Efficient Capture and Effective Sensing of Cr₂O₇^2- from Water Using a Zirconium Metal-Organic Framework

Highly efficient decontamination of heavily toxic Cr₂O₇^2- from water remains a serious task for public health and ecosystem protection. An easily regenerative and reused sorbent with suitable porosity may address this task. Herein, a series of water-stable and ecofriendly metal-organic frameworks (MOFs) with large surface areas were assessed for their ability to adsorb and separate Cr₂O₇^2- from aqueous solutions. Among these tested MOFs, NU-1000 shows an extraordinary capability to efficiently capture (within 3 min) Cr₂O₇^2- with a sorption capacity of up to 76.8 mg/g, which is the largest one for the neutral MOF-based Cr₂O₇^2- sorbents. NU-1000 also shows remarkable selectivity for Cr₂O₇^2- capture and can effectively reduce the Cr(VI) concentration from 24 ppm to 60 ppb, which is below the acceptable limit for the drinking water standard (100 ppb by the U.S. Environmental Protection Agency). Moreover, this adsorbent can be easily regenerated by Soxhlet extraction with an acidic methanol solution (2.5 M HCl) and can be reused at least three times without a significant loss of it adsorption ability. More intriguingly, NU-1000 can also serve as an efficient photoluminescent probe for the selective detection of Cr₂O₇^2- in aqueous media. The Cr₂O₇^2- detection limit is as low as 1.8 μM, and the linear range is from 1.8 to 340 μM. Our work shows that NU-1000 is a unique material combining both efficient sorption and exceptional fluorescent sensing of Cr₂O₇^2- in aqueous media.