A critical challenge in the development of novel carbon capture materials with engineered porous architectures is to understand and control the phenomenon of sorption hysteresis, whereby the path to adsorption of gas molecules by the porous host differs from that to desorption. We show that a one-dimensional (1D) microporous octahedral molecular sieve with manganese oxide framework (OMS-2) exhibits time dependent hysteresis behavior at 303 K and up to 25 bar, which persists at temperatures slightly above the critical temperature of bulk CO2 (304.25 K). We hypothesize that the cation inside the pore serves as a gate keeper that only allowing allows CO2 molecules to enter fully into the 1D tunnel-shaped pores via a highly unstable transition state when gas loadings exceed 0.75 mmol of CO2 per g OMS-2. The energy barrier associated with the gate-keeping effect suggests an adsorption mechanism in which kinetic trapping of CO2 is responsible for the observed hysteretic behavior.
Citation: Journal of the American Chemical Society
Pub Type: Journals
mircroporous materials, molecular sieves, CO2 adsorption, carbon capture, gas sorption hysteresis