A combined experimental and electronic-structure quantum mechanics approach for studying the kinetics and adsorption characteristics of zinc nitrate hexahydrate corrosion inhibitor on the graphene oxide nanosheets

The adsorption mechanisms and kinetics of zinc cations at the graphene oxide (GO) nanosheets-water interface were studied by experimental and theoretical approaches. Results showed that adsorption of zinc cations onto GO surface forms a monolayer and obeys Langmuir isotherm. Meanwhile, the kinetics of sorption best fits with the pseudo-second-order model, suggesting that the sorption process is more than one-step. Various characterization techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), ultraviolet-visible spectrophotometry (UV-Vis) and field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS) were conducted to describe the mechanism of the adsorption process. EIS and polarization tests results showed that zinc cations adsorption on the GO sheets provided active corrosion inhibition on mild steel in the chloride solution. The zinc binding to GO surface was further probed from a theoretical perspective applying electronic quantum mechanics (QM) methods. Theoretical results clarified the adsorption of zinc cations onto active sites of GO sheets. The electronic-structure quantum mechanics approach revealed that zinc cation more strongly binds to the surface of GO(OH) compared with the other two mono-functionalized models namely GO(COOH) and GO(O). This finding was in good agreement with X-ray photoelectron spectroscopy (XPS) analysis.