Effect of carbon quantum dots on the anticorrosive action of the tin coatings

Carbon quantum dots or carbon dots (CDs) are a new class of nanomaterials with a nearly spherical shape and a size smaller than 10 nm. The literature reports on studying metallic composites using other carbon allotropes, such as carbon nanotubes and graphene oxide. However, no studies have applied carbon quantum dots to metallic coatings. Tin is a metal widely used industrially due to its resistance to oxidation, corrosion resistance, and weldability. However, the thickness and microstructure of the material can impact its resistance. Therefore, this work studied composite coatings of tin (Sn) and CDs at different concentrations to improve the material's corrosion resistance. Different concentrations of CDs were analyzed to obtain Sn – CD composite coatings: 0.03, 0,04, 0.05, 0.07, and 0.09 g L −1 . Mild steel plates were used as substrate using electrodeposition in galvanostatic mode with j = 6.25 mA cm −2 . The performance of the coatings was evaluated by electrochemical measurements such as open circuit potential, electrochemical impedance, and potentiodynamic polarization curve. In addition, characterizations of the CDs and composite films were carried out by Fourier Transform Infrared Spectroscopy (FTIR), Zeta Potential (ζ), Dynamic Light Scattering (DLS), UV-VIS Spectroscopy, Fluorimetry, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Excited Photoelectron Spectroscopy X-Ray (XPS). The electrochemical tests show an optimal working concentration equivalent to 0.05 g L −1 of CDs in the bath. The SEM and XDR show that this concentration favored the growth of the film in a more uniform manner, providing a more homogeneous barrier when compared to the pure Sn film. The XPS indicated that the pure Sn film oxidized more than the composite film, suggesting that the addition of CDs improved the resistance of this material.