Photo-DAC: Light-Driven Ambient-Temperature Direct Air Capture by a Photobase.

Area of Science:

• Chemical Engineering
• Environmental Science
• Materials Science

Background:

• Direct air capture (DAC) technologies are crucial for reducing atmospheric CO2 but face challenges with high energy demands.
• Current aqueous-based DAC methods incur significant energy penalties due to heating and boiling for solvent regeneration.
• Photochemical approaches offer a potential alternative by utilizing light energy for solvent regeneration.

Purpose of the Study:

• To develop and demonstrate an energy-efficient photochemical direct air capture (photo-DAC) process.
• To investigate the use of a novel photobase for pH-swing-enabled CO2 capture and release.
• To assess the recyclability and efficiency of the proposed photo-DAC system over multiple cycles.

Main Methods:

• A novel photochemically driven DAC process (photo-DAC) was developed using an aqueous glycylglycine (GlyGly) solution activated by a pyridine-substituted diiminoguanidine (PyDIG) photobase.
• CO2 capture was achieved by UV light-induced photoisomerization of PyDIG, increasing its pKa and activating GlyGly for deprotonation.
• CO2 release was induced by returning the system to dark, ambient conditions, causing PyDIG to isomerize back and lower the pH.

Main Results:

• The GlyGly/PyDIG solvent demonstrated efficient CO2 capture activated by a pH swing induced by UV light.
• Six consecutive DAC cycles were completed, showing good recyclability of the solvent.
• Average cyclic CO2 capacity ranged from 0.21-0.26 mol CO2 per mol of GlyGly/PyDIG.

Conclusions:

• The developed photo-DAC process offers an energy-efficient alternative to conventional thermal regeneration methods.
• This approach avoids the high energy penalties associated with heating and boiling aqueous solvents.
• The findings present a promising pathway for scalable and cost-effective direct air capture at ambient conditions.