A combined experimental and theoretical study of papain as a biological eco-friendly inhibitor for copper corrosion in H2SO4 medium

Papain freeze dried (PFD) was used as a novel, eco-friendly and efficient inhibitor for copper corrosion in H2SO4 medium via experimental and theoretical calculation methods. These WA methods include classical weight loss experiment, electrochemical measurements, surface morphology researches, and theoretical calculations. The data of weight loss experiment proves that with the increase of temperature, PFD still exhibits excellent anti-corrosion performance. The corrosion inhibition efficiency of PFD can still be maintained at about 95% at 313 K. The results of electrochemical experiments indicate that PFD is the mixed-type inhibitor that can simultaneously restrain the reaction of anode and cathode. Both the impedance experiment results and polarization experiment data show that the corrosion inhibition efficiency of PFD exceeds 95%. The atomic force microscope (AFM) and scanning electron microscope (SEM) test results intuitively show the excellent inhibition performance of PFD. The X-ray photoelectron spectroscopy (XPS) experimental data demonstrated the formation of N-Cu bond, indicating that PFD can effectively separate the corrosive medium by chemical adsorption on the copper surface. Molecular dynamics simulations (MDS) manifest that PFD can adsorption on the Cu (1 1 1) surface via the parallel pattern. Besides, the adsorption process of PFD on copper surface obey the Langmuir mono-layer adsorption.