Hierarchical hollow α-FeO/ZnFeO/MnO Janus micromotors as dynamic and efficient microcleaners for enhanced photo-Fenton elimination of organic pollutants.

Micro/nanomotors that can promote mass transport have attracted more and more research concern in the photocatalysis field. Here we first report a newly-designed hierarchical α-FeO/ZnFeO/MnO magnetic micromotor as a heterogeneous photocatalyst for the degradation of cationic dye methylene blue (MB) from wastewater. The resulting three-dimensional (3D) flower-like hollow Janus micromotors are fabricated through a green and scalable strategy, in which each component has different functions. ZnFeO microspheres serve as a magnetic scaffold for the nucleation and growth of α-FeO nanosheets and for the recycling of the micromachine. α-FeO nanosheets have shown great potential as an ideal semiconductor material for the photocatalytic decontamination of pollutants. MnO nanoparticles are mainly utilized as a catalyst to produce O bubbles to propel the autonomic movement of the micromotors in the presence of HO fuel and also as a Fenton-like catalyst to decompose HO to generate reactive oxygen species. Furthermore, the resultant micromotors exhibited linear-like motion form with an average speed of 189.1 μm s in 5 wt% HO solution. Moreover, the self-driven micromotors exhibited a superior catalytic degradation property toward MB, which was attributed to the synergistic effect of heterogeneous photocatalyst and the boosted micro-mixing and mass transfer caused by the vigorous motion of the micro-actuator. The possible degradation intermediates and passways of MB by α-FeO/ZnFeO/MnO micromotor were identified with time of flight mass spectroscopy (TOF-MS). The 3D Janus micromotors have the potential to be used as a high-efficiency and active heterogeneous photocatalyst for the degradation of organic pollutants.