Reconfigurable self-assembly of photocatalytic magnetic microrobots for water purification

• Published in: Nature communications 2023-11, Vol.14 (1), p.6969-13, Article 6969
• Main Authors: Urso, Mario, Ussia, Martina, Peng, Xia, Oral, Cagatay M., Pumera, Martin
• Format: Article
• Language: English
• Subjects: 147/135; 639/301/1005/1006; 639/301/357/339; Active control; Atomic layer epitaxy; Automation; Clusters; Concentration gradient; Degradation; Dichlorophenoxyacetic acid; Dipole interactions; Ferric oxide; Ferromagnetism; Hematite; Herbicides; Humanities and Social Sciences; Hydrogen peroxide; Irradiation; Light irradiation; Magnetic dipoles; Magnetic fields; Magnetic properties; Manufacturing engineering; Microparticles; Microrobots; multidisciplinary; Nanotechnology devices; Persistent organic pollutants; Pesticides; Photocatalysis; Reconfiguration; Robotics; Science; Science (multidisciplinary); Self-assembly; Swarming; Swarming behavior; Titanium dioxide; Water purification
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-42674-9

The development of artificial small-scale robotic swarms with nature-mimicking collective behaviors represents the frontier of research in robotics. While microrobot swarming under magnetic manipulation has been extensively explored, light-induced self-organization of micro- and nanorobots is still challenging. This study demonstrates the interaction-controlled, reconfigurable, reversible, and active self-assembly of TiO 2 /α-Fe 2 O 3 microrobots, consisting of peanut-shaped α-Fe 2 O 3 (hematite) microparticles synthesized by a hydrothermal method and covered with a thin layer of TiO 2 by atomic layer deposition (ALD). Due to their photocatalytic and ferromagnetic properties, microrobots autonomously move in water under light irradiation, while a magnetic field precisely controls their direction. In the presence of H 2 O 2 fuel, concentration gradients around the illuminated microrobots result in mutual attraction by phoretic interactions, inducing their spontaneous organization into self-propelled clusters. In the dark, clusters reversibly reconfigure into microchains where microrobots are aligned due to magnetic dipole-dipole interactions. Microrobots’ active motion and photocatalytic properties were investigated for water remediation from pesticides, obtaining the rapid degradation of the extensively used, persistent, and hazardous herbicide 2,4-Dichlorophenoxyacetic acid (2,4D). This study potentially impacts the realization of future intelligent adaptive metamachines and the application of light-powered self-propelled micro- and nanomotors toward the degradation of persistent organic pollutants (POPs) or micro- and nanoplastics. Microrobot collectives promise new functions beyond individuals’ capability. Here, nature-inspired reconfigurable self-assembly of microrobots was created, driven by their photocatalytic and magnetic properties, showing potential application in water purification.