Synergy between Fenton process and DBD for methyl orange degradation

Materials Research Bulletin 120 (2019) 110581

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Synergy between Fenton process and DBD for methyl orange degradation a,⁎

a

a

Xumei Tao , Chen Yang , Zhenhui Wei , Liang Huang Ruoyu Xiea, Dongyan Xua a b

b,⁎

a

a

, Jingxuan Chen , Wenwen Cong ,

T

College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042 Shandong, China College of Electromechanical Engineering, Qingdao University of Science and Technology, Qingdao 266042 Shandong, China

ARTICLE INFO

ABSTRACT

Keywords: Fenton reaction DBD plasma Methyl orange Synergistic effect CuFe-LDHs

Dielectric barrier discharge was synergized with Fenton process using CuFe layered double hydroxides as catalysts for methyl orange degradation. The synergistic process achieved better effects than that of DBD alone and Fenton alone, which showed high degradation efficiency and loose pH requirements. The effects of Cu/Fe molar ratios, catalyst dosage, hydrogen peroxide dosage and the reaction kinetics were investigated, and the mechanism of the reaction process was proposed. The degradation rate of 200 mL (100 mg/L) methyl orange could reach up to 99.9% within 13.5 min, under the conditions that discharge voltage of 7.5 kV, CuFe-LDHs of 1 g/L, Cu/Fe molar ratio of 4, H2O2 dosage of 0.6 mL.

1. Introduction Advanced oxidation technologies (AOTs) are considered as the most promising and highly competitive water and wastewater treatment methods for the removal of bio recalcitrant compounds [1–3]. Advanced oxidation process (AOPs) can directly mineralize or increase the biodegradability of pollutants through oxidation, and produce reactive oxygen species (ROS) which can attack and degrade a broad range of persistent organic pollutants (POPs) [4]. It has great advantages in the treatment of trace amounts of harmful chemicals such as environmental hormones. Advanced oxidation technology is characterized by the production of hydroxyl radicals (·OH) with strong oxidizing power [3]. According to the way of generating free radicals and the reaction conditions, it can be divided into photochemical oxidation [5–11], catalytic wet oxidation [12], sonochemical oxidation [13], ozone oxidation [14], electrochemical oxidation [15], Fenton oxidation [16], ect. Among them, Fenton oxidation method utilizes the chain reaction between Fe and H2O2 to catalyze the formation of ·OH radicals, while ·OH radicals have strong oxidizing properties and can oxidize various toxic and refractory organic compounds to achieve the removal of pollutants [17,18]. It has the advantages of simple operation process, low operation cost, low equipment investment and environmental friendliness. Hu et al. [19] and Martínez et al. [20] studied Fe-droped catalysts for wastewater treatment and achieved good results. However, conventional Fenton process is confined by low pH levels (around 3) [21] to prohibit iron precipitation due to the generation of ferric hydroxide sludge. Meanwhile, the difficulties in separation and recycling of the catalyst from ⁎

the solution and long reaction time also limits the further application of homogeneous Fenton process in some aspects. Plasma oxidation technology introduces energy into the reaction zone to generate highly active species to attack and degrade pollutant molecules [22,23]. Plasma discharge generates free radicals (such as ·O2− and ·OH), ultraviolet light, shock waves, which can produce direct pyrolysis on pollutant molecules [24–26], and shows high removal efficiency and environmental compatibility for treating organic pollutants [27]. In our previous work [28], two-level dielectric barrier discharge (DBD) plasma technology was used to degrade methyl orange (MO) and achieved excellent results. Therefore, Fenton oxidation and plasma oxidation can achieve better treatment effect on printing and dyeing wastewater. In recent years, many studies have focused on the synergy between Fenton and plasma. Son et al. [29] explored the synchronized methylene blue removal using Fenton-like reaction induced by phosphorous oxoanion and submerged plasma irradiation process. Slamani et al. [30] studied using plasma gliding arc discharge as the initiation to degrade paracetamol in water and increased the degradation and mineralization rate. Layered double hydroxides (LDHs) are a general term for hydrotalcite (HT) and hydrotalcite-like compounds (HTLCs) [17]. The catalytically active species are intercalated between the hydrotalcite layers and the hydrotalcites are used as a precursor. LDHs, with the characteristics of small crystalline grains, uniform distribution of active sites, large surface area, sintering resistance and good stability, which are beneficial to the catalytic performance, has been widely used in the field of catalysts or catalyst carriers.

Corresponding authors. E-mail addresses: [email protected] (X. Tao), [email protected] (L. Huang).

https://doi.org/10.1016/j.materresbull.2019.110581 Received 2 June 2019; Received in revised form 15 July 2019; Accepted 12 August 2019 Available online 13 August 2019 0025-5408/ © 2019 Published by Elsevier Ltd.

Materials Research Bulletin 120 (2019) 110581

X. Tao, et al.

Fig. 1. Reaction device diagram (a) and experimental flow chat of synergetic process of DBD and CuFe-LDHs for MO degradation (b).

2. Experimental 2.1. Preparation of CuFe-LDHs CuFe-LDHs with different Cu/Fe molar ratios were prepared by coprecipitation method. A certain amount of nitrate solid powder was separately dissolved in deionized water named salt solution A; meanwhile, a certain amount of anhydrous NaCO3 and NaOH were dissolved in deionized water to prepare alkali solution B. A and B were added dropwise to a four-necked flask under vigorous stirring. The temperature was kept constant at 80 ℃, and the pH was controlled between 9.3 and 9.7 during the reaction. Stirring was continued for 30 min after the completion of the dropwise addition of the salt solution. The obtained product was crystallized at 60 ℃ for 24 h, washed, suction filtered, and dried to obtain CuFe-LDHs. Samples with Cu/Fe molar ratios of 2, 3, and 4 were named as LDH-2, LDH-3, and LDH-4, respectively.

Fig. 2. XRD results of CuFe-LDHs with different Cu/Fe molar ratios.

2.2. Fenton process

Table 1 Average particle size of CuFe-LDHs with different Cu/Fe molar ratios. Sample

Average particle size (nm)

LDH-2 LDH-3 LDH-4

14 29 7

A 200 mL (100 mg/L) MO solution was placed in a beaker and CuFeLDH was added into it. The pH of the solution was adjusted to 3 with diluted hydrochloric acid. A certain amount of H2O2 (30% wt) was pipetted into the beaker while the reaction solution was stirred with a magnetic stirrer. After the reaction was started, a certain amount of the reaction solution was taken out every 10 min, and the suspension was centrifuged at 3000 rpm. The MO concentration in the supernatant was analyzed at 463 nm using a UV–vis spectrophotometer. The degradation rate of the MO solution was defined as equation (1-1).

Table 2 Composition of CuFe-LDHs with different Cu/Fe molar ratios. Element

Cu Fe O

Degradation rate (%) = (1-C/C0) × 100% = (1 − A/A0) × 100% (1-1)

EDS wt% LDH-2

LDH-3

LDH-4

56.96 35.17 7.86

57.68 28.48 13.84

75.44 17.69 6.86

Where, C0 and C were the initial and changed concentrations of MO, and A0 and A represented the initial and changed absorbance of MO at 463 nm, respectively. 2.3. DBD process

In this paper, CuFe-LDHs were used as catalysts to degrade MO solution by synergy between Fenton oxidation method and DBD plasma oxidation method. The structure of CuFe-LDHs under different metal element molar ratios and the role it played in the reaction were analyzed in order to find a more efficient wastewater treatment method.

The DBD reactor was shown in Fig. 1(a). The reactor was a casing structure, with aluminum foil on the outer surface as the high voltage electrode, and a metal rod as the low voltage electrode. The wastewater flowed into the inner tube could be simultaneously regarded as the low voltage electrode since it was conductive and was connected to the low 2

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Fig. 3. SEM images of CuFe-LDHs with different Cu/Fe molar ratios. (a, b, c) LDH-2; (d, e, f) LDH-3; (g, h, i) LDH-4.

voltage electrode. After the wastewater filled the inner tube, it overflowed to the outer tube, so that a liquid film was formed on the outer wall of the inner tube. When the plasma was generated, the active particles generated in the annular space acted on the liquid film. The experimental flow chat of synergetic process of DBD and CuFeLDHs for MO degradation was shown in Fig. 1(b). An air pump was connected to the reactor to continuously provide air atmosphere. 200 mL (100 mg/L) MO solution with a certain amount of CuFe-LDHs was pumped into the reactor by a peristaltic pump. The voltage and discharge power of DBD plasma were adjusted to be 7.5 kV and 117.5 W, respectively. After the reaction was started, a certain amount of the reaction solution was taken out every 10 min, and the suspension was centrifuged at 3000 rpm. The MO concentration in the supernatant was analyzed at 463 nm using a UV–vis spectrophotometer.

150 mA. XRD patterns were scanned in the 2θ range of 3°–80° at a scan rate of 10°/min (step size 0.02°/s). Energy dispersive spectroscopy (EDS) was used to quantitatively analyze the surface elements. Scanning electron microscope (SEM) was conducted with JSM-6700 F, a Japanese electronics company, to characterize the surface morphology of the sample. The X-ray photoelectron spectra (XPS) was measured with an ESCALAB 250xi spectrometer, monochromatic radiation from the Al Kα radiation (150 W), and the Al Kα monochromatic line (1486.6 eV) was adopted for the high-resolution analysis. The position of the C1 s peak (284.8 eV) was used to amend the XPS binding energies for the samples for possible charging effects.

2.4. Synergy of DBD and Fenton processes

3.1.1. XRD results Fig. 2 showed the XRD patterns of CuFe-LDHs with different Cu/Fe molar ratios. The reflection peaks at 2θ = 31.4°, 35.5°, 39.0°, 48.4°, 58.2° could be attributed to the presence of CuO tenorite phase (JCPDS card 05-0661). Meanwhile, the diffractogram also showed changes in the baseline through the rising of a broad background, indicating the formation of an amorphous phase of Fe-based oxides [31]. This was fundamentally related to the Jahn-Teller effect. Cu(OH)2 was unstable in highly alkalinous media and could be easily converted to CuO [32]. This suggested that the CuO detected in the samples came from Cu (OH)2 formed in the co-precipitation step that was transformed into CuO during the crystallization process. With the increase in Cu/Fe molar ratio, the diffraction peak became sharper and the crystallinity of LDHs increased.

3. Results and discussion 3.1. Characterization analysis of CuFe-LDHs

The synergy of DBD and Fenton process was similar as Fig. 1(b). Before the reaction, CuFe-LDHs and a certain amount of H2O2 were added to the reaction system and mixed uniformly. After the reaction was started, a certain amount of the reaction solution was taken out every 10 min, and the suspension was centrifuged at 3000 rpm. The MO concentration in the supernatant was analyzed at 463 nm using a UV–vis spectrophotometer. 2.5. Materials characterization X-ray diffraction (XRD) was carried out by a Japanese Rigaku D/max-rA type X-ray diffractometer with a Cu kα radiation operated at 40 kV and 3

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Fig. 4. XPS spectrum of CuFe-LDHs with different Cu/Fe molar ratios. (a) survey spectrum; (b) Cu 2p; (c) Fe 2p. Table 3 Binding energies of Cu 2p and Fe 2p. Sample

Percentage of Cu+ (%)

Binding energy (eV) Cu 2p3/2 +

LDH-2 LDH-3 LDH-4

Fe 2p3/2 2+

+

Cu

Cu

Cu

sat.

933.47 933.48 933.45

934.91 934.96 934.9

941.67 941.57 941.54

2+

Cu

sat.

943.61 943.51 943.5

Fe

2+

2p3/2

711.07 710.94 711.18

Fe 2p1/2 Fe

3+

2p3/2

713.38 713.37 713.96

satellite peak

Fe2+ 2p1/2

Fe3+ 2p1/2

718.83 718.78 718.98

724.62 724.22 723.59

727.75 726.41 726.09

55.09 54.56 55.24

Fig. 5. Effect of (a) Cu/Fe molar ratios (b) LDH-4 dosage on Fenton catalytic activity.

According to the XRD spectrum, the average particle size of CuFeLDHs with different Cu/Fe molar ratios were calculated, as shown in Table 1. The estimated error of the average particle size generally corresponded to ± 0.5 nm. It could be seen that LDH-4 had the smallest average particle size. The smaller the particle size presented larger specific surface area, which could expose more active sites and be

beneficial to the catalytic performance. 3.1.2. EDS results EDS quantitative analysis was carried out on the surface of CuFeLDHs as shown in Table 2. The results showed that Cu/Fe molar ratios were 1.6, 2.6 and 4.2, respectively, which was basically in agreement 4

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chemical state of the elements in CuFe-LDHs. Fig. 4(a) displayed the XPS survey spectrum obtained from LDH-2, LDH-3 and LDH-4, whose peaks were mainly attributed to C 1s, O 1s, Fe 2p and Cu 2p regions [33]. The Cu 2p3/2 spectra (Fig. 4(b)) exhibited two broad peaks in the range of 933–935 eV and 936–944 eV, which could be deconvolved into 4 peaks: the main Cu 2p3/2 peak of Cu2+ and Cu+ around 935 eV and 933 eV, respectively, as well as their shake-up satellite lines around 943 eV and 940 eV, respectively [34–36]. The binding energies of these peaks and the percentage of Cu+ calculated by the peak area were listed in Table 3. Concerning the Cu 2p spectra, the main peak of Cu 2p3/2 and a satellite located on the higher binding energy side, indicating that the Cu cations were present as Cu2+. For all samples, the main Cu 2p3/2 peak was broad and asymmetric on lower binding energies side [37]. The presence of Cu+ suggested an electron transfer between metals in CuFe-LDHs. For LDH-4, 55.24% Cu cations were present as Cu+. Four peaks at around 711.0 eV, 713.5 eV, 718.8 eV and 726.4 eV (Fig. 4(c)) assigned to Fe2+ 2p3/2, Fe3+ 2p3/2, Fe2+ 2p1/2 and Fe3+ 2p1/2, respectively, indicating that this catalyst was composed of Fe2+ and Fe3+ species [38]. The presence of Fe2+ also suggested an electron transfer between metals in CuFe-LDHs. Meanwhile, a satellite bands at around 718.8 eV was recorded which was also regarded as an indicator of Fe3+ valence state. XPS results suggested that the obtained material already existed metal elements Cu+, Cu2+, Fe2+ and Fe3+, and coincided with the data stated before.

Fig. 6. Degradation of MO with DBD and combination of DBD and CuFe-LDHs.

with the theoretical ratio, confirming that the composition of samples agreed with the nominal values. 3.1.3. SEM results The SEM images of CuFe-LDHs with different Cu/Fe molar ratios were shown in Fig. 3. It could be seen that the morphology of CuFeLDHs was lamellar, and CuFe-LDHs with different Cu/Fe molar ratios had obvious differences in surface morphology. When the molar ratio of Cu/Fe was 4, the sheet structure was arranged neatly. When the molar ratio of Cu/Fe was 3, the lamellar structure was scattered, relatively disordered, and partially agglomerated.

3.2. Synergistic effect of Fenton and DBD process on MO degradation To evaluate the Fenton performance of CuFe-LDHs, experiments were carried out with 1 g/L CuFe-LDHs of different Cu/Fe molar ratios and 0.6 mL of H2O2, as shown in Fig. 5(a). The results showed that CuFe-LDHs exhibited Fenton performance, and LDH-4 was superior to

3.1.4. XPS results X-ray photoelectron spectroscopy (XPS) was performed to reveal the

Fig. 7. Effect of H2O2 dosage on synergistic effect of Fenton and DBD process on MO degradation (a) LDH-2; (b) LDH-3; (c) LDH-4.

5

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where kobs was the pseudo-first-order apparent rate constant, and t was the reaction time. By plotting -ln(C/C0) as a function of t and calculating kobs from the slope of the line. The kinetics parameters shown in Table 4 indicated that the degradation of MO on CuFe-LDHs samples could be fitted by the pseudo-first-order model, which was also similar to many studies [39,40]. Comparison of MO degradation under different reaction conditions was shown in Fig. 9. The optimum reaction conditions for MO degradation was LDH-4 of 1 g/L, H2O2 of 0.6 mL, synergy of Fenton and DBD process, with 99.9% degradation rate of MO within 13.5 min. Five times recycling experiments were performed to probe the recyclability and reusability of CuFe-LDHs in the Fenton and DBD process. As shown in Fig. 10, the samples still maintains more than 80% degradation efficiency for MO after five times cycles.

Fig. 8. Effect of LDH-4 dosage on synergistic effect of Fenton and DBD process on MO degradation.

3.3. Synergistic mechanism of Fenton and DBD process on MO degradation

others with nearly 90% degradation rate of MO within 90 min. The effect of LDH-4 dosage on Fenton performance was shown in Fig. 5(b). The degradation rate of MO increased with increasing dosage of LDH-4. To investigate the catalytic performance of CuFe-LDHs, experiments were conducted with DBD alone, as well as the combination of DBD and CuFe-LDHs, as shown in Fig. 6. It was indicated that degradation of MO with DBD was much more effective than that of Fenton catalysis. CuFeLDHs played a vital role when combined with DBD for MO degradation, and LDH-4 was slightly superior than others. Combination of Fenton and DBD process on MO degradation was carried out under the condition of 1 g/L CuFe-LDHs as shown in Fig. 7. Fenton and DBD process had obvious synergistic effect on MO degradation. However, the proper H2O2 dosage for CuFe-LDHs with different Cu/Fe molar ratios when combined Fenton and DBD process was different, as 0.6 mL of H2O2 was proper for LDH-2 and LDH-4, while 0.8 mL of H2O2 was proper for LDH-3. LDH-4 exhibited the highest efficiency with synergy of Fenton and DBD process for MO degradation. Effect of LDH-4 dosage with 0.6 mL H2O2 on synergistic effect of Fenton and DBD process on MO degradation was shown in Fig. 8. The degradation efficiency was the highest when 1 g/L catalyst was added. Adding too much or too little would change the discharge characteristics of the DBD plasma and had an adverse effect on the degradation effect. The degradation kinetics of MO in the DBD process and the synergistic process of Fenton and DBD were investigated. Cu/Fe molar ratios and H2O2 dosage were chosen as two significant factors affecting the MO degradation. The degradation kinetics of MO followed pseudofirst-order reaction kinetics as equation (3-1)

In order to figure out the role of various active specials on MO degradation in Fenton and DBD process and to discuss the reaction mechanism, Tert-butanol (TBA), benzoquinone (BQ) and EDTA were used as the capture agents of % OH, O %2− and photogenerated hole (h+ ), respectively [41–43]. As shown in Fig. 11, after the addition of the capture agents, the reaction efficiency was reduced because the capture agents consumed the active species in the reaction system that contributed to the degradation of MO. It proved that active species including ·OH, ·O 2 − and h + were generated during the reaction and they played a vital role in the degradation process of MO. Combined with the above characterization and experimental results, we thus proposed a possible mechanism of MO degradation in the synergistic Fenton and DBD process. The mechanism diagram was shown in Fig. 12. The presence of Fe2+ and H2O2 could produce O%H during Fenton process. A series of active groups, including %OH and O%2−, whose oxidation ability was extremely strong, were generated [44] during the discharge process. Under the irradiation of ultraviolet light generated by DBD and strong electric field, photogenerated holes (h+) and photo-generated electrons (e−) were generated on the surface of CuFe-LDHs and catalytic redox reaction occurred to produce H2O2 and dissolved oxygen [45,46]. And this part of residual H2O2 could be utilized through Fenton reaction to produce more O%H [46], which further enhanced the degradation of MO. The degradation of MO was finally achieved by redox reactions of the active species.

ln(C/C0) = −kobst

Synergy of DBD and Fenton reaction for MO degradation achieved better effects than that of DBD alone and Fenton alone,

4. Conclusions

(3-1)

Table 4 The kinetics parameters of H2O2 dosage using samples in Fenton and DBD process. sample

LDH-2

LDH-3

H2O2 dosage /mL

kobs /min−1

R2

kobs /min−1

R2

kobs /min−1

R2

0 0.4 0.6 0.8

0.21882 0.37403 0.2838 0.42413

0.98238 0.96373 0.98808 0.90675

0.18186 0.28118 0.19652 0.21855

0.98814 0.91817 0.98776 0.99371

0.20821 0.37403 0.2838 0.42413

0.99406 0.94537 0.98644 0.92749

6

LDH-4

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Fig. 9. Comparison of MO degradation under different reaction conditions. Fig. 12. Synergistic mechanism of Fenton and DBD process on MO degradation.

Acknowledgements This work was supported by University Students Innovation and Entrepreneurship Training Program from Qingdao University of Science and Technology [grant number 201810426116]. We also would like to acknowledge the support of Chao Sun and Yuanyuan Han for useful discussions and helps. References [1] D.B. Luiz, A.K. Genena, H.J. José, R.F.P.M. Moreira, H.Fr. Schröder, Tertiary treatment of slaughterhouse effluent: degradation kinetics applying UV radiation or H2O2/UV, J. Water Sci. Technol. 60 (2009) 1869–1874, https://doi.org/10.2166/ wst.2009.583. [2] I. Oller, S. Malato, J.A. Sánchez-Pérez, Combination of advanced oxidation processes and biological treatments for wastewater decontamination-A review, J. Sci. Total Environ. 409 (2011) 4141–4166, https://doi.org/10.1016/j.scitotenv.2010. 08.061. [3] R. Andreozzi, V. Caprio, A. Insola, R. Marotta, Advanced oxidation processes (AOP) for water purification and recovery, J. Catal. Today 53 (1999) 51–59, https://doi. org/10.1016/S0920-5861(99)00102-9. [4] A. Khataee, P. Gholami, B. Vahid, Catalytic performance of hematite nanostructures prepared by N2, glow discharge plasma in heterogeneous Fenton-like process for acid red 17 degradation, J. J. Ind. Eng. Chem 50 (2017) 86–95, https://doi.org/10. 1016/j.jiec.2017.01.035. [5] P. Jantawasu, T. Sreethawong, S. Chavadej, Photocatalytic activity of nanocrystalline mesoporous-assembled TiO2 photocatalyst for degradation of methyl orange monoazo dye in aqueous wastewater, J. Chem. Eng. J. 155 (2009) 223–233, https://doi.org/10.1016/j.cej.2009.07.036. [6] J.N. Jebaranjitham, C. Mageshwari, R. Saravanan, N. Mu, Fabrication of amine functionalized graphene oxide – AgNPs nanocomposite with improved dispersibility for reduction of 4-nitrophenol, J. Composites, Part B 171 (2019) 302–309, https:// doi.org/10.1016/j.compositesb.2019.05.018. [7] C. Yang, Z. Xue, J. Qin, M. Sawangphruk, S. Rajendran, X. Zhang, R. Liu, Visible light-driven photocatalytic H2 generation and mechanism insights into Bi2O2CO3/ G-C3N4 Z-Scheme photocatalyst, J. J. Phys. Chem. C 123 (2019) 4795–4804, https://doi.org/10.1021/acs.jpcc.8b10604. [8] L. Gnanasekaran, R. Hemamalini, R. Saravanan, J. Qin, M.L. Yola, N. Atar, F. Gracia, Nanosized Fe3O4 incorporated on a TiO2 surface for the enhanced photocatalytic degradation of organic pollutants, J. Mol. Liq. 287 (2019) 110967, , https://doi.org/10.1016/j.molliq.2019.110967. [9] M. Zhang, J. Qin, R. Saravanan, X. Zhang, R. Liu, Heterostructured d‐Ti3C2/TiO2/ g‐C3N4 nanocomposites with enhanced visible‐light photocatalytic hydrogen production activity, J. ChemSusChem 11 (2018) 4226–4236, https://doi.org/10.1002/ cssc.201802284. [10] R. Saravanan, S. Agarwal, V.K. Gupta, M.M. Khan, F. Gracia, E. Mosquera, V. Narayanan, A. Stephen, Line defect Ce3+ induced Ag/CeO2/ZnO nanostructure for visible-light photocatalytic activity, J. J. Photochem. Photobiol. A 353 (2018) 499–506, https://doi.org/10.1016/j.jphotochem.2017.12.011. [11] C. Yang, J. Qin, R. Saravanan, X. Zhang, R. Liu, WS2 and C-TiO2Nanorods Acting as Effective Charge Separators on g-C3 N4 to Boost Visible-Light Activated Hydrogen Production from Seawater, J. ChemSusChem 11 (2018) 4077–4085, https://doi. org/10.1002/cssc.201801819. [12] J. Levec, A. Pintar, Catalytic wet-air oxidation processes: a review, J. Catal. Today 124 (2007) 172–184, https://doi.org/10.1016/j.cattod.2007.03.035. [13] E. Naffrechoux, S. Chanoux, C. Petrier, J. Suptil, Sonochemical and photochemical oxidation of organic matter, J. Ultrason. Sonochem. 7 (2000) 255–259, https://doi. org/10.1016/S1350-4177(00)00054-7. [14] S.V. Geluwe, L. Braeken, B.V. Bruggen, Ozone oxidation for the alleviation of

Fig. 10. Recyclability and reusability tests of CuFe-LDHs samples.

Fig. 11. Effect of capture agents on MO degradation in Fenton and DBD process.

which showed high degradation efficiency and loose pH requirements. CuFe-LDHs with Cu/Fe molar ratio of 4 exhibited excellent performance with synergy of DBD and Fenton process, attributed to higher crystallinity, smaller particle size, the presence of CuO and the electron transfer between metals in CuFe-LDHs. Active groups with strong oxidation ability, including %OH and O%2−, were generated during the DBD process and Fenton process and the degradation of MO was finally achieved by redox reactions of these active species. The degradation rate of 200 mL (100 mg/L) MO could reach up to 99.9% within 13.5 min, under the conditions that discharge voltage of 7.5 kV, CuFe-LDHs of 1 g/L, Cu/Fe molar ratio of 4, H2O2 dosage of 0.6 mL. The synergistic technology improved the efficiency of wastewater treatment, and also provided new ideas for researches in the field of pollutant degradation. 7

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[15] [16] [17]

[18] [19]

[20]

[21] [22] [23]

[24]

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