Environmental behavior, hazard and anti-corrosion performance of benzotriazole-based nanomaterials for sustainable maritime applications

Metal corrosion is a colossal technical, economic, and environmental challenge worldwide. Protective coatings containing corrosion inhibitors (CIs) are commonly used to address this natural process, particularly severe in immersed structures in seawater. However, high-performance CIs, such as benzotriazole (BTA), often exhibit toxicity towards aquatic organisms and leach prematurely. This study introduces safe and sustainable-by-design engineered nanomaterials, specifically layered double hydroxides loaded with BTA (Mg-Al LDH-BTA and Zn-Al LDH-BTA), as an innovative and eco-friendly approach compared to state-of-the-art CIs. This study aims to characterize both nanomaterials, assess their anti-corrosion performance when incorporated in polyurethane coatings, and evaluate their environmental behavior when dispersed in water, short-term acute and chronic effects on temperate marine species, and the environmental hazard. Key findings include a superior anti-corrosion performance of coatings containing Zn-Al LDH-BTA compared to BTA-coatings. Aqueous dispersions of nanomaterials exhibit instability of particle size and zeta potential over time, while concentrations of metals (Al, Zn) and nitrates reach high levels in the highest tested concentration due to partial dissolution, which may explain the observed toxicity patterns (median effect concentrations in the mg/L range). The tested compounds were not toxic for most tested species, apart from bacteria (Aliivibrio fischeri) and/or echinoderms (Paracentrotus lividus) and, in case of Mg-Al LDH-BTA, also on two microalgae species. The highest statistical PNEC value was observed for Mg-Al LDH-BTA (PNEC=0.326 mg BTA/L), while the highest deterministic PNEC value was found for Zn-Al LDH-BTA (PNEC=0.00041 mg BTA/L). These findings indicate that both nanomaterials are environmentally sound and efficient alternatives for anti-corrosion maritime applications.