Gas Adsorption Performance Research Articles

Isoreticular chemistry within metal–organic frameworks for gas storage and separation

• The application of isoreticular chemistry in MOF structure design, including microstructure design, pore size tailoring, secondary building unit modification, post-synthesis modification, and cooperative regulation are summarized and highlight. • The adsorption/separation function-oriented MOF structure design and high-throughput screening process are summarized. Based on isoreticular chemistry design and optimized high-performance MOF adsorbents and membranes, we are committed to exploring an energy-intensive and environmentally friendly alternative separation route, and strive to achieve efficient separation of hydrogen, carbon dioxide, natural gas, and petroleum-based platform compounds. Precise control of the pore size and environment of metal–organic framework (MOF) is a necessary condition for achieving high performance of gas adsorption and separation. After nearly two decades of development, the synthesis of MOF materials has gradually evolved from exploration and trial to precise-design, including function-oriented microstructure design and optimization, pore size tailoring, and secondary building unit (SBU) modification. The unique pore environments of MOF materials enable their advantages in gas adsorption and separation applications. In addition, the introduction of isoreticular chemistry within MOFs (with the same framework structure and different chemical components) provides opportunities for improving gas adsorption and separation performance. Isoreticular chemistry gives MOFs more functions to promote specific binding or sieving with gas molecules. Furthermore, MOF-based adsorbents and separation membranes exhibit superior separation performance in many industrial gas purification processes. In this review, we summarized and highlight the application of isoreticular chemistry in MOF structure design, including microstructure design, pore size tailoring, SBU modification, post-synthesis modification, and cooperative regulation. The gas adsorption and separation performances are improved through pore size and environment optimization. In addition, we also summarized the adsorption/separation function-oriented MOF structure design and high-throughput screening process. Based on isoreticular chemistry design and optimized high-performance MOF adsorbents and separation membranes, an energy-intensive and environmentally friendly alternative separation route is explored to achieve efficient separation of hydrogen, carbon dioxide, natural gas, and petroleum-based compounds. Finally, we provided an outlook based on prospect developments of isoreticular chemistry within MOFs for gas storage and separation.

Constructing Hierarchically Porous N-Doped Carbons Derived from Poly(ionic liquids) with the Multifunctional Fe-Based Template for CO2 Adsorption.

Nitrogen-doped hierarchical porous carbons with a rich pore structure were prepared via direct carbonization of the poly(ionic liquid) (PIL)/potassium ferricyanide compound. Thereinto, the bisvinylimidazolium-based PIL was a desirable carbon source, and potassium ferricyanide as a multifunctional Fe-based template, could not only serve as the pore-forming agent, including metallic components (Fe and Fe3C), potassium ions (etching carbon framework during carbonization), and gas generated during the pyrolysis process, but also introduce the N atoms to porous carbons, which were in favor of CO2 capture. Moreover, the hierarchically porous carbon NDPC-1-800 (NDPC, nitrogen-doped porous carbon) had taken advantage of the highest specific surface area, exhibiting an excellent CO2 adsorption capacity and selectivity compared with NDC-800 (NDC, nitrogen-doped carbon) directly carbonized from the pure PIL. Furthermore, its hierarchical porous architectures played an important part in the process of CO2 capture, which was described briefly as follows: the synergistic effect of mesopores and micropores could accelerate the CO2 molecules’ transportation and storage. Meanwhile, the appropriate microporous size distribution of NDPC-1-800 was conducive to enhancing CO2/N2 selectivity. This study was intended to open up a new pathway for designing N-doped porous carbons combining both PILs and the multifunctional Fe-based template potassium ferricyanide with wonderful gas adsorption and separation performance.

Selective adsorption of acidic gases from ternary mixture by acetate- and sulfonate-based ionic liquids at molecular level.

This paper attempts to elucidate the competitive adsorption mechanism of thin films of ionic liquids (ILs) on the surface of porous materials for acidic gases at a molecular level in order to design a proper material for the diminishment of gas emissions. Thin film 1-butyl-3-methylimidazalium ([BMIM]+) cation-based IL systems composed of four different anions such as [CH3CO2]- and [CF3CO2]- (acetate-based), and [CH3SO3]- and [CF3SO3]- (sulfonate-based) are created in contact with the gas phase containing ternary H2S/CO2/CH4:1/25/74 mixture. To define gas adsorption performance at gas-liquid interface and bulk liquid phase, classical molecular dynamics simulations are carried out. Adsorption of acidic gases is governed by the formation of an adsorbed gas layer on the surface of the ionic liquid based on thermodynamics aspects, and then the partial dissolution of gases in the bulk liquid phase is accompanied by the transport of gases. These behaviors are followed by several analysis methods in simulation approaches such as radial distribution function (RDF) of gases around specific atoms of ILs, lateral displacement of gas molecules, radial distance between gas and ILs, interaction energy between gases and ILs, and average number of hydrogen bonding between ions with and without adsorbed gases. Acetate-based ILs performed twice as good in CO2 adsorption capacity than sulfonate-based ILs. However, the one having -CF3 group in acetate-based ILs has short CO2 retention time and high CH4 adsorption capacity, diminishing the H2S+CO2/CH4 adsorption selectivity. High CO2 adsorption performance of acetate-based ILs is related to their strong anion-cation interaction and less hydrogen-bonding ability between cation tail and anion, which is the source for free space between anion and cation. Those with high adsorption capacities and long retention times are those that can ensure that CO2 molecules are coordinated in these free volumes between cation tails and anions. Therefore, here, the effect of different parameters on the CO2 and H2S adsorption over CH4 is revealed via atomistic design, and the importance of selection of suitable anions in IL for identifying potential nanocomposite adsorbent materials for acidic gas removal is highlighted.

Feedstock doping using iron rich waste increases the pyrolysis gas yield and adsorption performance of magnetic biochar for emerging contaminants

Magnetic carbons can significantly lower the costs of wastewater treatment due to easy separation of the adsorbent. However, current production techniques often involve the use of chlorinated or sulfonated Fe precursors with an inherent potential for secondary pollution. In this study, ochre, an iron-rich waste stream was investigated as a sustainable Fe source to produce magnetic activated biochar from two agricultural feedstocks, softwood and wheat straw. Fe doping resulted in significant shifts in pyrolysis yield distribution with increased gas yields (+50%) and gas energy content (+40%) lowering the energy costs for production. Physical activation transformed ochre to magnetite/maghemite resulting in activated magnetic biochars and led to a 4-fold increase in the adsorption capacities for two common micropollutants – caffeine and fluconazole. The results show that Fe doping not only benefits the adsorbent properties but also the production process, leading the way to sustainable carbon adsorbents.

Density functional theory study of Cu-doped BNNT as highly sensitive and selective gas sensor for carbon monoxide

The adsorption of CO, CO2, CH4, H2, N2 and N2O on armchair (5,5) boron nitride nanotube (BNNT) with and without the doping of transition metals (TM), i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn, was investigated using the density functional theory calculation. The results indicate all the considered gases are physically adsorbed by weak interaction on the pure BNNT, revealing that pure BNNT has poor sensing performance for these gases. TM are then doped in the B or N vacancy of BNNT to improve the sensitivity and selectivity. As a result, it was found that the gas adsorption performance of BNNT is obviously enhanced due to the introduction of TM dopant atom. In particularly, according to the results of adsorption energy, Cu doped BNNT (Cu-BNNT) system shows a high selectivity toward CO molecule compared with other metal doped systems. This is further confirmed by the density of state, energy gap and charge transfer analyses. Furthermore, based on the sensor performance analysis, it was found that Cu-BNNT also has favorable desorption characteristics for CO. Therefore, this study concluded that Cu-BNNT can be used as a superior sensor material with high sensitivity, selectivity and favorable recycle time for CO gas.

Graphene-facilitated synthesized vertically aligned hexagonal boron nitride nanowalls and their gas adsorption properties

The capability of hexagonal boron nitride (h-BN) to adsorb gas atoms may stimulate various promising applications in environment remediation and energy storage, while the interactivity with gas molecules yet remains challenging due to its inherent chemical inertness. In this article, we report a feasible and effective route for the scalable synthesis of vertically aligned h-BN nanowalls assisted by reduced graphene oxide (rGO) without metallic catalysts. The average thickness of the fine h-BN nanowalls is few-atomic layers about 3.7 nm, that grow on the large substrate-like flakes transformed from the pristine rGO. The hierarchical h-BN nanowalls exhibit an enhanced gas adsorption performance, not only through physisorption owing to the synergistic combination of different porous geometries, but also through chemisorption via the open edge groups. Moreover, it demonstrates a significantly enhanced adsorption of CO2 over CH4 as compared to the h-BN nanosheets with similar sizes. Density functional theory calculations reveal that the –OH edge groups can effectively increase the adsorption capability towards CO2, accompanied by a shortened adsorption distance when the gas molecule is energetically stabilized. The wetting characteristics of h-BN nanowalls was further examined by contact angle goniometry.

3D printed CuO semiconducting gas sensor for ammonia detection at room temperature

In this work, a new room-temperature ammonia gas sensor based on n-type copper oxide (CuO) semiconductor was fabricated by 3D printing with fused deposition modeling (FDM) technique and sintering method. The polylactic acid (PLA) was blended together with Cu particles and extruded into the filament form for FDM printing. The PLA/Cu composite was printed and calcined in a furnace to obtain semiconducting CuO. The structural characterization results of 3D printed sensor showed monoclinic CuO phase and scaffold structures, which provided active porous sites for enhanced gas adsorption and room-temperature gas-sensing performances. According to gas-sensing data, the 3D printed CuO gas sensor exhibited good repeatability, high stability (>3 months), low humidity dependency (25–65 %RH), high sensitivity and selectivity towards ammonia at room temperature. The sensor response increased linearly with increasing NH3 concentration from 25 to 200 ppm. The sensing mechanism of the 3D printed CuO sensor was proposed based on the resistance change via reaction on adsorbed surface oxygen species or direct electron transfer between ammonia molecules and CuO. This approach could open up new ways to fabricate semiconductor gas sensors with controllable sizes and shapes for future gas-sensing applications.

Synthesis, characterization and gas adsorption analysis of solvent dependent Zn-BTC metal organic frameworks

ABSTRACT Multidentate 1,3,5-benzene tricarboxylic acid copolymerizes with Zinc to form framework with rigid porosity for gas adsorption application. One of the barriers in commercialization of these MOFs for gas adsorption application is the usage of costly solvents and this research is based on identifying the effect of solvents on zinc and 1,3,5-benzene tricarboxylic acid-based MOFs, their gas adsorption capacities and costs. All the MOFs prepared were characterized and further tested for carbon dioxide adsorption capacities. The results highlight that the textural properties of prepared MOFs depend largely on solvents utilized and high surface area MOFs have high adsorption capacity. Also the carbon dioxide adsorption capacity of MOFs prepared using DMF showed better adsorption as compared with the one prepared with Ethanol:De-ionized water. This research also elaborates the fact that there is a possibility of replacing the expensive solvents for Zn-BTCs synthesis with low-cost solvents without compromising the gas adsorption performance.

Down-sizing the crystal size of ZK-5 zeolite for its enhanced CH4 adsorption and CH4/N2 separation performances

Down-sizing zeolite crystals to achieve enhanced gas adsorption and separation performances is largely unexplored and underestimated. Nano-sized zeolite can expose more adsorption sites and shorten the diffusion path compared to micro-sized counterparts; however, the synthesis of Nano-sized zeolite is still very challenging. Herein, nano-sized ZK-5 is successfully prepared for the first time via the regulation effects of β-cyclodextrin. The crystal size of ZK-5 can be reduced from micron-size (3 μm) to nano-size (50–100 nm), thus the nano-ZK-5 exhibits a superior surface area (370 cm2 g−1) and pore volume (0.22 cm3 g−1) than the micron-sized sample (149 cm2 g−1 and 0.07 cm3 g−1), which may be due to the reduction in crystal size, which in turn leads to more micropores being detected. The CH4 adsorption capacity on nano-sized sample increased by 64% compared to that of micron-sized ZK-5. Notably, the record-high CH4 adsorption capacity of 1.34 mmol g−1 at 298 K is obtained on the nano-ZK-5 among the commercial zeolites. The equilibrium adsorption selectivity of CH4/N2 (20/80, v/v) mixed gas is as high as 4.2 (IAST method) at 1 bar and 298 K. The adsorption kinetics experiments have illustrated the boosted gas diffusion and mass transfer rate. Furthermore, the breakthrough experiments have confirmed the practical feasibility of separating various gas-mixtures, such as CH4/N2 (20/80, v/v).

Influence of anion size and electronic structure on the gas separation performance of ionic liquid/ZIF-8 composites

Abstract We investigated the influences of the changes in the electronic structure and size of the anion of an imidazolium ionic liquid (IL) on gas adsorption and separation performance of the IL/ZIF-8 (zeolitic imidazolate framework) composites. We studied four different imidazolium ILs having the same cation, 1-n-butyl-3-methylimidazolium, [BMIM]+, with anions having structures allowing a systematic comparison of the changes in the electronic structure and size. To examine the influence of changes in the electronic structure, we considered anions representing the fluorination on the anion, methanesulfonate, [MeSO3]−, and trifluoromethanesulfonate, [CF3SO3]−. To investigate the change in the anion size, methyl sulfate, [MeSO4]−, and octyl sulfate, [OcSO4]−, were studied. Characterization of IL/ZIF-8 composites demonstrated successful incorporation of each IL in ZIF-8 without causing any detectable changes in the crystal structure and morphology of ZIF-8. Thermogravimetric analysis and infrared (IR) spectroscopy indicated the presence of direct interactions between ILs and ZIF-8, which directly control gas separation performance of the composite. Gas adsorption measurements illustrated that incorporation of ILs significantly improves the gas separation performance of the pristine ZIF-8. [BMIM][MeSO4]/ZIF-8 composite had 3.3- and 1.8-times higher CO2/N2 and CH4/N2 selectivities compared to ZIF-8, respectively, at 1 bar. When the IL has a fluorinated anion, CO2/CH4 selectivity improved 3-times compared to its non-fluorinated counterpart. Upon the incorporation of IL with a small anion, IL/ZIF-8 composite showed higher CO2/N2 and CH4/N2 selectivities compared to the composite having an IL with a bulky anion. These results will contribute in guiding rational design of IL/MOF composites for different gas separations.

Optimization of Washing Processes in Solvothermal Synthesis of Nickel-Based MOF-74.

Solvothermal synthesis is the most preferable preparation technique of metal–organic frameworks (MOFs) that consists of reactants mixing, ultrasonication, solvothermal reaction, product washing, and solvent evacuation. Owing to fast reaction kinetics in solvothermal reaction, this technique allows for production of uniform MOF particles with high crystallinity, high phase purity, and small particle sizes. However, it exhibits some difficulties of washing processes that may involve the blockage of pores due to incomplete removal of reactive medium from MOF products. The present study proposes an improvement of washing processes by introducing centrifugal separations with optimized parameters at two different stages: after reaction and after product washing. Nickel-based MOF-74 was synthesized as the experimental material for this purpose. The quality of the produced sample was evaluated by gas adsorption performance using CO2 at 1 bar and 25 °C. The final sample of the optimized synthesis routes was able to adsorb 5.80 mmol/g of CO2 uptake, which was competitive with literature data and significantly higher than the sample of the basic synthesis. Fourier-transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) analysis revealed that the sample displayed much higher crystallinity structure and was clean from impurities after centrifugations. The outcome indicated the success of separation between MOF products and reactive medium during washing processes, leading to the effective pore activation of MOFs.

Preparation and characterization of polyacrylonitrile-based activated carbon nanofibers/graphene (gACNFs) composite synthesized by electrospinning

In this work, activated carbon nanofibers (ACNFs) and graphene-derived rice husk (GRH)/ACNF composites (gACNFs) were straightforwardly fabricated through a simple electrospinning process and were consequently activated by using a physical method. The morphological, structural, and textural properties of the resultant ACNFs and (GRH)/ACNFs were characterized by scanning electron microscopy–energy dispersive x-ray spectroscopy, transmission electron microscopy, Raman spectra, thermal gravimetric analysis, and a N2 adsorption isotherm. From the results obtained, gACNFs exhibit better thermal stability properties than pristine ACNFs with improved carbon yield (up to 60%) as well as enhanced adsorption capacity (220 cm3/g). The results including a high specific surface area (592 m2/g) and availability of 80% micropore volumes have demonstrated that gACNFs exhibited double gas adsorption performance as compared to pristine ACNFs.

Molecular simulation study on gas adsorption and separation performance of alkyl-functionalized HKUST materials

The atomic partial charges of three metal–organic frameworks (MOFs), including Cu-BTC (HKUST-1), Cu-MBTC (methyl-modified Cu-BTC) and Cu-EBTC (ethyl-modified Cu-BTC), are calculated by first-principle density functional method. According to the Grand Canonical Monte Carlo (GCMC) method and the Ideal Adsorbed Solution Theory (IAST), their gas adsorption and separation ability are studied, and the effects of alkyl functionalization on the performance are analyzed and discussed. Studies have shown that temperature and pressure have significant effects on the gas adsorption ability of Cu-BTC, Cu-MBTC and Cu-EBTC. Under 298 K, the order of adsorption amount of CH4, CO2, N2 is CO2 > CH4 > N2, which is consistent with the calculated results of adsorption heat. The molecular density distribution charts indicate that the alkyl functional groups may provide the new sites for the material to adsorb gas molecules. The results show that the addition of alkyl groups can change the pore volume, surface area and charge distribution of MOFs, which, in turn, modulates the gas adsorption and separation performance of the materials. The IAST simulation shows that compared with Cu-BTC and Cu-MBTC, Cu-EBTC shows higher selectivity for gas separation and can be potentially applied to absorption of CO2 greenhouse gases from air mixture.

Influence of the sputtering glancing angle on the microstructure and adsorption characteristics of Zr-Co-RE getter films

Zr-Co-RE non-evaporable getter films have excellent gas adsorption performance therefore can be used in vacuum sealed electronic devices. The microstructure of getter films has vital effect on adsorption performance. In this paper, Zr-Co-RE films deposited by DC magnetron sputtering at different glancing angles are investigated including microstructures and adsorption characteristics. The surface and cross-sectional morphologies demonstrate loose, porous and columnar-like structure which forms because of low lateral mobility of Zr and Co atoms and shadowing effect of non-perpendicular sputtering. Zr-Co-RE films are amorphous or nanocrystalline structure. The films deposited at 90° glancing angle show large grain size. After Zr-Co-RE films are heated at 350 °C for 15 min, the H2 adsorption capacity and pumping speed at ambient temperature are tested. The films grown at 90° glancing angle have highest initial pumping speed (103.9 ml s−1 cm−2), which owe to its more gas diffusion path and active surface, meanwhile, the adsorption capacity is lower than 60° because of difficult and limited diffusion process into getter matrix. The films grown at 60° glancing angle have best adsorption capacity (71.5 Pa.ml cm−2) and pumping speed stability.

Getting insight into the influence of coexisting airborne nanoparticles on gas adsorption performance over porous materials

Adsorption as one of the most important air cleaning methods has been extensively applied during which the coexisting airborne nanoparticles (NPs) with sizes close to adsorbent pore sizes could inevitably influence gas adsorption processes. In this work, the influence of sub-20 nm NPs on toluene adsorption on ZSM-5 zeolites exchanged with different cations (Li+, Na+ and K+) were studied based on gas-and-particle coexisting adsorption/filtration tests. Affinities for both toluene and NPs on adsorbents follow Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5 regarding the orders of charge density, pore size, and internal and external specific surface areas. The toluene adsorption was shown to be impaired by coexisting NPs from perspectives of thermodynamics and kinetics. For Li-ZSM-5, Na-ZSM-5 and K-ZSM-5, significant relative reductions of 10.4 %, 10.5 % and 16.0 % in toluene adsorption capacity at the lower feed concentration, and of 20.3 %, 15.2 % and 2.3 % in mass transfer coefficient at the higher feed concentration were observed, respectively. The influential mechanisms regarding competitiveness between toluene and NPs in interaction with cationic and porous surfaces were accordingly proposed, which are of practical significance for selecting robust adsorbents under realistic harsh air conditions.

Enhancing the Sonolysis Efficiency of SrTiO3 Particles with Cr-Doping

Sonolysis could be more practical for water treatment than traditional catalytic methods in some specific situations. However, the practical application is limited by the low degradation rate. In this work, the Cr doped SrTiO3 was prepared by hydrothermal method, and the Cr-doping results in the decreased crystal symmetry, which leads to the rough surface and a large number of pores of the sample. The appearance of a large number of holes increases the specific surface area and enhances the gas adsorption performance of the sample, which can promote the cavitation. The optimized Cr-doped SrTiO3 can degrade 95.4% rhodamine B (5 mg/L) in 10 min under ultrasound irradiation (53 kHz, 350 W). Furthermore, the improvement of sonolysis degradation with the Cr doped SrTiO3 is universal for dyes, such as methyl blue (MB), methyl orange (MO) and rhodamine B (RhB). The role of active species in ultrasonic catalysis and the synergistic mechanism of ultrasound and catalyst were systematically studied by adding sacrificial agents and changing the reaction atmosphere. This work indicates that the incorporation of finely modified inorganic particles is effective for efficient water treatment.

Design of robust rod-packing [In(OH)(BDC)] frameworks and their high CO2/C2-hydrocarbons over CH4 separation performance

The CO2/C2-hydrocarbons over CH4 separation processes are important for the purification of methane fuel. Towards to this purpose, we have designed two isostructural indium-terephthalate metal-organic frameworks (MOFs) decorated with inorganic OH− anions and/or organic –OH Lewis basic groups, namely SNNU-120 and -121. One-dimensional (1D) [In(OH)(COO)2] chains act as rod-shaped secondary building units (SBUs) linking adjacent four SBUs to form robust 3D rod-packing architecture with two types of 1D channels. Under 273 and 298 K, SNNU-120 and -121 have remarkable CO2, C2H2 and C2H4 uptakes but negligible CH4 adsorption. IAST calculations indicate both of them can effectively separate CO2/C2-hydrocarbons from CH4. The gas adsorption and separation performance of inorganic OH− and organic –OH group co-functionalized SNNU-121 MOF are superior to SNNU-120 only with inorganic OH− anions. Specially, the excellent IAST CO2/CH4 (214.4) and C2H4/CH4 (200) selectivity values for SNNU-121 are considered top-level among all rod-packing MOFs and also surpass the values of most famous MOF materials up to now.

Two-Dimensional Modeling of Pressure Swing Adsorption (PSA) Oxygen Generation with Radial-Flow Adsorber

Radial flow is an important type of flow direction for large-scale pressure swing adsorption (PSA) oxygen generation systems. In this study, a numerical simulation of a PSA oxygen generation process based on radial-flow adsorbers was performed with two-dimensional CFD modeling. The gas distribution, the maldistribution factor and the pressure difference were comparatively investigated at each flow type of the radial-flow adsorber. Considering the gas adsorption performance, the results indicated that the centripetal π-flow radial adsorber has the best flow characteristics for the PSA process. The oxygen purity distribution within the adsorption bed was studied to compare centripetal and centrifugal π-flows, and the former was shown to perform better on oxygen enrichment and adsorbent desorption. The steady state was achieved after eight cycles for the centripetal-π adsorber and each of the four steps of the PSA process was explored in detail to show the advantageous properties for oxygen generation in terms of adsorption and desorption. The relationships between the product flow rate and the oxygen purity and recovery were further investigated.

Fabrication of a functional microgel-based hybrid nanofluid and its application in CO2 gas adsorption

In this study, a novel hybrid nanofluid, composed of a composite core of poly(2-dimethylamino ethyl methacrylate) microgel and silica (PDMAEMA/SiO2) and a shell of polyetheramine (M2070), was fabricated via a combination of inversed emulsion polymerization, biomimetic silicification and grafting onto approach. Firstly, PDMAEMA microgel of ca. 300-nm diameter with good dispersity was prepared in water/cyclohexane system. Subsequently, walnut kernel-structured and solid spherical PDMAEMA/SiO2 composites were fabricated using swollen and contractive PDMAEMA microgel as catalytic template, respectively. Then 3-(2, 3-epoxypropoxy) propyl trimethoxysilane (KH560) modified M2070 was grafted on PDMAEMA/SiO2 composites to obtain two kinds of solvent-free PDMAEMA/SiO2@M2070 hybrid nanofluids with core@shell structure. Finally, the CO2 gas adsorption performance of these nanofluids was investigated under different CO2 pressure (0.5–4.5 MPa) at 25 °C. The results indicated that nanofluid with walnut kernel-structured core showed more excellent CO2 adsorption capacity than solid spherical one. Moreover, it still displayed good stability over ten adsorption-desorption cycles.

Acidity and Cd2+ fluorescent sensing and selective CO2 adsorption by a water-stable Eu-MOF.

A new Eu-MOF was designed from an amino-functionalized ligand and Eu(iii) ions under solvothermal conditions. It is a highly porous, water-stable, and luminescent material, exhibiting pH sensing in the acidic range of pH = 7-3 with selective detection for Cd2+ by an enhanced fluorescence of ∼23-fold against a series of metal ions. Gas adsorption performance shows that Eu-MOF exhibits a high CO2/N2 (15/85) selectivity of 109.4 at 273 K and 1 atm. This performance was superior to that of most reported Ln-MOFs owing to its appropriate pore size, dipole-dipole interaction and donor-acceptor Lewis affinities.