Construction And Motion Investigation Of Spherical Bubble-propelled TiO₂ MNMs

Self-propelled synthetic micro/nanomotor(MNMs)are actuators between the nanometer and micron scales that capture different types of energy,and convert them into mechanical motion.Among kinds of MNMs,bubble-propelled MNMs have been the most extensively studied.Platinum(Pt)is still the preferred material for the preparation of bubble-propelled catalytic MNMs due to its excellent catalytic properties.However,platinum is expensive and its practical use is limited.In addition,the Janus spherical micro-nano motor is the most common spherical motor system,which has an asymmetric structure based on Janus particles.However,the methods for synthesizing asymmetric architectures are still lacking.According to the mechanism of bubble-driven MNMs,the generation of recoil-force depends on the detachment of bubbles generated on the catalyst surface.Although the important role of bubble behavior in MNMs dynamics has been recognized,the study of bubble behavior in the Janus spherical MNMs system has stilled been limited.In the previous study,we proposed the synergistic effect of superhydrophilic TiO2,which significantly reduced the surface contact energy and produced bubbles of smaller size under higher pressure.Therefore,the surface properties of the substrate can affect the motion efficiency of the motor to a certain extent.In this work,we prepare a Janus spherical self-driven MNM via photocatalytic technology.We chose to use TiO2 nanoparticles as matrix material which has higher photocatalytic activity and availability with simple process to obtain.manganese dioxide(MnO2)as alternative to expensive traditional catalytic material platinum(Pt)with lower cost and eco-friendly nature,hydrogen peroxide solution as the fuel,and prepare a Janus TiO2/MnO2 bubble-propelled MNM with benign motion performance.Besides,we established a bulk MNMs community to study the effect of MNMs substrate more intuitiveon its motion.In addition,a theoretical model was constructed by observing the effects of substrates with different surface properties on the behavior of the motor group,including the size of bubble generation and the thrust generated by release.We believe that the hydrophilic and air-repellent properties of the surface of the motor substrate are of great significance for the efficient release of bubbles and thus the efficient movement of the bubble-driven MNMs.