Fish-Scale-Like Intercalated Metal Oxide-Based Micromotors as Efficient Water Remediation Agents

Abstract

With compelling virtues of a large specific surface area, abundant active sites, and fast interfacial transport, nanomaterials have been demonstrated to be indispensable tools for water remediation applications. Accordingly, micro/nanomotors made by nanomaterials would also benefit from these properties. Though tuning the surface architecture on demand becomes a hot topic in the field of nanomaterials, there are still limited reports on the design of active surface architectures in chemically driven tubular micro/nanomachines. Here, a unique architecture composed of a fish-scale-like intercalated (FSI) surface structure and an active layer with 5 nm nanoparticles is constructed, which composes of Fe 2 O 3 and ramsdellite MnO 2 , Mn 2 O 3 , in the tubular micromotor using a versatile electrodeposition protocol. Tailoring the electrodeposition parameters enables us to modulate the active MnO 2 surface structure on demand, giving rise to a pronounced propulsion performance and catalytic activity. Upon exposure to the azo-dye waste solution, the degradation efficacy greatly raises by around 22.5% with FSI micromotor treatment when compared to the normal compact motors, owing to the synergistic effect between the Fe-related Fenton reaction and a large catalytic area offered by the hierarchically rough inner surface. Such unique micromachines with a large active surface area have great potential for environmental and biomedical applications.

From Passive Inorganic Oxides to Active Matters of Micro/Nanomotors

“…[ 84a ] In addition, the catalytic capability of MnO 2 micromotor can be tailored by changing the electrodeposition modes. [ 45a ] The MnO 2 micromotors synthesized in PS mode exhibited the highest ability to degrade MB (200 mg L −1 micromotors completely faded 30 mg L −1 MB in 10 min) than the other PD and GS modes. Furthermore, the integration of high specific surface area in MnO 2 ‐based micromotor further enhanced the dye degradation efficiency.…”

“…[ 44 ] With considerable scientific attentions attracted on the strong bubble propulsion, low‐cost, easily prepared MnO 2 have been widely investigated for the design and fabrication of the micro‐ and nanomotors. [ 16a,26,28a,45 ] The most effective way of increasing the relatively low motion speed (only ≈120 µm s −1 at 21% H 2 O 2 ) [ 28a ] of commercial MnO 2 particles is to change the MnO 2 crystal forms. It is noticed that MnO 2 @MnCO 3 core–shell spheroidal micromotors with ε‐MnO 2 single phase and a rough surface structure show superior propulsion speed and operation lifetime than the amorphous MnO 2 microtubes and microrods (≈900 µm s −1 at 10% H 2 O 2 ).…”

“…MnO 2 can be obtained either by chemical or electrochemical synthesis, [ 16a,23a,26,46 ] and nevertheless electrodeposition of MnO 2 is controlled by electrical signal and could be precisely modulated by changing the electrical parameters. Recently, Liu et al [ 45a ] compared ramsdellite‐MnO 2 ‐based tubular micromotors using three electrochemical deposition methods: potentiodynamic (PD), potentiostatic (PS), and galvanostatic (GS), as illustrated in Figure A. It is found in the PD mode that the micromotors are produced more efficiently and have the maximum speed.…”

“…Subsequently, the same research group modified the MnO 2 ‐based tubular micromotor with a Fe 2 O 3 fish‐scale‐like layer (FSI) embedded structure by electrodeposition. [ 45b ] The special internal surface structure further increases the motion speed and enhances the degradation efficacy of azo‐dye (methyl blue). Compared with the speed of regular counterparts (around 30 µm s −1 ), the average velocity of FSI micromotor achieves up to 111 µm s −1 .…”

Bubble-propelled micromotors based on hierarchical MnO2 wrapped carbon nanotube aggregates for dynamic removal of pollutants

“…11,12 Many structures, including micro/nano tubes, nanorods, and Janus spheres, have been developed that contain a layer of catalyst to produce bubbles for propulsion. [13][14][15] Generally, tubular micromotors are fabricated by either roll-up nanotechnology or template-assisted synthesis. 8,16 Spherical micromotors are fabricated with the use of solid spheres in which a layer of a material is deposited by physical vapor deposition techniques to make Janus particles.…”