Fluorescent Polyamide-Based Rhodamine Hydrazide Moieties with Oxethyl as Spacer for Detection of Cr3+, Fe3+, and Hg2+ Ions in Water

An acrylic monomer bearing xanthene group, N-oxethyl acrylate-N′-rhodamine B hydrazide (ARBHE) was synthesized from N-hydroxyl ethyl-N′-rhodamine hydrazide (RBHE) and acryloyl chloride (Ac) in the presence of triethylamine in dry dichloromethane (CH 2 Cl 2 ) at room temperature. The synthesized ARBHE was identified by FTIR, 1 H NMR spectra and elementary analysis. Copolymer poly(AM-ARBHE) of ARBHE and AM was synthesized with thermal initiator by free radical precipitation polymerization and it was characterized by the method of FTIR and 1 H NMR. Its molecular weights (M η ) was 7.03 × 10 3  g mol −1 and the content of rhodamine units in the polymer chains was 1.44 % in mole fraction. The ability of the poly(AM-ARBHE) to detect different metal cations (Ag + , Ba 2+ , Cd 2+ Co 2+ , Cr 3+ , Cu 2+ , Co 2+ K + , La 3+ , Mg 2+ , Na + , Ni 2+ , Pb 2+ , Fe 2+ , Fe 3+ , Hg 2+ and Zn 2+ ) in water was investigated. Upon addition of Cr 3+ , Fe 3+ or Hg 2+ ions to the aqueous solution, visual color change and fluorescence enhancement were observed. Moreover, other metal ions did not induce obvious changes to the fluorescence spectra except to Fe 2+ . The detection limit of poly(AM-ARBHE) was less than 1 × 10 −11  M. The results suggest that this copolymer may offer potential as a polymeric sensor for Cr 3+ , Fe 3+ and Hg 2+ ions in water.