Improvement of the corrosion resistance of mild steel in sulfuric acid by new organic-inorganic hybrids of Benzimidazole-Pyrophosphate: Facile synthesis, characterization, experimental and theoretical calculations (DFT and MC)

Abstract In this work, a new generation of corrosion inhibitors composed of xMCl2-yNa4P2O7 (MCl2 = 2,2’-dibenzimidazolyl butane dichlorhydrates) hybrids materials have been synthesized successfully with five molar ratios (R1, R2, R3, R4, and R5) by soft chemistry route and characterized. The synthesis was performed in aqueous solutions by the ionic exchange between the pyrophosphate anions and the 2,2′-dibenzimidazolyl butane dichlorhydrates cations. The structure and morphology of the synthesized hybrids are studied by infrared spectroscopy (FT-IR), UV–Visible analysis (UV-vis), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The infrared results show the formation of a new band N-O-P confirming the hybrid structure. The crystalline structure was improved after adding pyrophosphate, confirming the phosphate nucleation and a better settlement of the crystals. These crystals were clearly shown in the SEM images. The corrosion inhibition performance of the prepared compounds were studied on mild steel in 0.5 M sulfuric acid by electrochemical impedance spectroscopy (EIS) and polarization studies. The inhibition efficiency increased with increasing inhibitor concentration, while the corrosion current density decreased. Indeed, the best inhibitor of these hybrids is R1 with an inhibition power of 97.1 % at 300 ppm. The effect of temperature on inhibitory efficiency in a range of 298 to 328K is discussed. The SEM images are also confirmed that the R1 retards the corrosion on the mild steel surface. The EDX analysis presented that this surface is mainly composed of N and P elements. The theoretical calculation results show that the benzimidazole cycle and the heteroatoms of N, O and P are the active sites of inhibitor R1.