Unidirectional Transport and Effective Collection of Underwater CO₂ Bubbles Utilizing Ultrafast-Laser-Ablated Janus Foam

Manipulating gas bubbles in aqueous ambient is of great importance for applications in water treatment, gas collection, and matter transport. Here, a kind of Janus foam is designed and fabricated by one-step ultrafast laser ablation of one side of the copper film, which is treated to be superhydrophobic. Janus foam exhibits not only the capability of unidirectional transport of underwater bubbles but also gas collection with favorable efficiency up to ∼15 mL cm^-2 min^-1. The underlying physical mechanism is attributed to the cooperation of the buoyancy, adhesion, and wetting gradient forces imposed on the bubbles. As a paradigm, the underwater chemical reaction between the unidirectional CO₂ gas flow and the alkaline phenolphthalein solution is demonstrated via Janus foam. This facile and low-cost fabrication approach for Janus foam will find broad potential applications in effective bubble transport, carbon capture, and controllable chemical reactions under aqueous conditions.