Generalized and Scalable Synthesis of Manganese Dioxide-Based Tubular Micromotors for Heavy Metal Ion Removal

Synthetic nano- and micromachines hold immense promise in biomedicine and environmental science. Currently, bubble-driven tubular micro/nanomotors have garnered increasing attention owing to their exceptional high-speed self-propulsions. However, complex and low-yield preparation methods have hindered their widespread applications. Herein, we present a generalized, scalable, and low-cost electrospinning-based strategy to fabricate MnO₂-based composite tubular micromotors (MnO₂-TMs) for efficient heavy metal ion removal. The inherent flexibility of precursor nanofibers derived from diverse matrix materials enables the creation of MnO₂-TMs with a wide range of morphologies. In response to morphology changes, the MnO₂-TMs, based on a bubble-propelled mechanism, exhibit multimodal motion patterns, including linear, circular, and spiral to stochastic swinging. To elucidate the underlying morphology-to-motion relationship, we conducted systematic simulations of fluid dynamics around the MnO₂-TMs. Furthermore, by incorporation of Fe₃O₄ nanoparticles, the capabilities of MnO₂-TMs can be expanded to include magnetic manipulation for directional navigation and efficient retrieval. Benefiting from these attributes, MnO₂-TMs excel in removing heavy metal ions from water. The developed MnO₂-MnWO₄@Fe₃O₄ TMs exhibit prominent adsorption capacities of 586.5 mg g^-1 for Cu²⁺ and 156.4 mg g^-1 for Pb²⁺. Notably, the magnetic property facilitates rapid separation and retrieval of the micromotors, and the absorbed ions can be simply recovered by pH adjustment. This work establishes a general framework for developing MnO₂-based tubular micro/nanomotors to address environmental challenges.