IsoIndigo derivatives as environmentally friendly corrosion inhibitors for mild steel in acidic environment and their study of corrosion inhibition properties

The presence of isoindigo, with heteroatoms (N, O) and flat conjugated structures, has been shown to be useful in protecting mild steel from corrosion. Furthermore, the development of new derivatives containing different end groups may assist in understanding how end groups can enhance corrosion inhibition. Herein, isoindigo derivatives (IIDBr-NBr and IIDBr-PyBr) designed and synthesized as environmentally friendly inhibitors for mild steel at acidic conditions by introducing trimethylamine and pyridine groups. In comparison with trimethylamine, IIDBr-PyBr with pyridine as the end group demonstrated a stronger capacity for adsorption on the mild steel matrix. The experiments demonstrated that the corrosion inhibiting efficiencies for the two isoindigo derivatives at a concentration of 80 mg L⁻¹ were 96.27 % and 96.80 %. Their adsorption onto the mild steel is consistent with the Langmuir adsorption model, and both are mixed corrosion inhibitors. The DFT and MD results indicate that IIDBr-PyBr has a stronger binding ability to the metal surface.