Synthesis and application of molybdate-doped mussel-inspired polydopamine (MI-PDA) biopolymer as an effective sustainable anti-corrosion substance for mild steel in NaCl solution.

In this research, the synergistic corrosion inhibition effect of hybrid organic/mineral inhibitors in a 3.5 wt.% NaCl solution was investigated. For this purpose, a polydopamine/molybdate hybrid was used for the first time. The reason for choosing polydopamine was the existence of unique functional groups in its structure and the ability of high adhesion to surfaces. At the same time, the rapid inhibitory behavior and the possibility of complex formation with organic substances and iron cations were essential factors in choosing molybdate as an inorganic inhibitor. Through open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and polarization analyses, the combined inhibitors' electrochemical behavior was explored. From the EIS analysis results, the maximum inhibition efficiency of 86% and synergism index of 1.33 were obtained for the sample dipped in the solution containing 250:750 ppm PDA and MoO₄²⁻ compounds after 24-h immersion at room temperature. The polarization test revealed that the notable decrease of i corr (corrosion current density) compared with the uninhibited sample 12.5 to 1.3 μ A / cm 2 and the maximum inhibition efficiency of 90% were related to the 250:750 ppm PDA:MoO₄²⁻ mixture among different inhibited samples. Fourier transform infrared spectroscopy (FT-IR) and Raman analyses were utilized to investigate the complex formation between PDA, MoO₄²⁻, and Fe cations. Furthermore, the morphology, elemental composition, and hydrophilicity/hydrophobicity of the submerged samples' surfaces were studied through field emission scanning electron microscope/energy-dispersive X-ray spectroscopy (FE-SEM/EDS) and water contact angle analyses. [ABSTRACT FROM AUTHOR]