Quenched breathing effect, enhanced CO2 uptake and improved CO2/CH4 selectivity of MIL-53(Cr)/graphene oxide composites

- Compositing GrO and MIL-53(Cr) yields a series of novel GrO@MIL-53(Cr) composites.
- GrO@MIL-53(Cr) exhibits high CO2 uptake and superior CO2/CH4 selectivity.
- 10% GrO doping results in a 16 times higher CO2/CH4 selectivity at 5 bar.
- 10GrO@MIL-53(Cr)'s CO2 uptake is improved by 62% at 5 bar compared to MIL-53(Cr).
- The enhanced performance is attributed to a quenched breathing effect proved by XRD.

Compositing graphene oxide (GrO) as a robust support into MIL-53(Cr) can provide a feasible strategy to stabilize its flexible structure from CO2-triggered shrinkage, resulting in an enhanced CO2 uptake together with a higher CO2/CH4 adsorptive selectivity of the GrO@MIL-53(Cr) composites for biomethane upgrade. In this work, a series of novel GrO@MIL-53(Cr) composites were prepared from GrO and MIL-53(Cr). Their adsorptive performance for CO2/CH4 separation was experimentally investigated. IAST was applied to predict their adsorptive selectivity for CO2/CH4 separation. Results show that a small amount of GrO doping (1%) could significantly improve surface area and pore volume of the resulting 1GrO@MIL-53(Cr), while a remarkably enhanced CO2 uptake was observed with sufficient GrO doping (10%) for 10GrO@MIL-53(Cr) at 5 bar and room temperature, which is 62% higher than that of its parental MIL-53(Cr). XRD indicates a quenched “breathing effect” could be responsible for the remarkably enhanced CO2 uptake. With this quenched breathing effect, 10GrO@MIL-53(Cr) shows a 16 times higher CO2/CH4 selectivity at 5 bar for the equimolar CO2/CH4 mixture. SEM and TEM show well-defined compositing structures, while IR, Raman and TG suggest GrO@MIL-53(Cr) composites manage to preserve most of the crystallographic and chemical characteristics of their parent MIL-53(Cr).

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