Dimeric imidazolium ionic liquids connected by bipyridiyl as a corrosion inhibitor for N80 carbon steel in HCl

A new type of the dimeric imidazolium-type amphiphile, BDBC_mIB (m = 1, 4 and 8), was synthesized using the bipyridiyl as the spacer, and its inhibition performance and mechanism for the corrosion of N80 carbon steel in 1.0 mol·L⁻¹ HCl were evaluated using chemical and electrochemical measurements, surface analyses and density functional theory (DFT) calculations. Results show that the inhibition efficiency of BDBC_mIBs increases with their concentrations and the length of tail chains. BDBC₈IB exhibits the best inhibition performance among them and its inhibition efficiency almost exceeds 90% in a wide concentration range from 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ mol·L⁻¹ mol·L⁻¹ at 25.0 °C, which attains the maximum over 95% at 5.0 × 10⁻⁴ mol·L⁻¹. Moreover, three BDBC_mIBs all display the high inhibition efficiency at 5.0 × 10⁻⁴ mol·L⁻¹, nearly exceeding 90%, in the temperature range from 25.0 to 55.0 °C. As a mixed-type inhibitor, BDBC_mIBs can retard both cathodic hydrogen evolution and anodic metal dissolution processes, since BDBC_mIB molecules bear the imidazolium-based heterocycle with the electron-donating ability and the bipyridine with the electron-accepting ability, thereby facilitating the formation of a protective film on the surface of N80 carbon steel via electrostatic interactions, coordinated and back-donating bonds. The adsorption of BDBC_mIBs obeys the Langmuir isothermal model. Our finding demonstrates that the introduction of the bipyridiyl at the spacer does favor improving the inhibition efficiency of such dimeric imidazolium-type amphiphiles, and meanwhile, the proper increase in the number of carbon atoms in the substituents on the imidazole rings can also enhance the inhibition efficiency.