Corrosion inhibition properties of expired Broclear medicine and its carbon dot as eco-friendly inhibitors for mild steel in 15% HCl

Eco-friendly, hydrophilic and economical carbon dot (CD) of expired dated Broclear tablets (EBD-CD) was synthesized by hydrothermal method and its identification as a carbon dot was confirmed by high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR), ultraviolet–visible spectroscopy (UV–vis) and photoluminescence (PL) spectroscopy. Corrosion inhibition efficiency of expired dated Broclear (EBD) and its carbon dot (EBD-CD) was analysed by gravimetric and electrochemical methods for mild steel (MS) in 15% HCl solution. The corrosion inhibition efficiency of synthesised EBD-CD was found higher at each concentration compared to EBD. The corrosion inhibition efficiency obtained from gravimetric method for EBD-CD and EBD was 95.2% and 89.1%, respectively, at 303 K and 100 ppm concentration. The inhibition efficiency of both inhibitors increases on increasing concentration and decreases on increasing temperature. The mixed type adsorption of inhibitor molecules on MS surface is the main factor to reduce corrosion of MS. Both inhibitors obey Langmuir adsorption isotherm. The surface study of uninhibited and inhibited MS surface was performed by using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) analysis. Whereas, the composition of adsorbed inhibitor film on MS surface was analysed by X-ray photoelectron spectroscopy (XPS) study.