Two Stable Zn (II) Coordination Polymers as Dual-Functional Luminescent Sensors for Efficient Detection of Nitrofurazone, Pefloxacin, and Cr2O72− in Water

Abstract

Two new Zn (II) coordination polymers, {[Zn (OBA)(L)]·H₂O}_n (1) and {[Zn₂(TCPA)₂(L)₂]·H₂O}_n (2), were synthesized under hydrothermal condition. Here, L = 2-(1H-imidazol-1-yl)methyl)-5,6-dimethyl-1H-benzo[d]imidazole, H₂OBA = 4,4′-dicarboxydiphenyl ether, H₂TCPA = tetrachloroterephthalic acid. Structural analyses revealed that 1 exhibits a 2D hcb topology of {6³} while 2 displays a four-connected 2D sql layer with the point symbol of {4⁴.6²}. Both 1 and 2 are extended to 3D supramolecular frameworks through hydrogen bonding interactions. These CPs demonstrate remarkable thermal and chemical stability across a wide pH range of 3 to 12. Notably, they can serve as dual-functional luminescent sensors for the sensitive, selective, and recyclable detection of nitrofurazone (NFZ)/Cr₂O₇²⁻ ions (for 1) and pefloxacin (PEF)/Cr₂O₇²⁻ ions (for 2) in aqueous solutions. The limits of detection (LODs) of 1 towards NFZ and Cr₂O₇²⁻ ions are 2.20 × 10⁻⁷ and 4.90 × 10⁻⁷ mol·L⁻¹, respectively. For 2, the LOD is 5.42 × 10⁻⁸ mol·L⁻¹ for PEF and 3.40 × 10⁻⁷ mol·L⁻¹ for Cr₂O₇²⁻ ions. It is worth noting that this is the first report of luminescent Zn (II)-CPs based on L ligands for the sensing of NFZ, PEF, and Cr₂O₇²⁻ ions. And the quenching mechanism was deeply investigated.