Design rationale of thermally responsive microgel particle films that reversibly absorb large amounts of CO2: fine tuning the pKa of ammonium ions in the particles†
Herein we revealed the design rationale of thermally responsive gel particle (GP) films that reversibly capture and release large amounts of CO2 over a narrow temperature range (30–75 °C). The pKa value of ammonium ions in the GPs at both the CO2 capture temperature (30 °C) and release temperature (75 °C) is found to be the primary factor responsible for the stoichiometry of reversible CO2 capture by the amines in the GP films. The pKa values can be tuned by the properties of GPs such as volume phase transition temperature (VPTT), size, swelling ratio, and the imprinted microenvironment surrounding the amines. The optimal GP obtained according to the design rationale showed high capture capacity (68 mL CO2 per g dry GPs, 3.0 mmol CO2 per g dry GPs), although the regeneration temperature was as low as 75 °C. We anticipate that GP films that reversibly capture other acidic and basic gases in large amounts can also be achieved by the pKa tuning procedures.