Nano-bubble retention in saturated porous media under repulsive van der waals and electrostatic conditions

Authors: HAMAMOTO, SCHOICHIRO - University Of Tokyo; SUGIMOTO, TAKUYA - University Of Tokyo; TAKEMURA, TAKATO - Nihon University; NISHIMURA, TAKU - University Of Tokyo; Bradford, Scott

Submitted to: Langmuir
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2019
Publication Date: 5/6/2019
Citation: Hamamoto, S., Sugimoto, T., Takemura, T., Nishimura, T., Bradford, S.A. 2019. Nano-bubble retention in saturated porous media under repulsive van der waals and electrostatic conditions. Langmuir. 35(21):6853-6860. https://doi.org/10.1021/acs.langmuir.9b00507.
DOI: https://doi.org/10.1021/acs.langmuir.9b00507

Interpretive Summary: The use of nano-bubbles (NBs) to efficiently deliver gases in soils to improve plant growth, alter the oxygen conditions, and/or remediate contaminated sites is currently being explored. However, relatively little research has studied the transport and retention of NBs in soil under different solution chemistry conditions. This study investigated the influence of solution ionic strength (IS), ion composition (monovalent and divalent cations) and pH on NB transport. Results showed increasing NB mobility with decreasing IS, increasing pH, and in the presence of monovalent cations due to the reduction in the repulsive force from sand roughness, hydrophobic interactions, and less adsorbed cations. This information will be of interests to scientists and engineers concerned with the delivery of gases in soils and aquifers.

Technical Abstract: An understanding of nano-bubble (NB) migration in porous media is needed for potential environmental applications. The solution chemistry is well-known to be a critical factor in determining interactions of other colloids and nanoparticles with surfaces. However, little quantitative research has examined the influence of solution chemistry on NB transport. One-dimensional column experiments were therefore conducted to investigate the transport, retention, and release of NBs in glass beads under different solution chemistry conditions. NB concentrations in the effluent were reduced with an increase in ionic strength (IS) or a decrease in pH due to a reduction in the repulsive force between the glass surface and NBs, especially when the solution contained Ca2+ as compared to Na+ and for larger NBs. This result was somewhat surprising because electrostatic and van der Waals interactions for NBs were both repulsive on a homogeneous glass bead surface. NB retention on the surface was explained by ubiquitous nanoscale roughness on the glass beads that significantly lowered the energy barrier, and localized attractive charge heterogeneity and/or hydrophobic interactions. In contrast to Na+, adsorbed Ca2+ ions produced charge heterogeneity that enhanced NB retention and inhibited release with IS reduction.