Susceptibility of hybrid sol-gel (TEOS-APTES) doped with caffeine as potent corrosion protective coatings for mild steel in 3.5 wt.% NaCl

A series of hybrid sol-gel matrices were synthesized using 3-aminopropyltriethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) incorporating caffeine extracted from leaves of tea. Corrosion inhibition performances of coated mild steel panels exposed to 3.5 wt.% NaCl were evaluated employing electrochemical measurements. Data acquired using complementary corrosion analyses were in accordance where 100 ppm caffeine-doped hybrid sol-gel coating offered the highest inhibition efficiency at 88.79 %. Tafel curves suggested that silane coatings mitigated both the anodic and cathodic reactions simultaneously, i.e. a mixed-type inhibition. Coatings were characterized using FT-IR, SEM/EDX and water contact angle measurements. IR absorption peak obtained at 954 cm(-1) revealed the formation of Fe-O-Si bonds. 100 ppm caffeine-doped silane coating offered the highest corrosion resistance since the corrosion protective barrier minimized the oxidation of mild steel to a greater extent where the EDX analysis showed a high intense signal of Fe. Water contact angle analysis depicted the hydrophobicity of coated panels suggesting the tendency of being less prone to water.