Excitation generated preferential binding sites for ethane on porous carbon–copper porphyrin sorbents: ethane/ethylene adsorptive separation improved by light

Abstract

Energy-efficient separation of C₂H₆/C₂H₄ is a great challenge, for which adsorptive separation is very promising. C₂H₆-selective adsorption has big implications, while the design of C₂H₆-sorbents with ideal adsorption capability, particularly with the C₂H₆/C₂H₄-selectivity exceeded 2.0, is still challenging. Instead of the current strategies such as chemical modification or pore space modulation, we propose a new methodology for the design of C₂H₆-sorbents. With a Cu-TCPP [TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin] framework dispersed onto a microporous carbon and a hierarchical-pore carbon, two composite sorbents are fabricated. The composite sorbents exhibit enhanced C₂H₆-selective adsorption capabilities with visible light, particularly the composite sorbent based on the hierarchical-pore carbon, whose C₂H₆ and C₂H₄ adsorption capacities (0 °C, 1 bar) are targetedly increased by 27% and only 1.8% with visible light, and therefore, an C₂H₆-selectivity (C₂H₆/C₂H₄ = 10/90, v/v) of 4.8 can be realized. With visible light, the adsorption force of the C₂H₆ molecule can be asymmetrically enhanced by the excitation enriched electron density over the adsorption sites formed via the close interaction between the Cu-TCPP and the carbon layer, whereas that of the C₂H₄ molecule is symmetrically altered and the forces cancelled each other out. This strategy may open up a new route for energy-efficient adsorptive separation of C₂H₆/C₂H₄ with light.