Controllable Preparation And Movement Of Bubble-propelled Round-bottom Flask-like Colloidal Motors

Inspired by the existence of a wide variety of natural molecular motors in nature,researchers have successfully prepared artificial colloidal motors by imitation.The chemical-driven colloidal motors can use the asymmetric distribution of catalyst on its surface to construct an asymmetric field around the colloidal motor to drive the colloidal motors,and the bubble-driven mechanism is the most typical driving mechanism in the chemical driven motor.Bubble-driven has the advantages of high energy efficiency and little influence by the electrolyte in solution,so it has a wide application prospect in biomedicine,environmental management,detection,and other fields.There are few reports about the colloidal motor with a hollow cavity structure powered by bubbles that can be prepared in batch.The purpose of this article is to construct a bubble-driven colloidal motor with a cavity structure,asymmetric structure,and sub-micron size,which can be prepared in large quantities,and to explore the mechanism of bubble-driven flask-shaped motors.By controlling the hydrothermal synthesis reaction time,flask-shaped colloidal particles with different neck lengths were synthesized,and the influence of the neck length on the motion behavior of the colloidal motors was studied,which provides new methods and ideas for the preparation and application of the bubble-driven colloidal motor.The ascorbic acid reduction method is used to prepare the platinum catalyst with tiny protrusions on the surface resembling a raspberry.Through vacuum infusion,the raspberry-like platinum nanoparticles are loaded into the cavity of the flask-shaped colloidal motors which are prepared by the hydrothermal synthesis method.The flask-shaped colloidal motor has a round-bottom flask-shaped appearance and a hollow cavity structure inside,which is connected to the outside through a hollow neck-shaped structure.The zeta potential of the motor is negative,and it has good photoluminescence ability.The amount of platinum catalysts loaded in the cavity of the flask-shaped colloidal motors is about 17.73%,which can catalyze the decomposition of hydrogen peroxide to generate oxygen bubbles to drive the motor to self-propel.In order to explore the movement mechanism of the flask-shaped colloidal motors,we used the vacuum sputtering method to prepare the spherical Janus silica colloidal motors with different particle sizes,and observed the bubble generation in the hydrogen peroxide solution.It was found that when the size of the Janus silica motor is less than 5 μm,it will not produce bubbles when placed in the hydrogen peroxide solution,while a flask-shaped colloidal motor with an inner cavity diameter of 550 nm can generate oxygen bubbles in the solution with the same concentration of hydrogen peroxide,indicating that the confinement effect of the cavity promotes the accumulation of small oxygen bubbles to form large oxygen bubbles.The self-propelled force is generated by the separation of the large oxygen bubbles from the flask mouth and the force pushes the flask-shaped colloidal motors to move.The influence of the hydrothermal reaction time on the morphology and the structure of the flask-shaped colloidal motors was studied.The results of scanning electron microscopy and transmission electron microscopy show that the flask-shaped colloidal motors prepared with different hydrothermal synthesis reaction time have different neck lengths.Thermogravimetric analysis and energy dispersive X-ray spectroscopy analysis show that the amount of the platinum nanoparticles in the three kinds of flask-shaped colloidal motors is the same.A combination of experiment and theoretical analysis was used to systematically study the effect of neck length on the driving performance of bubble-driven flask-shaped colloidal motors in solutions with different hydrogen peroxide concentrations.The results showed that the shorter the neck is,the faster the motors move.At the same time,the longer the neck is,the better the directionality of the motor is.In summary,the bubble driven flask-shaped colloid motors can be controlled based on the soft template hydrothermal method.The flask-shaped colloid motors with limited spatial structure,asymmetric structure,and loading catalyst platinum can be easily prepared in large quantities.By adding hydrogen peroxide solution,the movement behavior and velocity of the bubble driven flask-shaped colloid motors were observed to change due to the different lengths of the neck,and the movement mechanism of the bubble drive flask-shaped colloid motors was analyzed.