Stable metal–organic frameworks modulated by doping Tb3+ for multi-hazard detection and capture

Abstract

Considering the discharge of radioactive and non-radioactive effluents during the mining process, we report on a study that proposes to use optical sensing for the detection and monitoring of pollutants. This is realized by doping of Tb³⁺ ions in a metal–organic framework, namely UiO-66-(COOH)₂, and taking advantage of the host–guest interactions which allow analyte molecules to be pre-concentrated within the pores of the material, thus influencing the light absorption and emission profile of Tb³⁺ ions. Concentration-dependent spectroscopy analysis shows that Tb@UiO-66-(COOH)₂ has a luminescence turn-off behaviour which is more sensitive in the presence of Ni²⁺ and UO₂²⁺ ions as compared with monovalent (Ag⁺), bivalent (Co²⁺), trivalent (Fe³⁺), and tetravalent (Sn⁴⁺) cations. The relative luminescent intensity (I₀/I) as a function of the concentrations of both Ni²⁺ and UO₂²⁺ shows a linear response in a broad concentration range (10⁻⁷–10⁻³ M). The limit of detection (LOD) for Ni²⁺ is 5.7 μg L⁻¹, which is lower than the allowable concentration limit (0.02 mg L⁻¹) defined by the national environmental quality standard of surface water GB 3838. The LOD for UO₂²⁺ is 0.02 μg L⁻¹, far below the World Health Organization maximum standards for potable water (30 μg L⁻¹). Therefore, Tb@UiO-66-(COOH)₂ enables the detection of these ions with high sensitivity. Notably, the optical response measured at low concentrations of Ni²⁺ and UO₂²⁺ is not affected even in the presence of interfering metallic ions. These results demonstrate for the first time that Tb@UiO-66-(COOH)₂ is a versatile multi-hazard sensor for the detection of non-radioactive and radioactive elements. It also opens opportunities for the selective adsorption and extraction of UO₂²⁺ due to the high-stability functionality of Tb@UiO-66-(COOH)₂.