DFT-details & atomic-scale MC/MD simulations and experimental exploration of the Silybum extract bio-molecules effectiveness in mitigating aggressive effects of simulated corrosive concrete pore solutions

Abstract

The growing emphasis on sustainability and environmental awareness is paramount today. Corrosion control, often achieved through inhibitors, is a prominent approach, with plant extracts being favored for their accessibility and ease of extraction. Yet, their efficacy in alkaline environments, common in construction materials like cement and concrete, remains constrained. This study evaluates the potential of Silybum extract as a corrosion inhibitor within a simulated chloride-contaminated concrete setting, employing electrochemical and surface analyses to scrutinize the inhibitory characteristics and surface chemistry of the treated samples. Following the analysis of concentrations at 0.5%, 1%, and 2% Silybum extract in the simulated concrete solution, the optimal inhibition efficiency of 96.5% was obtained based on polarization measurements. The electrochemical impedance spectroscopy (EIS) confirmed that the log of impedance at low-frequencies (log|Z|10mHz) for the inhibited sample had a noticeable increment compared to the blank sample, rising from 4.60 to 5.13 after 48 h of exposure. The use of Silybum extract resulted in a remarkable 89% increase in total resistance after 5 h of immersion, as compared to the blank basic solution. Silybum exhibited a protective effect on metal substrates through three key mechanisms: forming a passive surface film via electron donation, inhibiting corrosion reactions through surface adsorption, and reducing corrosive species diffusion via physical surface coverage by heavy components. These mechanisms were supported by various surface studies which revealed the formation of a protective layer instead of corrosion products originating from Silybum components. Also, the interaction of cations in the basic solution with Silybum components and the adsorption of the obtained complex on the metal surface was demonstrated via computer modeling calculations. Theoretical studies revealed negative adsorption energies for the complexes (−1129.83 kcal/mol energy in molecular dynamics (MD) simulation for the [Ca(Silychristin)3]+2 complex), confirming their strong chemical affinity for interfacial attachment.