Effect of Cr Substitution in ZnFe2O4 Nanoparticles on the Electron Transfer at Electrochemical Interfaces

In this study, we explored the effect of Cr3+ substitution by partially and fully replacing Fe3+ in the normal spinel ZnFe2O4 crystal structure at electrochemical interfaces. The resulting ZnCrxFe2-xO4 nanomaterials exhibited an average particle size between 20 and 50 nm with a spherical morphology. The materials also demonstrated energy band gaps ranging from 2.1 to 3.1 eV X-ray diffraction (XRD) analysis confirmed that all the synthesized materials maintained a normal spinel structure, attributed to the octahedral site preference energy (OSPE) of Zn2+, Fe3+, and Cr3+ ions. Electrochemical performance assessments revealed that the ZnFe2O4-based sensor achieved a sensitivity of (37.8 f 0.2) mu A/mM with a kinetic rate constant of (13.1 f 2.8) ms-1, while the ZnCr2O4-based sensor exhibited a sensitivity of (32.4 f 0.5) mu A/mM and a kinetic rate constant of (3.73 f 0.55) ms-1 in the detection of paracetamol, whereas ZnCrFeO4 sensor has produced the second-best sensitivity (35.7 f 0.1 mu A/mM) and the rate constant (4.53 f 0.54 ms-1) with the lowest limit of detection (1.94 f 0.01 mu M). These differences in electrochemical performance were correlated with the variations in the energy band gaps caused by the restructuring of the normal spinel structure. Our findings indicate that the ZnFe2O4 sensor has a higher potential for direct electron transfer, whereas the other sensors are more likely to facilitate surface-mediated electron transfer.