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

Energy-efficient separation of CH/CH is a great challenge, for which adsorptive separation is very promising. CH-selective adsorption has big implications, while the design of CH-sorbents with ideal adsorption capability, particularly with the CH/CH-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 CH-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 CH-selective adsorption capabilities with visible light, particularly the composite sorbent based on the hierarchical-pore carbon, whose CH and CH adsorption capacities (0 °C, 1 bar) are targetedly increased by 27% and only 1.8% with visible light, and therefore, an CH-selectivity (CH/CH = 10/90, v/v) of 4.8 can be realized. With visible light, the adsorption force of the CH molecule can be asymmetrically enhanced by the excitation enriched electron density over the adsorption sites formed the close interaction between the Cu-TCPP and the carbon layer, whereas that of the CH 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 CH/CH with light.