A robust Zn(<scp>ii</scp>)/Na(<scp>i</scp>)-MOF decorated with [(OAc)₂(H₂O)₂]_n²ⁿ⁻ anions for the luminescence sensing of copper ions based on the inner filter effect

Abstract

Based on the inner filter effect, a luminescent Zn(ii)/Na(i) metal-organic framework (MOF) {[Zn2Na(L)(HL)2(H2O)2][OAc]·2H2O}n (1, H2L = 5-methyl-1,3-benzenedicarboxylic acid) with excellent stability was constructed for the fluorescence detection of Cu2+ ions. MOF 1 holds a 3D cationic framework in which [(OAc)2(H2O)2]n2n- anions are embedded into its 1D channels. Abundant hydrogen-bonding and π-π interactions in the MOF facilitate electron transfer from ligand-to-metal, resulting in a good luminescence peak at 412 nm and an efficient fluorescence quenching of MOF 1 in the presence of Cu2+ ions, due to the inner filter effect. The interactions between the Cu2+ ions and the OAc- anion in the channel endowed the Cu2+ ions with facile access to be adsorbed, and afforded the selective quenching of fluorescence. The MOF particles are well dispersed in water and the Cu2+ ions are pre-concentrated by adsorption, thus facilitating the determination of Cu2+ ions with a detection limit down to 0.65 μM. Our work thus paves a way for developing MOFs as an appealing platform to construct materials for environmental applications.