Cation-exchange strategy for a colorimetric paper sensor: belt-like ZnSe nanoframes toward visual determination of heavy metal ions

Abstract A colorimetric paper sensor based on a cation-exchange strategy has been developed for the visual determination of heavy metal ions. Belt-like ZnSe nanoframes as colorimetric reagents were prepared from ZnSe·0.5N2H4 hybrid nanobelts as precursors via a hydrothermal method. With the decomposition and release of N2H4 ligands, the regular belt-like nanostructures of the precursors evolved into belt-like nanoframes, which consisted of numerous ZnSe nanocrystals. Inspired by the cation-exchange characteristic of chalcogenides, the as-prepared belt-like ZnSe nanoframes were employed to fabricate a colorimetric paper sensor for the detection of heavy metal ions. Owing to the color change arising from a composition change, the colorimetric paper was successfully applied to detect Ag+, Cu2+, and Hg2+ at room temperature. Depending on the color change and its intensity, heavy metal ions of Ag+, Cu2+, and Hg2+ can be individually identified and their concentrations can be determined. Particularly for Cu2+, its visually detected concentration can be down to 1 ppm. More importantly, the fabricated colorimetric paper sensor displays excellent anti-interference properties from various typical cations and anions. Considering its low cost and practicality, expectedly it can be used for practical application.