Environmental Technology

ISSN: 0959-3330 (Print) 1479-487X (Online) Journal homepage: http://www.tandfonline.com/loi/tent20

Graphene-doped carbon black gas diffusion electrode for nonmetallic electrochemical advanced oxidation process under mild conditions Heng Dong, Xi Zhang, Han Yu & Hongbing Yu To cite this article: Heng Dong, Xi Zhang, Han Yu & Hongbing Yu (2017): Graphene-doped carbon black gas diffusion electrode for nonmetallic electrochemical advanced oxidation process under mild conditions, Environmental Technology, DOI: 10.1080/09593330.2017.1370022 To link to this article: http://dx.doi.org/10.1080/09593330.2017.1370022

Accepted author version posted online: 21 Aug 2017.

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Date: 26 August 2017, At: 12:34

Publisher: Taylor & Francis & Informa UK Limited, trading as Taylor & Francis Group Journal: Environmental Technology DOI: 10.1080/09593330.2017.1370022

Graphene-doped carbon black gas diffusion electrode for nonmetallic electrochemical advanced oxidation process under mild conditions Heng Dong*, Xi Zhang, Han Yu and Hongbing Yu* MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of

Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

Environmental Science and Engineering, Nankai University, No. 38 Tongyan Road, Jinnan District, Tianjin 300350, China. *Corresponding authors. E-mail: [email protected] (Heng Dong); [email protected] (Hongbing Yu)

ABSTRACT: Graphene-doped (< 3wt%) carbon black gas diffusion electrodes (GDEs) were prepared as the cathode for nonmetallic electrochemical advanced oxidation process (EAOP) in the neutral environment. The elemental composition, porous structure and active surface area were characterized and the concentration of H2O2 and OH• were determined. Bisphenol A (BPA) was used as a model pollutant to assess the performance of the EAOP for organic wastewater treatment. The results showed that oxygen in the atmosphere was reduced to OH• on the GDE, where carbon black catalyzed oxygen reduction to H2O2 and graphene provide Π-electrons for the following H2O2 decomposition. BPA with initial concentration of 20 mg L-1 was completely removed within 30 min and the total organic carbon (TOC) removal reached 44.60%. The EAOP with the graphene-doped carbon black GDEs exhibited significant advantages for organic wastewater treatment.

Keywords: Electrochemical advanced oxidation process; Gas diffusion electrode; Graphene; Hydrogen peroxide decomposition; Oxygen reduction reaction

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1. Introduction Hydrogen peroxide (H2O2) is a popular oxidizing agent used in advanced oxidation processes (AOPs) for achievement of radicals [1]. Aiming to reduce the potential costs and hazards related to the transport, storage and handling for H2O2, electro-generation of H2O2 via 2e-oxygen reduction reaction (ORR) has been introduced in AOPs, forming a cathode electrochemical AOP [2]. As a typical example, electro-Fenton technology has reached an excellent state of development, especially using the cheap carbon black as the catalyst for ORR [3, 4]. The optimal kinetics of the electro-generation of H2O2 are usually obtained in the neutral or basic Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

condition, however, that of the chemical Fenton’s reaction are usually obtained in the acidic condition. Because of the difference in the needed pH value for those two reactions, it is very hard to achieve OH• efficiently in the electro-Fenton system which need ORR reaction and Fenton reaction carry out simultaneously. In addition, iron minerals and transition metal ions are commonly used as catalyst for Fenton reaction [5, 6]. The secondary pollution to the receiving water caused by the metal catalysts, either in sediment formed during neutralizing treatment or aqueous solution, is undesirable [7, 8]. Hence, exploring an alternative nonmetallic catalyst for H2O2 decomposition to OH• is required urgently. The catalysis of activated carbons on H2O2 decomposition to OH• at a neutral condition have been reported by several researchers [4, 9, 10, 11, 12]. It is well known that the structure of the activated carbons is composed of the π- conjugated sp2 hybridize carbon and specific surface functional groups [13]. Therein, the πconjugated sp2 hybridize carbons exist with a hexatomic ring which is similar with the structure of a single-layer graphene. The proposed mechanism indicates that activated carbons act as an electron-transfer mediator similar to Fe (II) species [13, 14]. Specifically, a part of electron-transfer processes happen on the graphene layers which are rich in Π-electrons like Lewis bases [10, 15]. By that analogy, a single-layer graphene material, which are rich in the π- conjugated sp2 hybridize carbons and has no metal element, is much possible to catalyze H2O2 decomposition towards OH• without assistance of metal impurities. Since graphene possesses an attractive low energy dynamics of electrons and exhibits some exciting electronic properties through the 2D electron system [16, 17], it should be a higher efficient catalyst than activated carbons whose abundant porous structure results in their poor conductivity. 3

In this work, an electrochemical cell equipped with the home-made graphene-doped carbon black gas diffusion electrode (GDE) is constructed to verify the above hypothesis. Moreover, bisphenol A (BPA) was used as a model pollution to assess the degradation ability of the EAOP with graphene-doped carbon black GDE for refractory organic wastewater treatment in the neutral environment. 2. Material and methods The GDEs used here are sandwich-type, composed by a gas diffusion layer (GDL), a current collector (CC) and a catalyst layer (CL) (Fig. 1(a)). They were fabricated by a rolling method developed by our group previously [14]. The GDL was rolled from a Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

mixture of conductive carbon black (Jinqiushi Chemical Co. Ltd., Tianjin, China) and polytetrafluoroethylene (PTFE, 60wt %, Hesen, Shanghai, China) with mass ratio of 3:7. It was sintered at 340 °C to ensure a good waterproof. A stainless steel mesh (60 meshes, Detiannuo Commercial Trade Co. Ltd., Tianjin, China) was used as the CC. The CL was rolled from a mixture of catalyst and PTFE with mass ratio of 6:1 without sintering. Carbon black (Vulcan XC-72, Cabot Corporation, USA) doped with the single-layer graphene by 1 and 3wt% (XF0001W, XFNANO Materials Tech Co. Ltd., Nanjing, China) were the catalysts of the two target GDEs, respectively. For preparing the CL of the graphene-doped carbon black GDE, a certain amount of the graphene (1wt% or 3wt%) was preliminarily dispersed in the carbon black powder by mechanical mixing with ultrasound and agitation for 20 min. The carbon black GDE was prepared as control. There was about 0.40 g of catalyst in the CL for each GDE and the diameter of the GDE was 4 cm. The surface morphology and the porous structure of the CL were characterized by SEM (S4800, Hitachi Limited, Japan) and mercury porosimeter (Autopore IV, Micromeritics), respectively [15]. The graphene (0.1 g) and carbon black (0.1 g) powder used in the CL were digested with 8 mL of HNO3 (GR, CNW), 2 mL of H2O2 (GR, CNW), 1mL of HCl (GR, CNW) and 1 mL of HClO4 (GR, CNW) in a microwave digestion system and diluted to 10 mL with double deionized water (Milli-Q Millipore 18.2 MΩ cm-1 resistivity). Two blanks digestion were carried out in the same way (digestion conditions for the microwave system applied were: 2 min at 300 W, 2 min at 0 W, 6 min at 300 W, 5 min at 400 W, 8 min at 550 W, then vent for 8 min). After a filtration (0.45 μm filter membrane), the concentrations of iron and copper in the digestion solution were determined in a graphite furnace atomic absorption spectrometry using a deuterium background correction (GFAAS, 4

RayleighWFX210, Beijing Beifen-Ruili Analytical Instrument (Group) Co., Ltd.). Linear sweep voltammetry (LSV) (0.6 V ~ -0.6 V at 5 mV s-1), Cyclic voltammetry (CV) (0.6 V ~ -0.6 V at 5 mV s-1) and Tafel plots (overpotential from 0 mV to 100 mV at 5 mV s-1) were performed on an electrochemical workstation (Autolab PGSTAT302N, Metrohm Ltd., Switzerland) in a conventional three-electrode electrolysis reactor with a volume of 28 mL [16]. The GDE and Pt sheet (1 cm2) were used as the working electrode and the counter electrode respectively. An Ag/AgCl (saturated KCl, 0.197 V vs. SHE) reference electrode was used. The LSV curves, CV curves and Tafel plots with good reproducibility were adopted for analysis. Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

Electrochemical ORR and BPA degradation experiments were performed under constant potential in the same three-electrode electrolysis reactor (Fig. 1(b)) with 0.05 M Na2SO4 solution. A spectrophotometric method, based on the absorption of a titanium complex (λ= 410 nm), was adopted for the determination of the concentration of H2O2 [18]. The pH value was detected on a pH supervision instrument (Rex PHS-3C, Shanghai INESA Scientific Instrument Co. Ltd., China). 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to trap the free radicals for the electron spin resonance (ESR) detection [19]. The sample of 1.0 mL was thoroughly mixed with 1.0 mL DMPO solution (8.84 mM) for 1 min and then transferred to a capillary tube for analysis. The initial concentration of BPA was 20 mg L-1. BPA was analyzed by employing a high performance liquid chromatograph (HPLC, 1260, Agilent Corporation, USA) with Fluorescence Detector (with emission and excitation wavelengths at 230 and 315 nm) and equipped with a Waters XTerra C18 column (150 mm × 4.6 mm I.D) [42]. The analytical conditions were as follows: the mobile-phase was 65 % methanol and 35 % water with a flow rate of 0.1 ml min-1. The oven temperature was set at 25 °C. The mineralization of BPA was monitored from its total organic carbon (TOC) decrease, measured with a shimadzu VCSN total organic carbon analyzer. 3. Results and discussion 3.1. Catalyst layer characterization The rolled GDE had smooth surfaces and good mechanical property (Fig. 1(a)). The SEM images display a porous structure and uniform agglomerated state of the carbon black in the three CLs (Fig. 1(c), 1(d) and 1(e)). We provide a SEM image of the single-layer graphene covered on the surface of the control carbon black GDE as an inner image in Fig. 1(c). It can be found that the graphene doped in the CL of the 5

GDE cannot be seen obviously from Fig. 1(d) and 1(e), mainly due to the tiny doping amount of the graphene. The pore size diameters in the three CLs identically concentrated at about 40 nm (Fig. 1(f)). The cumulative pore area were increased by 0.35% for the GDE with 1wt% graphene and 1.75% for the GDE with 3wt% graphene. Similarly, as the additive amount of graphene was increased, the porosity was increased gradually and the increment were 1.00% for the GDE with 1wt% graphene and 1.57% for the GDE with 3wt% graphene (Table 1). The changes in the cumulative pore area and porosity were so tiny that they could almost be ignored. That is to say, the addition of graphene by such a small amount (1wt% and 3wt% here) had no Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

significant effect on the porous structure of the carbon black CL. Since the capacity of the GDE in oxygen transfer from the atmosphere to the CL mainly depended on its porous structure, the amount of the oxygen received by the three types of the CLs should be considered equal. The single-layer graphene produced by physical micro mechanical separation method was deliberately used here to avoid an introduction of metal elements. The Fe and Cu contents in the GDEs detected by GFAAS are listed in Table 1. Although Fe content in the GDE was increased (↑2.07 ~6.13%) by doping the graphene, they were all lower than 14 ppb. Cu content in the three GDEs were relatively higher (< 100 ppb), but similar with each other. 3.2. Electrochemical measurements The voltammetric charge (q*)

corresponding to electrochemically active surface

areas of the GDE was determined by integrating the area of the closed CV curve within the scanning potential window from -0.6 V to 0.6 V (Fig. 2(a)) [14]. The q* value of the carbon black GDE was increased by 58.41% and 117.28% as the addition of graphene by 1wt% and 3wt%, respectively (Table 1). The LSV curves are also given in the Fig. 2a as an inner image. It can be found that the ORR current was enhanced significantly as the amount of the graphene was increased during -0.2 ~-0.5 V. In that potential range, the 2e-ORR to H2O2 contributed to the current mostly. When the potential was more negative than -0.5 V, the current from the carbon black GDE was larger than that from the GDE doped with 1wt% graphene. It can be explained that hydrogen evolution reaction happened on the carbon black GDE but not on the GDE doped with 1wt% graphene. While the current from GDE doped with 3wt% graphene was still the largest one and it was possibly resulted from the 4e-ORR 6

to H2O. The exchange current density (j0) was calculated from the linear fitting for the linear region of the Tafel plots (Fig. 2(b)) [20]. The j0 value of the carbon black GDE was augmented by two orders of magnitude owing to the addition of graphene (Table 1). It can be concluded that the graphene enabled a significant improvement in the electrochemical activity of the carbon black GDE for ORR, agreeing with our initial prediction. 3.3. Electrochemical ORR experiments The H2O2 concentration in the cell as electrolysis time under a constant potential of -0.3 V vs. Ag/AgCl is displayed in Fig. 3(a). The values from the carbon black GDE Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

show a stable increase from 0 to 21.04 mg L-1 within a cycle of 60 min. After the graphene of 1wt% was doped in the CL, the concentration of H2O2 has an increase of 19.66% in the third interval of 15 min and of 10.15% in the fourth interval, much less than those of 63.08% and 33.96% obtained from the carbon black GDE, respectively. Moreover, a significant decrease in the H2O2 concentration is found for each sample time and the difference is enlarged from 30.50% at 15 min to 62.40% at 60 min. When the additive amount of graphene is increased to 3wt%, the plot displays a stable increase again and the values are higher than those obtained from the carbon black GDE by 19.96% ~ 24.24%. In addition, it can be seen obviously that the H2O2 concentration detected form the EAOP system with carbon black GDE was higher than that from the EAOP system with 1wt% graphene-carbon black GDE, while lower than that from the EAOP system with 3wt% graphene-carbon black GDE for the same sample time. It can be understood from the following two aspects. On one hand, H2O2 was produced from ORR which need oxygen, protons and electrons on our carbon black GDE, either with or without graphene. Carbon black is an efficient catalyst for that 2e-ORR process, which have been mentioned above. That was why we used carbon black as the support material of the CL. The aim of the graphene addition to the carbon black was to obtain OH• via H2O2 decomposition at a neutral condition. The experiment data indeed suggested the production of OH• which will be given in the following section. As the H2O2 decomposition, the amount of H2O2 detected in the electrolyte was decreased, as found in the EAOP with 1wt% graphene-doped GDE. On the other hand, good conductivity of the graphene may promote the electron transfer from the electrode to oxygen, accelerating the 2e-ORR to H2O2. If the increment portion of the H2O2 was not decomposed to OH• completely, an increase in the amount of H2O2 detected from the electrolyte would occur, as found in the EAOP 7

with 3wt% graphene-doped GDE. The pHs of the electrolyte in all the three systems were decreased slightly to close to/below 6 over time (Fig. 3(a)). The increased proton concentration was possibly caused by two ways. One was the hydrolysis reaction at the anode. Since most of the protons produced during that process would be used in ORR on the cathode, the contribution of this way to the pH decline should be mild. The other one was the BPA degradation to the small molecule organic acid, such as oxalic acid, lactic acid and fumaric acid, which has been reported in other researches with respect to BPA degradation by EAOP [21, 22]. According to the results of the BPA degradation in our Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

EAOP systems, we think the latter way should have more effect on the pHs. ESR was used to detect OH• by measuring the intensity of the DMPO-OH adducts signal (Fig. 3(b)). The specific spectrums (quartet lines with peak height ratio of 1:2:2:1) were distinctly observed from the graphene-doped GDEs, either containing 1wt% or 3wt%, and the intensity of the former one is almost five times more than that of the later one. It demonstrates that the single-layer graphene used in this work can electrochemically decompose H2O2 to OH• in-situ. Furthermore, the higher catalytic capacity of the GDE doped with 1wt% graphene made its lower H2O2 production reasonable. Since no metal catalyst was found in the graphene powder for H2O2 decomposition (Table 1), the possibility of the OH• production from Fenton process can be ruled out. In the process of the electrochemical ORR catalyzed by the graphene-doped carbon black GDEs, oxygen was the primary electron acceptor (Eq. (1)). After that, H2O2 becomes the secondary electron acceptor, leading to its decomposition to OH• (Eq. (2)). Since H2O2 is a scavenger of OH•, the obtained H2O2 concentration depends on the degree of Eq. (3). In this work, H2O2 and OH• were both in-situ produced on the graphene-doped GDE, Eq. (3) was more likely to occur. The higher intensity of OH• obtained from the GDE doped with 1wt% graphene may be attributed to a better sequential process from Eq. (1) to Eq. (2) with the equal reaction ratio. So that the Eq. (3) was restrained. O2+2H++2e-→H2O2

(1)

H2O2+e-→OH•+OH-

(2)

H2O2+OH•→H2O+HO2•

(3)

The chemical catalysis experiments of the graphene to H2O2 were also carried out. Two beakers filled with 100 ml H2O2 (20 mg L-1) were prepared and the graphene 8

powder of 0.1 g was added into one of them. After a stirring of 12 h (at ~298 K), the concentration of H2O2 in the two beakers were still about 20 mg L-1. It can be announced that, the electron-transfer ability of the graphene to H2O2 requires an impetus from an additional power source. The proposed mechanism for OH• production on the graphene-doped carbon black GDE was illustrated in Fig. 4. 3.4. Degradation of BPA Since OH• can be produced on the graphene-doped carbon black GDE via ORR, it can be used to construct EAOP for organic wastewater treatment. As can be seen from Fig. 5(a), 23% of BPA was removed in the AOP with carbon black GDE after an Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

electrolysis time of 30 min. When the graphene was doped in the carbon black GDE with 1wt%, BPA was completely removed in that time. While when the additive amount was increased to 3wt%, the remove rate of BPA within 30 min was decreased to 30%. It is in accordance with the result of ESR measurement, suggesting that OH• played a crucial role in the BPA removal. TOC removal was further investigated and a similar result with the removal rate of BPA was found. As shown in Fig. 5(b), the removal of TOC for the three GDEs were all continuously increased as time. After an electrolysis time of 30 min, the values are ranked as 44.60% (GDE doped with 1wt% graphene)> 5.45% (GDE doped with 3wt% graphene)> 5.36% (carbon black GDE). This confirms that BPA was degraded by OH• produced from ORR on the graphene-doped carbon black GDE. This work is the first research for BPA degradation in an electro-Fenton system. It is compared with the performance reported by the others using the Fenton system according to average BPA removal rate and TOC removal (Table 2). Although the performance of our graphene-doped carbon black GDE is not the top level, the simpler instrument and less chemical investment and secondary pollution indicates its great potential in refractory organic wastewater treatment. 3.5. Implication of the findings As the economic prosperity and the enhancement in human living standard, more and more refractory emerging contaminants have been found in water environment worldwide, such as pharmaceuticals, personal care product, pesticides and so on, which are resistant to biological process in the wastewater treatment [28, 29]. Electrochemical AOPs have been commonly suggested as the cost-effective method for the removal of persistent organic pollutants from aqueous systems [30, 31]. The experimental results all above have confirmed our hypothesis that the single-layer 9

graphene possesses significant ability to catalyze H2O2 decomposition towards OH• without assistance of metal impurities at the neutral condition. Moreover, electrolysis is an indispensable condition for that process. According to that, the graphene and even the reduced graphene oxide should be a promising catalyst for the cathodic electrochemical AOPs with a GDE, where the oxidant is produced in-situ from oxygen in the atmosphere. By improving the modification method of the graphene on the GDE, it is very hopeful to provide an efficient and economic electrochemical AOP for refractory organic wastewater treatment.

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4. Conclusions A nonmetallic EAOP was constructed by preparing a rolled graphene-doped carbon black GDE as the cathode. Under a constant potential, oxygen from the atmosphere was reduced to H2O2 in situ under the catalysis of the carbon black and then the graphene transferred an electron to H2O2 to produce OH•. An appropriate amount of graphene is required (1wt% in this work) for the sequential H2O2 production followed by OH• production with equal reaction ratio to avoid the self-reaction between H2O2 and OH• on the GDE. It may be overcame by loading the graphene on the surface of the carbon black CL as an independent layer, artificially constructing the divided reactions regions for oxygen reduction and H2O2 decomposition. In the EAOP with 1wt% graphene-doped carbon black GDE, 20 mg L-1 of BPA was completely removed within 30 min and the removal of TOC reached 44.60%, much higher than the value obtained from EAOP with carbon black GDE. This work provide an in-situ and environmental method for organic wastewater treatment under mild conditions. Acknowledgments The authors gratefully acknowledge financial support by the Research Project of Tianjin City for Application Foundation and Advanced Technology (BE026071).

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Figure Captions: Fig. 1 (a) Schematic diagram of the GDE and pictures of the CL (left) and GDL (right) of a rolled sample, (b) Schematic diagram the electrolysis reactor: 1. solid cover plate 2. electrolysis cell 3. cover plate with a circle hole 4. Pt sheet 5. Ag/AgCl reference electrode 6. Pt wire 7. gas diffusion electrode, (c) (d) and (e) SEM images of the CLs, (f) Pore size distribution in the CLs. The inner image of (c) is the graphene image covered on the surface of the carbon black CL. Fig. 2 (a) CV curves with the electrolyte of 0.5 M Na2SO4 (T = 25°C, pH = 6.5), inner

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image is the LSV curves obtained in the same conditions, (b) Tafel plots with the electrolyte of 0.5 M Na2SO4, the overpotential from 60 mV to 80 mV was linear fitted. Fig. 3 (a) H2O2 concentration and pH value of the electrolyte as electrolysis time, (b) ESR spectrum after an electrolysis time of 30 min. Fig.4 Illustration of OH• production mechanism on the graphene-doped carbon black GDE. Fig.5 (a) Degradation curves for BPA in the EAOP system with fresh and graphene-doped carbon black GDEs at neutral pH; (b) Corresponding TOC removal for the three systems.

13

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Fig. 1

14

Fig. 2

15

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Fig. 3

16

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Fig. 4

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Fig. 5

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Table 1. Results of the mercury porosimeter, GFAAS and electrochemical measurements. Carbon black

Graphene

Carbon black

Graphene-doped

Graphene-doped

(0.1 g)

(0.1 g)

GDE

GDE by 1wt%

GDE by 3wt%

Total pore area (m g )

85.5

85.8

87.0

Porosity (%)

70.1

70.8

71.2

2

-1

Fe content (ppb)

3.14

9.53

12.56

12.82

13.33

Cu content (ppb)

23.98

10.45

95.92

95.38

94.30

q* (mC)

19.21

-2

3.02×10

Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

j0 (A cm )

19

30.43 -6

1.10×10

41.74 -4

1.27×10-4

Table 2. Performance comparison of BPA degradation with literatures. Approach

Experimental conditions

Average BPA

TOC

removal

removal

-1

(mg h ) Plasma/Fenton

carbon steel cathode (7.79 cm2), [Fe2+] 20 -1

rate

References

(%)

6

-

[23]

0.95

39

[24]

4.95

-

[25]

9.13

54.9

[26]

0.41

-

[27]

1.44

44.6

This work

-1

mg L , [BPA]0 5 mg L , pH 5.5, V 600 ml, E 20 kV

Fenton

FexCo3−xO4

nanocages

(0.1

L-1),

g

-1

Downloaded by [JAMES COOK UNIVERSITY] at 12:34 26 August 2017

peroxymonosulfate (0.2 g L ), [BPA]0 20 mg L-1, pH 6, V 50 ml

Fenton

Hydrazine

(25.64

L-1),

mg -1

Fe[Co(CN)6]•2H2O (0.2 g L ), [BPA]0 20 mg L-1, [H2O2] 72 mg L-1, pH 4, V 25 ml Fenton

Sulfur-modified iron oxide (0.2 g L-1), -1

-1

[BPA]0 45.66 mg L , [H2O2] 72 mg L , pH 7, V 100 ml

Photoelectrocatalysis/F enton

CeO2- reduced graphene oxide co-modified 2

2+

TiO2 nanotube arrays (6 cm ), [Fe ] 56 mg L-1, [EDTA] 234 mg L-1, [BPA]0 10 mg L-1, [H2O2] 340 mg L-1, pH 6, V 100 ml, 50 mM Na2SO4, , light intensity 110 mW cm-2, E 5 V

CEAOP

Graphene-doped GDE (7 cm2), i 2.86 mA -2

cm , 50 mM Na2SO4, pH 6, [BPA]0 20 mg L-1, V 30 ml

20

Graphene-doped carbon black gas diffusion electrode for nonmetallic electrochemical advanced oxidation process under mild conditions.

Graphene-doped (...
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