Rize-Sourced Hazelnut Shell Ash as a Green Corrosion Inhibitor for Fe Metal in 1 % NaCl: Electrochemical Evaluation and Mechanistic Insightstion and Mechanistic Insights

The corrosion behavior of iron (Fe) in 300 mL of 1% NaCl solution containing different concentrations of hazelnut shell ash (HSA) 3.34% (v/v), 8.34% (v/v), and 25% (v/v) was investigated at 25°C using electrochemical techniques. The investigations carried out using open-circuit potential (EOCP), electrochemical impedance spectroscopy (EIS), and current–potential (Tafel) polarization techniques. The results showed that the addition of HSA significantly shifted the potential of the Fe in the cathodic direction and raised the pH of the solution (pH 5.8 to ~10) at all concentrations. Furthermore, containing 3.34 % of HSA, the corrosion rate (icorr) decreased from 0.50 µA cm⁻² to 0.15 µA cm⁻² according to Tafel results, Fe corrosion decreased by approximately 70%. Inductively coupled plasma mass spectrometry (ICP-MS) analyses revealed that Fe, Ni, Cr, and Co heavy metal ions migrated into the working solution; it was determined that the addition of HSA significantly reduced the concentration of these ions in the solution. The decrease was particularly pronounced for Fe ions; Fe²⁺/Fe³⁺ concentrations decreased from 203 ppb to <33 ppb (25% v/v), <35 ppb (8.34% v/v) and <22 ppb (3.34% v/v), respectively. The detection of lower ion concentrations at 3.34 % HSA indicated that HSA has a high inhibitory effect. These results demonstrated that HSA is an effective candidate for ‘green inhibitor’ in terms of reducing corrosion and can significantly reduce environmental impact by limiting the release of heavy metal into the environment. The ICP-MS findings found to be highly consistent with the electrochemical methods.