Efficient detection of Fe(III) and chromate ions in water using two robust lanthanide metal-organic frameworks

Developing high-performance fluorescent materials to detect toxic contaminants in water is of great importance due to heavy metal pollution which has aroused wide public concern. Herein, two robust lanthanide metal-organic frameworks {[Ln(L)(H2O)]center dot 7H(2)O)(n) (1-Ln; Ln = Eu and Tb. H3L = 5-(3',5'-dicarboxylphenyl)picolinic acid) were successfully constructed and structurally characterized. 1-Eu and 1-Tb are isomorphic and feature a three-dimensional highly porous pillared-layer framework. Notably, both 1-Eu and 1-Tb demonstrate good luminescence performance, and excellent water, thermal and chemical stability. Then, 1-Eu and 1-Tb were further utilized as multi-responsive fluorescent sensors for detection of Fe(III) and chromate ions in water with high sensitivity, fast response, high selectivity and excellent recycling usability. The detection limits toward Fe3+/CrO42-/Cr2O72- are calculated to be 0.67/0.53/0.32 mu M for 1-Eu and 126/0.75/0.57 mu M for 1-Tb, respectively, which are far below the maximum standard defined by the United States Environmental Protection Agency (EPA) for drinking water. Furthermore, the quenching mechanisms can be explained as the synergetic effect of the competitive absorption and energy-transfer between 1-Eu/1-Tb host and analyte ions.