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

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 (MnO 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 (KMnO) solution, featured with high yield and low cost. The distribution and amount of MnO can be easily controlled by varying the dipping time. The obtained motors are actuated and propelled by oxygen (O) bubbles generated from MnO-triggered catalytic decomposition of hydrogen peroxide (HO), 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 (FeO NPs) are adsorbed onto such motors via an electrostatic effect. Both the FeO-induced Fenton reaction and hydroxyl radicals from MnO-catalyzed HO 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.