Enhanced separation performance of a novel composite material GrO@MIL-101 for CO₂/CH₄ binary mixture

Abstract

A novel GrO@MIL-101 composite consisting of graphene oxide (GrO) and MIL-101(Cr) was synthesized, characterized and tested for separation of CO2/CH4 mixture. GrO@MIL-101 had higher BET surface area and better porosity than parent MIL-101. CO2 and CH4 isotherms were separately measured at different temperatures using a gravimetric method, and were fitted using the dual-site Langmuir–Freundlich (DSLF) model. The adsorption capacity of GrO@MIL-101 for CO2 was significantly improved over MIL-101, reaching 22.4 mmol g−1 at 25 bar and 298 K, much higher than traditional adsorbents and most other MOFs. The isotherms and selectivities of CO2/CH4 binary mixture were estimated using the ideal adsorbed solution theory (IAST). While calculated isotherms indicated CO2 was more favorably adsorbed on GrO@MIL-101 than CH4, the adsorption selectivity of GrO@MIL-101 composite was dramatically enhanced over pristine MIL-101. At 1.5 bar, the selectivity of GrO@MIL-101 for CO2/CH4 (10:90) mixture with a characteristic of natural gas was up to 32, which was more than three times of that of MIL-101. Isosteric heats of adsorption for CO2 and CH4 on GrO@MIL-101 were slightly above those on parent MIL-101. GrO@MIL-101 also displayed remarkable quasi-reversibility for CO2 adsorption, showing more than 95% desorption efficiency over five cycles.