Design Of Cyclic Extrusion Nanobubble Preparation Device And Self-assembly Of Nanobubbles And Nanoparticles

Nanobubbles are several hundred nanometers tiny bubbles in the solution.Due to their good stability,adsorption capacity and acoustic properties,they have been widely applied in ultrasound contrast agents,sewage treatment,environmental protection,industrial separation,and drug delivery.Until now,based on the mechanical or chemical reactions,many preparation methods such as mechanical agitation,electrolysis,and ultrasonic cavitation have been developed.However,these nanobubbles prepared by these methods have wide size distribution,low concentration and relatively poor stability.In this thesis,the cyclic extrusion method of gas-liquid mixture has been developed to fabricate uniform nanobubbles with high concentration.Then based on the stable free nanobubble solution,the nanoparticles encapsulated nanobubbles were studied.The gas-liquid interface self-assembly process and the possible mechanism of assembly of nanoparticles have also been investigated.The main research contents are as follows:(1)An automated nanobubble preparation device based on cyclic extrusion method was designed.The device consists of three parts:control unit,temperature control unit and motion unit.It can continuously adjust the extrusion speed in the range of 0-50 mm/s with the adjustment precision of 1 mm/s.The number of extrusions is continuously adjustable in the range of 0-1000 times with the adjustment precision of 1 time.The preparation temperature is continuously adjustable in the range of 4-50°C with the adjustment precision of 0.1°C.The device can realize three sets of samples prepared in parallel.The hydrodynamic size of the nanobubbles prepared by the device is about 200 nm,the Zeta potential is-50 mv.The bubble concentration is on the order of 10~9/ml,and the bubbles can be stable for more than one week.(2)Based on the principle of bubble bridging mechanism,the self-assembly between iron oxide nanoparticles and pre-prepared free nanobubbles was developed.The pre-prepared free nanobubbles were provided by the dissolved gas pump method and the cyclic extrusion device.The results show that the nanoparticles can be successfully assembled on the interface of nanobubbles prepared by cyclic extrusion device,which the mean diamter of the structure is 100-200nm and Zeta potential is-30mV.However,it is difficulty to form the nanoparticle-loaded nanobubbles when the bubble water prepared by the dissolved gas pump method incubated with nanoparticles.The reason is that the bubble water prepared by the dissolved gas pump method has a small bubble concentration and a small amount of dissolved gas.(3)Finally,the self-assembled structure of nanoparticle-encapsulated nanobubbles was constructed by cyclic extrusion method after the nanoparticles uniformly mixed with the degassed water.The effect of preparation parameters including cycle number,movement speed and nanoparticle concentration on the assembled structure were investigated.The results indicate that when the iron oxide nanoparticles solution(11.46 mg/L)was cyclically extruded 100 times at a moving speed of 30 mm/s,the stable self-assembled structures with a particle size of 100-200nm and Zeta potential of about-30mV could be successfully fabricated.Furthermore,the process mechanism of the nanobubble assembly structure was explored.The nanoparticles can be precipitated and attached on the surface of saturated dissolved gas by the principle of nanoparticle bridging during the cyclic extrusion process.