BACKGROUND
4‐Nitrophenol, as a representative hazardous contaminant, may pose potential risks to the environment in the process of production, storage, and use. Catalytic hydrogenation reduction offers a promising route to the removal of 4‐nitrophenol by its transformation into the less toxic and biodegradable 4‐aminophenol. In this work, nickel−cobalt bimetal oxide nanostructures were fabricated by the thermal decomposition of metal organic frameworks and cooperatively utilized for the catalytic reduction of 4‐nitrophenol.
RESULTS
The as‐fabricated oxide catalysts were characterized and analyzed with several physicochemical measurements, including X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, thermogravimetry, Fourier‐transform infrared spectroscopy, Raman spectroscopy, nitrogen adsorption, and electrochemical impedance spectroscopy. The catalytic reduction of 4‐nitrophenol was conducted in the presence of the as‐prepared oxide nanostructures with varying Ni/Co ratios to evaluate their catalytic activity. The optimal catalyst (Ni–Co–O) delivered the activity parameter of k’app = 12.0 min−1 mg−1, which was higher than either NiO (2.4 min−1 mg−1) or Co3O4 (3.6 min−1 mg−1). Moreover, the induction time of the 4‐nitrophenol reduction was significantly reduced by using the bimetal oxide catalyst. Based on the surface and electrochemistry analyses, the enhancement of catalytic activity for the Ni–Co bimetal oxide nanostructures was discussed.
CONCLUSION
The above results indicated that the cooperation of nickel with cobalt into bimetal oxide nanostructures exhibited an enhanced catalytic activity, which not only promoted the conversion rate of 4‐nitrophenol, but also shortened the reduction induction period.
BACKGROUND: Advanced oxidation processes based on sulfate radical have been widely employed for oxidation degradation of organic contaminants. Catalytic activation of peroxymonopersulfate (PMS) with transition metal oxides holds great promise for the generation of sulfate radical. In this work, laponite-decorated CoFe 2 O 4 porous nanostructures have been prepared through the thermal decomposition of laponite/oxalates, and evaluated as a magnetic catalyst to activate PMS for the oxidation of rhodamine B (RhB).RESULTS: The decoration of porous CoFe 2 O 4 microparticles with laponite was evidenced because of the presence of the vibration mode of Si O (at 1359 cm −1 ) in Fourier transform infrared spectra and the uniform distribution of Si and Mg elements from elemental mapping images. Decorating with laponite also resulted in an increase in amount of surface hydroxyl oxygen species, which facilitated the formation of Co OH complex for PMS activation. Furthermore, the enhanced activation of PMS with laponite-decorated CoFe 2 O 4 resulted in a faster removal (98.04%) of RhB as compared to undecorated CoFe 2 O 4 (79.62%) within 56 min. Meanwhile, the rate constant increased from 0.0288 (CoFe 2 O 4 ) to 0.0679 min −1 (laponite-decorated CoFe 2 O 4 ). The degradation rate of RhB progressively increased with reaction temperature and catalyst dosage. Scavenging and electron paramagnetic resonance tests manifested that the sulfate and superoxide radicals served as the major active species for the oxidation of RhB molecules.
CONCLUSION:The above results demonstrated positive effects of laponite on the textural property, surface chemical states and catalytic activity of porous CoFe 2 O 4 microparticles. This study provides an insight into the promising role of laponite as an additive in improving PMS activation.
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