Inhibition of iron corrosion by 5,10,15,20-tetraphenylporphyrin and 5,10,15,20-tetra-(4-chlorophenyl)porphyrin adlayers in 0.5 M H₂SO₄ solutions

5,10,15,20-tetraphenylporphyrin (TPP) and 5,10,15,20-tetra-(4-chlorophenyl)porphyrin (TClPP) were synthesized and formed adlayers on iron surface. The surface properties of the porphyrin adlayers on iron electrode were characterized by Fourier transform infrared reflection spectroscopy (FT-IR), fluorescence spectrum (FS), scanning electron microscopy (SEM) and electrochemical methods including electrochemical impedance spectroscopy (EIS) and polarization curves. FT-IR and FS results indicated that TPP and TClPP were able to form adlayers on the iron surface. The electrochemistry results showed that both adlayers of TPP and TClPP were able to protect iron from corrosion effectively and the protection efficiency of TPP was higher than that of TClPP. The surface state of iron was characterized by SEM after the iron electrode was corroded in H₂SO₄ solutions (0.5 M). Besides, quantum chemical calculation was applied to optimize the structure of the two molecules and was able to explain the experimental results to some extent. Results indicated that TPP and TClPP were good inhibitors for iron corrosion in H₂SO₄ solutions.