NOVEL HIGHLY ANTIBACTERIAL CORROSION RESISTANT NIP-CEO2-C3N4 NANO-COMPOSITE COATINGS

Abstract

Graphitic carbon nitride (g-C3N4) nano-materials are utilized as unique reinforcement in various applications due to their superior mechanical, thermal and protective properties. Moreover, recently, it has become attractive to be used in corrosion resistant coatings at a lab scale with potential to scale up to industrial application. The use of ethanol or ethylene glycol as a solvent in the preparation of C3N4 offer two different shapes, which are nanofiber and nanotubes, respectively, and also act as a carbon source. In this research, newly synthesized g-C3N4 nanofiber (C3N4/F) and g-C3N4 nanotubes (C3N4/T), as well as their modification with CeO2, producing (g-C3N4/CeO2/F) and (g-C3N4/CeO2/T), respectively, were incorporated in the metallic NiP coating using the electroless deposition method. Heat treatment at 400 oC for 1h is applied for the different produced nano-composite coatings. The as-prepared and heat-treated NiP-C3N4/F, NiP-C3N4/T, NiP-C3N4/CeO2/F and NiP-C3N4/CeO2/T nano-composite coatings were characterized for their structure, elemental composition, thickness, morphology, roughness, wettability, hardness, and corrosion protection as well as antibacterial properties to evaluate the modifying of C3N4 with CeO2 influence, as well as the impact of the different C3N4 shapes (fibers and tubes) on the NiP coating properties. The outcomes clarified that the microhardness of both fiber-shaped and tube-shaped C3N4 nano-composite coatings is higher than that of C3N4-free coating, which further increases with the addition of CeO2. Moreover, the microhardness of the tube-shaped C3N4 is higher than that of the fiber-shaped C3N4 in all as-prepared nano-composite coatings. The heat treatment causes a further improvement in the microhardness of the composite coatings, compared to their corresponding as-prepared ones. It is noteworthy to mention that the shape of the C3N4 does not play an effective role on the microhardness of the composite coatings after heat treatment. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP) results demonstrated that the corrosion resistances of fiber- and tube-shaped of unmodified and CeO2-modified C3N4 nano-composite coatings before and after heat treatment are higher than that of the C3N4-free coating. This observation arose from improved EIS and PP indicator parameters such as resistance of solution, pore and charge transfer. Moreover, based on EIS results, the existence of CeO2 in the C3N4/F and C3N4/T backbones enhance their corrosion resistances of their composite coatings with NiP by about 5 and 2 times, respectively. Furthermore, the shape of C3N4 significantly influences its corrosion resistance values. Specifically, the tubular shape results in an eightfold increase in corrosion resistance compared to its fibrous counterpart. On the contrary, notably, the heat treatment led to a decrease in the resistivity of composite coatings compared to their corresponding as-prepared ones. Therefore, it is noticed that the highest corrosion resistance is achieved on the as-plated and heat-treated tube-shaped NiP- C3N4/CeO2 coatings, which reached to 99.99% and 99.97%, respectively, indicating its capability to prevent the localized corrosion by filling the micro defects and pores of the NiP matrix. Therefore, generally, the novel prospective g-C3N4/CeO2 nano-materials, especially the tube-shaped one, can be utilized as effective reinforcement in enhancing the hardness and protective performance of metallic NiP coatings in saline media. The antibacterial assessments conducted on various coating samples, targeting both S. aureus and E. coli bacterial strains, revealed additional improvements with the inclusion of g-C3N4, particularly pronounced when combined with g-C3N4/CeO2, when compared to the blank NiP.