Electrochemical, surface analysis, and theoretical investigation of 3-hydroxy-5-(phenylamino)-4-(p-tolyldiazenyl)thiophen-2-yl)(phenyl)methanone as a corrosion inhibitor for carbon steel in a molar hydrochloric acid solution

In this work, a comprehensive study for using (3-hydroxy-5-(phenylamino)-4-(p-tolyldiazenyl)thiophen-2-yl)(phenyl)methanone as a corrosion inhibitor for carbon steel in a 1.0 M HCl was performed. For this purpose, different types of electrochemical and surface analysis techniques as well as a computational simulations have been applied. The obtained experimental results showed that the investigated compound is a promising corrosion inhibitor for carbon steel in acidic environments. Adding a low inhibitor concentration of about 5 x 10-5 M at room temperature resulted in an inhibition efficiency of up to 93.25 %. The inhibition efficiency increases with increasing inhibitor concentration while decreasing with increasing temperature. This trend has been demonstrated and discussed precisely by potentiodynamic polarization (PDP) measurements. SEM and AFM were used to examine the surface morphology of the electrode before and after inhibition. The inhibitor adsorbs on the surface of the steel, acting as a barrier at the steel/HCl acid interface and thus blocking the steel electrode's surface. DFT calculations and MC simulations were used to demonstrate the adsorption process. The findings also revealed that it is a mixed-type inhibitor that follows Henry's adsorption isotherm. The experimental and theoretical studies agree remarkably well. The inhibition mechanism has also been discussed.