2. This observed cation size-dependent adsorption behavior derives from a fine energetic balance between different framework configurations in these cation-controlled molecular sieves.

Synthesis of polyethylenimine-impregnated titanate nanotubes for CO2 capture: Influence of porosity and nitrogen content on amine-modified adsorbents

Amine-modified adsorbents have been of interest due to their excellent performance for carbon dioxide (CO2) capture. In this work, we have prepared titanate nanotubes (TNTs) with amine modification using polyethylenimine (PEI) for selective CO2 capture under flue gas. TNTs were prepared by the hydrothermal reaction, and PEI-functionalized TNTs (P-TNTs) were prepared by the wet impregnation method. Enhanced CO2 affinity through amine modification on TNTs allows for selective and favorable CO2 adsorption onto adsorbents. To confirm the CO2 capture in the post-combustion step, CO2 adsorption performances were investigated by the gravimetric method under 15% CO2 /85% N2 (binary) and 15% CO2/5% O2/80% N2 (ternary) gases as in flue gas conditions, respectively. Furthermore, our work provides evidence that the amine-modified adsorbents can be influenced by oxygen gas on CO2 capture performances, including regeneration ability.

Effect of heat treatment temperature on CO2 capture of nitrogen‐enriched porous carbon fibers

AbstractPorous carbon fibers (PCFs) were prepared from porous polyacrylonitrile fibers by cross‐linking, oxidation, and carbonization. X‐ray diffraction patterns revealed that graphite structures as well as disordered carbon coexisted in the PCFs. Nitrogen content was more than 15.3 wt% with the variation of oxidation temperature, and a maximum value was obtained at 275°C. Nitrogen was quickly released with carbonization temperature. Compared with the fiber prepared at elevated carbonization temperatures, those owning high nitrogen contents deserved better carbon dioxide (CO2) adsorption performance in the simulated flue gas environment (10% CO2/90% N2). The CO2 adsorption had a better relationship with nitrogen content rather than specific surface area and pore volumes. Especially, nitrogen was very useful to enhance the CO2 adsorption of the fibers with low microporosity. The heat of CO2 adsorption was in the range of 39.8–54.6 kJ mol−1, which indicated good selectivity of CO2 adsorption. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Ionic liquid gated 2D-CAP membrane for highly efficient CO2/N2 and CO2/CH4 separation

Recently, a two-dimensional conjugated aromatic polymer (2D-CAP) membrane has been synthesized, and it shows promising applications in the selected gas separation. However, the sub-nanometer pores of the 2D-CAP membrane are relatively large compared with small gas molecules like CO2, N2, and CH4, which impedes the efficiency of the gas separation. Here, we report a strategy to improve the gas separation performance of 2D-CAP membranes. Specifically, coating ultra-thin ionic liquid (IL) onto the 2D-CAP membrane was found to well harmonize the pore size of 2D-CAP membranes. In this work, the gas separation performance of this 2D-CAP supported IL membrane (2D-CAP SILM) was investigated using molecular dynamics simulations. An ultrahigh CO2 permeance of ~105 GPU, which is larger than many reported theoretically predicted results, was exhibited. Meanwhile, an excellent selectivity of CO2/N2 and CO2/CH4 beyond 40 was obtained. The ultrathin membrane and the high-density pore are responsible for the high gas permeance, and the selectivity could be ascribed to IL adsorption selectivity of CO2 over N2/CH4 and a fascinating gating effect that anion of IL ([BF4]−) suspending upside the pore center allows CO2 passage while prohibits N2/CH4 passage. The present work suggests a promising membrane for practical highly efficient CO2 separation.

Tuning Carbon Dioxide Adsorption Affinity of Zinc(II) MOFs by Mixing Bis(pyrazolate) Ligands with N-Containing Tags.

The four zinc(II) mixed-ligand metal-organic frameworks (MIXMOFs) Zn(BPZ)x(BPZNO2)1-x, Zn(BPZ)x(BPZNH2)1-x, Zn(BPZNO2)x(BPZNH2)1-x, and Zn(BPZ)x(BPZNO2)y(BPZNH2)1-x-y (H2BPZ = 4,4'-bipyrazole; H2BPZNO2 = 3-nitro-4,4'-bipyrazole; H2BPZNH2 = 3-amino-4,4'-bipyrazole) were prepared through solvothermal routes and fully investigated in the solid state. Isoreticular to the end members Zn(BPZ) and Zn(BPZX) (X = NO2, NH2), they are the first examples ever reported of (pyr)azolate MIXMOFs. Their crystal structure is characterized by a three-dimensional open framework with one-dimensional square or rhombic channels decorated by the functional groups. Accurate information about ligand stoichiometric ratio was determined (for the first time on MIXMOFs) through integration of selected ligands skeleton resonances from 13C cross polarized magic angle spinning solid-state NMR spectra collected on the as-synthesized materials. Like other poly(pyrazolate) MOFs, the four MIXMOFs are thermally stable, with decomposition temperatures between 708 and 726 K. As disclosed by N2 adsorption at 77 K, they are micro-mesoporous materials with Brunauer-Emmett-Teller specific surface areas in the range 400-600 m2/g. A comparative study (involving also the single-ligand analogues) of CO2 adsorption capacity, CO2 isosteric heat of adsorption (Qst), and CO2/N2 selectivity in equimolar mixtures at p = 1 bar and T = 298 K cast light on interesting trends, depending on ligand tag nature or ligand stoichiometric ratio. In particular, the amino-decorated compounds show higher Qst values and CO2/N2 selectivity vs the nitro-functionalized analogues; in addition, tag "dilution" [upon passing from Zn(BPZX) to Zn(BPZ)x(BPZX)1-x] increases CO2 adsorption selectivity over N2. The simultaneous presence of amino and nitro groups is not beneficial for CO2 uptake. Among the compounds studied, the best compromise among uptake capacity, Qst, and CO2/N2 selectivity is represented by Zn(BPZ)x(BPZNH2)1-x.

An Enhanced Carbon Capture and Storage Process (e-CCS) Applied to Shallow Reservoirs Using Nanofluids Based on Nitrogen-Rich Carbon Nanospheres.

The implementation of carbon capture and storage process (CCS) has been unsuccessful to date, mainly due to the technical issues and high costs associated with two main stages: (1) CO2 separation from flue gas and (2) CO2 injection in deep geological deposits, more than 300 m, where CO2 is in supercritical conditions. This study proposes, for the first time, an enhanced CCS process (e-CCS), in which the stage of CO2 separation is removed and the flue gas is injected directly in shallow reservoirs located at less than 300 m, where the adsorptive phenomena control CO2 storage. Nitrogen-rich carbon nanospheres were used as modifying agents of the reservoir porous texture to improve both the CO2 adsorption capacity and selectivity. For this purpose, sandstone was impregnated with a nanofluid and CO2 adsorption was evaluated at different pressures (atmospheric pressure and from 3 × 10−3 MPa to 3.0 MPa) and temperatures (0, 25, and 50 °C). As a main result, a mass fraction of only 20% of nanomaterials increased both the surface area and the molecular interactions, so that the increase of adsorption capacity at shallow reservoir conditions (50 °C and 3.0 MPa) was more than 677 times (from 0.00125 to 0.9 mmol g−1).

Direct Observation of Li+ Ions Trapped in a Mg2+-Templated Metal-Organic Framework.

Herein we report the first example of a metal-organic framework (MOF) in which the location of Li+ ions trapped in the porous confinement can be unambiguously defined by single-crystal X-ray diffraction. Furthermore, the Li+-doped MOF shows significant enhancement in gas uptake as well as selective adsorption of CO2 over CH4.

High dispersion of polyethyleneimine within mesoporous UiO-66s through pore size engineering for selective CO2 capture

As a result of the low partial pressure of CO2 in most industrial waste gases, capturing CO2 especially at low pressure was a priority. A facile method was utilized to build mesoporous UiO-66s with adjustable pore sizes via crystal defect engineering. The mesopores were generated through the removal of instable Cu clusters and lauric acid after reaction. The pore sizes could be controlled via adjusting the molar ratios of Cu2+ to Zr4+. Moreover, these meso-type UiO-66 MOFs reserved the stability after washing by HCl solution, which was more suitable for modification in harsh environment and CO2 capture from flue gases or biogases. The most suitable dispersion of appended polyethyleneimine (PEI) inside pores was then achieved via the controllable pore sizes for CO2 capture. The active –NH2 from incorporated PEI could interact with CO2 to enhance the uptake at low pressure and improve adsorption selectivities of CO2 over N2 and CH4. The high dispersion of PEI also allowed guest molecules to interact with more active sites, which enhanced the affinity between CO2 and frameworks. The strong interaction between 50PEI@meso-UiO-66-0.2Cu and CO2 was confirmed by higher isosteric heats of adsorption (Qst). Even so, the CO2 uptake of sample was without drop after five cycles, and the sample could be regenerated under a mild condition.