Polydopamine functionalised ceria-zirconia nanoparticles embedded water-borne epoxy nanocomposite for anti-biofouling coatings

Biofouling, the accumulation of microorganisms, plants, algae on wet surfaces is one of the major issues adversely affecting the overall hydrodynamic performance of the marine vessels. Ceria (CeO2) nanoparticles (NPs) are effectively used as anti-biofouling agent to prevent the deterioration of steel structures, due to their excellent redox capacity. Various approaches are being investigated to enhance the antifouling activity of ceria NPs. Here, we report the development of novel polydopamine (PDA) functionalised ceria-zirconia nanoparticles filled water-borne epoxy nanocomposite coating to prevent the microbial-induced corrosion of mild steel. Ceria NPs were functionalised with PDA to enhance the dispersibility and improve their ability to resist biofouling in water-borne epoxy resin coatings against microbial species. As the anti-biofouling activity of ceria depends on their oxygen storage capacity, zirconium was incorporated to create a defective crystal structure with more active oxygen storage and release sites. Ceria and ceria-zirconia NPs were synthesised by precipitation method and functionalised with PDA. The functionalisation of ceria-zirconia (CZ) NPs was confirmed by Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Confocal Raman spectroscopy and X-ray Photon spectroscopy (XPS). Thermogravimetric analysis (TGA) shows that incorporation of zirconium increases the amount of oxygen vacancies in the crystal lattice there by enhancing ceria's redox potential. Anti-biofouling and anti-biocorrosion properties of the coatings were explored against different microbial strains. The antibacterial tests show that colony-forming units (CFU) of PDA functionalized ceria-zirconia epoxy (EPCZ) nanocomposites were suppressed by 93 % and 87 % in the case of Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) bacteria, respectively. Biofilm inhibition studies show that EPCZ nanocomposite coatings have higher biofilm inhibition efficiency against gram-negative bacteria (96.37 %) than gram-positive bacteria (62.67 %) due to the differences in their morphology. The practical applicability of the nanocomposite coatings was studied using cultured seawater consortia, and the results reveal that PCZ nanoparticles provide superior biofilm inhibition. Electrochemical impedance spectroscopy (EIS) reveals that the EPCZ coatings exhibit significant enhancement in charge transfer resistance and coating resistance. The synergistic effect of PDA functionalisation and zirconium incorporation in ceria leads to the exceptional biocorrosion resistance in corrosive bacterial environments.