Reconfigurable self-assembly of photocatalytic magnetic microrobots for water purification

Abstract

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 TiO2/α-Fe2O3 microrobots, consisting of peanut-shaped α-Fe2O3 (hematite) microparticles synthesized by a hydrothermal method and covered with a thin layer of TiO2 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 H2O2 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.

Understanding the Behaviors of Plasmon-Induced Hot Carriers and Their Applications in Photocatalysis

“…Meanwhile, other metals such as Al, Cu, and Ni, which exhibit plasmonic resonances in shorter wavelength, can be combined with semiconductors to broaden the spectral absorption range and enhance the absorption efficiency of semiconductor materials. (5) In addition, it is also important to use theoretical calculations to help us understand the behavior of hot carriers at a deeper level. This will further deepen and broaden our understanding of SPR-mediated chemical reactions, providing valuable guidance for the design of more efficient plasmonic metal−semiconductor hybrid photocatalytic materials.…”

“…Due to the increasingly serious environmental pollution and energy crisis, the efficient use of solar energy in renewable energy is particularly urgent. This makes photocatalytic materials based on semiconductors have been widely developed for photocatalytic water splitting, organic degradation, carbon dioxide reduction, etc. − However, a significant number of semiconductor photocatalytic materials are hindered by low efficiency due to their inherent limitations. One of the most significant restrictions is that most semiconductors have wide band gaps (>3.1 eV), allowing them to only absorb ultraviolet light, which accounts for approximately 4% of solar radiation. , Additionally, the short lifetimes and limited migration distances of carriers lead to the easy recombination of electron–hole pairs, thereby reducing the light utilization efficiency of semiconductor materials. , Therefore, broadening the solar spectrum absorption range, increasing the light absorption efficiency, and promoting the efficient separation and transmission of photogenerated carriers is the key to improving the performance of semiconductor photocatalysis.…”

A Survey of Recent Developments in Magnetic Microrobots for Micro-/Nano-Manipulation

“…Microrobots containing magnetic materials can react to external magnetic fields, allowing for directional guidance and the generation of propulsive forces [27][28][29][30]. Furthermore, to preserve additional characteristics of microrobots, such as structural rigidity, biocompatibility, and biodegradability, it is essential to incorporate non-magnetic materials [31][32][33][34].…”

Magnetic Microrobot Swarms with Polymeric Hands Catching Bacteria and Microplastics in Water

“…However, the fine control of densely packed mobile microrobot groups with internal coordination remains a significant threat due to the tendency of dense magnetic particles to cluster together in response to magnetic fields, drastically affecting their locomotion and wireless control. Moreover, while micro/nanorobots swarms have shown results in micromanipulation and biomedical applications, ,− such as drug delivery, − navigable contrast agents, , lab-on-a-chip biosensing systems, hyperthermia agents, and mechanical lysis of fibrin gels, their exploration in the field of water purification is still in its infancy. − …”

“…Moreover, while micro/nanorobots swarms have shown results in micromanipulation and biomedical applications, 41 , 47 − 52 such as drug delivery, 53 − 57 navigable contrast agents, 58 , 59 lab-on-a-chip biosensing systems, 60 hyperthermia agents, 61 and mechanical lysis of fibrin gels, 62 their exploration in the field of water purification is still in its infancy. 63 − 65 …”