Water-Stable Metal–Organic Frameworks for Fast and High Dichromate Trapping via Single-Crystal-to-Single-Crystal Ion Exchange

Two metal–organic frameworks [Zn2(Tipa)2(OH)]·3NO3·12H2O (FIR-53, FIR denotes Fujian Institute of Research, Tipa = tris(4-(1H-imidazol-1-yl)phenyl)amine)) and [Zn(Tipa)]·2NO3·DMF·4H2O) (FIR-54) with large nanotubular channels were synthesized via Zn(II) ions coordinate the neutral Tipa ligand. The framework of FIR-53 contains 1D channels along the c axis with a cross section of 18 × 13 Å2. FIR-54 also consists of large channels with the 10.5 × 10.5 Å2 open windows. These porous materials efficiently trap Cr2O72– inorganic pollutant ions via the single-crystal-to-single-crystal (SC-SC) approach. The Cr2O72– uptake capacities of FIR-53 and FIR-54 are high to 74.2 and 103 mg/g, respectively. Furthermore, the Cr2O72– trapping–releasing process of FIR-53 displays good regeneration. Meaningfully, the structure of FIR-53 after ion exchange can be accurately obtained by single-crystal X-ray diffraction, which further elaborates the SC-SC transformation.