Transition from Antagonistic to Synergistic Interactions between Corrosion Inhibitors and Biocides: Role of Hydrogen Bonding Networks─Experimental and Theoretical Insights

CO2/SRB-induced corrosion in shale gas pipelines is investigated with an emphasis on the synergistic interaction between a morpholine-based gemini surfactant (BDHM) and gallic acid (GA). At 100 ppm, an optimal BDHM:GA molar ratio of 5:1 reduces the corrosion rate from 0.9858 to 0.1288 mm·a–1, corresponding to an inhibition efficiency of 87%. Electrochemical measurements show nearly 1 order of magnitude decrease in corrosion current density and a 3-fold increase in polarization resistance, indicating enhanced interfacial protection. AFM analysis reveals a reduction in surface roughness, with Sa decreasing from 39.7 to 27.4 nm and Sq improving from 50.9 to 34.9 nm. XPS results indicate that adsorption is dominated by oxygen-containing species. Quantum chemical calculations and molecular dynamics (MD) simulations demonstrate that intermolecular hydrogen bonding between GA and BDHM promotes their coaggregation into stable, high-performance clusters, enhancing adsorption on both steel surfaces and bacterial membranes. Antibacterial experiments confirm the enhanced inhibition of SRB activity.