Cooperative lattice theory for CO2 adsorption in diamine-appended metal organic framework at humid direct air capture conditions

TL;DR

This study investigates how humidity influences CO2 adsorption in amine-functionalized metal organic frameworks, revealing a transition from cooperative to non-cooperative binding with increasing humidity, explained by a new lattice kinetic theory.

Contribution

The paper introduces a novel lattice kinetic theory that accurately models the effect of humidity on CO2 adsorption mechanisms in metal organic frameworks.

Findings

At low humidity, CO2 adsorption shows an anomalous induction effect.

Increasing humidity shifts adsorption from cooperative to non-cooperative.

The theory explains the transition from type V to type I adsorption behavior.

Abstract

The effect of humidity on the cooperative adsorption of CO2 from air on amine appended metal organic frameworks is studied both experimentally and theoretically. Breakthrough experiments show that at low relative humidities there is an anomalous induction effect, where the kinetics at short times are slower than kinetics at long times. The induction effect gradually vanishes as relative humidity is increased, corresponding to an increase in CO2 adsorption rate. A new theory is proposed based on the Lattice Kinetic Theory (LKT) which explains these experimental results. LKT is able to accurately represent the measured data over the full range of humidities by postulating that the presence of adsorbed water shifts the equilibrium clusters from cooperatively bound chains to non-cooperatively bound CO2. A consequence of this transition is that CO2 exhibits type V adsorption in dry air, and type I adsorption in humid air.