# Can Gas Absorption be Tuned in a Multifunctional Ionic Liquid?

## TL;DR

A new ionic liquid can efficiently absorb CO2 and is enhanced with ZIF-8, though CO2 exposure reduces its effectiveness.

## Contribution

A multifunctional ionic liquid with CO2 absorption and tunable properties is introduced, combined with ZIF-8 for enhanced performance.

## Key findings

- The ionic liquid shows high CO2 absorption capacity and selectivity over CH4.
- ZIF-8 addition enhances physical absorption but causes porosity loss in CO2 presence.
- The material maintains stability and porosity after CH4 absorption.

## Abstract

The challenge of CO2 separation and management in biogas upgrading processes is addressed, which remains a critical bottleneck when considering biomethane as a competitive and sustainable alternative to natural gas. Ionic liquids offer a promising alternative to existing sorbents due to their negligible volatility and their tunable properties. Herein, a multifunctional phosphonium triazolate ionic liquid capable of reacting reversibly with CO2 without loss of fluidity through both cation and anion is presented. Using a combination of experiments and reaction models the interplay of different absorption mechanisms is demonstrated at varying temperatures and pressures, which lead to high capacity for CO2 absorption and excellent selectivity for CO2 over CH4. The multifunctional phosphonium triazolate can be used to prepare a porous ionic liquid with enhanced physical gas absorption by dispersing up to 10% w/w of ZIF‐8. The stability and porosity are maintained after CH4 absorption but are lost upon prolonged exposure to CO2 due to dissolution of the porous solid. These findings provide crucial insights for the development and modeling of ionic liquid‐based absorbents, paving the way for biogas upgrading technologies with reduced carbon footprint.

A multifunctional phosphonium triazolate ionic liquid is capable of reversibly absorbing CO2 at high capacity while decreasing viscosity. The addition of ZIF‐8 leads to a porous ionic liquid with enhanced physical absorption, however, an unexpected loss of porosity occurs in the presence of CO2.© 2025 WILEY‐VCH GmbH