TY - JOUR

T1 - Intrinsic CO2 nanobubbles in alkaline aqueous solutions

AU - Zarei, Talie

AU - Fuchs, Elmar C.

AU - Agostinho, Luewton L.F.

AU - Gebauer, Denis

AU - Woisetschläger, Jakob

AU - Offerhaus, Herman L.

N1 - Publisher Copyright: © 2024 The Authors

PY - 2024/11/20

Y1 - 2024/11/20

N2 - Nanobubbles (NBs) and their derivative, bulk nanobubbles (BNBs), have been widely studied due to their potential wide range of applications. However, the stable existence of intrinsic NBs and BNBs in solutions is still controversial. This study investigates the existence and behaviour of unknown nano-entities in dilute alkaline solutions using Field-Flow Fractionation Multi-Angle Light Scattering (FFF-MALS), resulting in the first report of the presence, size distribution, and size distribution changes under different treatments. The results suggest that neutral and acidic pure solutions of salts at concentrations below the solubility product do not contain detectable nano entities. Alkaline solutions, on the other hand, such as carbonate buffer and sodium hydroxide, do contain nano scatterers in the range of ∼100 nm diameter that cannot be removed by boiling or filtration. Reducing the pH of the solutions or freezing reduces their number densities. The freeze-thaw procedure strongly suggests that these nano entities are BNBs. Zeta Nanoparticle Tracking Analysis (ZNTA) shows the zeta potential and the concentration in agreement with previous literature. It can be concluded that intrinsic BNBs in alkaline solutions are an integral part of the total nano-entity population. This study highlights the importance of considering intrinsic BNBs when investigating nanoparticles in alkaline solutions with analytical methods such as Static Light Scattering (SLS), which can detect low number densities in the original liquid state that may not be plausible by other detection methods due to their detection thresholds or acquisition of sample preparation methods of drying or freezing that do not allow real-time observations.

AB - Nanobubbles (NBs) and their derivative, bulk nanobubbles (BNBs), have been widely studied due to their potential wide range of applications. However, the stable existence of intrinsic NBs and BNBs in solutions is still controversial. This study investigates the existence and behaviour of unknown nano-entities in dilute alkaline solutions using Field-Flow Fractionation Multi-Angle Light Scattering (FFF-MALS), resulting in the first report of the presence, size distribution, and size distribution changes under different treatments. The results suggest that neutral and acidic pure solutions of salts at concentrations below the solubility product do not contain detectable nano entities. Alkaline solutions, on the other hand, such as carbonate buffer and sodium hydroxide, do contain nano scatterers in the range of ∼100 nm diameter that cannot be removed by boiling or filtration. Reducing the pH of the solutions or freezing reduces their number densities. The freeze-thaw procedure strongly suggests that these nano entities are BNBs. Zeta Nanoparticle Tracking Analysis (ZNTA) shows the zeta potential and the concentration in agreement with previous literature. It can be concluded that intrinsic BNBs in alkaline solutions are an integral part of the total nano-entity population. This study highlights the importance of considering intrinsic BNBs when investigating nanoparticles in alkaline solutions with analytical methods such as Static Light Scattering (SLS), which can detect low number densities in the original liquid state that may not be plausible by other detection methods due to their detection thresholds or acquisition of sample preparation methods of drying or freezing that do not allow real-time observations.

KW - Alkaline solutions

KW - Nanobubbles

KW - Static light scattering

KW - Zeta potential

UR - http://www.scopus.com/inward/record.url?scp=85199778576&partnerID=8YFLogxK

U2 - 10.1016/j.colsurfa.2024.134895

DO - 10.1016/j.colsurfa.2024.134895

M3 - Article

AN - SCOPUS:85199778576

VL - 701

JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects

JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects

SN - 0927-7757

M1 - 134895

ER -