Abstract
The effective detection of chromate anion in aqueous solution ishighly desirable due to its high solubility, environmental mobility,carcinogenicity, and bioaccumulation effect. New strategy for precise detectionof chromate anion in the presence of large excess of other anions such as Cl‒, NO3‒, HCO3‒ indrinking water and natural water systems remains highly desirable. Herein, ahydrolytically stable cationic luminescent europium(III) based metal organicframework (MOF) 1 is successfully synthesized and investigated as a luminescentsensor which exhibits instant and selective luminescence quenching propertytoward chromate ions in aqueous solutions. Moreover, 1 can be introduced intohigh ionic strength water system (e.g. seawater) for chromate detection as aconsequence of the excellent sensing selectivity. The real environmentalapplication of 1 as the chromate probe is studied in deionized water, lakewater, and seawater, respectively, The detection limits in these aqueous mediaare calculated to be 0.556 ppb, 2.88 ppb, and 1.75 ppb, respectively. All thesevalues are far below the maximum contamination standard of CrVI indrinking water of 100 ppb defined by United States Environmental ProtectionAgency (EPA). This excellent chromate sensing capability originates from thefast enrichment of chromate ions in solids of 1 from solutions followed by anefficient energy transfer from the MOF skeleton to the chromate anion, as demonstrated by the solution absorption spectroscopy, X-ray diffraction, and chromate uptake kinetics and isotherm investigations. To the best of our knowledge, 1 possesses the lowest chromate detection limit among all reported MOFs up to date and is the only MOF material reported for chromate sensing application under environmentally relevant conditions with high ionic strengths.
