Quaternized Engineered Hydrogels for Subsaturated Moisture-Driven CO₂ Capture

Area of Science:

• Materials Science
• Environmental Science
• Chemical Engineering

Background:

• Atmospheric carbon dioxide removal is crucial for achieving net zero emissions.
• Direct air capture (DAC) technologies are essential for removing CO2.
• Current moisture-swing DAC systems often require high humidity for regeneration, limiting their operational range.

Purpose of the Study:

• To develop a novel material for direct air capture that operates under a wider range of environmental conditions.
• To broaden the passive operating window for moisture-swing DAC by enabling regeneration under subsaturated relative humidity (RH).

Main Methods:

• Development of a quaternized poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) hydrogel, termed PDMH.
• PDMH combines humidity-responsive quaternary ammonium sites with a phase-transition temperature for hydration control.
• Testing CO2 uptake and regeneration efficiency under various temperature and RH conditions, including a 24-hour diurnal cycle.

Main Results:

• PDMH achieved a CO2 uptake of 1.06 mmol g-1 at 40°C and 30% RH with 400 ppm CO2.
• Regeneration efficiencies of 92% at 90% RH and 79% at 80% RH were achieved at 25°C.
• Over 40 cycles, PDMH demonstrated stable working capacity (0.97-1.05 mmol g-1) and >90% CO2 release during desorption.
• Comparative energy analysis indicated superior energy efficiency compared to other evaluated sorbents.

Conclusions:

• Passive diurnal moisture-swing hydrogels (PDMHs) offer a promising solution for direct air capture under subsaturated RH conditions.
• The developed PDEAEMA-based hydrogel broadens the climatic window for passive CO2 capture, enhancing operational flexibility.
• PDMHs present an energy-efficient alternative for atmospheric carbon dioxide removal, contributing to net zero emission strategies.