Branched ZnO Wire Structures for Water Collection Inspired by Cacti

Abstract

In this work, motivated by an approach used in a cactus to collect fog, we have developed an artificial water-collection structure. This structure includes a large ZnO wire and an array of small ZnO wires that are branched on the large wire. All these wires have conical shapes, whose diameters gradually increase from the tip to the root of a wire. Accordingly, a water drop that is condensed on the tip of each wire is driven to the root by a capillary force induced by this diameter gradient. The lengths of stem and branched wires in the synthesized structures are in the orders of 1 mm and 100 μm, respectively. These dimensions are, respectively, comparable to and larger than their counterparts in the case of a cactus. Two groups of tests were conducted at relative humidity of 100% to compare the amounts of water collected by artificial and cactus structures within specific time durations of 2 and 35 s, respectively. The amount of water collected by either type of structures was in the order of 0.01 μL. However, on average, what has been collected by the artificial structures was 1.4-5.0 times more than that harvested by the cactus ones. We further examined the mechanism that a cactus used to absorb a collected water drop into its stem. On the basis of the gained understanding, we developed a setup to successfully collect about 6 μL of water within 30 min.

Bioinspired Special Wettability Surfaces: From Fundamental Research to Water Harvesting Applications

“…Due to the diameter gradient from the top to the bottom, the condensate microdrops on the top tend to be driven to the bottom. Based on the achievement showed above, Heng et al further verified that the amount of water collected by the man‐made structures was 1.4–5.0 times higher than the cactus ones due to the absorption ability of cactus stems …”

“…G) Water drops collected by (G1) artificial (A1) and (G2) cactus (C1) structures in the first group of tests at 35 s. Water drops collected by (G3) artificial (A1) and (G4) cactus (C1) structures in the second group of tests at 2 s. The scale bars are 1 mm. Reproduced with permission . Copyright 2014, American Chemical Society.…”

Superhydrophobic and superoleophobic properties in nature

“…The group of Jiang also reported than the cactus Opuntia microdasys, which originates from the Chihuahua Desert, can also collect water from fog thanks to their spines [89][90][91][92] Images of superhydrophobic gecko foot with high adhesion at different magnifications, able to walk on vertical surfaces. [74], Copyright 2012.…”

Ag Nanoparticles Decorated Cactus-Like Ag Dendrites/Si Nanoneedles as Highly Efficient 3D Surface-Enhanced Raman Scattering Substrates toward Sensitive Sensing

“…Nevertheless, these tips were short and of low density, and the hydrophobic surface challenged the detection of the analytes in water due to the poor affinity. [23][24][25][26] Silicon (Si) nanomaterials have been reported as excellent SERS platform by He's group because of their biocompatibility, stable chemical structure, hydrophilic properties, and luminescence quenching. 27 The needle-like Si tips rather than nanorods or spherical particles were chosen as building blocks to offer additional SERS enhancement by optical antenna effect.…”