Fergusonite-type rare earth niobates ANbO4 (A = Nd, Sm, and Eu) as electrode modifiers: deep insights into A site variations towards bifunctional electrochemical sensing applications

Abstract

Lanthanide orthoniobates, LnNbO₄ (Ln = Nd, Sm, and Eu), are a domineering class of binary metal oxides with significant catalytic behavior and effective charge transfer ability, acting as eminent candidates to be explored as electrode materials. However, niobates have limitations to be used in sensing platforms due to the complicated synthetic procedures, which have been addressed in this study by proposing a facile hydrothermal tactic based on in situ homoleptic complex formation. All three niobates are isostructural with the monoclinic form of fergusonite structure, which was confirmed by XRD studies. The impact of the A site variation in the fergusonite crystal was verified by FTIR spectroscopy analysis, and the elemental composition was determined by XPS studies. FESEM with EDX spectroscopy obviously proved the morphological differences. Furthermore, a LnNbO₄-modified GCE was employed to detect pharmaceutical pollutants, namely, furazolidone (FZD) and dimetridazole (DMZ). Cyclic voltammetry studies were used to optimize the parameters of the sensing platform, and differential pulse voltammetry was performed to obtain the detection limits and linear range. SmNbO₄/GCE exhibited superior performance to other electrodes with a wide linear range of 0.01 μM to 264 μM and LOD values of 4 nM and 2 nM for FZD and DMZ, respectively. Finally, the feasibility of the proposed electrode in real-time analysis was studied by extending the voltammetry experiment to saliva and water samples.