Onu, Uchenna Lynda2026-03-232026-03-232025-06Onu, C. L. (2025). Synthesis, characterization and corrosion inhibition applications of cerium (iii) metal complexes derived from some salicyaldehyde-based shiff bases [Unpublished Doctoral Thesis]. Federal University of Technology, Owerri, Nigeriahttps://repository.futo.edu.ng/handle/20.500.14562/2447This thesis was submitted for the award of Doctor of Philosophy (PhD) in Organic ChemistryThis present research work focuses on the synthesis , characterization and corrosion inhibition efficiency of three synthesized salicylalde - based Schiff bases with their Cerium(III) complexes, namely: 2-hydroxyphenyl-phenylimine or (Salicyalideneaniline (SALAN)), Bis(2- hydroxyphenyl) imine or (Salicyalidene-2- aminophenol (SAL2AP)), Bis (2-hydroxyphenyl) -1,2- Benzenediimine or (Salicyalidene-O-phenylenediamine (SALPD)), Ce(III)-2-hydroxyphenylphenylimine (CeSALAN), Ce(III)-Bis(2-hydroxyphenyl) imine (CeSAL2AP), and Ce(III)-Bis (2- hydroxyphenyl) -1,2-Benzenediimine (CeSALPD) in 1 M HCl solution. The compounds were characterized by physicochemical methods such as colour, melting point, solubility test, molar conductivity measurement, magnetic usceptibility and elemental analysis. There is variation in colour, pH, melting point, conductivity, and elemental compositions of the of the Schiff bases compared to their metal complexes. Magnetic susceptibility measurements values recorded for the metal complexes shows their paramagnetic nature. The high molar conductivity values of the metal complexes (> 0.1 mSCm2 ) shows their electrolytic nature, while the Schiff bases were found to be non- electrolytic. The compounds were also analyzed spectrally by Uv. Vis. Spectroscopy, 1 H, and 13C NMR, FTIR, and EDXRF. The effect of inhibitor- concentration, temperature, and immersion time, on the inhibition efficiency of the compounds were studied by weight loss methods. ElS technique was used to investigate the nature of the protective film, EIS measurement shows that the addition of the inhibitors into the corrosion medium inhibited corrosion by increasing the system resistance (Rs), transfer charge resistance (Rct) while reducing the double layer capacitance (Cdl). PDP polarization techniques were used to study the nature of the inhibitors, and they were found to be mixed- type inhibitors. The corrosion potentials (Ecorr), and corrosion current (Icorr) due to the blank was reduced in the presence of the inhibitors. Increase in IE was observed due to increase in concentration of the inhibitors, with highest I.E value of 82.95 % recorded for the overall best inhibitor–compound CeSALPD at concentration of 0.4 mmol/dm3 . Effect of temperature on IE of inhibitors at temperature of 30 oC, 40 oC, 50 oC, 60 oC, and 70 oC shows decrease in IE due to increasing temperature (i.e. physical adsorption process). Thermodynamics parameters calculated for the inhibited reaction system shows increase in values of enthalpy (∆H), entropy (∆S), and activation energy (∆Ea) compared to values for blank. This obtained positive values of ∆ H shows endothermic nature of the reaction system, and negative values of ∆S shows reduction in disorderliness of the system due to the action of the inhibitors. Negative values for ∆G, obtained for the inhibited systems shows the spontaneous adsorption process. Effect of immersion time on IE of the compounds shows decrease in I.E with immersion time (i.e. physisorption adsorption process). Langmuir, Temkin, and Frumkin models were used to determine the adsorption mode of the compounds. Langmuir model with regression square (R2 ) value upto 0.99, best suits the adsorption process. Generally, for all the analytical techniques employed for the study of the IE, i.e. (weight- loss method, PDP and EIS), the I.E of the metal complexes were found to be higher than those of the parent Schiff bases. The quantum chemical parameters obtained from the Computational analysis and modelling of the Schiff bases such as EHOMO, ELUMO, shows that the reactivity of the Schiff bases follow the order: SALPD > SALAN > SAL2AP. The result from the weight–loss method is in agreement with the computational analysis. Conclusively, the compounds under study performed excellently as inhibitors, however, due to physisorption process of adsorption of the inhibitor molecules on the mild- steel surface, the compounds may not efficiently inhibit corrosion for a long - term duration. Hence, synergism with nano particles such as metal oxides i.e., (ZnO, TiO2, Al2O3), may enhance their IE for the longterm process.enAttribution-NonCommercial-ShareAlike 4.0 InternationalCorrosionschiff basescomplexesinhibition efficiencyDepartment of ChemistryinhibitorsDoctoral Thesis