Thioglycoluril derivative as a new and effective corrosion inhibitor for low carbon steel in a 1 M HCl medium: Experimental and theoretical investigation

Thioglycoluril (3a,6a−bistolylthioglycoluril (BSTGCU)) was first introduced as a new and green corrosion inhibitor for low carbon steel in a 1 M HCl medium. The inhibition properties of BSTGCU in a 1 M HCl were fully characterised by the gravimetric, thermodynamic, potentiodynamic polarisation (PDP), electrochemical impedance spectroscopy (EIS), electrochemical noise (EN), electrochemical frequency modulation (EFM), density functional theory (DFT), molecular dynamics (MD) simulations, scanning electron microscopy (SEM) and energy dispersive X−ray spectrometry (EDX) methods. The experimental results confirmed that the maximum inhibition efficiency of BSTGCU was over 96% at 100 mg/L in a 1 M HCl medium. The electrochemical results indicated that BSTGCU acted as a mixed−type inhibitor and spontaneously adsorbed on the metal surface by physical and chemical adsorption mechanisms according to its Langmuir adsorption isotherms. The SEM−EDX results of the inhibited steel sample revealed that the surface morphology was significantly improved with the presence of inhibitor. Theoretical calculations confirmed that the inhibition properties depended on the molecular structure of BSTGCU, and its inhibition performance was better in its protonated form than in its neutral form in the aqueous phase.