A new three-dimensional zinc-based metal-organic framework as a fluorescent sensor for detection of cadmium ion and nitrobenzene

In this study, a novel three-dimensional zinc-based metal-organic framework (Zn-MOF), i.e., {Zn₂(L)₂(DMF)₂H₂O}_n (L = 2,5-bis(phenylamino)-1,4-benzenedicarboxylic acid) was designed and developed under solvothermal condition. As a proof-of-principle, a π-conjugated framework of carboxylate ligand capable of "bottom up" synthesis was integrated with metal ion to construct a novel MOF for sensing applications. As expected, the synthesized Zn-MOF exhibited fluorescence enhancement for cadmium ion (Cd²⁺) and sensing of nitrobenzene (NB) through fluorescence quenching. The detection limits were calculated to be 0.12 μM for Cd²⁺ and 1.19 μg mL^-1 for NB based on signal-to-noise ratio of 3:1. Moreover, various techniques and density functional theory investigations verified that the possible sensing mechanisms for Cd²⁺ and NB included ion exchange and photoinduced electron transfer, respectively. Finally, their practical applications on real samples also demonstrated that the Zn-MOF-based sensor can be effectively utilized for detection and imaging of Cd²⁺ present in the real water samples and living cells. This study may inspire future research and design of target fluorescent MOFs with specific functions.