Femtosecond laser fabrication of shape-gradient platform: Underwater bubbles continuous self-driven and unidirectional transportation

The capture and directional transportation of gas bubbles in an aqueous environment are important aspects of modern science and technology including methane harvesting, CO2 capture/reduction and electrochemical H-2 generation and collection. However, designing and fabricating a device that functions to both harvest air bubbles from the aqueous solution and to directionally transport those bubbles with no external force remains a challenge. In this work, we develop a facile method to fabricate micro/nanoscale hierarchical structures on a trapezoidal platform using femtosecond laser direct cutting and surface structuring technology. The geometry-gradient platform surface exhibits superhydrophobicity in air and superaerophilicity in water and allows air bubbles to self-transport from the minor side onto the large side but not in the opposite direction. Furthermore, the as-prepared platform exhibits robust stability in corrosion and friction tests. In addition, a superaerophilic trapezoidal platform with a cross-shaped structure is developed that spontaneously captures, unidirectionally transports, and collects bubbles in a supersaturated gas solution. This superaerophilic trapezoidal platform exhibits tremendous potential in applications for advanced self-driven transport devices and is a promising tool in solving energy and environment problems.