Further study on the inclusion complex of 2-phosphonobutane-1,2,4-tricarboxylic acid with β-cyclodextrin: A new insight of high inhibition efficiency for protecting steel corrosion

The present studies were performed to further investigate the inclusion reaction of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) with β-cyclodextrin (β-CD) and the inhibition performance of the inclusion complex of PBTCA with β-CD (β-CD-PBTCA). The inclusion behavior of PBTCA with β-CD was investigated by UV–vis absorption spectrum and the formation of the inclusion complex was proved by Fourier transform infrared spectroscopy (FT-IR). The results showed that the PBTCA characteristic absorption band at 221.5 nm in inclusion complexes was strengthened and functional groups portion of PBTCA have penetrated the cavity of β-CD, due to the formation of β-CD-PBTCA inclusion complex. The study of thermodynamics indicated that the inclusion reaction of β-CD with PBTCA can spontaneously carry on and the inclusion process is exothermic. In addition, the inhibition performance was evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electronic microscopy (SEM). The results of potentiodynamic polarization and EIS measurements on the corrosion inhibition of Q235 carbon steel in the 0.1 M sulfuric acid (H2SO4) solution revealed that the highest inhibition efficiency of it over 90% is obtained, which means that the inclusion complex can act as a more efficient corrosion inhibitor for carbon steel. Also, SEM observations of the electrode surface confirmed that the presence of the inclusion complex better achieves the anti-corrosion property in aggressive medium than is the case with PBTCA alone.