Mass transfer enhancement in continually replenished aerophilic surfaces

Abstract

Absorption of gas in liquid media is an important step in applications ranging from environmental remediation to bioreactor design, yet it is often limited by slow interfacial mass transport. Here, we show how continually replenished aerophilic surfaces significantly enhance gas uptake across a gas–liquid interface. Similar to superhydrophobic surfaces, they feature hierarchical micro/nanotextures designed to retain a stable trapped gas layer underwater known as the plastron. We fabricate aerophilic surfaces with microcapsule features covered with nanoscopic pinning points and varying inter-feature spacings using laser ablation. Testing for CO2 uptake in a potassium hydroxide solution at near-neutral pH, we find that they attain 80% of the maximum saturation concentration within one hour, while conventional diffusion from an overhead CO2 atmosphere reaches only 20%. Using bromothymol blue colorimetry, we observe a 20-fold enhancement in the mass transfer rate from aerophilic surfaces compared to an equivalent planar gas–liquid interface with the same projected area. Counterintuitively, the enhanced mass transfer rate is not driven by an increase in interfacial area. Instead, it arises from a 24-fold increase in the liquid-side mass transfer coefficient, likely resulting from reduced resistance to mass transfer across the gas–liquid interface in the plastron. Environmental scanning electron microscopy confirms our plastron model of hemispherical gas caps pinned atop microtextures, with interfacial area calculations corroborating findings from colorimetry. These results highlight the potential of dynamically replenished aerophilic surfaces to overcome mass transport limitations in multiphase systems with gases and liquids, with potential applications in carbon capture and sustainable energy.