Polyethyleneimine functionalised nanocarbons for the efficient adsorption ofcarbon dioxide with a low temperature of regeneration

Polyethyleneimine (PEI) conjugates with a range of nanocarbons (NCs) have been prepared, and their performances with regard to carbon dioxide absorption and liberation are compared. PEI-functionalised multi-walled carbon nanotubes (PEI-MWNTs) prepared by the reaction of branched PEI (25,000 Da) with F-MWNTs in the presence of pyridine, showed a lower CO2 capacity at 25 degrees C (5wt%, 1.1mmol CO2/g adsorbent) as compared to PEI-SWNTs (9.2wt%, 2.1mmol CO2/g adsorbent), consistent with the interior layers of the MWNTs adding weight to the base NC without adding functionality. PEI-functionalised graphite/graphene was prepared by three routes: fluorinated graphite intercalation compounds, prepared from natural graphite powder, were reacted with PEI in EtOH with pyridine; exfoliated natural graphite powder was reacted with Boc-Phe(4-N-3)-OH, and subsequently PEI to give PEI-Phe(4-N-G); graphite oxide (GO) was reacted with PEI in the presence of NEt3 to give PEI-GO. The CO2 capacity of PEI-GO at 25 degrees C (8wt%, 1.8mmol CO2/g adsorbent) was comparable to that of PEI-SWNTs making GO a valid and cheaper alternative to the SWNT scaffold. The temperature of CO2 desorption of the PEI-NCs was 75 degrees C, providing a lower energy load for regeneration compared to current amine-based scrubbing units. The rate of CO2 uptake is seen to depend on the curvature of the NC substrate.