Improved Corrosion Resistance of Q235 Steel in 3.5 wt% NaCl Solution by N, P Co-Doped Carbon Dots with Efficient Antibacterial and Fluorescent Properties

The carbon steel is susceptible to corrosion in a humid and complex marine environment, resulting in economic losses and environmental pollution. Harmful microorganisms, such as metal-reducing bacteria, can induce Microbiologically Influenced Corrosion (MIC), which accelerates the corrosion rate and shortens the service life of metallic instruments. In this paper, nitrogen and phosphorus codoped CDs (N, P-CDs) were prepared through a commonly used solvothermal method with ammonium citrate tribasic and diammonium hydrogen phosphate as precursors. Structural characterizations indicated that N, P-CDs contained vast heteroatoms such as N, O, and P atoms and heteroatom-containing functionalities. The corrosion inhibition performance of N, P-CDs on Q235 steel in 3.5 wt % NaCl solution was evaluated. Electrochemical experiments revealed that the corrosion inhibition efficiency was 97.8% in a 150 mg/L N, P-CDs solution at 298 K. Morphology and adsorption isotherm demonstrated that the N, P-CDs protected Q235 steel by forming a composite film through physical and chemical adsorption. The N, P-CDs were used as a fluorescence probe to detect the corrosion process of QS. The N, P-CDs showed substantial dose-dependent bactericidal effects against <i>P. aeruginosa</i> and <i>S. aureus</i> within the 1-500 ppm range. The minimum inhibitory concentration (MIC) of the N, P-CDs toward <i>P. aeruginosa</i> and <i>S. aureus</i> was 1.95 mg mL^-1. The N, P-CDs showed a bactericidal rate of 99.06% and 88.79% toward <i>P. aeruginosa</i> and <i>S. aureus</i> at 500 ppm, respectively. Therefore, the as-prepared N, P-CDs provide great potential as ecofriendly corrosion inhibitors with efficient antibacterial and fluorescent properties for Q235 steel protection.