For the first time, the influences of phase purity and crystallinity on the electrochemical and electrocatalytic properties of CuCo2O4 (CCO) and CuFe2O4 (CFO)-based electrochemical sensors for the detection of chloramphenicol (CAP) are reported. A series of CCO and CFO nanoparticles were prepared by a modified coprecipitation method and then annealed at different temperatures under air (400 °C, 600 °C, 800 °C, and 1000 °C). Surface morphology, the evolution of the crystallite size, and crystalline phase transition, as well as phase purity of CCO and CFO at each annealing temperature, were characterized via different techniques. Their electrochemical properties were analyzed using cyclic voltammetry and differential pulse voltammetry measurements conducted with a PalmSens3 workstation. Results obtained show that the phase purity and crystallinity have decisive effects on their electrocatalytic activity, conductivity, and adsorption efficiency. Under an optimized condition (more namely, annealed 600 °C), both CCO and CFO samples offer high phase purity with low percent of CuO side phase (below 38%), small enough size with a large number of defects and available active sites; particularly, the cubic CFO nanoparticles are present due to its tetragonal phase transition. The modified electrodes with CCO-600 and CFO-600 exhibit a better voltammetric response, a higher synergistic electrocatalytic activity, and a greater electrochemical performance of comparing to other modified electrodes. They respond linearly to chloramphenicol (CAP) in the range from 2.5 to 50 μM. Furthermore, they display am excellent long-term stability, reproducibility, and good selectivity, as well as their capacity of detecting CAP in the real milk sample.
In this study, silver nanoparticles (AgNPs) were functionalized by various molecules, including sodium borohydride (NaBH4), polyhexamethylene biguanide hydrochloride (PHMB), and Tween 80 to investigate the long-term stabilization of AgNPs in an aqueous dispersion. PHMB-functionalized silver nanoparticles (AgNPs/PHMB) exhibited better stability than others and could be stored at ambient temperature for at least 180 days. In addition to creating stabilization based on the electrostatic repulsion, the use of PHMB helped to increase the degree of stability of the colloidal AgNPs for a long time owing to strong interactions between Ag atoms on AgNPs with nitrogen (N) positions in PHMB molecules. The formed bond led to improving maintenance ability of the electrostatic repulsion layer among independent nanoparticles. The applicability of the as-prepared AgNPs/PHMB was also examined for Mn2+ detection via a colorimetric approach. The calibration curve was found to be linear over the range of 0–100 mM with a correlation coefficient of 0.97. The amine groups of PHMB brought out a cooperative effect to form of ion-templated chelation with Mn2+, which caused the aggregation of AgNPs/PHMB. This suggested that the AgNPs/PHMB could be used as a potential probe in the detection of Mn2+ ions. More importantly, the long-term stability of AgNPs/PHMB paved a great promising path to provide many further solutions for the producer in practical applications.
MoS 2 -GO composites were fabricated by an ultrasonication method at room temperature. Raman spectra, emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM) images were used to study the structural characteristics, morphologies, and sizes of the synthesized materials. An MoS 2 -GO/SPE (screen-printed electrode) was prepared by a facile dropping method and acted as an effective electrochemical sensor toward clenbuterol (CLB) and 4-nitrophenol (4-NP) detection. Based on the obtained results, the influence of analyte molecular structure on the adsorption ability and electronic interoperability between the targeted analyte and electrode surface were investigated in detail and discussed as well, through some electrochemical kinetic parameters (electron/proton-transfer number, electron transfer rate constant (k s ), charge transfer coefficient, and adsorption capacity (Γ)). In particular, it should be stressed that 4-NP molecules possess a simple molecular structure with many positive effects (electronic, conjugation, and small steric effects) and flexible functional groups, resulting in fast electron transport/charge diffusion and effective adsorption process as well as strong interactions with the electrode surface. Therefore, 4-NP molecules have been facilitated better in electrochemical reactions at the electrode surface and electrode−electrolyte interfaces, leading to improved current response and electrochemical sensing performance, compared with those of CLB.
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