ZnO-based Micromotors And Their Swarming Behaviors

Chemical fuel-driven micro/nanomotors(MNMs)are micro/nano-scale intelligent devices that can convert surrounding chemical energy into kinetic energy for autonomous motion.Based on its flexibility and intelligence at the microscale,MNMs have considerable application prospects in biomedicine,environmental remediation and detection at microarea.But there are still many disadvantages of MNMs,such as the need for additional fuel with poor biocompatibility and their poor intelligence.In addition,MNMs can exhibit cluster effects and phenomena on different scales like organisms in nature.Because these clusters can exhibit behavioral performance and task execution capabilities that individuals do not possess,they are very promising for applications in the fields of cargo transportation,pattern microfabrication,and partial repair.However,there are still many shortcomings in today's clusters.On the one hand,the configuration and motion behaviors of the MNM clusters cannot be precisely controlled due to their monotonic collective behaviors.On the other hand,most clusters are homogeneous,which has caused the groups to exhibit more isotropic behaviors than anisotropic ones,making it difficult to achieve cluster diversity,multi-behavior and environmental adaptability even in the presence of external stimuli.As researched,in addition to the high chemical reactivity and excellent photocatalytic performance of ZnO particles in pure water,they also have a remote mutual exclusion effect with surrounding particles.Therefore,based on these advantages,we developed an intelligent MNM based on ZnO driven by biocompatible fuels,and ZnO-TiO₂micromotor cluster systems that can be accurately controlled in real time and reconstruct forms.First of all,we demonstrate a chemotactic ZnO/SiO₂ Janus micromotor fueled by atmospheric CO₂.As atmospheric CO₂ molecules can dissolve in water through interface with the atmosphere to form H₂CO₃ and supply H⁺,the ZnO/SiO₂Janus micromotor reacts with H⁺and autonomously moves with the ZnO end forward in water based on self-electroosmosis.In the presence of a local chemical source with high CO₂ concentration,the micromotors can sense the CO₂(or H⁺)gradient,and meander toward the chemical source through positive chemotaxis.Theoretical calculation and numerical simulation confirm that the micromotors can sustainably and rapidly acquire CO₂ fuel from air,and perform a positive chemotaxis along the chemical gradient by rotational reorientation under the self-electroosmotic torque.Our discovery opens a window of opportunity to develop intelligent biocompatible micro/nanomotors fueled by air,and thus,has far-reaching implications for targeted drug delivery and environmental remediation.Secondly,we have researched in-situ construction of the ZnO-TiO₂ heterogeneous micromotor system by near-infrared(NIR)light-induced convections and its UV-controlled reconfigurations.Under the near-infrared light-induced convections,the dispersed TiO₂ microparticles gather around the ZnO microneedle in the center of the NIR light spot to form a ZnO-TiO₂ heterogeneous micromotor system.When oblique UV light is applied,the ZnO microneedle exhibits strong positive phototactic motion based on electrolyte diffusiophoresis.In contrast,TiO₂ microparticles produce weak negative phototactic motion based on non-electrolyte diffusiophoresis.Therefore,by dynamically adjusting the direction of the incident light,the motion directions and trajectories of ZnO micromotor with strong positive phototaxis can be controlled in real time,thus performing complex cutting(such as straight,circular,and multiple cutting)on the weak negative phototactic TiO₂ swarm to achieve complex manipulation of split subgroups in the size,shape,and numbers,as well as system reconfigurations.This study will provide new strategies for the morphological control of micromotor swarms and the construction of intelligent multi-functional micromotor swarm systems,promoting their applications in dynamic micro-patterning and micro/nano assembly and fabrication.