A selective and sensitive “naked-eye” rhodamine-based “turn-on” sensor for recognition of Hg2+ ion in aqueous solution

• Once Hg2+ ion was added to sensor 4, a 91.4-fold enhancement of the absorption at 570 nm was observed.
• Its selectivity toward Hg2+ ion was very high, and little interference was detected for other commonly coexistent metal ions.
• It demonstrated that Hg2+ could be detected at least down to 3 × 10−8 M.

A selective and sensitive “naked-eye” rhodamine-based “turn-on” chemosensor for detection of Hg2+ ion over other metal ions such as Ni2+, Ca2+, Ba2+, Cs+, Fe3+, Mn2+, Cd2+, Zn2+, Mg2+, K+, Ag+, Hg2+, Co2+, and Pb2+ in aqueous solution was prepared. Meanwhile, a new method for the synthesis of rhodamine amide directly from rhodamine hydrazide in the presence of NaH was reported for the first time. It was observed that once Hg2+ ion was added to the sensor 4, a 91.4-fold enhancement of the absorption at 570 nm was observed. Its selectivity toward Hg2+ ion was very high, and little interference was detected for other commonly coexistent metal ions. The fluorescent intensity was almost a constant minimal value when pH = 5–8 in aqueous solution. It demonstrated that Hg2+ could be detected at least down to 3 × 10−8 M. Moreover, the Hg2+-promoted selective desulfurization reaction was further confirmed by MS spectra. The present probe could be used to determine Hg2+ ion concentrations in aqueous environments.

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