A dual-ligand lanthanide-based metal–organic framework for highly selective and sensitive colorimetric detection of Fe2+

Accumulation of heavy metals in humans and mammals causes health problems due to their abundance as transition metal ions. Iron (Fe²⁺) serves significantly in numerous biological processes as a heavy metal ion. In this study, we have designed and prepared a metal-organic framework (MOF) utilizing a one-step solvothermal process, incorporating a dual-ligand combination of terephthalic acid (H₂BDC) and α,α',α''-tert-pyridine (TPY) with Eu³⁺ as the metal node. For this MOF, we termed it Eu-BDC/TPY. Eu-BDC/TPY has superior selectivity over other metal cations. It provides an accurate, sensitive, broad linear range colorimetric method for detecting Fe²⁺ in a concentration range of 1-50 μM with a modest limit of detection (0.33 μM). Eu-BDC/TPY detects the absence of Fe²⁺ quickly (within 5 seconds), which is very valuable in practical applications. In addition, the results can be used to create a digital image colorimetric card (DIC) using colorimetric software, enabling instantaneous detection of Fe²⁺ concentration using a smartphone.