Elsevier

Chemical Engineering Journal

Volume 262, 15 February 2015, Pages 854-861
Chemical Engineering Journal

Activation of peroxymonosulfate with magnetic Fe3O4–MnO2 core–shell nanocomposites for 4-chlorophenol degradation

https://doi.org/10.1016/j.cej.2014.10.043Get rights and content

Highlights

  • The synthesized Fe3O4–MnO2 core–shell nanocomposites showed high capacity for heterogeneous activation of peroxymonosulfate.

  • The nanocomposites with Fe/Mn molar ratio of 4 had the highest catalytic activity.

  • The high activity of catalyst is attributed to the synergetic interaction of Fe3O4 and MnO2.

  • The catalyst exhibited high stability and good reusability.

  • The catalytic mechanism was proposed according to the results.

Abstract

Heterogeneous catalysts with low cost, little hazardous, high effective and facile separation from aqueous solution are highly desirable. In this study, magnetic Fe3O4–MnO2 core–shell nanocomposites with various Fe/Mn weight ratios were synthesized through a facile one pot method and then characterized. These as-synthesized solids were applied to activate the peroxymonosulfate (PMS) for 4-chlorophenol degradation. The sample 3 with a Fe/Mn molar ratio of 4:1, which can be separated conveniently through external magnetic field, exhibited higher activity than other Fe3O4–MnO2 nanocomposites, pure MnO2 and physical mixture of Fe3O4 and MnO2. The effects of operational parameters on the catalytic activity of sample 3, including initial Oxone and pollutant dosage, pH and catalyst dosage, were assessed. The catalyst had high stability and good reusability according to five successive repeated reaction. The reactive radicals generated in the PMS/Fe3O4–MnO2 nanocomposites system were sulfate radical (SO4radical dot) and hydroxyl radical (radical dotOH). The enhancement of the nanocomposites may be attributed to the interaction of Fe3O4 with MnO2 on the basis of the in situ ATR-FTIR analysis and XPS spectrum.

Introduction

Excess organic compounds in the aqueous solutions should be eliminated due to their hazards to the environment and humans [1]. However, degradation of refractory organic pollutants can be hardly achieved using conventional wastewater treatment technology due to the stable structure of organic compounds. Advanced oxidation is a promising pathway to mineralize the refractory organic pollutants through the activation of the oxidants and thus generating highly oxidizing radical species [2], [3].

Compared to hydroxyl radicals (radical dotOH, 1.8–2.7 V), sulfate radicals (SO4radical dot) based advanced oxidation technologies have attracted great attentions due to its high redox potential (2.5–3.1 V) at neutral pH [4] and more selective for oxidation [5]. Homogeneous catalysis of peroxymonosulfate (PMS) with transition metal ion is an efficient route for production of sulfate radicals to destroy organic matters in aqueous solution [6], [7], [8], [9], [10], [11], [12] because every single catalytic entity can act as a single active site [13]. However, the application of homogeneous catalysis was limited because of the harm to the environment of most dissolved metal ion.

Heterogeneous catalysis with metal oxides are increasingly replacing homogeneous catalysis of PMS to present the accumulation of soluble metal ion in aqueous solution. As effective PMS activators, cobalt or cobalt oxide can reduce the cobalt ion in the water significantly. However, leaching of potentially carcinogenic Co2+/Co3+ [14] is still inevitable. On the other hands, previous studies found magnetic spinel ferrites CuFe2O4 had high catalytic activity to PMS [15], [16]. Nevertheless, the complicated preparation method and high calcination temperature may hamper its wide application.

As an environmental friendly material, MnO2 can also efficiently activate PMS for degradation of pollutants [17], [18], [19] and is a promising alternative to Co3O4 in Oxone activation. Unfortunately, MnO2 tend to form superfine particles in aqueous solution, leading to the solid–liquid separation difficult to achieve [20]. Fe3O4 and Fe3O4-based materials not only have unique and novel properties but also could be easily separated and collected from water by the employment of magnetic process for reusability [21], [22], [23]. Moreover, iron ion leached from Fe3O4 can react with Oxone to produce sulfate radicals. Thus, hybrid materials containing MnO2 and Fe3O4 could be an ideal catalyst with great potential for Oxone activation, despite no report has been published.

In this study, Fe3O4–MnO2 core–shell nanocomposites were synthesized through a facile one pot method and characterized. The obtained magnetic nanocomposites were applied for catalytic activation of PMS for degradation of 4-chlorophenol (4-CP). To the best of our knowledge, this is the first report using Fe3O4–MnO2 core–shell nanocomposites as a PMS activator for the degradation of 4-CP. And then, the radical generation mechanism were proposed according to the results of ATR-FTIR and XPS analysis.

Section snippets

Materials

All chemicals used in the experiment were analytical grade and without further purification. MnCl2·4H2O and Poly (vinylpyrrolidone) (PVP, K-30) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ferrus sulfate (FeSO4·7H2O), potassium permanganate (KMnO4), sodium hydroxide (NaOH), ethanol and tert-butyl alcohol (TBA) were obtained from Xilong Chemicals, Ltd. (Shantou, China). 4-Chlorophenol (4-CP) and Oxone (PMS, KHSO5·0.5KHSO4·0.5K2SO4) were purchased from Aladdin

Synthesis and characterization of Fe3O4–MnO2 nanocomposites

During the synthesis process, five samples were prepared with initial Fe/Mn molar ratios of 6:1(sample 1), 5:1(sample 2), 4:1(sample 3), 3.3:1(sample 4) and 2.7:1(sample 5). After the dark green suspension formed, KMnO4 solution was added into the mixture, and then the dark brown solids were generated. The main reaction can be expressed as Eqs. (S1) and (S2). According to the Eq. (S2), the stoichiometric molar ration of Fe/Mn is 4.5. When the Fe2+ was excessive (sample 1 and sample 2), the

Conclusions

In summary, magnetic Fe3O4–MnO2 nanocomposites with low cost and little hazard were synthesized through a facile one pot method, and then used as PMS activators for the degradation of 4-CP. Sample 3 with a Fe/Mn molar ratio of 4:1 exhibited the much higher catalytic activity compared with other Fe3O4–MnO2 nanocomposites with various Fe/Mn molar ratio and pure MnO2. The catalyst showed stability in element valence, crystallinity and catalytic activity during the successive repeated reactions.

Acknowledgments

We gratefully acknowledge the financial support by the Funds for Creative Research Groups of China (Grant 51121062), State Key Laboratory of Urban Water Resource and Environment (Harbin Institute of Technology) (Grant 2013TS06), Scholarship Award for Excellent Doctoral Student granted by Ministry of Education of China (2012) and Fundamental Research Funds for the Central Universities (Grant 01508043).

References (50)

  • E. Saputra et al.

    Α-MnO2 activation of peroxymonosulfate for catalytic phenol degradation in aqueous solutions

    Catal. Commun.

    (2012)
  • Y. Guan et al.

    Efficient degradation of atrazine by magnetic porous copper ferrite catalyzed peroxymonosulfate oxidation via the formation of hydroxyl and sulfate radicals

    Water Res.

    (2013)
  • Y. Ding et al.

    Sulfate radicals induced degradation of tetrabromobisphenol A with nanoscaled magnetic CuFe2O4 as a heterogeneous catalyst of peroxymonosulfate

    Appl. Catal. B

    (2013)
  • H. Liang et al.

    Excellent performance of mesoporous Co3O4/MnO2 nanoparticles in heterogeneous activation of peroxymonosulfate for phenol degradation in aqueous solutions

    Appl. Catal. B

    (2012)
  • E. Saputra et al.

    Manganese oxides at different oxidation states for heterogeneous activation of peroxymonosulfate for phenol degradation in aqueous solutions

    Appl. Catal. B

    (2013)
  • A. Lv et al.

    Catalytic ozonation of toxic pollutants over magnetic cobalt-doped Fe3O4 suspensions

    Appl. Catal. B

    (2012)
  • T. Ishikawa et al.

    Formation of magnetite in the presence of ferric oxyhydroxides

    Corros. Sci.

    (1998)
  • E. Saputra et al.

    A comparative study of spinel structured Mn3O4, Co3O4 and Fe3O4 nanoparticles in catalytic oxidation of phenolic contaminants in aqueous solutions

    J. Colloid Interface Sci.

    (2013)
  • J. Yan et al.

    Degradation of sulfamonomethoxine with Fe3O4 magnetic nanoparticles as heterogeneous activator of persulfate

    J. Hazard. Mater.

    (2011)
  • L. Xu et al.

    Fenton-like degradation of 2,4-dichlorophenol using Fe3O4 magnetic nanoparticles

    Appl. Catal. B

    (2012)
  • J. Zhao et al.

    Enhanced oxidation of sulfamethoxazole using sulfate radicals generated from zero-valent iron and peroxydisulfate at ambient temperature

    Sep. Purif. Technol.

    (2010)
  • M. Cheng et al.

    Visible-light-assisted degradation of dye pollutants over Fe(III)-loaded resin in the presence of H2O2 at neutral pH values

    Environ. Sci. Technol.

    (2004)
  • G.P. Anipsitakis et al.

    Degradation of organic contaminants in water with sulfate radicals generated by the conjunction of peroxymonosulfate with cobalt

    Environ. Sci. Technol.

    (2003)
  • T. Zhang et al.

    Production of sulfate radical from peroxymonosulfate induced by a magnetically separable CuFe2O4 spinel in water: efficiency, stability, and mechanism

    Environ. Sci. Technol.

    (2013)
  • E. Saputra et al.

    Different crystallographic one-dimensional MnO2 nanomaterials and their superior performance in catalytic phenol degradation

    Environ. Sci. Technol.

    (2013)
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