Research On The Generation Method And Properties Of Nanobubble Based On Ultrasonic Cavitation

Bulk nanobubbles' various and unique properties have drawn the attention and become the hot field for the last few years.However,experiments on bulk nanobubble are correctly criticized for a lack of direct evidences that the nanoparticles being observed are really consisted of gas while the surface nanobubbles are directly imaged via atomic force microscopy AFM(Atomic Force Microscopy).Another important issue is that so far scientists have not given a convincing explanation on nanobubbles' generation and their long-time stability in the bulk solution while a lot of people believe the theory of Epstein and Plesset,from which they believed the bulk nanobubbles are contamination or other nanoparticles.Despite the limited number of researches into bulk nanobubbles,bulk nanobubbles have already shown their huge potential in many industrial fields such as groundwater and wastewater treatment,foam flotation,slag dehydration,etc.Thus the fundamental research on bulk nanobubble would be great help on its application and lead the research on the behavior of bubble in the nanoscale.Also it‘s worth noting that in nanobubble researching field the way to produce it is significant and complex,because nanobubble has always been in connection with contamination,how to generate in an effective and clean method is very important.So we focus highly on the unique cavitation property of ultrasonic wave in liquid solution.In this paper,we use ultrasonic to produce bulk nanobubbles in the pure water and give a comprehensive study on the bulk nanobubbles properties and generation.The ultrasonic wave gives rise to constant oscillation in water where positive and negative pressure appears alternately.With the induced cavitation and presence of dissolved air,the bulk nanobubbles formed.“Nanosight”(a special instrument that combines Dynamic Light Scattering with Nanoparticle Tracking Analysis)was used to analyze the track and concentration of nanobubbles.The results are shown in the following parts:First,we demonstrated that the nanoparticles we generated and measured are indeed bulk nanobubbles.By comparing the nanobubbles concentration before and after degassing we confirm our assumption is correct,and due to some doubts that the nanoparticles might be the Volatile nano-oildroplets,the concentration of dissolved oxygen before and after ultrasonic was measured and it was found that the dissolved air decreased in ultrasonic process which means the air molecule may form the nanobubble.We also make sure the nanobubble has an average distribution in the bulk solution from which we believe the position we take samples will not influence the result.Then we studied further into this phenomenon to measure the nanobubbles' change in the bulk solution.It was shown than nanobubbles firstly reached to a maximum value then decreased in amount with ultrasonic time increases and the mean diameter of nanobubble produced is growing slowly at the same time.We also measured the distribution of diameter,found that most of the nanobubble we produced exist within a certain range.The stability of nanobubble was proven to be good in at least 24 h according to our research.Finally,different solution was used to find out whether this method could be useful in different fields and obviously this method is universal through the result.In the last we explained the mechanism of bulk nanobubble generation with ultrasonic,basing on that,we are looking forward to see our method could have broad application in various fields.