The healable and early warning waterborne epoxy coatings integrated with graphene oxide and HMTNs nanocontainer loaded with 8-hydroxyquinoline for the long-term corrosion protection of Q235 steel

In order to satisfy the long-term corrosion protection of metal in harsh environments, the development of smart polymer coatings with self-repairing and self-warning functions can reach their anticipated application prospects. Herein, a new CS@HMTNs-8HQ nanocontainer, composed of a core of mesoporous hollow titanium dioxide (HMTNs) loaded with 8-hydroxyquinoline (8HQ) and a shell of chitosan (CS), was designed via simple template and vacuum-assisted technique. Grafting CS@HMTNs-8HQ nanocontainer onto the graphene oxide (GO) platform and further introducing into the waterborne epoxy (WEP) coatings imparted the healable and self-warning intelligent properties to carbon steel (Q235). It was found that the mesoporous hollow structure of HMTNs constructed by high-temperature calcination and alkaline etching yielded a high specific surface area of 190.82 m 2 /g and suitable pore size of 3 nm, thus achieving a high loading capacity of corrosion inhibitor (33.6 wt%) and ensuring long-term protection of metal substrate. The results of electrochemical impedance spectroscopy (EIS) indicated that the designed WEP coating displayed excellent healable ability. Benefiting from the synergistic effect of GO and CS@HMTNs-8HQ, the low-frequency impedance of the composite coating reached 7.63×10 9 Ω cm 2 after 90 days of immersion in 3.5 wt% NaCl, verifying its long-term protection. In addition, the WEP composite coating indicated a distinctive black-green colour in damaged areas after 120 h of salt spray testing, demonstrating the unique early warning ability. This intelligent coating with passive self-repairing and self-warning functions shows great potential prospect in practical anti-corrosion applications.