Composites (GrO@Cu-BTC) based on Cu-BTC and graphene oxide were synthesized by a solvothermal method for the separation of CO2/CH4 binary mixtures. The as-synthesized composites were then characterized. The isotherms of CO2 and CH4 on the as-synthesized materials were measured by the volumetric method. The isotherms and adsorption selectivities of CO2/CH4 binary mixtures were estimated on the basis of ideal adsorbed solution theory (IAST). The results showed that the composite 1GrO@Cu-BTC had a higher BET surface area and pore volume compared to the parent Cu-BTC. More importantly, its adsorption capacity for CO2 improved significantly in comparison with that of Cu-BTC, which was up to 8.19 mmol/g at 1 bar and 273 K. The dual-site Langmuir–Freundlich (DSLF) model was applied favorably for fitting experimental isotherm data of CO2 and CH4 adsorption on the samples. The predicted isotherms of the binary mixture based on IAST showed that CO2 was more favorably adsorbed than CH4 on the sample 1GrO@Cu-BTC. TPD showed that the desorption activation energy of CO2 on 1GrO@Cu-BTC was higher than that on Cu-BTC, indicating a stronger interaction between CO2 molecules and 1GrO@Cu-BTC. Thus, the CO2/CH4 adsorption selectivity of the composite 1GrO@Cu-BTC was significantly higher than that of Cu-BTC, namely, 14 at 1 bar, or 2.6 times that of Cu-BTC.

An efficient mechanochemical method was proposed to synthesize MOF-5 with high BET area within minutes. The effects of parameters such as solvents activation, the metal/ligand ratio, grinding speed and time were carefully studied and the optimized MOF-5-B was used to investigate its adsorption properties of linear alkanes (C1–nC7). The results showed that solvents activation played an important role in the formation of MOF-5. Besides, the Zn2+/BDC ratio had a great impact on the formation of crystalline MOF-5, and the appropriate Zn2+/BDC ratio was 3:1 for mechanochemical synthesis of MOF-5. Grinding for 60 min could lead to a better crystallinity and the highest surface area of MOF-5-B. The resulting MOF-5-B possessed BET area of 3465.9 m2·g–1. More importantly, MOF-5-B showed a preferential adsorption for long alkanes over short alkanes at low pressures. The saturated adsorption capacities of nC4–nC7 decreased with the increase of hydrocarbon chain length. The isosteric heats of C1–nC7 increased with the increase of the alkyl chain length. Furthermore, the adsorption capacities of the alkanes (C3–nC7) on MOF-5-B were much higher than those of conventional activated carbons and zeolites.

•CPL-1 showed adsorptive separation of C3H6 over C3H8 via gate opening effect at 273 K.•CPL-1 had an excellent desorption property of C3H6 at 298 K.•The desorption activation energy of C3H6 on the CPL-1 was only 22.81 kJ/mol.•The hydrogen bonding was a key factor governing the selective adsorption of C3H6 over C3H8 in CPL-1.The separation of olefin/paraffin mixtures is of great importance for the petrochemical industry, mainly achieved by using energy-intensive cryogenic distillation. We herein reported a flexible pillared-layer framework CPL-1 possessing a thermoresponsive gate opening behavior for C3H6 adsorption. We measured the C3H6 and C3H8 adsorption and desorption isotherms of CPL-1 at six different temperatures (273, 278, 283, 288, 293 and 298 K), respectively. Results showed that the gate opening pressure of C3H6 adsorption for CPL-1 increased with an increase of the adsorption temperature from 273 K to 288 K. However, no gate opening effect was observed within the measured pressure (<100 kPa) as the temperature increased to 293 and 298 K. In contrast, C3H8 adsorption for CPL-1 only occurred surface adsorption without appreciable amount adsorbed due to the closed phase of pores under all measured conditions. Thus, we investigated the adsorptive separation of C3H6 over C3H8 for CPL-1 at 273 K and developed the regeneration process at room temperature (298 K), based on its unique thermoresponsive property. Breakthrough experiments demonstrated the superior C3H6/C3H8 separation performance of CPL-1. Static and dynamic regeneration experiments showed that CPL-1 had excellent stability and high desorption efficiency after five consecutive adsorption-desorption cycles. Particularly, CPL-1 can be easily regenerated at 298 K since the desorption activation energy of C3H6 on CPL-1 was only 22.81 kJ/mol. Furthermore, molecular dynamics (MD) simulation revealed that the hydrogen bonding was a key factor governing the selective adsorption of C3H6 over C3H8 in CPL-1. This investigation highlighted the central importance of flexibility of adsorbent, and suggested that CPL-1 could be an interesting material for C3H6/C3H8 separation and had excellent regeneration property.Download high-res image (231KB)Download full-size image

•MOF-505@GO composites were successfully synthesized.•MOF-505@5GO composite exhibits excellent moisture stability.•MOF-505@5GO exhibits a high CO2 adsorption capacity of 3.94 mmol/g.•The CO2/N2 and CO2/CH4 selectivities of MOF-505@5GO are higher than those of pristine MOF-505.Novel MOF-505@GO composites comprised of a copper-based metal-organic framework and graphite oxide (GO) were synthesized by a solvothermal method for effective separation of CO2/CH4 and CO2/N2, which are challenging chemical separations in industry. The composites were characterized by various techniques including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and porosity measurement through nitrogen adsorption at cryogenic temperature. Single component adsorption isotherm measurements of CO2, CH4 and N2 were performed at different temperatures. The selectivities of CO2/CH4 and CO2/N2 were estimated on the basis of ideal adsorbed solution theory (IAST). MOF-505@GO composites showed higher porosity and enhanced CO2 adsorption compared to its parent compound MOF-505. MOF-505@5GO exhibited the highest CO2 uptake of 3.94 mmol/g at 298 K and 100 kPa, having an increase of 37.3% in comparison with the parent MOF-505. The significant improvement of CO2 uptakes could be attributed to not only new micropores and unsaturated metal sites formed in the MOF-505@GO, but also enhanced surface dispersive forces of the composites. The experimental adsorption isotherms of CO2, CH4 and N2 were well fitted with dual site Langmuir-Freundlich (DSLF) model. The CO2/CH4 and CO2/N2 adsorption selectivities were up to 8.6 and 37.2 at 298 K and 100 kPa, respectively, predicted by IAST. More strikingly, the composites showed excellent moisture stability, which was confirmed by PXRD analysis. These superior performances suggested that the MOF-505@GO composites are promising candidates for industrial CO2 capture.Download high-res image (157KB)Download full-size image

•An indium based metal-organic framework InOF-1 was successfully synthesized by mechanochemical method in 20 min.•InOF-1 retains its structure and porosity after being soaked in water for 12 h.•InOF-1 has not only high CO2 adsorption capacity of 4.03 mmol/g at 273 K and 100 kPa but also high CO2/CH4 and CO2/N2 adsorption selectivities.Mechanochemical synthesis, induced by mechanical grinding, is demonstrated to be rapid and efficient for metal-organic frameworks (MOFs) synthesis. For this purpose, a mechanochemical synthesis route was proposed for the first time for preparation of water stable indium metal-organic frameworks InOF-1. The effects of preparation conditions such as the addition of solvents and grinding time were discussed, and the InOF-1 synthesized through optimized condition was used to investigate its selective CO2 adsorption. Results showed that using liquid-assisted grinding for 20 min with CH3CN (0.4 mL) could lead to highly crystalline and porous InOF-1 with a Brunauer-Emmett-Teller (BET) surface area of 707 m2/g. The addition of a small amount of solvent into the system could dramatically improve the crystallinity and porosity of InOF-1. More importantly, the synthesized product with the highest specific surface area retained its crystallinity and porosity after being soaked in water for 12 h. Its CO2 adsorption capacity reached as high as 4.03 mmol/g at 273 K and 100 kPa, and CO2/CH4 and CO2/N2 adsorption selectivities were up to 7.5 and 45, respectively. The superior performance of the mechanochemically synthesized InOF-1 makes it a potential candidate for CO2 adsorption and separation.Download high-res image (195KB)Download full-size image

A novel mechanochemical method was proposed to reconstruct quickly moisture-degraded HKUST-1. The degraded HKUST-1 can be restored within minutes. The reconstructed samples were characterized, and confirmed to have 95% surface area and 92% benzene capacity of the fresh HKUST-1. It is a simple and effective strategy for degraded MOF reconstruction.

The adsorption performance of the MIL-101@GO composite for a series of linear long chain alkanes (from n-pentane to n-octane) was investigated for the first time. The MIL-101@GO composite based on MIL-101(Cr) and graphite oxide (GO) was prepared, characterized and tested for adsorption and desorption of n-alkanes. Isotherms of a series of n-alkanes on MIL-101@GO were measured. Temperature-programmed desorption (TPD) experiments were conducted to estimate desorption activation energies of n-alkanes on MIL-101@GO. Results showed that the adsorption capacities of n-alkanes on MIL-101@GO increased with the hydrocarbon chain length at regions of low pressure, while the trend was reversed at regions of high pressure. The adsorption capacities of n-alkanes on MIL-101@GO were about 1.6–11 times higher than those of conventional activated carbons and the zeolites. The isotherms of n-alkanes could be fitted favorably by the Langmuir–Freundlich equation. The desorption activation energy increased linearly with the carbon number of the n-alkanes. Consecutive cycle experiments of adsorption–desorption showed the isotherms of n-octane in all five cycles were nearly overlapping, suggesting that MIL-101@GO had excellent reversibility of n-alkane adsorption.

A novel mechanochemical method was proposed to reconstruct quickly moisture-degraded HKUST-1. The degraded HKUST-1 can be restored within minutes. The reconstructed samples were characterized, and confirmed to have 95% surface area and 92% benzene capacity of the fresh HKUST-1. It is a simple and effective strategy for degraded MOF reconstruction.