Smart sol-gel nanocomposite containing inhibitor-stabilized g-C3N4 nanoplates for corrosion protection of magnesium alloy

Graphitic carbon nitride (g-C3N4) nanoplates were synthesized by heating dicyandiamide. Then, losartan potassium (LP) was stabilized on their surface as a corrosion inhibitor. Field Emission Scanning Electron Microscopy (FESEM) images of g-C3N4 nanoplates showed a layered structure. By stabilizing LP, the aggregation tendency of the g-C3N4 nanoplates is slightly reduced. The specific surface area (as, BET) of g-C3N4 was reduced from 33.16 to 31.70 m2 g−1 after LP stabilizing. Compact sol-gel film without any micrometric cracks was obtained on AM60B magnesium alloy after incorporating 100 ppm g-C3N4 due to chemical interaction between free amine groups of the nanoplates and epoxide groups of the coating, which was confirmed by Fourier-Transform Infrared Spectroscopy (FTIR). Also, uniform and compact coating was achieved by incorporating the same concentration of the LP-stabilized g-C3N4. Transmission Electron Microscopy (TEM) images showed the uniform distribution of LP-stabilized g-C3N4 nanoplates inside the sol-gel nanocomposite. Additionally, the mean size of the g-C3N4@LP nanoplates in the sol was calculated using Dynamic Light Scattering (DLS), yielding a value of 803 nm. Atomic Force Microscopy (AFM) showed that the surface roughness of the sol-gel coating was changed from 1.77 to 1.19 and 1.60 μm after incorporation of pristine and LP-stabilized g-C3N4 nanoplates, respectively. Considerable enhancement in the corrosion resistance of the neat sol-gel coating in simulated acid rain solution was achieved after incorporating 100 ppm LP-stabilized nanoplates. The results of Electrochemical Impedance Spectroscopy (EIS) showed that the polarization resistance of the sol-gel film containing LP-stabilized g-C3N4 was about 1.782 MΩ cm2 after 120 h immersion, which was more than 18 times higher than the value of the neat coating. Ultraviolet-visible (UV–vis) spectroscopy was used to confirm the intelligent release of losartan potassium, and its absorption on the alloy surface.