Corrosion protection of 304 stainless steel from a smart conducting polypyrrole coating doped with pH-sensitive molybdate-loaded TiO₂ nanocontainers

TiO₂ nanotubes with an average size of 6–9 nm were synthesized using a hydrothermal method and loaded with molybdate corrosion inhibitors. Then, the molybdate-loaded TiO₂ nanotubes were incorporated into conducting polypyrrole (PPy) coatings using an electrochemical method for the corrosion protection of 304 stainless steel (304SS). The structure and morphology of the TiO₂ and molybdate-loaded TiO₂ nanotubes were characterized in details. UV–vis (UV–vis) results indicated that the loaded molybdate corrosion inhibitors in TiO₂ nanotubes were slowly released in the natural environment. Scanning electron microscopy (SEM) images indicated the PPy/TiO₂@Mo coating (5.59 ± 0.42 μm) was much thicker and smoother than PPy (2.27 ± 0.57 μm) and PPy/TiO₂ (4.16 ± 0.51 μm) coatings. The corrosion behavior and electroactivity of PPy coatings with/without TiO₂ nanotubes were evaluated using electrochemical methods in 3.5 % NaCl solution. Results confirmed the excellent anti-corrosion properties and electroactivity of the PPy/TiO₂@Mo coating during 720 h of immersion. The notable improvement in the anti-corrosion performance of PPy/TiO₂@Mo coating was attributed to the superior physical barrier, anodic protection and the loaded molybdate corrosion inhibitors being efficiently released from TiO₂ nanotubes.