Grafted sepiolite as smart nanocontainer for Daphne Gnidium plant extract: PH-dependent controlled release and effective green anti-corrosion coating

Abstract

This study focuses on advancing the development of environmentally sustainable and efficient active anti-corrosion coatings for metal substrates in various engineering applications. A novel smart anti-corrosive container was developed using fibrous sepiolite clay (Sep). Sep was first subjected to grafting with 3-Aminopropyl-diethoxy-methylsilane (APDEMS). Subsequently, the grafted-Sep (Sep-G) was used to load a Daphne Gnidium plant extract (DGE) as a natural corrosion inhibitor. The modification process of Sep was carefully monitored and characterized through Zeta potential, scanning electron microscopy, X-ray diffraction, UV/visible spectroscopy, and Fourier transform infrared spectroscopy. The results highlighted the successful clay modification with a silane loading of 7.68 % and a DGE adsorbed amount of approximately 58 mg/g. The DGE release behavior of the elaborated nanocomposite (Sep-G@DGE) was studied at different pH values and showed distinct pH-dependent release profiles. The rates were in the following order: acidic > alkaline > neutral. Electrochemical properties of Sep-G@DGE were investigated on a bare mild steel electrode in 0.1 M NaCl solution, demonstrating a corrosion inhibition efficiency of 90 % for a 24-hour immersion time at a concentration of 1 g/L. Moreover, the beforehand prepared nanocontainer, Sep-G@DGE, was incorporated into an alkyd resin to formulate a smart anti-corrosion coating. This coating exhibited enhanced anti-corrosion properties and sustained inhibitory effects over time compared to that of a pure alkyd coating. The coating's efficiency is attributable to the high dispersion of the layered clay mineral structure, which allowed an on-demand release of the DGE inhibitor. In addition, the presence of free APDEMS NH3+ group leads to the formation of electrostatic interactions with the adsorbed chloride ions on the metal surface, acting thus as a barrier against corrosive agents and inhibit rust formation in paint cracks.