Investigations on eco-friendly corrosion inhibitors for mild steel in acid environment: Electrochemical, DFT and Monte Carlo Simulation approach

Corrosion is one of the challenging problems faced by most of the industries. Corrosion inhibitors are required to overcome the corrosion problem in these industries. Although a large number of organic corrosion inhibitors are reported in literature but most of them are toxic and effective at larger concentrations. Therefore there is a need to search eco-friendly corrosion inhibitors which should be effective even at a very lower concentration. In present investigation, eco-friendly corrosion inhibitors, namely, 2- (5-(4-cyanophenyl) -2,4,6,8-tetraoxo- 1,2,3,4,6,7,8,9 - octahydropyrido [2,3-d:6,5-d']dipyrimidin-10 (5 H)-yl)-3-(1H-imidazol-4-yl) propanoic acid (CTDP) and 4-(2,4,6,8-tetraoxo-2,3,4,5,6,7,8,9-octahydro-1H-pyrano[2,3-d:6,5-didipyrimidin-5-yl)benzonitrile (OPDB) were synthesized and their corrosion inhibitive properties on mild steel (MS) in 15 % HCl solution was studied by using gravimetric, electrochemical and theoretical calculations. The inhibitors CTDP and OPDB exhibited inhibition efficiency of 68.22 and 63.46 %, respectively, even at a very low concentration of 10 ppm whereas 94.01 and 91.11 %, respectively at 80 ppm concentration and 303 K temperature. Electrochemical studies suggested that CTDP and OPDB act as mixed type inhibitor. Adsorption of both inhibitors obeys Langmuir adsorption isotherm model. FESEM and AFM studies suggested the adsorption of CTDP and OPDB on MS surface to reduce the corrosion. Experimental outcomes support the outcomes obtained from DFT and Monte Carlo Simulation (MCS).