Alginate-based hydrogel beads for ultrasensitive detection and effective adsorption of terbium and europium in water

Abstract

Developing sustainable difunctional materials that allow for selective visual detection and efficient removal of rare earth elements ions (REE³⁺) is crucial for fostering an eco-friendly economy and protecting the environment. However, achieving both dual functionalities represents a significant challenge. In this work, we fabricated a unique hydrogel bead (DPA/GB) characterized by a high density of carboxyl groups and pyridine nitrogen atoms, through the hybridization of dipicolinic acid (DPA) and sodium alginate (SA) with calcium as a cross-linker. Notably, the cost of DPA/GB is only USD 0.25 per gram. The resulting bead exhibited fluorescence turn-on capability and on-site detection for terbium (Tb³⁺) and europium (Eu³⁺), with exceptional anti-interference ability. Furthermore, their limits of detection (LOD) were determined to be 0.23 and 0.85 nM over a wide concentration range of 0.2–1000/6–600 μM for Tb³⁺/Eu³⁺. DPA/GB demonstrated a higher adsorption capacity for Tb³⁺ (270 mg/g) and Eu³⁺ (301 mg/g) at pH = 5.02. Infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and energy-dispersive spectroscopic analysis were performed to gain insight into the underlying mechanisms. These studies confirmed the synergistic effects of complexation, electrostatic interaction, and ion exchange between Tb³⁺/Eu³⁺ and DPA/GB. This work presents an innovative and viable approach for the luminescence detection and efficient adsorption of Tb³⁺/Eu³⁺ in water.

Hypothesis statement

Alginate-based sustainable materials modified by the non-covalent assembly strategy facilitate the visual detection and efficient adsorption of terbium and europium ions simultaneously, aiming to advance the development of polysaccharide-based multifunctional adsorbent materials.