Self-Assembled Monolayers of Passiflora edulis Sims Peel Extract on Copper Surface: Microstructure and Corrosion Protection Performance

Green self-assembled monolayers (SAMs) were formed on the copper surface using Passiflora edulis Sims peel extract (PESPE). The functional groups of active constituents in PESPE and their self-assembly behavior were characterized by Fourier-transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The effects of PESPE-SAMs on the surface roughness and hydrophobicity of copper were investigated utilizing atomic force microscopy (AFM) and a contact angle goniometer. The corrosion protection performance of PESPE-SAMs for copper in a 3.5% NaCl solution was evaluated through electrochemical measurements and an analysis of the corrosion morphology. Results indicate that functional groups such as C–O, C=O, and C=N within PESPE are adsorbed onto the copper substrate, forming a hydrophobic protective film (i.e., PESPE-SAMs). Notably, the corrosion rate of copper is significantly reduced, with a corrosion protection efficiency of approximately 86.7%. Pitting and flocculent corrosion products on the copper surface are almost entirely inhibited. Therefore, PESPE serves as an effective and renewable agent for SAMs formation, demonstrating extensive potential applications.