Exploring electrochemical kinetic behaviors and interfacial charge transfer of pure and Ni-doped ZnFe2O4 nanoparticles-based sensing nanoplatform for ultra-sensitive detection of chloramphenicol

ZnFe₂O₄ (ZFO) nanomaterial was doped with a divalent transition metal cation of Ni²⁺ (Ni_xZn_1-xFe₂O₄, x=0, 0.2, 0.4, and 0.8) and characterized by various analytical techniques. Powder X-ray diffraction revealed the formation of a single-phase cubic spinel structure, while the stabilization of crystal structure for Ni²⁺-doped samples was observed. The average crystalline size, d-spacing, and lattice parameters increased with increasing in Ni²⁺ concentration within Ni_xZn_1-xFe₂O₄, due to differences in the ionic radius, the cation distribution at A-B sites, and the creation of surface oxygen vacancies within ZFO structure. From electrochemical measurements, Ni_xZn_1-xFe₂O₄-based electrodes showed excellent enhancements in charge transfer ability and conductivity with the highest rate constant (0.018 ms⁻¹), the lowest peak-to-peak separation (206 mV), the lowest R_ct (118 Ω), and the largest electrochemical active area (0.248 cm²), compared to that of bare SPE. Among them, Ni_0.8Zn_0.2Fe₂O₄/SPE provided outstanding electrochemical behaviors and achieved the best sensing performance with the widened concentration linear range from 0.25 to 50 μM and a rather low detection limit of 0.2 μM for chloramphenicol detection. The most important reason for this positive advance comes from the unique synergistic effects of Ni doping into the ZFO host structure. The excellent enhancements in adsorption capacity (Г) (1.4 times higher), number of oxygen vacancies, charge transfer rate constant (approximately 1.15 times higher), and catalytic rate constant (30 times greater) were recorded at Ni-doped ZFO-based electrodes, compared to pure ZFO-based electrode. Furthermore, the detailed hypotheses and possible mechanisms explaining these impressive enhancements were explored. Our work provides insight into the correlation between the Ni-doping and electrochemical characteristics, which has implications for tailoring the electrochemical performance of spinel ferrites across diverse applications and the design of novel spinel ferrite nanomaterials.