Correlating Carbon Dioxide Capture and Chemical Changes in Pyrolyzed Polyethylenimine-C60

Nitrogen functionalities play a crucial role in determining the sorption capacity and selectivity of organic-based CO 2 solid sorbents. Two main types of solid sorbents are (1) amine-rich compounds used for their distinctive reactivity of amino groups with CO 2, and (2) N-doped carbons where CO 2 -philic nitrogens impart chemoselectivity to otherwise pure carbon physisorbents. It is of interest to correlate the CO 2 sorption performance of these materials to the chemical changes involved in going from amine-rich polymers to N-doped carbons. To this end, we pyrolyzed amine-rich polyethylenimine-C 60 (PEI-C 60 ) to N-doped carbons and focused our investigation on how chemical changes and CO 2 capture correlate. In particular, we found that upon thermal treatment in inert atmosphere, PEI-C 60 undergoes an inversion in CO 2 sorption behavior. PEI-C 60, which better absorbs CO 2 at high temperature (0.13 g/g at 90 °C), is converted into pyrolyzed materials with improved CO 2 capture performance at low temperature (0.12 g/g at 25 °C). X-ray photoelectron spectroscopy (XPS), Fourier transfer infrared (FTIR), and Raman characterizations reveal a progressive conversion of PEI-C 60 to disordered graphitic carbon including pyrrolic and pyridinic aromatic nitrogens, where the transition from one material to the other goes through a drastic drop of CO 2 capture performance due to the breakdown of the carbon backbone of PEI.