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Composites (GrO@Cu-BTC) based on Cu-BTC and graphene oxide were synthesized by a solvothermal method for the separation of CO 2 /CH 4 binary mixtures. The as-synthesized composites were then characterized. The isotherms of CO 2 and CH 4 on the as-synthesized materials were measured by the volumetric method. The isotherms and adsorption selectivities of CO 2 /CH 4 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 CO 2 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 CO 2 and CH 4 adsorption on the samples. The predicted isotherms of the binary mixture based on IAST showed that CO 2 was more favorably adsorbed than CH 4 on the sample 1GrO@Cu-BTC. TPD showed that the desorption activation energy of CO 2 on 1GrO@Cu-BTC was higher than that on Cu-BTC, indicating a stronger interaction between CO 2 molecules and 1GrO@Cu-BTC. Thus, the CO 2 /CH 4 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.

Here, we reported a strategy for channel methylation to construct a robust ultramicroporous metal–organic framework (MOF) Ni­(TMBDC)­(DABCO)0.5 through hydrothermal synthesis method and investigated its adsorption performance for recovering ethane (C2) and propane (C3) from natural gas. The as-synthesized Ni­(TMBDC)­(DABCO)0.5 featured ultramicroporosity with a uniform pore size of 0.5 nm. The resulting sample showed a strong adsorption interaction with C3H8 and C2H6, and its C3H8 adsorption capacity at a low pressure of 1 kPa was up to 2.80 mmol/g and its C2H6 adsorption capacity at a low pressure of 10 kPa reached as high as 2.93 mmol/g, exhibiting strong binding affinity for ethane and propane. The enhanced adsorption can be attributed to the presence of the dense and accessible methyl and methylene groups in the channels of the sample. Grand Canonical Monte Carlo (GCMC) simulations also confirmed that the methylene groups from the DABCO pillar and the methyl groups from the TMBDC ligand play an important role in enhancing the adsorption of ethane and propane. Its ideal adsorbed solution theory (IAST)-predicted selectivity of C2H6/CH4 reached unprecedentedly 29, much higher than most of the reported data for MOFs. The stability test confirmed that the crystal structure of Ni­(TMBDC)­(DABCO)0.5 still remained intact after it was exposed to moist air with a relative humidity of 100% for days. The breakthrough experiment demonstrated that the CH4/C2H6/C3H8 ternary mixture was completely separated using a fixed bed of Ni­(TMBDC)­(DABCO)0.5 at ambient temperature, showing a great potential for recovering the low content of ethane and propane from natural gas.