Taking
inspirations from nature, we endeavor to develop catalytically
self-propelled nanojets from a type of tubular clay minerals, halloysite
nanotubes (HNTs), and utilize them as catalysts targeted for catalysis
where the traditional means of mechanical agitation cannot be implemented.
Nanojets of Fe3O4@HNTs/Pt were prepared by impregnating
platinum nanoparticles (Pt NPs) in lumens of HNTs and selective grafting
of magnetite (Fe3O4) particles on the external
surface. The HNT-based nanojets were validated to be highly suitable
both in free bulk solution and in microfluidic flow. An example of
Fenton degradation catalyzed by these jets was demonstrated. The powerful
movement of Fe3O4@HNTs/Pt (368 ± 50 μm·s–1) fueled by 5.0% wt. H2O2 was
found to follow a bubble propulsion mechanism, and the motion exhibits
collective behavior as swarms. The clay tubes were for the first time
observed to self-assemble into fish-like aggregates during swimming,
reflecting natural occurrence of motion-evolution philosophy. Guided
motion was realized by employing magnetic manipulation which makes
jets feasible for reactors with complex microchannels/reactors.
Halloysite-based tubular nanorockets
with chemical-/light-controlled
self-propulsion and on-demand acceleration in velocity are reported.
The nanorockets are fabricated by modifying halloysite nanotubes with
nanoparticles of silver (Ag) and light-responsive α-Fe2O3 to prepare a composite of Ag–Fe2O3/HNTs. Compared to the traditional fabrication of tubular
micro-/nanomotors, this strategy has merits in employing natural clay
as substrates of an asymmetric tubular structure, of abundance, and
of no complex instruments required. The velocity of self-propelled
Ag–Fe2O3/HNTs nanorockets in fuel (3.0%
H2O2) was ca. 1.7 times higher under the irradiation
of visible light than that in darkness. Such light-enhanced propulsion
can be wirelessly modulated by adjusting light intensity and H2O2 concentration. The highly repeatable and controlled
“weak/strong” propulsion can be implemented by turning
a light on and off. With the synergistic coupling of the photocatalysis
of the Ag–Fe2O3 heterostructure and advanced
oxidation in H2O2/visible light conditions,
the Ag–Fe2O3/HNTs nanorockets achieve
an enhanced performance of wastewater remediation. A test was done
by the catalytic degradation of tetracycline hydrochloride. The light-enhanced
propulsion is demonstrated to accelerate the degradation kinetics
dramatically. All of these results illustrated that such motors can
achieve efficient water remediation and open a new path for the photodegradation
of organic pollutions.
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