ANTI-CORROSIVE POTENTIALS OF NAPHTHO-QUINONE/NAPHTHA-ALDEHYDE SCHIFF BASES FOR MILD STEEL IN HCL MEDIUM: SYNTHESIS, CHARACTERIZATION AND DFT STUDIES

Abstract

The corrosion inhibition of four ligands; L1, L2, L3 and L4 synthesized through reflux condensation, and characterized via spectroscopic methods were examined using weight loss measurements and Density Functional Theory(DFT). Factors like ligand’s chemical structure, immersion time, concentration, and temperature which affect efficiency of corrosion inhibition were evaluated. The experimental results revealed declined weight losses from 0.02-0.004g, 0.06-0.00625g and 0.11450- 0.06938g at 303K, 333K, and 363K temperature for concentration increase from 100-500ppm. The increase in weight loss arose from temperature (303-363K) increase. Obtained data denotes declined corrosion rate in the presence of the inhibitors in the acid solutions but decreased as the inhibition concentration increased at each temperature. The highest inhibition efficiency (%ᶯwL) for the ligands at 303K, 333K and 363K temperatures and 500 ppm concentration were observed as 89.39% (L3), 88.36% (L2) and 55.00% (L2) respectively. The exceptional inhibition proficiency of the ligands could be due to the availability of heteroatoms and aromatic rings with π-electrons within their structures. The increase in %ᶯwL for 5 hours immersion was in the order L2<L4<L1<L3, L1<L3<L4<L2 and L3<L1<L4<L2 at 303K, 333K, and 363K temperature respectively with L3 having the highest %ᶯwL at 89.39% at 303K. The desorption process of the ligands upon the mild steel surface (mss) followed Langmuir adsorption isotherm. The ∆Gads values acquired were amid -18.1709 to -35.6765KJ mol-1 suggestive of adsorption of the studied inhibitors on mss been physisorption. Chemical calculations and molecular descriptors of dipole moment(μ), energy gap, EHOMO, and ELUMO were acquired via B3LYP level with 6-31G (d, p) basis, while global reactivity descriptors; global softness(S), global hardness(η), electrophilicity index(ω) were derive and analyze using Koopman’s theorem. The ligands were found to be in good agreement with both experimental and theoretical results. The L3 ligand had the highest EHOMO value of - 8.4696567 denoting greater inhibition potency and conforming to the result obtained from corrosion %ᶯwL. The structural assemblages of the ligands were confirmed using spectroscopic and analytical methods.