Surface-Enhanced Raman Detection of the CO₂ Moisture Swing

Area of Science:

• Materials Science
• Chemical Engineering
• Spectroscopy

Background:

• Scalable, energy-efficient carbon dioxide (CO2) capture is vital for net-zero emissions.
• Moisture swing (MS) sorbents offer a promising, energy-efficient alternative to thermal regeneration for CO2 capture.
• Understanding anion speciation dynamics is key to optimizing MS sorbent performance.

Purpose of the Study:

• To investigate anion speciation dynamics in two MS sorbent materials.
• To utilize in situ surface-enhanced Raman spectroscopy (SERS) for real-time monitoring of ion transformations.
• To validate mechanistic models of humidity-driven anion exchange in MS sorbents.

Main Methods:

• Employed SERS with Ni-coated Ag nanowire substrates for enhanced signal detection.
• Monitored carbonate (CO3^2-), bicarbonate (HCO3^-), and hydroxide (OH^-) species under controlled humidity.
• Utilized sorption measurements alongside SERS for comprehensive analysis.

Main Results:

• Observed humidity-dependent interconversion between anionic species, confirming reversible hydrolysis reactions.
• Detected depletion of bicarbonate and increase of carbonate under humid conditions, indicating moisture-induced CO2 desorption.
• Identified hydroxide formation in activated carbon samples, further elucidating the MS mechanism.

Conclusions:

• Validated mechanistic models for humidity-driven anion exchange in MS sorbents.
• Demonstrated SERS as a practical operando diagnostic tool for CO2 capture media.
• Provided insights for designing and optimizing next-generation direct air capture sorbents.