ZnO-based microrockets with light-enhanced propulsion

Abstract

Improving the propulsion of artificial micro-nanomotors represents an exciting nanotechnology challenge, especially considering their cargo delivery ability and fuel efficiency. In light of the excellent photocatalytic performance of zinc oxide (ZnO) and chemical catalytic properties of platinum (Pt), ZnO-Pt microrockets with light-enhanced propulsion have been developed by atomic layer deposition (ALD) technology. The velocity of such microrockets is dramatically doubled upon irradiation by 77 mW cm ultraviolet (UV) light in 10% HO and is almost 3 times higher than the classic poly(3,4-ethylenedioxythiophene)-Pt microrockets (PEDOT-Pt microrockets) even in 6% HO under the same UV light. In addition, such micromotors not only retain the standard approach to improve propulsion by varying the fuel concentration, but also demonstrate a simple way to enhance the movement velocity by adjusting the UV light intensity. High reversibility and controllable "weak/strong" propulsion can be easily achieved by switching the UV irradiation on or off. Finally, light-enhanced propulsion has been investigated by electrochemical measurements which further confirm the enhanced photocatalytic properties of ZnO and Pt. The successful demonstration of ZnO-based microrockets with excellent light-enhanced propulsion is significant for developing highly efficient synthetic micro-nanomotors which have strong delivery ability and economic fuel requirements for future practical applications in the micro-nanoscale world.

Hybrid Nanovehicles: One Machine, Two Engines

“…Furthermore, light stimuli can also serve as a speed accelerator or gas pedal. For example, exposure to UV light enhances the decomposition of the H 2 O 2 fuel on a ZnO/Pt microrocket and hence leads to doubling the speed from 249 to 471 µm s −1 upon UV light irradiation …”

Light‐Driven Sandwich ZnO/TiO2/Pt Janus Micromotors: Schottky Barrier Suppression by Addition of TiO2 Atomic Interface Layers into ZnO/Pt Micromachines Leading to Enhanced Fuel‐Free Propulsion

“…The light-triggered motion is usually achieved by an asymmetrical micromotor design, i.e., Janus or two-face (semi-)spherical microparticles, which needs less complex material development in comparison with tubular micromotors. [13,14] Scheme 1 illustrates a common design of a binary and improved ternary light-driven Janus micromotor. The conventional binary micromotors consist a semiconducting photocatalyst with a specific bandgap such as ZnO, which is situated close to a metal such as platinum (Pt) with a Fermi-level comparable to the photocatalyst conduction band (CB) level.…”

“…Unlike catalytic micromotors, which require destructive/toxic chemical fuels such as H 2 O 2 , the use of light power to activate the motion of these micromachines represents a more environmentally friendly approach that guarantees their potential use in disinfection applications. The light‐triggered motion is usually achieved by an asymmetrical micromotor design, i.e., Janus or two‐face (semi‐)spherical microparticles, which needs less complex material development in comparison with tubular micromotors …”

Multifunctional Visible‐Light Powered Micromotors Based on Semiconducting Sulfur‐ and Nitrogen‐Containing Donor–Acceptor Polymer

“…There is a considerable amount of photocatalytic systems exploited as light‐driven micromachines, including commonly employed TiO 2 [ 9 ] and its modified analogs, [ 10 ] or alternatively, Ag 3 PO 4 , [ 11 ] WO 3 /Au, [ 12 ] ZnO/Pt [ 13 ] to name a few. Despite their excellent photocatalytic performance, there are certain drawbacks, which hinder the widespread usage of such microdevices.…”