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

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 (3D-Zn-MOF). This 3D-Zn-MOF has two different types of pores (4.5
× 4.5 Å2, 5.7 × 5.7 Å2).
The crystalline 3D-Zn-MOF could be prepared into nanomaterials
(3D-N-Zn-MOF) 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 3D-N-Zn-MOF 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 3D-ZN-N-MOF were 2.7241 ns and 3.02%, respectively. The maximum experimental
adsorption capacity of 3D-N-Zn-MOF 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 3D-N-Zn-MOF was
a spontaneous (△G < 0) and exothermic (△H < 0) process. It could be found that 3D-N-Zn-MOF was a bifunctional material with potential applications by comprehensive
analysis of the fluorescence and adsorption Cr(VI) performance.