Activation of Self-Assembled CaWO ₄ Nanocrystals via Mn-Incorporation toward Nonenzymatic Electrocatalytic Glucose Oxidation

Integrating foreign metal ions into mixed metal oxide scaffolds, such as CaWO 4, by a wet chemistry coprecipitation method is an efficient approach for regulating the chemical composition, which determines the structure and properties and, in turn, offers a versatile platform for enhancements of intrinsic properties and introduction of additional attributes in the host material. In this work, a series of Ca 1– x Mn x WO 4 was prepared via a coprecipitation process at 30 °C to exhibit sphere-like hierarchical structures assembled from individual nanocrystals. The solid solubility limit of Mn in CaWO 4 is estimated to be ∼24% for this synthetic approach. The nanocrystals exhibit nonstoichiometric amorphous layers on the surface, which are expected for this type of materials synthesized under such mild conditions. The successful incorporation of Mn into the crystal lattice of CaWO 4 led to an isotropic contraction of the crystal unit cells as well as the shifting and merging of several vibrational modes. Cyclic voltammetry confirmed the activity of Ca 1– x Mn x WO 4 for the electrooxidation of glucose, which is directly linked to the presence of Mn in CaWO 4 . With the highest Mn content, Ca 0.759 Mn 0.241 WO 4 achieved sensitivities of 3.80 and 1.00 μA·mM –1 ·cm –2 for glucose concentrations in the ranges of 0.002–0.2 and 0.2–1 mM, respectively, which are 237 and 60 times increases from that of CaWO 4 . The limit of detection and lower limit of quantitation were estimated to be 14 and 48 μM, respectively, with reasonable reproducibility and repeatability.