A colorimetric chemosensor for F− based on Alizarin complexone and layered double hydroxide ultrafilms

The fabrication of the ordered colorimetric molecule/layered double hydroxide (LDH) ultrathin films (UTFs) by the LBL deposition technique was reported, and demonstrates their application as a colorimetric chemosensor for F−. The structural and surface morphology studies show that the UTF is continuous and uniform with stacking order in the normal direction of the substrate. The LDH nanoparticles isolate Alizarin complexone (AC) molecules from each other. The AC/LDH UTFs display a stepwise and regular growth of upon increasing deposition cycles proved by UV-vis absorption and a periodical layered structure perpendicular to the substrates with a thickness of 5.96-6.28 nm per bilayer observed by X-ray diffraction and scanning electron microscopy. Moreover, the (AC/LDH)20 UTF displays an excellent behavior as colorimetric chemosensor for F− with a low detection limit (12.9 μM), good regeneration and reversibility, high stability (light and storage stability) as well as selectivity. In addition, the mechanism of measurement-regeneration cycle for the colorimetric chemosensor indicates F− enters/departs from the AC/LDH UTF giving rise to reversible change in chemical composition and surface morphology of the UTF. Therefore, this work provides new opportunities for fabrication and application of chromophore/LDH UTFs as colorimetric chemosensors.