Nanobubble-assisted formation of non-gaseous nanoparticles in water

For the past decade, there has been an intense debate over the existence of stable bulk nanobubbles in water. To distinguish gaseous particles from solid particles and liquid droplets, a key quantity to be measured is the mass density of the nanoparticles. Here, the mass density of the nanoparticles formed in the process of nanobubble generation was determined by the observation of sedimentation equilibrium and Brownian motion of the nanoparticles. The diameter was about 450nm, whereas the measured mass density was 1.06 to 1.07g/cm3 which was larger than that of water. Thus, the detected nanoparticles in our experiments, which were often called stable bulk nanobubbles, were not gaseous. A comparison between the results of treated and untreated solutions demonstrated that the generation of nanobubbles assists in the formation of non-gaseous nanoparticles, and they sediment in water under gravity.