Surface interaction of microbubbles and applications of hydrogen-bubble method for cleaning and separation

Microbubble (MB) technology is important for the separation and purification of micro/nanomaterials from waste water. The recovery of these materials from water is required to reduce the risk of cytotoxicity. To investigate surface interactions related to the separation of micro/nanoparticles in water, we attempted to float TiO₂, SiC, multi-walled carbon nanotubes (MWCNTs), and carbon fiber (CF) using MBs generated by electrolysis. After MBs were generated for 5-10 min by applying a voltage between two electrodes, SiC, MWCNT, and CF were aggregated on the surface of the tap water in the container. However, hydrophilic TiO₂ remained well dispersed in water and did not aggregate after the generation of MBs. These results demonstrated that hydrophobic micro/nanoparticles in water can be separated by floatation and aggregation on the surface of water using this MB-generating method. We also measured the ζ-potential of MB-containing water; the recorded potentials ranged from -12 mV to -19 mV. The pH of this MB-containing water was 5.6. Based on the measured ζ-potential, the electrostatic interaction between MBs and the floating particles would not contribute to adsorption of MB and these particles. Therefore, the hydrophobic interaction with MBs can be used for the purification and separation of hydrophobic micro/nanoparticles.