A Bifunctional Three-Dimensional Zn(II) Metal–Organic Framework with Strong Luminescence and Adsorption Cr(VI) Properties

Abstract

The mixed ligand 3-amino-1,2,4-triazole (Hatz) and terephthalic acid (H₂pta) reacted with Zn(NO₃)₂·6H₂O to synthesize a three-dimensional binuclear Zn(II) metal-organic framework: {[Zn₂·(atz)₂·(pta)]·3H₂O}_n (<b>3D-Zn-MOF</b>). This <b>3D-Zn-MOF</b> has two different types of pores (4.5 × 4.5 Ų, 5.7 × 5.7 Ų). The crystalline <b>3D-Zn-MOF</b> could be prepared into nanomaterials (<b>3D-N-Zn-MOF</b>) with particles of approximately 100 nm by a cell fragmentation apparatus. Compared with the solid-state luminescence of Hatz and H₂pta, it was found that <b>3D-N-Zn-MOF</b> exhibited strong luminescence performance and significant red-shift phenomenon. Due to the decrease in electronegativity and rigidity of ligands, as well as the effect of ligand metal charge transfer (LMCT), the fluorescence lifetime and quantum yield of <b>3D-ZN-N-MOF</b> were 2.7241 ns and 3.02%, respectively. The maximum experimental adsorption capacity of <b>3D-N-Zn-MOF</b> could reach 125.52 mg/g, which was superior to the majority of MOF adsorbents under the optimal adsorption conditions (25 °C, pH = 7, and the adsorbent concentration is 0.2000 g/L). The thermodynamic analysis of adsorption showed that the adsorption of Cr(VI) by <b>3D-N-Zn-MOF</b> was a spontaneous (△<i>G</i> < 0) and exothermic (△<i>H</i> < 0) process. It could be found that <b>3D-N-Zn-MOF</b> was a bifunctional material with potential applications by comprehensive analysis of the fluorescence and adsorption Cr(VI) performance.