Water-stable multifunctional Zn(II)-organic framework for highly selective detection of Fe3 + ions and NFT/NFZ antibiotics, and effectively catalyzing CO2 into cyclic carbonates

Metal-organic framework (MOF) materials have many fascinating applications such as fluorescence sensing and catalyzing CO₂ cycloaddition reaction. In the work, a new MOF [Zn₂(L)(DMA)₂] (Zn-MOF-1) was successfully constructed through the self-assembly of Zn²⁺ ions and organic ligand 4,4′-di(3,5-dicarboylphenoxy)biphenyl (H₄L) under solvothermal conditions. Zn-MOF-1 displayed a three-dimensional framework in which the tetranuclear [Zn₄((COO)₈] clusters were cross-linked by L^4- ligands, forming (4,4,8)-connected nets with the point symbol of (4⁴·6²)(4⁴·6²)(4¹³·6¹¹·8⁴). Interestingly, Zn-MOF-1 was confirmed to possess high thermal stability and outstanding chemical stability in pH = 2–12 aqueous phase as well as in organic solvents. What’s more, Zn-MOF-1 also exhibited excellent fluorescence emissions and could be used to detect Fe³⁺ ions and nitrofuran antibiotics (nitrofurantoin (NFT) and nitrofurazone (NFZ)) in aqueous solutions via quenching fluorescence effects. Moreover, the fluorescence quenching effects demonstrated high selectivity, short response time and good recyclability. Meanwhile, the fabricated Zn-MOF-1/PVDF (poly(vinylidene fluoride)) film demonstrates a rapid visual fluorescence response to Fe³⁺, NFT and NFZ in water. In addition, the activated Zn-MOF-1 (Zn-MOF-1a) possessed abundant exposed Zn²⁺ sites as Lewis acid, which could promote the fixation of CO₂ with various epoxides to form cyclic carbonates under solvent-free and mild conditions (1 atm of CO₂, 12 h, 60 °C). Besides, Zn-MOF-1a also exhibited excellent recyclability for at least five cycles without an appreciable loss in catalytic efficiency. The possible mechanisms of fluorescence quenching and the conversion of CO₂ to cyclic carbonates were discussed in detail. The experimental results suggested that Zn-MOF-1 could be utilized as a multifunctional material for fluorescence sensing and CO₂ conversion in the field of environmental protection.