(126E) Guanidinium Polyelectrolytes for the Direct Air Capture of Carbon Dioxide

This research furthers the study of strong selectivity and high sorption capacity amines for the direct air capture (DAC) of CO2 by examining the addition of guanidinium polyelectrolytes to porous activated carbon. Poly(guanidinium styrene sulfonate), made via the reaction of guanidine carbonate with poly(4-styrenesulfonic acid), was impregnated at different loadings into activated carbon. In isothermal sorption testing under 100% CO2 (30 °C, ~40% relative humidity, 1 atm) pure activated charcoal captured between 1.10 and 1.18 mmol/g. The addition of PGSS at 1.0% weight loading increased sorption capacity to 1.25 mmol/g. Past 1.0% weight loading, capacity decreased, hypothesized to be because of sorbent pore clogging due to the polymer addition and supported by SEM images showing a decrease in pore size. Modifications to reduce clogging involved surface treating the support directly with guanidinium and hydroxylating the support via strong acid baths prior to treating with guanidinium. Preliminary results of modified sorbents suggest increased sorption capacities past 1.25 mmol/g. Humidity was not seen to significantly affect sorption as samples in 65% RH had capacities between 90% to 105% that of samples under dry conditions, indicating applicability to DAC. Desorption occurs below 200 °C without requiring vacuum, which suggests reduced energy requirements for sorbent regeneration, increasing net CO2 removal. This work shows that guanidinium polyelectrolytes on activated carbon support represent a potential avenue for DAC due to their increased capacities over pure activated carbon, ability to capture at atmospheric conditions, including humidity, and their lower temperatures for desorption compared to liquid solvent technologies.