Toward a comprehensive understanding of effect of cation distribution and M2+ constituent in spinel ferrite nanocrystals MFe2O4 (M = Co, Mn, and Ni) on the electrochemical response in sensitive detection of chloramphenicol

This paper focuses on investigating the effect of the (M2+) cation constituent and the inverse degree within the lattice structure of MFe2O4 (M = Co, Mn, and Ni) nanocrystals on their electrochemical characteristics and sensing performance under the same experimental condition. Using Rietveld refinement of powder X-ray diffraction (XRD), Raman, and scanning electron microscopy (SEM), physical characterizations of CoFe2O4 (CFO), MnFe2O4 (MFO), and NiFe2O4 (NFO) are observed and analyzed. In particular, a detailed study on current response and kinetic parameters for the electron transfer reactions in the presence of K3/K4 probes and chloramphenicol (CAP) analyte is carried out, respectively, highlighting the positive influence of the electrode modification and comparing the electrochemical characteristics and sensing performance. The ordering of their electrochemical performance is listed as follows: CFO/SPE> NFO/SPE> MFO/SPE. The reason for their electrochemical performance difference is discussed in detail. Namely, the CFO sample possessing high crystallization and phase purity, uniform primary particle size, and especially wholly inversed spinel structure possessing multiple valence states (Co2+ and Co3+) on the octahedral sites offered many unique features, which are beneficial for electrical conductivity, charge transferability, surface area, and electrocatalytic active sites. Despite also being the inversed spinel structure, the NFO with the existence of impurity phases and larger grain size, as well as a lower degree of inversion than the CFO sample showed a lower enhancement in electrochemical response. However, its electrochemical signal response still is higher than that of the normal spinel MFO structure, further confirming the critical role of (M2+) cation constituent and the inverse degree to the electrochemical characteristics and sensing performance.