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)]center dot 4H(2)O }(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 Ln(3+) ions. 1-Ln was isostructural and exhibited a similar porous framework. Thermogravimetry analysis (TGA), powder X-ray diffraction (PXRD) and N-2 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 cm(3) 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 mu M) and CrO42-/Cr2O72- (LOD: 0.79/0.42 mu M) 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.