Carbon Dots as Green Corrosion Inhibitor for Mild Steel in HCl Solution

Two carbon dots namely, S, N co-doped (CD1) and N doped (CD2) were synthesized by solvothermal treatment of pyromelletic acid in presence of thiourea, urea and DETA at 180 degrees C. The synthesized carbon dots were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Transmission electron microscopy (TEM) and Raman spectroscopy analysis. The dimension of synthesized carbon dots were found in the range of 1.63 nm to 2 nm with significant graphitic carbons. These carbon dots (CD1 and CD2) were used as green corrosion inhibitor to mitigate corrosion of mild steel (MS) in 15 % HCl solution using gravimetric and electrochemical methods. Studied carbon dots, CD1 and CD2 exhibited inhibition efficiency of 96.40 and 90.00 %, respectively, at 100 ppm concentration and 303 K temperature. The observed corrosion inhibition occurs due to adsorption of the carbon dots to the MS surface. Both the carbon dots follow Langmuir adsorption isotherm model and show physisorption on the MS surface. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis was used to study the morphology of the uninhibited and inhibited surface of the sample. The interaction of the carbon dots and composition of adsorbed layer on the MS surface was confirmed using X-ray photoelectron spectroscopy (XPS). The XPS analysis revealed that heteroatoms present in the structural moiety of the carbon dots efficiently binds on the MS surface.