The high energy footprint of commodity gas purification and increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable separation by molecular size or shape exclusion. Physisorbents must exhibit the right pore diameter to enable separation, but the 0.3–0.4 nm range relevant to small gas molecules is hard to control. Herein, dehydration of the ultramicroporous metal–organic framework Ca‐trimesate, Ca(HBTC)⋅H2O (H3BTC=trimesic acid), bnn‐1‐Ca‐H2O, affords a narrow pore variant, Ca(HBTC), bnn‐1‐Ca. Whereas bnn‐1‐Ca‐H2O (pore diameter 0.34 nm) exhibits ultra‐high CO2/N2, CO2/CH4, and C2H2/C2H4binary selectivity, bnn‐1‐Ca (pore diameter 0.31 nm) offers ideal selectivity for H2/CO2and H2/N2under cryogenic conditions. Ca‐trimesate, the first physisorbent to exhibit H2sieving under cryogenic conditions, could be a prototype for a general approach to exert precise control over pore diameter in physisorbents.
Single‐layer graphene containing molecular‐sized in‐plane pores is regarded as a promising membrane material for high‐performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching‐based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade‐off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. In this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are precisely maintained. As a result, single‐layer graphene membranes with the highest H2/CH4separation performances recorded to date (H2permeance > 4000 GPU and H2/CH4selectivity > 2000) are fabricated by manipulating growth temperature, precursor concentration, and non‐covalent decoration of the graphene surface. Moreover, it is identified that nanoscale molecular fouling of the graphene surface during gas separation where graphene pores are partially blocked by hydrocarbon contaminants under experimental conditions, controls both selectivity and temperature dependent permeance. Overall, the direct synthesis of porous single‐layer graphene exploits its tremendous potential as high‐performance gas‐sieving membranes.
more » « less- Award ID(s):
- 1907716
- PAR ID:
- 10446378
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 33
- Issue:
- 44
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The high energy footprint of commodity gas purification and increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable separation by molecular size or shape exclusion. Physisorbents must exhibit the right pore diameter to enable separation, but the 0.3–0.4 nm range relevant to small gas molecules is hard to control. Herein, dehydration of the ultramicroporous metal–organic framework Ca‐trimesate, Ca(HBTC)⋅H2O (H3BTC=trimesic acid), bnn‐1‐Ca‐H2O, affords a narrow pore variant, Ca(HBTC), bnn‐1‐Ca. Whereas bnn‐1‐Ca‐H2O (pore diameter 0.34 nm) exhibits ultra‐high CO2/N2, CO2/CH4, and C2H2/C2H4binary selectivity, bnn‐1‐Ca (pore diameter 0.31 nm) offers ideal selectivity for H2/CO2and H2/N2under cryogenic conditions. Ca‐trimesate, the first physisorbent to exhibit H2sieving under cryogenic conditions, could be a prototype for a general approach to exert precise control over pore diameter in physisorbents.
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Abstract Porous graphene and other atomically thin 2D materials are regarded as highly promising membrane materials for high‐performance gas separations due to their atomic thickness, large‐scale synthesizability, excellent mechanical strength, and chemical stability. When these atomically thin materials contain a high areal density of gas‐sieving nanoscale pores, they can exhibit both high gas permeances and high selectivities, which is beneficial for reducing the cost of gas‐separation processes. Here, recent modeling and experimental advances in nanoporous atomically thin membranes for gas separations is discussed. The major challenges involved, including controlling pore size distributions, scaling up the membrane area, and matching theory with experimental results, are also highlighted. Finally, important future directions are proposed for real gas‐separation applications of nanoporous atomically thin membranes.
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