Manganese oxide (MnO) has recently emerged as a promising alternate material for the fabrication of self-propelled micromotors. Platinum (Pt) has been traditionally used as a catalytic material for this purpose. However, the high cost associated with Pt restricts its widespread use toward practical applications where large amounts of material are required. MnO exists in different crystalline forms (polymorphs), which govern its catalytic behavior. In spite of this, the recent reports on MnO based micromotors have seldom reported on the polymorphic form involved. In the present work, we synthesized six different types of MnO based micromotors, which represent different geometrical designs (i.e., spherical, rod-like, and tube-like microparticles) and polymorphs, and characterized their motion behavior in different chemical environments. Out of all micromotors tested, the hollow spherical MnO microparticles reached the maximum velocity of ∼1600 μm s, which represents the fastest MnO based catalytic micromotor reported until date. The findings of this study will have a profound impact on the design and application of the next-generation synthetic micro- and nanomotors based on MnO as a low-cost and environment friendly material.

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Platinum-based micromotors have shown many exciting applications when functionalized using gold-thiol chemistry. However, thiols are known to bind to the Pt surface, which can lead to serious deactivation of the catalyst. In this paper, it is demonstrated that MnO can be used to protect Pt-based micromotors prior to the thiol treatment, thus fully avoiding the catalyst poisoning. This approach will greatly facilitate the use of the functionalized Pt micromotors for which the thiol toxicity has been a limiting factor.

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