A Dy(III) Coordination Polymer Material as a Dual-Functional Fluorescent Sensor for the Selective Detection of Inorganic Pollutants

A Dy(III) coordination polymer (CP), [Dy(spasds)(H₂O)₂]_n (<b>1</b>) (Na₂Hspasds = 5-(4-sulfophenylazo)salicylic disodium salt), has been synthesized using a hydrothermal method and characterized. <b>1</b> features a 2D layered structure, where the spasda^3- anions act as pentadentate ligands, adopting carboxylate, sulfonate and phenolate groups to bridge with four Dy centers in <i>η</i>₃-<i>μ</i>¹: <i>μ</i>², <i>η</i>₂-<i>μ</i>¹: <i>μ</i>¹, and monodentate coordination modes, respectively. It possesses a unique (4,4)-connected net with a Schläfli symbol of {4⁴·6²}{4}₂. The luminescence study revealed that <b>1</b> exhibited a broad fluorescent emission band at 392 nm. Moreover, the visual blue color has been confirmed by the CIE plot. <b>1</b> can serve as a dual-functional luminescent sensor toward Fe³⁺ and MnO₄^- through the luminescence quenching effect, with limits of detection (LODs) of 9.30 × 10^-7 and 1.19 × 10^-6 M, respectively. The LODs are relatively low in comparison with those of the reported CP-based sensors for Fe³⁺ and MnO₄^-. In addition, <b>1</b> also has high selectivity and remarkable anti-interference ability, as well as good recyclability for at least five cycles. Furthermore, the potential application of the sensor for the detection of Fe³⁺ and MnO₄^- was studied through simulated wastewater samples with different concentrations. The possible sensing mechanisms were investigated using Ultraviolet-Visible (UV-Vis) absorption spectroscopy and density functional theory (DFT) calculations. The results revealed that the luminescence turn-off effects toward Fe³⁺ and MnO₄^- were caused by competitive absorption and photoinduced electron transfer (PET), and competitive absorption and inner filter effect (IFE), respectively.