Enhancing the corrosion inhibition performance of Ocimum gratissimum crude extract in 3.5 % NaCl through synergism with Zinc Sulphate Heptahydrate: Experimental and Computational Studies.

This study investigates the corrosion inhibition action of Ocimum gratissimum (OG) biomass extract and the blend with Zinc Sulphate heptahydrate (ZS) on mild steel corrosion in 3.5 Wt. % NaCl environment. Combined gravimetric and advanced characterization techniques including gas chromatography–mass spectrometry (GC-MS) and ultraviolet, visible, near-infrared (UV-VIS-NIR) spectroscopic studies were employed in the investigation. The results of the gravimetric studies revealed a very low inhibition efficiency with maximum value of 21.9% for the biomass at concentration of 0.25 g/L whereas, upon blending with the optimal amounts of ZS, higher inhibition efficiency values reaching 93.1%, was obtained. Unlike in the unblended system, the obtained IE% values for the blends were almost stable even at 120 h of immersion time. The study of the synergistic index of the extract and the additives showed a cooperative interaction. The GC-MS analysis revealed a number of biomass extract constituents that contain hetero-atoms like sulfur, oxygen, and nitrogen, validating their propensity to inhibit the mild steel coupon corrosion in 3.5 wt%. NaCl environment with Methylene Chloride, Thymol and Benzene, 1 methyl-3-(1-methylethyl) as major constituents of the extract. The UV-VIS-NIR studies also showed that the biomass final blends do not loose chromophore at intervals of 24 h, 72 h, 96 h and 120 h, indicating that the active constituents in the final blends do not degrade within the investigation period. Quantum Chemical studies were used to complement experimental and surface probe analysis.