Cost-Effective, High-Yield Production of Biotemplated Catalytic Tubular Micromotors as Self-Propelled Microcleaners for Water Treatment

Abstract

Micro/nano-motors (MNMs) that combine attributes of miniaturization and self-propelled swimming mobility have been explored for efficient environmental remediation in the past decades. However, their progresses in practical applications are now subject to several critical issues including a complicated fabrication process, low production yield, and high material cost. Herein, we propose a biotemplated catalytic tubular micromotor consisting of a kapok fiber (KF, abundant in nature) matrix and manganese dioxide nanoparticles (MnO₂ NPs) deposited on the outer and inner walls of the KF and demonstrate its applications for rapid removal of methylene blue (MB) in real-world wastewater. The fabrication is straightforward via dipping the KF into a potassium permanganate (KMnO₄) solution, featured with high yield and low cost. The distribution and amount of MnO₂ can be easily controlled by varying the dipping time. The obtained motors are actuated and propelled by oxygen (O₂) bubbles generated from MnO₂-triggered catalytic decomposition of hydrogen peroxide (H₂O₂), with the highest speed at 615 μm/s (i.e., 6 body length per second). To enhance decontamination efficacy and also enable magnetic navigation/recycling, magnetite nanoparticles (Fe₃O₄ NPs) are adsorbed onto such motors via an electrostatic effect. Both the Fe₃O₄-induced Fenton reaction and hydroxyl radicals from MnO₂-catalyzed H₂O₂ decomposition can account for the MB removal (or degradation). Results of this study, taken together, provide a cost-effective approach to achieve high-yield production of the MNMs, suggesting an automatous microcleaner able to perform practical wastewater treatment.