Expired Glucosamine Drugs as Green Corrosion Inhibitors for Carbon Steel in H2SO4 Solution and Synergistic Effect of Glucosamine Molecules with Iodide Ions: Combined Experimental and Theoretical Investigations

Abstract

Glucosamine is a natural drug widely used for treating osteoarthritis and is usually left until it expires, which will cause a waste of resources if treated as garbage. However, its molecule contains many heteroatoms, entitling it to be a potential corrosion inhibitor. In this investigation, the corrosion inhibition activities of two types of expired glucosamine drugs (glucosamine hydrochloride and glucosamine sulfate) on carbon steel were estimated by electrochemical methods in the acidic solution. The results demonstrated that the glucosamine drugs were mixed-type corrosion inhibitors. Glucosamine hydrochloride could inhibit the carbon steel corrosion more significantly than that of sulfuric style at the same glucosamine content, suggesting a possible synergistic effect of glucosamine molecules with halide ions. Then, the co-adsorption behaviors of glucosamine sulfate with iodide ions were studied by experimental research, as well as theoretical investigations. The results indicated that the inhibition effect could be significantly enhanced when the glucosamine drug was utilized in combination with iodide ions. The electronic structures played a critical role in the synergistic inhibition of glucosamine drugs and iodide ions. Neutral molecules could interact with the metallic surface vertically through the amino and carbonyl groups, while protonated molecules were able to adsorb on it in parallel with the help of multiple functional groups. Since glucosamine molecules would be protonated and positively charged in the acidic solution, they were difficult to adsorb on the solid surface with metallic cations. When the iodide ions were presented, they preferentially adsorbed on the carbon steel surface and induced it to be negatively charged. Therefore, protonated glucosamine molecules could adsorb on the metallic surface using iodide ions as a bridge and form a protective film to mitigate the carbon steel corrosion.