Non-thermal plasma synthesis, characterization and electrochemical study of metal oxide nanoparticles

This work investigates the inhibitory efficiency of zinc oxide nanoparticles (ZnO NPs) as an eco-friendly inhibitor against the corrosion of XC70 mild steel (MS) pipelines in a 1M HCl aggressive medium. ZnO NPs were synthesized for the first time using a non-thermal plasma method (NTP), specifically the gliding arc discharge-assisted (GAD) method, which is a sustainable, chemical solvent-free, and safe approach utilizing humid air as the vector gas and distilled water as the solvent. Multiple characterization techniques were used in this work, including UV-visible (UV-vis) spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS). The Dynamic Light Scattering (DLS) analysis confirmed a positive zeta potential of +16 mV and moderate stability of the nanoparticles in aqueous media. XRD showed that the ZnO NPs have a hexagonal wurtzite structure with a median particle size of ~65 nm. XPS analysis confirmed that zinc is predominantly in the Zn2+ oxidation state and oxygen is in the form of oxide O2-. Additionally, this work also assessed the corrosion process in acidic environments and the impact of ZnO nanoparticles on the corrosion of XC70 mild steel. The experiment was conducted using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques, varying the concentration of the inhibitor and the temperature range from 298 to 333K, along with different immersion times. Furthermore, it included topographical and morphological using SEM and AFM to evaluate the inhibition efficacy of the inhibitor under study. The findings indicated that increasing the concentration of ZnO NPs enhanced their corrosion inhibition ability, with an optimal concentration of 70 mg/L achieving a high effectiveness of 90.71% at room temperature. AFM and SEM analyses confirmed the formation of a protective barrier film on the inhibited substrate, effectively preventing the diffusion of corrosive ions. Additionally, the DFT method was used to investigate the corrosion mitigation mechanism. These results confirmed the success of the synthesis process and highlighted the significant inhibiting properties of ZnO NPs in preventing corrosion of XC70 mild steel in a 1M hydrochloric acid environment.