Green Synthesis of TiO2 Nanoparticles Using Annona muricata Extract and Their Application as CO2 Corrosion Inhibitor for 1018 Carbon Steel

The corrosion inhibition performance of green-synthesized TiO2 nanoparticles on CO2-induced corrosion of 1018 carbon steel was evaluated using potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) techniques. The polarization results revealed that TiO2 nanoparticles behave as an effective mixed-type inhibitor, with inhibition efficiency increasing with concentration and reaching its maximum at 600 ppm. Thermodynamic analysis demonstrated that the adsorption process deviates from ideal behavior and accurately fits Kokalj’s general-purpose Type-1 isotherm, involving a spontaneous, combined physisorption–chemisorption mechanism. Their presence facilitates the formation of a protective film, as demonstrated by lower corrosion current densities and higher charge transfer resistance values as compared to the uninhibited system. Specifically, the corrosion current density decreased by one order of magnitude, while the polarization resistance showed a notable increase upon nanoparticle addition. Similarly, the impedance modulus increased as a result of nanoparticle adsorption. In the absence of the inhibitor, the steel exhibited high susceptibility to severe uniform corrosion. In contrast, surface degradation was significantly reduced when TiO2 nanoparticles were present. However, at higher concentrations (800 ppm), structural defects and localized pitting were observed, likely due to nanoparticle agglomeration.