Fig. 1: Schematic of a CNT-bot composed of a –COOH-functionalised MWCNT cluster doped with a ferrous (Fe2+) salt and magnetite nanoparticles (FeONPs) before being coated with a Mg film.
From: Multimodal chemo-/magneto-/phototaxis of 3G CNT-bots to power fuel cells
The CNT-bot was capable of undergoing two reactions in acidic and alkaline water (e.g. Mg + H2O → Mg(OH)2 + H2, Mg + HCl → MgCl2 + H2 and NaHCO3 + MWCNT-COOH → MWCNT-COONa + H2O + CO2) and the Fenton reaction (in the absence of light) and photo-Fenton reaction (in the presence of UV light) in a peroxide fuel (Fe2+ + H2O2 → Fe3+ + H2O + O2), as shown in the image. Subsequently, the motor moved by ejecting hydrogen bubbles in acidic water, carbon-dioxide in alkaline water, and oxygen bubbles in the peroxide fuel. The motors showed directionality in their motion under acid and alkali gradients, leading to acid- and alkali-taxis, as shown in the images. The scheme also shows that hydrogen and oxygen serve as fuels of the PEM fuel cell and that the CNT-bot can also perform a dye degradation function.
