An ultra-sensitive selective fluorescent sensor based on a 3D zinc-tetracarboxylic framework for the detection and enrichment of trace Cu2+ in aqueous media

Abstract

Herein, a novel and fluorescent zinc-organic framework sensor [Zn₃(μ₃-Hbptc)₂(μ₂-4,4′-bpy)₂(H₂O)₄]_n·2nH₂O (1) (H₄bptc = 2,3,3′,4′-biphenyl tetracarboxylic acid, 4,4′-bpy = 4,4′-bipyridine) is synthesized and characterized, demonstrating its excellent fluorescence performance for Cu²⁺ detection and the enrichment of Cu²⁺ in aqueous media. The fluorescence intensity of 1 can be selectively quenched by Cu²⁺ in a linear range of Cu²⁺ concentrations of 0–0.7 μM. The limit of detection (LOD) value is as low as 32.4 nM, which is superior to those of most of the fluorescent sensors based on metal–organic frameworks (MOFs). It is also far below the maximum allowable concentration of Cu²⁺ in drinking water as defined by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO), so it is employed for the detection of Cu²⁺ in actual water samples. More importantly, the nature of the interaction between the active coordination site (COO⁻) of 1 and Cu²⁺ determines the quenching mechanism, that is Cu²⁺ in the analyte is captured by MOF 1, which has been investigated by ICP, luminescence, UV-vis, XPS, and lifetime studies. Besides, the chemosensor shows regeneration performance without the loss of performance in five consecutive cycles. So MOF 1 is a simple and convenient probe used not only for the rapid detection but also for the enrichment of trace amounts of Cu²⁺ in aqueous media, and the application can be further extended to a variety of environmental and biological analysis processes.