An optical sensor based on H-acid/layered double hydroxide composite film for the selective detection of mercury ion

A novel optical chemosensor was fabricated based on 1-amino-8-naphthol-3,6-disulfonic acid sodium (H-acid) intercalated layered double hydroxide (LDH) film via the electrophoretic deposition (EPD) method. The film of H-acid/LDH with the thickness of 1 μm possesses a well c-orientation of the LDH microcrystals confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fluorescence detection for Hg(II) in aqueous solution was performed by using the H-acid/LDH film sensor at pH 7.0, with a linear response range in 1.0 × 10−7 to 1.0 × 10−5 mol L−1 and a detection limit of 6.3 × 10−8 mol L−1. Furthermore, it exhibits excellent selectivity for Hg(II) over a large number of competitive cations including alkali, alkaline earth, heavy metal and transitional metals. The specific fluorescence response of the optical sensor is attributed to the coordination between Hg(II) and sulfonic group in the H-acid immobilized in the LDH matrix, which was verified by NMR spectroscopy and UV–vis spectra. In addition, density functional theory (DFT) calculation further confirms that the coordination occurs between one Hg2+ and two O atoms in the sulfonic group, which is responsible for the significant fluorescence quenching of the H-acid/LDH film. The results indicate that the H-acid/LDH composite film can be potentially used as a chemosensor for the detection of Hg2+ in the environmental and biomedical field.

Graphical abstract. The H-acid/LDH film used as a chemosensor for the detection of Hg2+ exhibits a broad linear response range, low detection limit and high selectivity.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights• A novel optical chemosensor for Hg(II) was fabricated by using the H-acid/LDH composite material. • The linear response ranges in 1.0 × 10−7 to 1.0 × 10−5 mol L−1 with a detection limit of 6.3 × 10−8 mol L−1. • The chemosensor exhibits excellent selectivity and stability for the determination of Hg(II). • The response mechanism is based on the fluorescence quenching resulting from the coordination between Hg2+ and H-acid.