Visible Light-Driven CO₂ Capture and Release Using Photoactive Pyranine in Water in Continuous Flow

The urgent need to address climate change and its environmental consequences demands innovative carbon capture technologies, given the relationship between rising global temperatures and increased atmospheric CO₂ levels. Here, we present a reversible photochemical carbon capture and release strategy and system utilizing photoactive pyranine in an aqueous bicarbonate buffer system. Control experiments suggested that the photoacid effect occurs at the surface which contributes to CO₂ release, complemented by the photothermal effect at the surface and in the bulk. A continuous flow setup employing a tube-in-tube configuration with a hollow fiber membrane demonstrates the efficiency and reliability of the visible light-driven carbon capture system, with the release of CO₂ captured from a 15% CO₂ feed in the dark, at a rate of 0.48 mmol CO₂ per hour to a nitrogen sweep stream under light irradiation at 200 W/m², a level comparable to solar intensity of visible light (150 W/m² of blue light -250 W/m² of blue and green light). The robustness and scalability of the system has been demonstrated, with long-term operation over 7 days yielding 60 mmol (1.34 L CO₂ at STP) of cumulated CO₂ separation. Additionally, we explored the potential for direct air capture, yielding 3 μmol of CO₂ separation over 2 h of operation from a bicarbonate buffer solution saturated with ambient air (420 ppm). This work introduces the prospect of photoswing of carbon capture systems, which can avoid external energy input beyond solar irradiation, offering promising avenues for addressing the challenges associated with climate change.