Dual ligand based 3D Eu(iii) MOF as a multifunctional sensor for trace amounts of NACs, Cr3+ and Hg2+ in aqueous medium: synthesis, crystal structure and latent fingerprint detection

Abstract

A novel 3D luminescent metal–organic framework (MOF) named as [Eu(HPyzdc)(NITA)(H₂O)]_n (Cj-3) has been synthesized with the dual ligand approach involving nitro functionalised isophthalic acid (H₂NITA) and pyrazine based dicarboxylic acid (2,3-H₂Pyzdc) via a solvothermal method. Analysis of its structure reveals that Cj-3 is composed of tetranuclear secondary building units (SBUs) with uncoordinated carbonyl and hydroxyl groups, which serve as potential recognition sites for interacting with analytes. Cj-3 shows unique luminescence features and is projected for its potential in detecting metal ions (Fe³⁺ and Cr³⁺) as well as picric acid (PA) and amine-substituted NACs (nitroanaline). The luminescence experiments show distinct luminescence quenching and enhancement effects, particularly towards nitroaniline (p-NA and o-NA), picric acid (PA), Hg²⁺ and Cr³⁺ ions. Cj-3 displays exceptional selectivity and sensitivity towards Cr³⁺, Hg²⁺, and PA, along with rapid response times and excellent recyclability. Competitive absorption of excitation energy and electron transfer are probable mechanisms for sensing nitroaromatic compounds, while host–guest interactions are responsible for detecting metal ions. Additionally, visual luminescent test papers based on Cj-3 have been developed which can selectively detect NACs and metal ions. Moreover, Cj-3 can generate latent fingerprints on diverse surfaces, with intricate details observable upon magnification. These findings suggest significant potential for applying Cj-3 as a luminescent MOF in security applications.