Continuous reactive-roll-to-roll growth of carbon nanotubes for fog water harvesting applications

A simple method is presented for the continuous generation of carbon nanotube forests stably anchored on stainless-steel surfaces using a reactive-roll-to-roll (RR2R) configuration. No addition of catalyst nanoparticles is required for the CNT-forest generation; the stainless-steel substrate itself is tuned to generate the catalytic growth sites. The process enables very large surfaces covered with CNT forests to have individual CNT roots anchored to the metallic ground through primary bonds. Fog water harvesting is demonstrated and tested as one potential application using long CNT-covered wires. The RR2R is performed in the gas phase; no solution processing of CNT suspensions is used, contrary to usual R2R CNT-based technologies. Full or partial CNT-forest coverage provides tuning of the ratio and shape of hydrophobic and hydrophilic zones on the surface. This enables the optimization of fog water harvesters for droplet capture through the hydrophobic CNT forest and water removal from the hydrophilic SS surface. Water recovery tests using small harp-type harvesters with CNT-forest generate water capture of up to 2.2 g/cm2·h under ultrasound-generated fog flow. The strong CNT root anchoring on the stainless-steel surfaces provides opportunities for (i) robustness and easy transport of the composite structure and (ii) chemical functionalization and/or nanoparticle decoration of the structures, and it opens the road for a series of applications on large-scale surfaces, including fog harvesting.

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