Novel Damsissa carbon quantum dots (DCQDs) to improve the protection efficiency of permanganate phosphate conversion coats (PPC) on steel

Carbon quantum dots (CQDs) are spherical zero dimensional nanoparticles, generally below 10 nm in size, which received increasing attention in diverse application fields owing to their important characteristics and advantages as good water solubility, potential of environmental protection and preparation from abundant and sustainable raw materials. In this work, Damsissa carbon quantum dots (DCQDs) were generated via hydrothermal reaction microwaves irradiation. The DCQDs material was characterized by FTIR, TEM, EDX, XRD, and XPS to confirm the morphological and functionality aspects as well as particle size distribution, elemental composition, crystallite structure, and elemental identification in terms of chemical state. The FTIR analysis referred to associated assignments of C-H, C=O, C=C, C-N, besides other groups. The TEM study confirmed a ranged homogenous particle distribution at 3-6 nm. The EDX and XPS results verified carbon, nitrogen and oxygen as the main elements in DCQDs. The protection efficiency performance of permanganate phosphate conversion coat (PPC) was investigated and monitored by using different concentrations of DCQDs in the coating bath utilizing the potentiodynamic polarization technique, besides electrochemical impedance spectroscopy. The results referred to 97.4% maximum protection efficiency for the coat in presence of 400 mg/L DCQDs. The impedance results showed that as the concentration of DCQDs increase, the capacity of the double layer (Cdl) decreases due to the adsorption ofDamsissa carbon dots on the steel surface. However, the potentiodynamic polarization results indicated that the presence of DCQDs in HCl solution could lead to the polarization of the cathodic and anodic curves to denote that these retard the cathodic and anodic reactions at the steel surface inhibiting the corrosion process. The coats synthesized in absence and in presence of diverse amounts of DCQDs were examined by the TEM, EDX, XPS, and XRD studies to elucidate the role of DCQDs in the improvement of the corrosion protection of the coat. The results indicated that the DCQDs molecules ofDamsissa were adsorbed at the steel surface to efficiently retard the dissolution of iron and decrease the Fe2+ ions concentration in the coating solution causing higher nucleation rate over the crystal growth and thus leading to the formation of a uniform protective film.