Liying Wu,Qian Zhang,Junming Hong,Zhengyu Dong,Ji Wang
This research describes the function of oxygen vacancy on CoFe 2 O 4-x for persulfate (PS) activation. Novel CoFe 2 O 4-x with different vacancy degrees that were successfully developed via hydrogen calcination were characterized using X-ray diffraction analyzer (XRD), Fourier transform infrared (FTIR) spectra, Raman spectroscopy , scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), H 2 temperature-programmed reduction (H 2 -TPR), cyclic voltammetry (CV), electrochemical impedance spectra (EIS), nitrogen adsorption-desorption isotherms and dynamic light scattering. The activation of catalysts was analyzed using Bisphenol A (BPA) as pollutant, and the main active species generated during the reaction were identified by using N 2 bubbling and scavenger experiments. Possible oxidation degradation pathways of BPA were speculated using gas chromatography–mass spectrophotometry (GC-MS) and total organic carbon (TOC) analysis. Findings indicated that the oxygen vacancies promoted electronic transfer and participated in the redox cycle from Co 3+ /Fe 3+ to Co 2+ /Fe 2+ to generate 1 O 2 and O 2 - . O 2 - , OH and SO 4 - generated from oxygen vacancy; moreover, PS activation could further degrade BPA to small molecules, such as benzenes and quinones . Finally, the toxicity of the reaction mixtures was evaluated and found that the acute toxicity to Daphnia magna decreased after 120 min treatment.
The rational design of photocatalytic nanomaterials with unique structures is critical for remediating environmental problems and thus reducing ecological risks. In this work, we employed H2 temperature-programmed reduction to modify MFe2O4 (M = Co, Cu, and Zn) photocatalysts for obtaining additional oxygen vacancies. After activation of PMS, naphthalene and phenanthrene degradation rates in the soil phase were increased by 3.24-fold and 1.39-fold, respectively, and 1.38-fold for naphthalene in the aqueous phase by H-CoFe2O4−x. The extraordinary photocatalytic activity is attributed to the oxygen vacancies on the H-CoFe2O4−x surface, which promote electron transfer and thus enhance the redox cycle from Co(III)/Fe(III) to Co(II)/Fe(II). In addition, oxygen vacancies are used as electron traps to hinder the recombination of photogenerated carriers and accelerate the generation of hydroxyl and superoxide radicals. Quenching tests showed that the addition of p-benzoquinone resulted in the greatest decrease in the degradation rate of naphthalene (inhibition of about 85.5%), demonstrating that O2˙− radicals are the main active species in the photocatalytic degradation of naphthalene. H-CoFe2O4−x showed improved degradation performance in synergy with PMS (82.0%, kapp = 0.00714 min−1) while maintaining excellent stability and reusability. Hence, this work provides a promising approach for the design of efficient photocatalysts to degrade persistent organic pollutants in soil and aqueous environments.
Liying Wu,Yongbo Yu,Qian Zhang,Junming Hong,Ji Wang,Yuecheng She
Through direct and indirect radical mechanism of peroxymonosulfate (PMS) activation, novel CoFe 2 O 4−x catalysts were successfully developed via hydrogen calcination to overcome popular disadvantages of the dependence on pH. Bisphenol A (BPA) was selected as the model pollutant to decipher the mechanism of catalysts for peroxymonosulfate (PMS) activation. Possible degradation pathways of Bisphenol A were proposed via analysis of liquid chromatograph mass spectrometer (LC-MS). The findings indicated that catalytic activation of CoFe 2 O 4−x was not dependent upon the initial pH, as the direct and indirect radicals seemed to be generated in parallel. FTIR analysis confirmed that surface hydroxyl groups were actively involved in the activation of PMS under alkaline conditions. During the reaction, the oxygen defects promoted electron transfer and participated in the redox cycle from Co 3+ /Fe 3+ to Co 2+ /Fe 2+ to generate 1 O 2 and O 2 − . Hydroxyl (OH ) and sulfate (SO 4 − ) radicals were generated on the surface of CoFe 2 O 4−x by the synergistic interactions among oxygen defects, transition metal, and surface hydroxyl groups. To the best of our knowledge, this combined mechanism of direct and indirect radical generation for advanced oxidation was a first-attempt study to be disclosed in public domain.
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