The azo dye model wastewater was treated by microwave assisted with Fenton catalytic wet oxidation, the kinetics of the process and the decolorization mechanism were investigated. The result showed that the reaction of decolorization of methyl orange (MO) by microwave assisted with Fenton reagent followed a pseudo-first-order model. In the treatment process, TN in the solution decreased, and NO 3- -N increased, while NO 2- -N and NH 4+ -N increased first and then decreased. At the end of the process, nitrogen existed mainly in the form of NO 3- -N. This indicated that the decreased nitrogen, after a series of reaction with hydroxyl radical (·OH), might be converted to some kind of nitrogen compounds diffusing into the air. The high performance liquid chromatography profiles of MO with different treatment time also confirmed the complete degradation of MO. The conjugated structure and the "benzene-like" structures in MO molecules and its intermediates were broken down step by step.
Electrocatalytic CO2-to-CO conversion with a high CO Faradaic efficiency (FECO) at low overpotentials and industrial-level current densities is highly desirable but a huge challenge over non-noble metal catalysts. Herein, graphitic N-rich porous carbons supporting atomically dispersed nickel (NiN4–O sites with an axial oxygen) were synthesized (denoted as O–Ni–Nx–GC) and applied as the cathode catalyst in a CO2RR flow cell. O–Ni–Nx–GC showed excellent selectivity with a FECO over 92% at low overpotentials ranging from 17 to 60 mV, and over 99% at 80 mV. The FECO was ∼100% at industrial-level current densities from 200 to 900 mA·cm–2. Impressively, O–Ni–Nx–GC delivered a state-of-the-art FECO of >96% at 1 A·cm–2 with a turnover frequency of 81.5 s–1 in a 1 M KOH electrolyte. O–Ni–Nx–GC offered excellent stability during long-term operation for 140 h at 100 mA·cm–2, maintaining a FECO > 99%. Mechanism studies revealed that the axial oxygen at the atomically dispersed nickel sites enhanced electron delocalization, with the graphitic N-rich porous carbon support lowering the CO2-to-CO energy barrier and inducing a negative shift in the Ni-3d d-band center, effectively promoting the formation of the *COOH intermediate while weakening the adsorption of the *CO intermediate, thus optimizing the catalytic activity/selectivity to CO under practical conditions.
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