Ho(III)-Based Metal–Organic Framework for Water Pollution Treatment: Insights into Sensitive Phosphate Removal and Sensing in Aqueous Solution

Abstract

The existence of phosphate in aquatic ecosystems generates eutrophication. As a novel alternative to tackling this problem, this study reported a Ho(III)-based metal−organic framework (MOF) for removing and detecting phosphate molecules. Ho-bpdc MOF shows an outstanding maximum adsorption capacity of 311.9 mg g −1 , with high pH (4−10) stability. PSO and Freundlich's models reveal that the chemical interaction between the phosphate molecules and Ho-bpdc plays the main role during the removal process. The combination of FTIR and XPS characterizations confirmed the possible interaction mechanism involving a ligand-exchanged process. Thus, the formation of Ho−O−P sites was determined due to the relatively strong base character for the phosphate ion. Moreover, Ho-bpdc exhibited outstanding fluorescence properties for the sensing of phosphate molecules. The fluorescence experiments showed a LOD of 2.57 ppm, based on the solidstate emission spectra of Ho-bpdc at different phosphate concentrations (5−100 ppm). Ho-bpdc exhibited a characteristic turn-on effect after the phosphate interaction due to the increments of the electronic π* → π transition of ligands. This work demonstrated the remarkable properties of Ho-bpdc in the adsorption and sensing of phosphate.