Fluorescent Polyamide-Based Rhodamine Hydrazide Moieties with Oxethyl as Spacer for Detection of Cr(3+), Fe(3+), and Hg(2+) 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 (CH2Cl2) 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 (Mη) 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.