Nanomolar level detection of chemotoxic [UO2]2+ ions by a free carboxylate anchored metal–organic framework

Abstract

The enrichment of chemotoxic uranium in the environment due to the rapid expansion of the nuclear industry to fulfil the growing energy demand has led to serious risks to human and ecological health. Despite the development of several analytical techniques for detecting uranyl ([UO₂]²⁺) ions in water, the development of sensors that offer exceptional sensitivity, selectivity, and structural stability remains a pressing challenge. In this work, a novel zirconium(IV)-based luminescent metal–organic framework (MOF), denoted as 1 with a tricarboxylic acid functionalized ligand, was solvothermally synthesized. The activated form of the MOF (1′) was utilized as a fluorometric sensor for [UO₂]²⁺ ions. Remarkably, the [UO₂]²⁺ ions interact with the free carboxylate functionality of 1′, inducing significant quenching of the luminescence of 1′. The sensor exhibits outstanding detection with a high Stern–Volmer (S–V) constant (K_SV = 3.34 × 10⁶ M⁻¹) and an ultra-low limit of detection (LOD) of 3.2 nM (0.76 ppb). Further validation in real-world samples revealed high detection performance, even in the presence of various competing ions. The MOF maintained high sensitivity towards [UO₂]²⁺ in various natural water systems, including lake water, river water, and seawater. The mechanistic aspects of sensing were thoroughly studied with various analytical techniques and literature reviews. The ground state complexation (GSC) between MOF functionality and [UO₂]²⁺ led to the selective detection of [UO₂]²⁺ by 1′.