Design rationale of thermally responsive microgel particle films that reversibly absorb large amounts of CO(2): fine tuning the pK(a) 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 CO(2) over a narrow temperature range (30–75 °C). The pK(a) value of ammonium ions in the GPs at both the CO(2) capture temperature (30 °C) and release temperature (75 °C) is found to be the primary factor responsible for the stoichiometry of reversible CO(2) capture by the amines in the GP films. The pK(a) 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 CO(2) per g dry GPs, 3.0 mmol CO(2) 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 pK(a) tuning procedures.