Comparison of the heterogeneous GO-FePO4/electro-Fenton against the homogeneous Fe(II) ion and Fe(III)-oxalate complex/electro-Fenton for the degradation of metronidazole

https://doi.org/10.1016/j.jwpe.2021.102265Get rights and content

Highlights

  • The GO-FePO4 catalyst was tested for heterogeneous electro-Fenton process.

  • GO-FePO4 showed an effective performance for the degradation of MTZ antibiotics.

  • 65.5% mineralization was achieved by using GO-FePO4 catalyst in 5 h.

  • GO-FePO4 was successfully reused in four consecutive electrolysis cycles.

  • The activity of GO-FePO4 was compared with FeII ions and FeIII-oxalate catalysts.

Abstract

This study compared the effect of the homogeneous and the heterogeneous electro-Fenton (EF) processes on the degradation of Metronidazole (MTZ). Graphene oxide (GO)-FePO4 synthesized for use in the heterogeneous electro-Fenton process was characterized using FTIR, FE SEM-EDS and XRD analysis. The analyses showed that the amorphous composite structure formed as a result of FePO4 structures dispersed between the GO layers has an average particle size distribution of 141 nm. The activity of the GO-FePO4 catalyst was more effective at pH 3 than pH 5 which is the own pH value of metronidazole. In the heterogeneous EF process, the mineralization percentage was determined as 66% at pH 3, 0.5 g L−1 catalyst dosage after 5 h. No difference was observed in the structure of GO-FePO4, which can be used repeatedly with high performance, even after 4 cycles. In the homogeneous EF process, 0.2 mM Fe2+ ion and Fe(III)-oxalate complex containing the same amount of Fe ions were used for comparison under the same conditions. When Fe2+ ion and Fe(III)-oxalate complex were used at pH 3, 57% and 70% mineralization percentages were achieved respectively, in 5 h. However, the mineralization efficiencies of the Fe(III)-oxalate complex decreased to 47% at pH 5 and 41% at pH 7. The pseudo-first-order model to kinetically describe the removal mechanism of MTZ showed the best fit with the experimental kinetic data in all EF processes. Finally, active oxygen species were determined as hydroperoxyl radicals for the heterogeneous EF method and as hydroxyl radicals for the homogeneous EF method.

Introduction

Nowadays, water pollution caused by organic pollutants has reached serious levels and has become an important problem for all living things on earth. Antibiotics are one of the most important of these organic pollutants. In particular, the widespread and broad-spectrum use of antibiotics makes them the most important group of contaminants in environmental waters. Metronidazole (MTZ) is one of the commonly used antibiotics, is used to treat a wide variety of infections caused by some bacteria and parasites. MTZ is identified in several wastewater effluents like urban, hospital, fish farms, and meat production facilities which produce large amounts of wastewaters [1]. In the United States, MTZ was 119th most commonly prescribed medication in 2018 [2]. It is also on the World Health Organization's List of Essential Medicines [3]. On the other hand, as a result of the studies, metronidazole was reported to be carcinogenic [4]. Metronidazole has high mobility in the soil because of its KOC (soil adsorption coefficient) value [5] and it has been reported to be low biodegradable in the environment [[6], [7], [8]]. Due to the lack of effective treatment in effluent treatment plants, high concentrations of such pollutants are released into the environment. For instance, MTZ levels as high as 34 mg L−1 have been determined in the sample of the Waste Water Treatment Plant of a pharmaceutical manufacturing company in Nigeria [9,10]. Therefore, effective studies to be carried out on the degradation of MTZ in wastewater will help to solve an important problem.

Electrochemical advanced oxidation techniques (EAOPs) have attracted great attention in consequence of their environmental-friendliness, moderate application condition, compatibility, versatility, high efficiency, limited operative costs, and suitability for automation [[11], [12], [13], [14]]. EAOPs can be used to effectively degrade persistent organic pollutants [15]. Electro-Fenton (EF) method is also a prominent member of EAOPs. In the Fenton method, the ferrous ion and H2O2, which are named Fenton reagents, react to produce hydroxyl radical in the bulk solution (Eq. (1)).Fe2++H2O2Fe3++OH+OHk=53M1s1

However, in the EF method, it is possible to be electro-generated H2O2 at a suitable cathode fed with O2/air (Eq. (2)) or produce Fe2+ ions using a sacrificial iron anode. It can also be applied by adding catalytic amounts of iron ions (Fe2+ or Fe3+) into the reaction medium. In EF process, regeneration of Fe3+/Fe2+ performs by direct reduction on the cathode (Eq. (3)) [16].O2g+2H++2eH2O2E0=0.695V/NHEFe3++eFe2+E0=0.771V/NHE

Also, coupling electro-Fenton processes, which are also environmentally friendly, with biological treatment techniques, allows the use of environmentally friendly high-efficiency new methods by improving existing biological treatment processes. Aboudalle et al. performed the mineralization of metronidazole using combined the Fenton process with biological treatment processes [17,18]. They showed that when electro-Fenton was applied before biological treatment, the rate of metronidazole removal doubled compared to using two different bacterial strains alone for 120 h. As a result, by combining the two processes, they achieved a mineralization efficiency of 97% with a significant reduction in 16-day processing time compared to previous traditional biological treatment methods [17]. Some chemicals, such as pesticides, accumulate in the soil and may get mixed with groundwater after irrigation or rains. Contreras et al. proposed an EF pre-treatment to improve the biodegradability of polluted soil washing effluent with clopyralid, also showed that the groundwater can be used as a natural electrolyte instead of adding synthetic electrolytes [19].

Traditionally, homogeneous Fenton applications have some limitations, such as the application of acidic pH (~pH = 3) [20] and the inability to recover Fe2+ ions. Also, reproducing the Fe2+ ion, which is depleted as a result of the Fenton reaction (Eq. (1)), limits the Fenton process. It has been reported that adding low molecular weight organic acids to the solution in a homogeneous photo-Fenton process increases the amount of degradation. For this purpose, oxalic acid, acetic acid, citric acid, malic acid, and tartaric acid were tested [[21], [22], [23], [24]]. These acids form a soluble strong complex with the Fe(III) ion [25]. The optimum molar ratio was reported as 1:3 for the Fe(III)-oxalate complex and it was determined as 1:1 for the others, too [[26], [27], [28]]. The reasons for increasing the degradation efficiency of the Fe(III)-oxalate complex; i) facilitating the Fe(III)/Fe(II) cycle in the photo-Fenton process [[29], [30], [31], [32]], ii) reacting faster with hydrogen peroxide than the free Fe3+ ion (Fe(III)-aqua complexes), and iii) providing degradation in a wide pH range [21].

Recently studies conducted with the heterogeneous EF method showed that pH values can be changed from acidic to neutral and the iron source can be reused. Generally, Fe2+ (or Fe3+, Fe(III)-Ligand complexes) is used in homogeneous Fenton applications but in recent studies, the surface of heterogeneous structures containing iron such as goethite (α-FeOOH) [33,34], wustite (FeO) [33], magnetite (Fe3O4) [33,35,36], hematite (α-Fe2O3) [33], iron molybdophosphate (FeMoPO) [37], iron-loaded alginate beads [38], zero-valent iron (ZVI) [36], pyrite (FeS2) [[39], [40], [41]], laterite [42], ZnFe2O4 nanoparticles [43], and Fe-Cu allophane [44] acts as the active site for heterogeneous electro-Fenton applications.Moreover, it is possible to use heterogeneous catalysts obtained by loading iron sources on various support groups such as sepiolite [45], zeolite [46], carbon [47], organic polymers [48], and resin [49]. One of these support materials is graphene oxide (GO). GO has oxygenated functional groups in its two-dimensional lamellar structure which allows the obtaining of composite materials with various compositions [50,51]. Graphene, graphene oxide, and reduced graphene oxide composite materials such as GO-Fe3O4, GO-FeIIFeIII, FeIIFeII-Carbon felt, graphene-FeO dispersed onto Ni foam, graphene/carbon nanotube−based carbon aerogel/Fe3O4, iron-graphene-based particle, γ-FeOOH graphene polyacrylamide carbonized aerogel, can be used as a cathode material or catalyst in the electro-Fenton process [[52], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62]]. In these structures, the p orbitals of graphene-based support materials overlap with the d orbitals of the transition metal atoms to form composite structures with appropriate geometry. Composite materials significantly increase catalytic activity and stability through synergistic interaction [62]. In addition, electrostatic interactions may occur between oxygenated functional groups in the GO structure and metal oxide structures [[63], [64], [65]]. Consequently, we can summarize some of the most important advantages of these synergetic interactions as follows; i) metal oxides are dispersed in the high surface area of the GO active areas, ii) agglomeration is prevented [65], iii) leakage of metal ions is reduced and finally catalyst stability is increased [66]. In Fenton reactions, one of the iron sources used in graphene-based composite materials is FePO4 [67,68]. Guo et al. [67] investigated the effect of GO-FePO4 composite on the degradation of rhodamine B by the photo-Fenton process and achieved 100% removal with the use of 100 mM H2O2 and 1 g L−1 catalyst. Zhou et al. (2018), also performed photo-Fenton degradation of methylene blue under simulated sunlight irradiation using GO-FePO4 composite (GO 10% w/w) and showed that this catalyst would be used 3 times without losing its photocatalytic activity and stability [68].

This work aimed to synthesize and characterize GO-FePO4 and to investigate the removal of metronidazole from aqueous solutions by the heterogeneous electro-Fenton process. The effects of catalyst amount, pH, and electrolysis time on degradation and mineralization were investigated. In addition, the reusability of GO-FePO4 catalyst, and Fe ion release into solution were investigated. To compare the performance of GO-FePO4 in the heterogeneous Fenton reactions, Fe(II) ions, and Fe(III)-oxalate compounds were selected as homogeneous catalysts. Finally, degradation products of MTZ were identified.

Section snippets

Chemicals

Graphite powder (325 mesh, 99.99% purity), and metronidazole (99%), were obtained from Alfa Aesar. Phosphorus pentoxide (P2O5), potassium persulfate (K2S2O8), sodium nitrate (NaNO3), potassium permanganate (KMnO4), hydrogen peroxide (H2O2, 30%), iron (II) sulfate heptahydrate (FeSO4·7H2O), sodium sulfate (Na2SO4), sodium hydroxide (NaOH), nitric acid (HNO3), ammonium dihydrogen phosphate (NH4H2PO4), iron (III) nitrate Fe(NO3)3, sodium fluoride (NaF), ferric chloride (FeCl3), salicylic acid (C7H6

Characterization of GO-FePO4

As seen in Fig. 1a, the GO-FePO4 catalyst showed a uniform particle size distribution with a maximum of 141.3 nm. While C, O, Fe, and N elements were seen in the EDS spectrum belonging to the GO-FePO4 structure, no result for phosphorus was obtained. However, the reason for the absence of phosphorus may be its low amount (the FePO4 structure constitutes only 10% of the composite by mass) or overlapping with the spectra of the elements (Pt, and Pd) used in the coating (Fig. 1b).

In Fig. 2, the

Conclusions

The degradation of MTZ antibiotic solution was compared using heterogeneous and homogeneous EF processes. In the work, GO-FePO4 catalyst was used as a heterogeneous catalyst, Fe2+ ion and Fe(III)-oxalate complex were used as homogeneous catalysts. The characterization of the GO-FePO4 structure was performed by XRD, FE SEM-EDS, and FT-IR analysis. It was determined that the GO-FePO4 composite was more effective at pH 3 in the heterogeneous EF process, and the maximum mineralization percentages

Declaration of competing interest

Authors declare no conflict of interest.

Acknowledgments

We would like to thank Mersin University Advanced Technology Education, Research, and Application Center (MEITAM) where the analyses were carried out.

References (82)

  • J.H.O.S. Pereira et al.

    Process enhancement at near neutral pH of a homogeneous photo-Fenton reaction using ferricarboxylate complexes: application to oxytetracycline degradation

    Chem. Eng. J.

    (2014)
  • F. Gulshan et al.

    Various factors affecting photodecomposition of methylene blue by iron-oxides in an oxalate solution

    Water Res.

    (2010)
  • J.M. Monteagudo et al.

    Photodegradation of Reactive Blue 4 solutions under ferrioxalate-assisted UV/solar photo-Fenton system with continuous addition of H2O2 and air injection

    Chem. Eng. J.

    (2010)
  • C. Zhao et al.

    Reductive and oxidative degradation of iopamidol, iodinated X-ray contrast media, by Fe(III)-oxalate under UV and visible light treatment

    Water Res.

    (2014)
  • G. Zhou et al.

    Fenton-like degradation of Methylene Blue using paper mill sludge-derived magnetically separable heterogeneous catalyst: Characterization and mechanism

    J. Environ. Sci.

    (2015)
  • C.M. Sanchez-Sanchez et al.

    Goethite as a more effective iron dosage source for mineralization of organic pollutants by electro-Fenton process

    Electrochem. Commun.

    (2007)
  • A. Baiju et al.

    Combined heterogeneous Electro-Fenton and biological process for the treatment of stabilized landfill leachate

    J. Environ. Manag.

    (2018)
  • S.B. Hammouda et al.

    Effective heterogeneous electro-Fenton process for the degradation of a malodorous compound, indole, using iron loaded alginate beads as a reusable catalyst

    Appl. Catal. B Environ.

    (2016)
  • S. Ammar et al.

    Degradation of tyrosol by a novel electro-Fenton process using pyrite as heterogeneous source of iron catalyst

    Water Res.

    (2015)
  • N. Barhoumi et al.

    Pyrite as a sustainable catalyst in electro-Fenton process for improving oxidation of sulfamethazine. Kinetics, mechanism and toxicity assessment

    Water Res.

    (2016)
  • M. Kamagate et al.

    Use of laterite as a sustainable catalyst for removal of fluoroquinolone antibiotics from contaminated water

    Chemosphere

    (2018)
  • J. Wu et al.

    Removal of benzotriazole by heterogeneous photoelectro-Fenton like process using ZnFe2O4 nanoparticles as catalyst

    J. Environ. Sci.

    (2013)
  • E.G. Garrido-Ramirez et al.

    Preparation and characterization of bimetallic Fesingle bondCu allophane nanoclays and their activity in the phenol oxidation by heterogeneous electro-Fenton reaction

    Microporous Mesoporous Mater.

    (2016)
  • O. Iglesias et al.

    Heterogeneous electro-Fenton treatment: preparation, characterization and performance in groundwater pesticide removal

    J. Ind. Eng. Chem.

    (2015)
  • C. Zhang et al.

    Heterogeneous electro-Fenton using modified iron‑carbon as catalyst for 2,4-dichlorophenol degradation: influence factors, mechanism and degradation pathway

    Water Res.

    (2015)
  • E. Rosales et al.

    Decolourisation of dyes under electro-Fenton process using Fe alginate gel beads

    J. Hazard. Mater.

    (2012)
  • C. Xu et al.

    Graphene oxide TiO2 composite filtration membranes and their potential application for water purification

    Carbon

    (2013)
  • J. Zhang et al.

    High-capacity graphene oxide/graphite/carbon nanotube composites for use in Li-ion battery anodes

    Carbon

    (2014)
  • W. Chen et al.

    Iron oxide containing graphene/carbon nanotube based carbon aerogel as an efficient E-Fenton cathode for the degradation of methyl blue

    Electrochim. Acta

    (2016)
  • G. Divyapriya et al.

    An innate quinone functionalized electrochemically exfoliated Graphene/Fe3O4 composite electrode for the continuous generation of reactive oxygen species

    Chem. Eng. J.

    (2017)
  • H. Ghanbarlou et al.

    Synthesis of an iron-graphene based particle electrode for pesticide removal in three-dimensional heterogeneous electro-Fenton water treatment system

    Chem. Eng. J.

    (2020)
  • F. Görmez et al.

    Degradation of chloramphenicol and metronidazole by electro-Fenton process using graphene oxide-Fe3O4 as heterogeneous catalyst

    J. Environ. Chem. Eng.

    (2019)
  • J. Shen et al.

    Aerosol synthesis of Graphene-Fe3O4 hollow hybrid microspheres for heterogeneous Fenton and electro-Fenton reaction

    J. Environ. Chem. Eng.

    (2016)
  • Y. Wang et al.

    Electrosorption enhanced electro-Fenton process for efficient mineralization of imidacloprid based on mixed-valence iron oxide composite cathode at neutral pH

    Chem. Eng. J.

    (2013)
  • Y. Wang et al.

    γ-FeOOH graphene polyacrylamide carbonized aerogel as air-cathode in electro-Fenton process for enhanced degradation of sulfamethoxazole

    Chem. Eng. J.

    (2019)
  • W. Yang et al.

    Highly efficient and stable FeIIFeIII LDH carbon felt cathode for removal of pharmaceutical ofloxacin at neutral pH

    J. Hazard. Mater.

    (2020)
  • S. Navalon et al.

    Metal nanoparticles supported on two-dimensional graphenes as heterogeneous catalysts

    Coord. Chem. Rev.

    (2016)
  • S. Guo et al.

    Enhanced photo-Fenton degradation of rhodamine B using graphene oxide–amorphous FePO4 as effective and stable heterogeneous catalyst

    J. Colloid Interface Sci.

    (2015)
  • H. Zhou et al.

    Graphene oxide-FePO4 nanocomposite: synthesis, characterization and photocatalytic properties as a Fenton-like catalyst

    Ceram. Int.

    (2018)
  • J. Ma et al.

    Mesoporous amorphous FePO4 nanosphere@Graphene as a faradic electrode in capacitive deionization for high-capacity and fast removal of NaCl from water

    Chem. Eng. J.

    (2019)
  • A.K. Abdessalem et al.

    Experimental design methodology applied to electro-Fenton treatment for degradation of herbicide chlortoluron

    Appl. Catal. B.

    (2008)
  • Cited by (13)

    View all citing articles on Scopus
    View full text