Highly effective Q235 steel corrosion inhibition in 1 M HCl solution by novel green strictosamide from Uncaria laevigata: Experimental and theoretical approaches

Traditional corrosion inhibitors are not popular due to high toxicity. Instead, green corrosion inhibitors are appearing. Here, strictosamide as a green corrosion inhibitor was firstly separated from Uncaria laevigata, showing excellent solubility in hydrochloric acid solution. By means of electrochemical test, morphology measurement, and theoretical analysis, the corrosion inhibition ability of strictosamide on Q235 steel in corrosive medium was evaluated. Electrochemical results suggested that strictosamide revealed significant corrosion inhibition efficiency of 94.25% at 25 °C. Moreover, the inhibition effect was still strong with extension of immersion time, and the highest inhibition efficiency reached up to 94.90% for 48 h at 160 mgL⁻¹. After the samples were immersed in the inhibited solution for 24 h, scanning electron microscopy and atomic force microscopy observations indicated that strictosamide was firmly attached to Q235 steel surface by making a protective film. Then, according to X-ray photoelectron spectroscopy results, Fe-N bonds existed on the steel showed the presence of chemisorption between metal ions and strictosamide molecules. Mainly because N atoms were complexed with Fe (II) to form stable complexes attached to the active position on steel. Hence, the stability and compactness of the adsorption film on metal surface were strengthened. Additionally, the inhibition mechanism of strictosamide was illustrated by molecular dynamics. Overall, strictosamide may exhibit the potential to replace the traditional toxic corrosion inhibitors in the industry.