Bulk nanobubble generation by gas supersaturation method.

For the past decade, nanobubbles have been shown to have numerous applications due to their unique properties. Despite its potential in enhancing gas-liquid operations, limited to no studies have been conducted on nanobubble generation in pure organic solvents with strong scientific evidence. Furthermore, there is no direct evidence that explains the generation of nanobubbles by gas supersaturation mechanism. Since there is a strong dependence of gas solubility over temperature, therefore, a solvent at a high temperature, when, mixed with the same solvent at a low temperature releases the excess gas that may nucleate to form nanobubbles. The nanobubble generation was carried out with the variation in the temperature difference between hot and cold solvents ranging from 10°C to 80 °C in the alcohols i.e., butanol, propanol, ethanol, methanol, and water. The nanobubbles are characterized by NTA (Nanoparticle Tracking Analysis) and DLS (Dynamic Light Scattering) in terms of bubble diameter, population and zeta potential. The results reported the formation of nanobubbles to be higher with maximum concentration in the range of 7.78×10⁸ bubbles/mL at ∆T = 50-60°C. The zeta potential in water, methanol, and ethanol was observed to be negative while it shifted toward positive for propanol and butanol. The refractive index value calculation using Mie scattering theory confirmed the existence of nanobubbles as the values for all samples were close to unity (RI for air =1).