Green auto-combustion derived V-type hexagonal ferrite nanoparticles: local atomic structure by XAFS and dual...

The use of caffeine in food and beverage products, along with its reported harmful effects at high levels, has made its accurate and reliable detection a regulatory requirement. In contrast, conventional electrochemical sensors are generally not very sensitive, selective or stable, especially for caffeine quantification in complex real-world matrices, which inspires the development of new electrode materials. To overcome this, here, we report the glassy carbon electrode (GCE) modified with V-type hexagonal ferrite nanoparticles (SrSnFe₈O₁₅-NPs), prepared by a sol-gel-based green auto-combustion route for the development of a high-performance platform for the sensing of caffeine. The as-synthesized nanoparticles were characterized extensively; the single-phase crystalline structure was confirmed by X-ray diffraction (XRD) analysis, and the local atomic coordination environment was confirmed by X-ray absorption fine structure (XAFS) analysis with an average crystallite size larger than 30 nm. The surface morphology and particle size were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively, and Brunauer-Emmett-Teller (BET) analysis confirmed that the high surface area of 209.6 m² g^-1 is another characteristic structural feature that is responsible for the improved electrochemical performance of the electrode. The nanoparticles were found to exhibit soft magnetic properties during vibrating sample magnetometry. Furthermore, the synthesized V-type hexagonal ferrites were employed to modify a glassy carbon electrode (GCE), developing SrSnFe₈O₁₅-NPs/GCE for the electrochemical sensing of caffeine. Cyclic voltammetry studies revealed conductive and diffusion-controlled behavior, with the SrSnFe₈O₁₅-NPs/GCE demonstrating high sensitivity and selectivity for caffeine detection (linear ranges: 0.5 to 80 µM; detection limits: 0.025 µM, while the LOQ was 0.078 µM. The sensor was successfully tested in real commercial soft drink samples, demonstrating its potential as a reliable and sensitive sensor for the monitoring of beverage safety in the real world.