A luminescent lanthanide functionalized hydrogen-bonded organic framework hydrogel: Fluorescence sensing platform for copper and iron ions detection

The excessive presence of the metal ions Cu²⁺ and Fe³⁺ in the environment poses a serious threat to ecosystems and human health, so timely and accurate detection of them has become essential and urgent. In this paper, a novel hydrogel-based fluorescent sensor, named ME-IPA@SA-TbZn, was fabricated facilely through an in-situ cross-linking modification method and was used for the detection of Cu²⁺ and Fe³⁺ in water bodies. The ME-IPA@SA-TbZn is essentially a hybrid hydrogel bead that exhibits vibrant fluorescence, employing Tb and Zn functionalized hydrogen-bonded organic frameworks (HOFs) as the fluorescence functional core and sodium alginate (SA) as the hydrogel matrix. The synthesized hydrogel sensor ME-IPA@SA-TbZn exhibits remarkable capabilities in detecting and distinguishing between Cu²⁺ and Fe³⁺ with high selectivity and sensitivity. Specifically, it achieves limits of detection (LODs) of 1.275 μM for Cu²⁺ and 0.549 μM for Fe³⁺, respectively, both are below the maximum allowable concentrations set by the U.S. Environmental Protection Agency (EPA) for drinking water. Importantly, the hydrogel sensing platform delivers intuitive and visible results under simple operating conditions, and has been successfully applied to Cu²⁺ and Fe³⁺ detection in river samples. In addition, it was demonstrated that disruption of the "antenna" effect, absorption competition quenching (ACQ) effect, and ion exchange (IE) effect are the main mechanisms leading to fluorescence quenching. Based on these results, ME-IPA@SA-TbZn hold promise as a fluorescent sensor for detecting Cu²⁺ and Fe³⁺ ions.