The
shortage of freshwater is threatening sustainable economic
development and ecological security worldwide. Janus membrane, as
a highly efficient method to collect the invisible fog water in the
wet environment, is still hindered by some inherent limitations: (1)
poor condensation of fog droplets on the superhydrophobic side due
to the ultralow adhesive force of droplets with substrate and (2)
insufficient detachment of droplets from the superhydrophilic side
in time, which hampers the continuous water transport in the micropores.
Herein, inspired by the desert beetle’s back with alternating
hydrophobic/hydrophilic bumps and the cactus thorn with an asymmetric
geometry, we design and fabricate a kind of hierarchical hydrophilic/hydrophobic/bumpy
Janus (HHHBJ) membrane by femtosecond laser ablation on an aluminum
membrane to achieve the self-driven fog collection, which achieves
over 250% enhancement in the water collection efficiency over the
conventional Janus membrane. Even when the mist flow is applied to
the surface at an incident angle of 45°, the collection efficiency
increases by 600%. The mechanism of the HHHBJ film with excellent
fog collection efficiency is mainly related to the continuous efficient
fog condensation on the top surface and droplet removal on the bottom
surface in time. We believe the proposed multi-bioinspired HHHBJ film
with droplet self-driven collection ability provides insights to conceive
and construct a highly efficient fog collection system in broad fields.
Inspired by natural creatures, bubble manipulation by surface microstructures in aqueous media has attracted great attention due to its promising applications in industrial production. Herein, a superhydrophobic/hydrophilic Janus aluminum membrane with tapered micropore arrays was fabricated by femtosecond laser drilling, surface fluorination, and subsequent fluorination removal. Compared with the single interception or penetration of double-faced hydrophilic or superhydrophobic membranes, the Janus membrane showed a distinctive unidirectional air bubble transport ability. In experiment, the air bubbles introduced on the lower hydrophilic surface could spontaneously move to the upper superhydrophobic surface, but they were prevented in the inverse direction. The dynamic process of unidirectional transport was in-situ monitored, and the physical mechanism was systemically investigated. In addition, the concepts of air-participating chemical/physical processes were demonstrated such as discoloration of purple litmus solution by CO2 injection, which proved the Janus membrane practicability.
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 CO 2 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.
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