ANTI-CORROSIVE POTENTIALS OF NAPHTHO-QUINONE/NAPHTHA-ALDEHYDE SCHIFF BASES FOR MILD STEEL IN HCL MEDIUM: SYNTHESIS, CHARACTERIZATION AND DFT STUDIES
AbstractThe 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 ligandâ€™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 (%á¶¯wL) 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 Ï€-electrons within their structures. The increase in %á¶¯wL 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 %á¶¯wL at 89.39% at 303K. The desorption process of the ligands upon the mild steel surface (mss) followed Langmuir adsorption isotherm. The âˆ†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(Î¼), 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(Î·), electrophilicity index(Ï‰) were derive and analyze using Koopmanâ€™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 %á¶¯wL. The structural assemblages of the ligands were confirmed using spectroscopic and analytical methods.
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