Ti3C2Tx MXene@STPP novel waterborne long-term anti-corrosion coating with "3 + 1" multiple high-performance active-passive protection barrier mechanisms

Although environmentally friendly waterborne epoxy (WEP) coatings have the advantage of low volatile organic compounds (VOCs), their barrier performance is rather inferior to achieve long-term corrosion protection. Herein, we grafted the coupling agents KH560 and KH550 onto the etched Ti3C2Tx and sodium tripolyphosphate (STPP), respectively. On the one hand, Ti-O-Si covalent bonds can be formed to improve the water dispersion stability, and on the other hand, as a bridging agent, the functionalized modification yielded the interface-enhanced Ti3C2Tx@STPP filler. The Ti3C2Tx@STPP/WEP composite coating exhibits a high impedance value of 7.981 × 1010 Ω·cm2 after 120 days of saltwater immersion, which is at least two orders of magnitude higher than that of the pure WEP coating. Likewise, the chelating-passivation advantage of STPP with metal cations is fully exploited. The precipitation-oxidation self-healing corrosion inhibition mechanism was proposed and demonstrated by Tafel, EIS, XPS, and Raman experiments. The remarkable long-term corrosion protection performance can be concluded as (1) interface-enhanced two-dimensional Ti3C2Tx with extraordinary physical barrier to prolong the corrosion path; (2) due to high barrier properties, the further electrochemical reactions of steel surfaces can be effectively inhibited under low utilization of water and oxygen, and the Fe(OH)3 and Fe(OH)2 are converted into non-conductive Fe3O4 and/or Fe2O3 films after water loss, (3) and active protection by the chelation of STPP with iron ions to form iron tripolyphosphate passivation films, and (4) passive defense by the coating and resin itself. Therefore, a novel "3 + 1" high-performance protective coating, which integrates interface enhancement, physical barrier, and active-passive protection, is successfully prepared to achieve long-term corrosion protection of the coating.