Thermodynamic study and adsorption characteristics of mild steel corrosion inhibition in 0.1 M $$H_{2}SO_{4}$$ solution by orange peels (Citrus sinensis)

The development of efficient and eco-friendly corrosion inhibitor is necessary because mild steel corrosion in acidic conditions present serious industrial issues. The potential of orange peel (Citrus sinensis) extract as a green corrosion inhibitor for mild steel in 0.1 M H2SO4 solution is investigated in this study. The hydrogen evolution method was used to assess the inhibition efficiency, corrosion rate, as well as adsorption and thermodynamic models. Thermodynamic parameters such as activation energy, enthalpy change, and entropy change were computed. Langmuir, Freundlich and Temkin adsorption isotherms were used to examine the extract’s adsorption behavior on the mild steel surface. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were also used for surface characterization. Effective corrosion inhibition is confirmed by the results, which shows an increase in inhibition efficiency (IE) and decrease in corrosion rate with increasing inhibitor concentration. With increase in temperature, the inhibition efficiency drops and corrosion rate increases. At 303 K and 4.0 g/L concentration of the orange peels extract recoreded maximum IE% of (92.9%), (65.1%), and (69.0%) for hydrogen evolution, electrochemical impedance spectroscopy, and potentiodynamic polarization techniques, respectively. The result also revealed the inhibited system’s activation energy to be higher than the unrestrained systems. An endothermic reaction is suggested by the positive enthalpy change with values less than 100 kJ/mol. The Langmuir isotherm offered the best fit, implying monolayer adsorption on a homogeneous surface, with negligible lateral interaction, thereby strengthening the proposed adsorption mechanistic pathway. The adsorption process is spontaneous and primarily physical when the negative Gibbs free energy of adsorption is smaller than − 20 kJ/mol. When the inhibitor was present, protective barrier layers formed on the mild steel surface, according to SEM and AFM investigations. Citrus sinensis extract effectively inhibits mild steel corrosion in 0.1 M H2SO4 solution by physical adsorption and surface barrier development, indicating its potential as a sustainable and ecofriendly corrosion inhibitor. All the methods used in this study agreed.