pH-Responsive Fluorescent Metal-Organic Framework as a Functional Nanofiller for Smart Coatings

A zirconium-based UiO-type UiO-66-(OH)(2) metal-organicframework@carbon dot composite (Zr-MOF@CD) is synthesized througha facile solvent-free thermal method. The Zr-MOF@CD exhibits pH-responsivefluorescence behavior, which emits blue fluorescence for pH < 9at an emission wavelength of 470 nm. At pH > 9, the fluorescencecolorturns from blue to yellow, with the emission behavior at 535 nm. Zr-MOF@CDscan serve as functional nanofillers in the epoxy coating for the fabricationof a smart coating, which can realize coating damage warning and metalcorrosion reporting. The blue fluorescence can be observed in thearea of coating damage with just a minor scratch. Once the scratchis severe enough to expose the metal substrate, the cathodic reactionof oxygen reduction in the corrosion galvanic cell causes an increasedpH, where the emission of yellow fluorescence can be identified. Thestable fluorescence response is free from the influence of concentration,time, temperature, and the interfering substance. Zr-MOF@CDs can alsoserve as nanocontainers for loading with the corrosion inhibitor andrealizing the repairing of metal corrosion. The development of thesmart coating with dual functions of autonomous reporting and repairingholds great potential to improve the lifetime of metals in variousindustrial applications. Auniversal smart coating based on a pH-responsive fluorescentmetal-organic framework for coating damage warning and metalcorrosion reporting/repairing.