Preparation of magnetized coal-based CoFe@Coal-C nano-composites: Efficient Fenton-like degradation of quinoline

Abstract

To maximize the utilization of coal resources and efficiently remove quinoline from coal chemical wastewater, a CoFe@Coal-C composite material is prepared using lignite as raw material, which is applied as the heterogeneous Fenton-like catalyst for quinoline degradation. First, lignite is treated by acid washing and polyvinylpyrrolidone modification, and then loaded with Prussian blue analogs (CoFe-PBA), and subsequently calcined at high temperature to finally obtain the product CoFe@Coal-C. The results show that the CoFe@Coal-C has an appropriate specific surface area and pore structure, which provides some transmission channels for active species and is conducive to charge transfer. At the same time, the CoFe@Coal-C also exhibits typical superparamagnetic properties, which is bene-ficial to its separation from aqueous solutions. The effects of different reaction systems, catalyst dosage, initial quino-line concentration, solution pH value, and coexisting substances in water on quinoline degradation efficiency are inves-tigated. In the presence of only H2O2 and only the catalyst, the removal rate of quinoline is almost negligible. Therefore, it can be considered that reactive oxygen species are the main factor leading to the decrease in quinoline concentration, and the catalyst is a necessary condition for catalyzing H2O2 to produce reactive oxygen species. Under the optimal experimental conditions (initial quinoline concentration is 10.0 mg/L, catalyst dosage is 0.6 g/L, pH = 7), the degradation efficiency of quinoline catalyzed by CoFe@Coal-C/H2O2 reaches up to 99.2% within 30 minutes. In addi-tion, compared with pure CoFe alloy and pure Coal-C, the degradation rate constant of quinoline over CoFe@Coal-C increases by 1 and 3 orders of magnitude respectively, indicating that the synergistic effect of CoFe alloy and Coal-C is the culprit for the improved catalyst activity. Coexisting anions (such as Cl−, \begin{document}${\mathrm{HCO}}_3^{-} $\end{document}, \begin{document}${\mathrm{SO}}_4^{2-} $\end{document}, \begin{document}${\mathrm{H}}_2{\mathrm{PO}}_4^{-} $\end{document}, etc.) and the initial pH value have little effect on the performance of CoFe@Coal-C/H2O2 for quinoline degradation. Free radical quenching experiments and electron paramagnetic resonance spectroscopy show that ·OH is the main reactive oxygen species. The intermediate products of quinoline degradation are detected by high-performance liquid chromatography-mass spectrometry (HPLC-MS), and the possible degradation pathways are speculated. This study shows that the magnetic CoFe@Coal-C composite is an efficient catalyst for the removal of quinoline pollution in the coal wastewater. In addition, the present work provides a reference for the rational design of a high-performance het-erogeneous Fenton-like catalyst that can be used in various complex water environments.

Keywords

• lignite
• quinoline
• fenton-like reaction
• degradation
• magnetic materials