Simple-Structured Micromotors Based on Inherent Asymmetry in Crystalline Phases: Design, Large-Scale Preparation, and Environmental Application

Abstract

The key principle of designing a micro/nanomotor is to introduce asymmetry to a micro/nanoparticle. However, micro/nanomotors designed based on external asymmetry and inherent chemical and geometrical asymmetry usually suffer from tedious small-scale preparation, high cost, and/ or complexity of external power and control devices, making them face insurmountable hurdles in practical applications. Herein, considering the possible distinct properties of different polymorphs, we propose a novel design strategy of simple-structured micromotors by introducing inherent asymmetry in crystalline phases. The inherent phase asymmetry can be easily introduced in spherical TiO 2 particles by adjusting the calcination temperature to control the phase transition and growth of primary grains. The as-designed anatase/rutile TiO 2 micromotors not only show efficient autonomous motions controlled by light in liquid media stemming from the asymmetric surface photocatalytic redox reactions but also have a promising application in environmental remediation due to their high photocatalytic activity in "on-the-fly" degradation of organic pollutants, facile large-scale fabrication, and low cost. The proposed design strategy may pave the way for the large-scale productions and applications of micro/nanomotors.

Cooperative transport by flocking phototactic micromotors

“…Like other photochemical TiO 2 -based micromotors, the gathered TiO 2 micromotors can be powered by photocataltically decomposing surrounding H 2 O 2 fuels. [44][45][46][47][48][49][50] Under a sidewise UV irradiation, the gathered TiO 2 micromotors perform negative phototaxis as a flock (TiO 2 -MF) in the medium with the H 2 O 2 fuel, 43,44 and thus can also be driven to approach and load a large cargo on the fly. The on-the-fly cargo loading is illustrated in Fig.…”

Synthesis of Snowman‐shaped Photocatalytic Microrotors and Mechanical Micropumps

“…In order to obtain anatase TiO 2 with high photocatalytic activity, the as‐prepared SiO 2 −TiO 2 snowman‐shaped particles were calcined at 400 °C for 2 hours, which transforms the original amorphous TiO 2 into the anatase TiO 2 [29–31] . The diffraction peaks of the calcined particles are consistent with those of anatase TiO 2 and confirm the successful conversion to anatase by calcination (see Figure S4).…”

Titania-Based Micro/Nanomotors: Design Principles, Biomimetic Collective Behavior, and Applications

“…As a consequence, the photogenerated O 2 molecules concentrated on the illuminated side of microsphere and enabling non-electrolyte diffusiophoresis to propel the particle. The same group utilized the calcination temperature to control the phase transition and composition of the TiO 2 microspheres [12]. The anatase/rutile phases coexist at temperatures above 500°C and are asymmetrically distributed in spherical microparticles, which results in efficient separation and migration of electron-hole pairs, triggering the self-phoretic motion of the microparticles.…”

“…As shown in Figure 6A,B, in the presence of UV irradiation, the TiO 2 -Au and TiO 2 -Pt Janus micromotors can self-propel in an aqueous environment, resulting in rapid oxidative degradation of dissolved dyes and explosives through redox reactions and by the generated reactive oxygen species [22,34,80]. The anatase/rutile TiO 2 micromotors can also degrade dyes in the presence of H 2 O 2 under UV light [12]. Cargo Delivery A potential application for MNMs is as carriers for payloads like drugs, proteins, cells, and passive micro/nanoparticles [3,81].…”

“…TiO 2 micro/nanoparticles can be fabricated through well-established methods (e.g., sol-gel chemistry, hydrothermal processing, dry spinning, and emulsion evaporation) in large scale and at low cost, with adjustable morphology, sizes, and structures [8][9][10][11]. TiO 2 exists in two active crystalline phases, anatase and rutile, which can be obtained using different calcination temperatures [12].…”