Tunable Anticorrosive Effects of Newly Synthesized Benzothiazole Azo Dyes by Potassium Iodide Synergism for Carbon Steel in 1 M HCl: Combined Experimental and Theoretical Studies

Herein, we synthesized three novel benzothiazole azodyes, including4-chloro-2-(4-methyl-benzothiazol-2-ylazo)-phenol (CMBTAP), 1-(6-chloro-benzothiazol-2-ylazo)-naphthalen-2-ol(CBAN), and 2-(6-chloro-benzothiazol-2-ylazo)-4-methyl-phenol (CBAMP),and investigated their corrosion inhibition effect on carbon steel.The dyes were characterized by Fourier transform infrared spectroscopy, H-1 nuclear magnetic resonance (NMR), C-13 NMR, andmass spectroscopy. Weight loss, electrochemical impedance spectroscopy,and potentiodynamic polarization measurements were performed to investigatethe corrosion inhibition effect of the dyes on carbon steel in a 1.0M HCl solution. The synergistic effects of the dyes with potassiumiodide (KI) were also investigated. The inhibition efficiency (IE%)was enhanced by increasing the dose of the dyes (1 x 10(-5) to 2 x 10(-4) M) and decreased as the temperatureincreased from 25 to 45 & DEG;C. The addition of KI to a 1.0 M HClsolution containing the dyes improved the performance and efficiencyas iodide ions promoted the formation of inhibition films on the surfaceof carbon steel. The dyes are mixed-type inhibitors, according toTafel polarization. Scanning electron microscopy and energy dispersiveX-ray analysis were used to evaluate the surface morphology of carbonsteel sheets. Quantum theory calculations were utilized to evaluatethe relationship between the dyes' chemical structures andtheir inhibitory efficiency, which confirmed the experimental results.The calculations revealed that the dyes have low energy gap and Millikenand Fukui indices. Among all of the dyes, CMBTAP showed the highestadsorption energy. The corrosion IE was in the order CMBTAP > CBAMP> CBAN.