Simple and prompt protonation of new dyes containing double conjugated imine bonds to strengthen the protection of copper in aggressive sulfuric acid solution

This study employs a simple and rapid protonation method for organic dyes to intensify solubility, adsorption and corrosion resistance to copper in sulfuric acid solution. Thus, three novel dyes including double conjugated imine bonds and fatty chain linkers were synthesized as targets. For a contrast, the dyes including a single imine bond were also prepared as references. The chemical structures of these dyes were characterized by nuclear magnetic resonance (NMR), mass spectrometry (MS), elemental analysis, etc. The results suggest that the target dyes can be dissolved rapidly in sulfuric acid solution due to strong protonation. The electrochemistry measurements show that the target dyes present a corrosion resistance effect better for copper in sulfuric acid solution than the reference dyes (the maximal corrosion inhibition efficiency, the target dyes, 97.5% versus the referenced dyes, 86.7%). The chemical adsorption of the target dyes on the copper surface was well demonstrated by various means. Accordingly, more hydrophobic and tougher adsorption layers of the target dyes carrying more protonated positive charges were yielded on the copper surface compared to the reference dyes. The adsorption isotherms of the target and reference dyes on the copper surface were also analyzed and discussed.