Supramolecular corrosion protection: Eco-friendly synthesis and efficacy of a β-cyclodextrin/o-phenylenediamine complex

Background: In corrosion science, organic inhibitors were widely used to protect the metal from corrosion. However, the greenness and effectiveness are a problem for organic inhibitors. Therefore, environmentally friendly and cost-effective corrosion inhibitors are important tasks in the material and engineering sciences. The solubility of organic inhibitors are also problem. In this work, these solutions were tried to solve. Methods: In this research work, the green supramolecular complex (beta-CD/o-PhDA) was first synthesized from the beta-cyclodextrin (beta-CD) and o-phenylenediamine (o-PhDA). The structure, physical interactions and structural changes of beta-CD/o-PhDA were confirmed by the FT-IR, H-1 NMR and Raman spectroscopic results. Main findings: It was found that the supramolecular system of beta-CD/o-PhDA was more stable with the van der Walls and hydrophobic interactions. The corrosion inhibition performance of beta-CD/o-PhDA on the St20 steel corrosion in 0.5 M hydrochloric acid (pH=0.3) was first investigated by various experimental and theoretical investigations. It is indicated that the corrosion protection of beta-CD/o-PhDA was over 95-96% in the aggressive solutions. The beta-CD/o-PhDA formed the thin defender layer on the metal surface by the formation of N-Fe and Fe-O bonds. The protonation process affects the corrosion inhibition of the host-guest complex on the metal surface. The adsorption energies of beta-CD/o-PhDA on the metal surface are more negative and depend on the adsorption positions. The beta-CD/o-PhDA acts as a mixed type of corrosion inhibitor. The beta-CD/o-PhDA was suggested as good water soluble, low-cost, stable and green protective agent for the acidizing-scaling processes in the chemical industries.