Advanced Protective Epoxy Coatings with Photoactive TiO₂-LDO Nanofillers for Corrosion Protection and Potential NOx mitigation

Epoxy resins serve as anticorrosive coatings due to their robust mechanical properties, chemical resistance, and adhesion. Enhancing these coatings with nanoparticles—particularly titanium dioxide (TiO₂)—has proven effective in improving both corrosion resistance and other functional properties. In this work, we synthesized a photoactive TiO₂-based ZnAl-layered double oxide (TiO₂-LDO; 1:10) nanocatalyst via a wet impregnation method and incorporated it into an epoxy matrix. The epoxy resin, formulated with 2 wt.% TiO₂-LDO, was applied to AA2024 substrates using a coating bar coater, yielding a cured film thickness of 20 ± 2 µm. The developed TiO₂-LDO nanocatalyst exhibited high selectivity in the NOx abatement and a minimum NO₂ release (3-4%), achieving remarkably up to an 80% NO photoconversion efficiency under 20 W/m² of irradiation in a customized continuous-flow portable photoreactor, designed specifically for NOx studies. In comparison, while TiO₂ (anatase) achieved a similar NO conversion efficiency, it generated 20–25% NO₂ as a byproduct, which is even more toxic than NOx, whereas LDO alone produced minimal NO₂ but achieved a lower NO conversion efficiency of 25–30%.

Electrochemical impedance spectroscopy (EIS) over 28 days revealed that incorporating TiO₂-LDO into the epoxy coating provided a comparable corrosion resistance to the pure resin. However, the improvement was pronounced when the systems were exposed to UV irradiation (10 days of aging with fluorescent source with λ_max = 365 nm, 20 W·m⁻²), which induces micropore formation in the pure epoxy film compared to epoxy with TiO₂-LDO, and thus improved corrosion resistance for the epoxy composite on AA2024. The results underscore the dual functionality of TiO₂-LDO as both a photoactive nanocatalyst (air pollution) and an effective anticorrosion additive, offering a promising, environmentally friendly solution for UV-resistant corrosion protection.