Gaofeng Zhou,Runyu Zhou,Yiqing Liu,Li Zhang,Linyue Zhang,Yongsheng Fu
A novel heterogeneous peracetic acid (PAA)-based advanced oxidation process (AOP), viz. zero-valent cobalt activated PAA (ZVCo/PAA), was developed to remove sulfamethoxazole (SMX) in this study. About 99% SMX could be removed by ZVCo/PAA under neutral condition in 5 min. According to the characterization results of ZVCo before and after reaction by scanning electron microscopy (SEM), ZVCo was corroded to provide Co 2+ which was primarily responsible for the activation of PAA. The X-ray photoelectron spectroscopy (XPS) analysis of fresh and used ZVCo suggested that heterogeneous catalysis also occurred on the surface of ZVCo. Radical scavenging experiments indicated that organic radicals (i.e., CH 3 C(O)O • and CH 3 C(O)OO • ) were the dominant reactive species for SMX degradation in ZVCo/PAA system. SMX could be degraded well in a wide pH range especially at near-neutral pH. Increasing PAA or ZVCo dosage could enhance SMX removal, while excess ZVCo inhibited its degradation. The addition of SO 4 2− , NO 3 − or Cl − had a negligible effect on SMX degradation, while an obvious inhibition was observed in the presence of HCO 3 − or natural organic matter (NOM). ZVCo still presented an excellent activation ability for PAA to degrade SMX after 4 cycles, indicating its good stability and reusability. The probable reaction sites in SMX molecular structure were predicted by density functional theory (DFT) calculation and wave function analysis. Combining the results of DFT calculation and five identified transformation products , four possible degradation pathways of SMX in ZVCo/PAA system were proposed, including nitration , cleavage of S-N bond, coupling reaction and hydroxylation.
A novel heterogeneous Co-containing Fenton-like catalyst consisting of mesoporous reduction state cobalt (RSCo)-doped silica (SiO 2 ) nanospheres ( mp -RSCo-SiO 2 NSs) was prepared by an enhanced hydrothermal process. The catalyst exhibited very high activity and stability for a series of refractory pollutant degradation in a very wide pH range of 3.1–10.9. The Fenton-like reaction rate constant of this Co-containing catalyst was approximately 290 times higher than that of Co 3 O 4 for pollutant degradation under the neutral and mild conditions. Based on the characterization, the catalyst possessed a porous nanosphere morphology, and the reduction state cobalt species, including nano-zero-valent cobalt (nZVCo) and Co 2+ , were found to be generated in the SiO 2 framework through forming Co O Si bonds. During the Fenton-like reaction, the electron donation effect of organic pollutants was successfully realized through the interaction of “Pollutants → Co 2+/0 -SiO 2 ”. The obtained electrons from pollutants were transferred to the catalyst surface and captured by H 2 O 2 , resulting in the generation of hydroxyl radicals ( OH). Therefore, a dual-pathway degradation of the pollutants was realized: (I) oxidation and degradation as the electron donors for the system and (II) attacking and destruction by OH radicals. This work provided a new perspective on the effective utilization of the electrons of pollutants and the improvement of Fenton reaction efficiency.
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