Two nanocomposite corrosion inhibitors were synthesized from Aloe vera extract: one incorporating sodium thiosulfate and the other silver nitrate. Both nanocomposites were subjected to structural characterization using atomic force microscopy (AFM), which revealed distinct morphological features. The sodium thiosulfate-based nanocomposite exhibited uniform and well-dispersed nanoparticles with an average size of 47.51 nm, suggesting a stable and homogeneous distribution. In contrast, the silver nitrate-based nanocomposite displayed slightly larger particles with an average diameter of 58.34 nm, indicating a tendency toward moderate aggregation. The corrosion inhibition performance of these nanocomposites for carbon steel (CS1137) was investigated in a 3.5% NaCl solution at room temperature using potentiodynamic polarization measurements. Results showed that increasing the concentration of Aloe vera extract significantly enhanced inhibition efficiency, with the maximum performance observed at 50 ppm. The inhibition effect is primarily attributed to the adsorption of bioactive phytochemicals naturally present in Aloe vera, including polyphenols, tannins, anthraquinones, and saponins. These compounds contain heteroatoms and π-electrons that facilitate strong adsorption onto the metal surface, thereby forming a compact protective film that impedes both anodic dissolution and cathodic reactions. A comparative evaluation revealed that the silver nitrate-based nanocomposite consistently outperformed plain Aloe vera extract and the sodium thiosulfate-modified system. At 50 ppm, the silver nitrate nanocomposite achieved the highest inhibition efficiency (~77%) and polarization resistance, highlighting its superior protective capability. Overall, these findings emphasize the promise of Aloe vera-derived nanocomposites as sustainable, cost-effective, and environmentally friendly corrosion inhibitors, particularly for safeguarding carbon steel in aggressive marine environments.
