Nanobubble-Induced Oxygen Gradients Control Corrosion Mode and Bacterial Adhesion on Martensitic Stainless Steel

Abstract

Biofilm formation is a large problem in corrosion prevention and can be part of a positive feedback loop, where a corroded surface is prone to bacterial adhesion, and bacteria themselves provide an environment that increases the corrosion rate of the metal surface. Nanobubbles are increasingly recognized as active modifiers of solid–liquid interfaces; however, their role in coupled corrosion and biofilm formation remains unclear. Here, we show that gas-specific nanobubble dispersions control both the corrosion mode of martensitic stainless steel (4H13) and the resulting Escherichia coli adhesion. Steel samples were immersed in oxygen or nitrogen nanobubble dispersions under varying salinity conditions up to 1.0 M NaCl. Oxygen nanobubbles induced spatially heterogeneous corrosion, characterized by localized pitting and differences along the sample height, while nitrogen nanobubbles resulted in uniform surface degradation, even in deionized water. These corrosion patterns directly translated into distinct biofilm structures: patchy biofilms formed on oxygen-treated surfaces, whereas nitrogen nanobubbles promoted a uniform biofilm. These observations are consistent with nanobubble-driven oxygen transport at the interface. We propose that an oxygen concentration gradient along the length of the steel coupon promotes differential aeration cells and pitting corrosion, whereas nitrogen nanobubbles deoxygenate the system, destabilizing the passive layer and leading to uniform corrosion. Consistent qualitative observations from both crystal-violet and DAPI staining reveal a strong coupling between nanobubble-mediated oxygen gradients, corrosion morphology, and microbial colonization. These findings highlight nanobubbles as a simple tool for controlling interfacial electrochemical processes and biofilm formation.