Hydrogel‐Based Janus Micromotors Capped with Functional Nanoparticles for Environmental Applications

Abstract

Janus nano/micromotors have been developed into various sizes, shapes, and functions for a blaze of applications especially in biomedical and environmental fields. Here, a fabrication method of Janus micromotors is reported by capping hydrogel microspheres with functional nanoparticles (NPs). Microspheres are prepared in droplet microfluidics relying on hydrogel polymerization to obtain spheres with diameters from 20 to 500 µm. By solidifying a hydrogel layer onto microspheres, functional NPs of MnO2 (catalyst of H2O2), TiO2 (photocatalyst), and Fe3O4 (magnetic guidance) are adhered onto microspheres resulting in Janus micromotors revealing different functionalities. Dynamics of Janus micromotors (diameter around 250 µm) are explored by analyzing their trajectories in terms of mean squared displacement when immersed in H2O2 solutions of different concentrations, illuminated by light and guided in an external magnetic field. TiO2 Janus micromotors perform well for water purification tasks as is exemplarily demonstrated with a degradation of Methylene Blue dye in water. The proposed fabrication method is versatile and enables to achieve adjustable coverage of a microsphere with NPs as well as to realize multifunctional Janus micromotors by adhering different NPs (e.g., MnO2 and Fe3O4) on a sphere. This method provides an attractive way to fabricate multifunctional Janus micromotors in a cost‐effective manner for environmental applications.

Manganese‐Based Micro/Nanomotors: Synthesis, Motion, and Applications

“…As shown in Figure 4a, [50] particle-like Janus Mn-micro/ nanomotors perform linear locomotion under different concentrations of H 2 O 2 (0-30 wt%). The corresponding mean squared displacement (MSD) increases with increased H 2 O 2 concentration.…”

“…[17,20,33,44,45] Under different types of vector fields established by corresponding signal sources, micro/nanomotors are propelled by the aligning or direct torque. On this basis, diverse fabrication methods have been developed to build micro/ nanomotors with asymmetric structures, such as porous template-assisted synthesis, [17] hydrothermal formation, [46,47] chemical coprecipitation, [48] and microfluidic production, [49,50] which are summarized in Table 1. Among them, the electrochemical deposition method receives mainstream interest in the synthesis of Mn-micro/nanomotors using template-based and template-less approaches, owing to the facile design strategy, flexible modification, as well as simple operation.…”

“…[74] The coated manganese layer protected Pt from thiol toxicity while it reduced the catalytic efficiency for H Reproduced with permission. [50] Copyright 2020, Wiley-VCH. b) Trajectories and simulation of oxygen concentration distribution produced by poly(3,4-ethylenedioxythiophene)/Fe-MnO 2 microtubes with a fish-scale-like structure.…”

“…In recent research, the propelling force of micro/nanomotors gradually changed from a single propulsion mode (e.g., chemical, ultrasound, magnetic, and light) to a dual propulsion mode (such as chemical/light, chemical/magnetic, chemical/ultrasound, and ultrasound/magnetic). [50,67,91] For a more complex application, even three propulsion stimuli have been designed (Figure 8a). [66] For instance, Maria-Hormigos et al [54] synthesized chemical/light-powered CdS quantum dots/ C 60 /MnO 2 tubular micro/nanomotors with a smart "on-the-fly" acceleration feature, which could adjust the velocity through a switch of an "on-off" mode.…”

Hydrogel‐Based Motors

“…This method can not only provide people with an efficient method for integrating multifunctional subsystems, but also can realize high-throughput manufacture of chemical micromachines in reasonable sizes and quantities. [9][10][11] Micromotors consisting of hydrogel as the substrate material and superparamagnetic iron oxide nanoparticles incorporated inside were fabricated assisted with microfluidic devices. [12] Hydrogel materials provide higher degree of flexibility for their structures, compared to rigid structure.…”