Zirconium metal organic frameworks-based DGT technique for in situ measurement of dissolved reactive phosphorus in waters

Abstract

In an effort to provide early warnings for the occurrence of eutrophication, it is highly desirable to develop an accurate and efficient technique to ensure continuous monitoring of dissolved reactive phosphorus (DRP) in the aquatic environment from the viewpoint of environmental management. Herein, a new diffusive gradient in thin film (DGT) technique was developed and evaluated for in situ measurement of DRP in waters, in which Zr-based metal organic frameworks (MOFs, UiO-66) were utilized as aqueous binding agent (abbreviated as UiO-66 DGT). As expected, the UiO-66 DGT demonstrated high uptake capacity towards phosphorus (20.8 μg P cm−2). Meanwhile, an excellent linearity between the accumulated DRP mass and deployment time over 5 d (R2 = 0.996) was obtained regardless of high or low phosphate solution. In addition, effective diffusion coefficients (D) of DRP increased exponentially with increasing ionic strengths (R2 = 0.99). Based on the rectified D, the performance of the UiO-66 DGT was independent of solution pH (6.5–8.5) and ionic strengths (ranging from 0.01 to 100 mmol L−1). Furthermore, field deployments of the UiO-66 DGT were undertaken in a natural eutrophic lake (Lake Chaohu, China). It was noteworthy that DRP could be continually accumulated by the UiO-66 DGT for more than 14 d and good agreements were obtained between the concentrations measured by DGT (CDGT) and those by ex situ chemical extraction method in solution (Csol), as reflected by CDGT/Csol of 0.9–1.1. In situ determination of DRP speciation was also carried out at different sites across Lake Chaohu. Overall, this study contributed to a better constructing of liquid binding phase DGT for the measurement of DRP in waters, facilitating the widespread application of the UiO-66 DGT as a routine monitoring technique and for large-scale environmental analysis.