Robust lanthanide metal–organic frameworks with “all-in-one” multifunction: efficient gas adsorption and separation, tunable light emission and luminescence sensing

Combining the porous structure and fluorescence properties of metal–organic frameworks (MOFs) with rational design to realize multifunction application is of great significance from an energy and environmental standpoint. Herein, a new series of lanthanide metal–organic frameworks (Ln–MOFs), {[Ln(L)(H2O)]·4H2O }n (1-Ln, where Ln = Eu, Tb, Gd, and EuxTb1−x), were constructed by using a rigid 5-(2′,5′-dicarboxylphenyl) picolinic acid ligand and Ln3+ ions. 1-Ln was isostructural and exhibited a similar porous framework. Thermogravimetry analysis (TGA), powder X-ray diffraction (PXRD) and N2 adsorption measurements revealed that 1-Eu exhibits excellent thermal, water and chemical stabilities. As expected, 1-Eu-a (activated 1-Eu) shows a high adsorption capacity for C2H2 (109.2 cm3 g−1) as well as excellent selective separation with ideal adsorbed solution theory (IAST) selectivity for C2H2/CO2 (4.1–3.3), C2H2/CH4 (23–17) and CO2/CH4 (5.6–5.4) at room temperature. More importantly, density functional theory (DFT) calculations and breakthrough experiments were carried out, which highlight its great potential to address challenging industrially important separation. Moreover, a series of bimetallic MOFs 1-EuxTb1−x were constructed by changing the ratio of Eu3+ and Tb3+ and showed excellent linear color tunability (from green to red), indicating that they are suitable for barcode applications. Furthermore, luminescence studies revealed that 1-Eu is an excellent fluorescent probe for sensing Fe3+ (LOD: 0.57 μM) and CrO42−/Cr2O72− (LOD: 0.79/0.42 μM) ions in water, with a fast response, high sensitivity, selectivity and recyclability. To the best of our knowledge, 1-Eu is the first reported Ln–MOF material with all-in-one multifunction, including excellent gas adsorption and separation, tunable light emission and efficient luminescence sensing.