Exploration of novel polyaspartic acid derivatives as fluorescent eco-friendly corrosion inhibitors for the carbon steel: Electrochemical, surface analysis (SEM/XPS) and theoretical calculation

The addition of corrosion inhibitors can effectively improve the hazards posed by the corrosion of carbon steel in circulating cooling water. From the economic and environmental perspective, it makes sense to develop eco-friendly corrosion inhibitors that can be monitored online. In the present work, three polyaspartic acid (PASP) derivatives modified with benzothiazole compounds (R-ABT: R=H, Me and OMe) were synthesized as fluorescent green corrosion inhibitors for the first time, which have good thermostability and allow online detection by fluorescence spectroscopy. The corrosion performance of three inhibitors on carbon steel in cooling water was investigated using the electrochemical test, weight loss measurement, scanning electron microscopy, atomic force microscopy, contact angle test, X-ray photoelectron spectroscopy, density functional theory (DFT) and molecular dynamic (MD) simulation. The electrochemical tests indicate that all three derivatives are mixed-type inhibitors and their corrosion inhibition capacity is ranked as follows: PASP-OMe-ABT (96.45%) > PASP-Me-ABT (91.38%) > PASP-H-ABT (89.38%). The three inhibitor molecules improve the carbon steel surface by physisorption and chemisorption as shown by weight loss tests and surface analysis. XPS analysis further confirms the presence of a compound film on the metal surface. Meanwhile, the difference in the radial distribution function and diffusion coefficient of the three derivatives on the Fe (110) surface was also in-depth revealed by quantum chemical calculation based on DFT and MD simulation. The theoretical data obtained strongly support the experimental results and confirm that the introduction of methoxy enhances the corrosion inhibition performance.