ZnCo-based metal-organic frameworks (MOFs) based on ZIF-8 and ZIF-67 were synthesized at room temperature. Direct carbonization of the ZnCo-MOF under nitrogen atmosphere produced a nanoporous ZnCo/C composite which exhibited a large surface area (1111.499 m2∙g−1) and narrow pore-size distribution (1 ∼ 2 nm). A glassy carbon electrode was modified with the nanoporous ZnCo/C and Nafion for the electrochemical determination of the antibiotic metronidazole by linear sweep voltammetry. Under optimal conditions, the reduction peak current (observed at −0.66 V vs Ag/AgCl) increased linearly with increasing metronidazole concentration in the range of 0.05–100 μM, with a detection limit estimated at 17 nM. These results are attributed to the large surface area, porous structure, high nitrogen content, and synergistic effects of the Zn and Co constituents. The sensor was satisfactorily used for metronidazole analysis in pharmaceutical samples.
The hydrogenation of 4-nitrophenol (4-NP) has attracted much attention, since it is typically used as a model reaction for evaluating newly developed catalysts, but its mechanism is still debated. Herein, Co(OH)2-modified CuO catalyst (Co(OH)2/CuO) was used for the reduction of 4-NP to 4-aminophenol (4-AP) in an aqueous sodium borohydride (NaBH4) solution. The reaction mechanism was investigated by UV-Vis spectroscopy (UV-Vis), high-performance liquid chromatography (HPLC), HPLC-Q-orbitrap high-resolution mass spectrometry (LC-MS/MS), and 1HNMR spectroscopy (1HNMR) as an integrated technology at different concentrations of NaBH4. Samples were taken at specified time intervals and monitored using UV-Vis, HPLC, LC-MS/MS, and 1HNMR. With the help of comprehensive analysis, eight intermediates, including azo and azoxy compounds, were effectively captured, and the variation tendency of each intermediate was determined, revealing that the hydrogenation of 4-NP proceeds via a coexistence of the direct and condensation routes. The integrated analysis methods were powerful technical supports for the study of the catalysis mechanism.
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