Capturing CO₂, usually from its mixture with N₂, is a key environmental and engineering issue. The traditional liquid amine process and the newly developed solid adsorbent method are all energy inten-sive and a high CO₂ selectivity is always accompanied with the difficulty of regeneration due to a large adsorption energy. Membrane strategy provide a feasible alternative for gas separation; among which carbon nanotube (CNT) membrane stands out featured by an exceptionally fast mass transport rate. For CO₂ capture, the enhancement of the CO₂/N₂ selectivity of CNT membranes remains a big challenge. Inspired by the phenomenon that nitrogen-containing compounds with significant electrons accumula-tion on nitrogen could chemically grab CO₂, we propose that a nitrogen incorporated CNT with exces-sive electron density on nitrogen might exhibit high CO₂ adsorption energy. Our molecular simulation verified this and we hence further propose a scheme with a fundamentally different mechanism for con-trollable carbon dioxide capture with high energy efficiency.
The models are based on (7,7) single walled CNT. Density functional theory plus dispersion calcula-tions of gas adsorption on CNTs were performed using DMol3 with PBE functional. The minimum en-ergy pathways for CO2 capture and release were searched by Linear Synchronous Transit algorithm.
A high CO2 adsorption energy was obtained on negative charge carrying pyridine-CNT, and which could further increase with more electron numbers injection. Furthermore, when the extra electrons are subsequently dismissed from the system, the pre-adsorbed CO2 could spontaneously desorb via a barri-erless reaction pathway to realize an energy-efficient desorption. In comparison, N2 adsorption is not affected by the changing of charge carrying state. Our results suggest that CNT membrane with pyri-dinic nitrogen doping is an excellent CO2 capture material with controllable feature, high selectivity, and facile operation. This charge controlled capture scheme opens a new avenue for efficient CO2 separation technology and clean energy storage/conversion.