Micro/nanostructured MgO hollow spheres with selective adsorption performance and their application for fluoride monitoring in water

The search for suitable adsorbents for fluoride removal and accurate measurement are important issues in the field of water research. Adsorbents with micro/nanostructure are beneficial to highly efficient adsorption due to their high surface area and structural stability. Inspiredly, novel micro/nanostructured porous MgO hollow spheres were prepared by a hydrothermal and subsequent annealing process. The obtained product exhibited micro/nanostructured porous hollow sphere morphology with a diameter of approximately 5 μm and a BET surface area of 43.10 m²·g⁻¹. Importantly, the hollow spheres showed enhanced adsorption performance toward fluoride ions with a maximum adsorption capacity up to 175.00 mg·g⁻¹ and an adsorption rate of 17.72 mg·g⁻¹ ·min⁻¹ compared with the commercial MgO nanoparticles with such value of 149.19 mg·g⁻¹ and 3.92 mg·g⁻¹·min⁻¹, respectively. Ion-exchange coupled with electrostatic interactions was responsible for the adsorption mechanism. Such micro/nanostructured MgO is suited for use in a diffusive gradient in thin films (DGT) as a binding phase to measure trace fluoride ions in aqueous environments. Laboratory experiments verified that the performance of MgO-DGT was independent of pH and ionic strength. Furthermore, field deployments were achieved in Yihai Lake of our campus with C_DGT-YH and C_soln-YH (the active grab sampling) results of C_DGT-YH/C_soln-YH = 1.01. Therefore, MgO-DGT can accurately monitor trace fluoride concentration in water bodies. This work not only reveals a strategy for preparing micro/nanostructured MgO with enhanced adsorption performance but also provides a new micro/nanostructured MgO based DGT for fluoride monitoring in natural water bodies.