Two novel and high-efficiency optical chemosensors of detecting Fe3+ and CrO42− based on Metal−organic frameworks of Cd(Ⅱ)

Metal−organic frameworks (MOFs)-based sensors for sensing and monitoring toxic chemicals in water have profound significance to the ecological environment and human health. Hence, under hydrothermal conditions, two novel 3D Cd-MOFs, {[Cd3(NTB)2(bibp)4]•6H2O}n (Ⅰ) and [Cd(HNTB)(bibp)]n (Ⅱ) were synthesized, where H3NTB ​= ​4,4′,4″-nitrilotrisbenzoic acid and bibp ​= ​4,4′-bis(imidazolyl)biphenyl. The title Cd-MOFs were characterized via IR spectra, elemental analysis, thermogravimetric analyses (TGA), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Brunauer−Emmett−Teller (BET). Furthermore, both Ⅰ and Ⅱ present ligand-based blue emission in the solid state and can act as sensors for recognition of Fe3+ and CrO42− in water through fluorescence quenching with good selectivity, sensitivity and chemical stability. Notably, Cd-MOFs exhibit high quenching constants and low detection limits, which are higher or comparable to those chemical sensors reported. Subsequently, the possible sensing mechanisms were disclosed carefully by PXRD, ICP-AES, UV spectroscopy and XPS.