Eu(iii)-doped downconverting nanophosphors (GdVO4:Eu3+) for selective and sensitive detection of arsenic(iii) in water

Abstract

Heavy metal ions pose a major threat to both organisms and the environment. Among various heavy metals, arsenic (As³⁺) or arsenite is one of the most toxic ions present in groundwater. Long-term exposure to arsenic-contaminated water triggers a number of health hazards including lung cancer and harms the liver and kidneys. Therefore, detection of this heavy metal in water samples is of paramount importance. Herein, we have synthesized citrate-stabilised GdVO₄:Eu³⁺ downconverting nanophosphors (DCNPs) with a facile hydrothermal process and studied them as an efficient photoluminescence probe for highly selective and sensitive detection of As³⁺ ions in water. The energy transfer from the vanadate group (VO₄³⁻) to the lanthanide dopant (Eu³⁺) causes these nanophosphors to exhibit sharp, strong and steady luminescence emission upon excitation in the UV-visible range. Since As³⁺ is predominantly detected in the form of HAsO₃²⁻ in aqueous environment under neutral to slightly basic conditions, during the detection process it selectively binds covalently to the Eu–OH groups present on the DCNP surface, resulting in the quenching of sharp DCNP emission. Other metal ions were found to have a much lesser quenching effect due to their non-selectivity. The limit of detection (LOD) was found to be as low as 0.039 μM (39 nM), which is much lower than the WHO-allowed contamination levels of As³⁺ in drinking water (0.13 μM). This nanosensor can efficiently detect As³⁺ in a wide range of pH. Further, as interfering ions do not influence the detection process, this is a promising approach for the selective and sensitive detection of As³⁺ ions in complex aqueous specimens.