Magnetically Modulated Pot-Like MnFe2O4 Micromotors: Nanoparticle Assembly Fabrication and their Capability for Direct Oil Removal

This work demonstrates a simple-structured, low-cost magnetically modulated micromotor of MnFe2O4 pot-like hollow microparticles as well as its facile, versatile, and large-scale growing-bubble-templated nanoparticle (NP) assembly fabrication approach. In this approach, the hydrophobic MnFe2O4@oleic acid NPs in an oil droplet of chloroform and hexane assembled into a dense NP shell layer due to the hydrophobic interactions between the NP surfaces. With the encapsulated oil continuously vaporizing into high-pressured gas bubbles, the dense MnFe2O4 NP shell layer then bursts, forming an asymmetric pot-like MnFe2O4 micromotor by creating a single hole in it. For the as-developed simple pot-like MnFe2O4 micromotor, the catalytically generated O-2 molecules nucleate and grow into bubbles preferentially on the inner concave surface rather than on the outer convex surface, resulting in continuous ejection of O-2 bubbles from the open hole to propel it. Dexterously integrating the high catalytic activity for H2O2 decomposition to produce O-2 bubbles, excellent magnetic property with the instinctive surface hydrophobicity, the MnFe2O4 pot-like micromotor not only can autonomously move in water media with both velocity and direction modulated by external magnetic field but also can directly serve for environmental oil removal without any further surface modification. The results here may inspire novel practical micromotors.