Highly Efficient Degradation of Polyacrylamide by an Fe-Doped Ce0

Subscriber access provided by BUFFALO STATE

Energy, Environmental, and Catalysis Applications

High Efficient Degradation of Polyacrylamide by Fedoped Ce0.75Zr0.25O2 Solid Solution / CF Composite Cathode in Heterogeneous Electro-Fenton Process Liangbo Xie, Xueyue Mi, Yigang Liu, Yi Li, Yan Sun, Sihui Zhan, and Wenping Hu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b06396 • Publication Date (Web): 30 Jul 2019 Downloaded from pubs.acs.org on July 30, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

High Efficient Degradation of Polyacrylamide by Fe-doped Ce0.75Zr0.25O2 Solid Solution / CF Composite Cathode in Heterogeneous ElectroFenton Process Liangbo Xie1, Xueyue Mi2, Yigang Liu3, Yi Li1*, Yan Sun2, Sihui Zhan2*, Wenping Hu1 1

Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry,

School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China. 2

Key Laboratory of Pollution Processes and Environmental Criteria (Ministry of Education),

College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China. 3

Bohai Oilfield Research Institute, Tianjin Branch, CNOOC China Limited, Tianjin 300459,

China.

1

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: Polyacrylamide (PAM) in environmental water has become a major problem in water pollution management due to its high molecular mass, corrosion resistance, high viscosity and non-absorption by soil. Composite of Fe-doped Ce0.75Zr0.25O2 solid solution (Fe-Ce0.75Zr0.25O2) loading on carbon felt (CF) was fabricated by using hydrothermal synthesis method, which was used as the cathode in heterogeneous electro-Fenton (EF) system for the degradation of PAM. It showed that the degradation efficiency of PAM by Fe-Ce0.75Zr0.25O2/CF cathode was 86% after 120 min, and the molecular mass of PAM decreased by more than 90% after 300 min. Total organic carbon (TOC) removal reached 78.86% in the presence of Fe-Ce0.75Zr0.25O2/CF, while the value was only 38.01% in the absence of Fe-Ce0.75Zr0.25O2. Further studies showed that the breaking of the chain begins with the amide bond, and then the carbon chain was cracked into a short alkyl chain. As degradation progressed, both the complex viscosity and elasticity modulus of PAM solutions were decreased nearly 50% at 300 min. It indicated that ·OH were the most significant active species for the degradation of PAM. This novel Fe-Ce0.75Zr0.25O2/CF composite is an efficient and promising electrode for the removal of PAM in wastewater.

KEYWORDS: electro-Fenton, Fe-Ce0.75Zr0.25O2/CF, polyacrylamide, degradation, hydroxyl radical

2


Page 2 of 32

Page 3 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction Generally, polyacrylamide (PAM) is considered as a kind of water-soluble non-toxic polymer molecule, which widely exists in wastewater discharged from papermaking, mineral processing, oil production and other industries. In particular, it consumes hundreds of thousands of tons of PAM per day in oil field. However, PAM-containing sewage could increase the total organic carbon (TOC) value in water, which caused a series of environmental issues.1 Therefore, more efforts should be devoted to the conversion of PAM-containing wastewater into non-toxic and low molecular mass substances. The electro-Fenton (EF) technology can produce a strong oxidizing hydroxyl radical (OH) (Eo = 2.80 V/SHE), which is a potential candidate for the removal of organic pollutants.2 With the increasing attention to environmental issues in the world, heterogeneous EF has become the focus of research in the field of sewage treatment, which provides an attractive picture for the sewage purification. Heterogeneous EF process uses solid catalyst source to decompose H2O2 into OH, which avoids the shortcomings of homogeneous EF in the production of iron-containing sludge, low utilization rate of H2O2, poor catalyst circulation and so on. Therefore, the construction of a reasonable electrode material for heterogeneous EF process is of central importance for effective removing of PAM in wastewater. At present, carbon-based materials have been widely used in fuel cells, water vapor conversion, especially in the field of sewage treatment because of their large specific surface area, excellent conductivity, easy modification and high stability.3 Related studies have shown that metal oxide surface modified carbon-based materials have incomparable advantages in adsorbing organic pollutants and providing catalytic active sites, and are widely used in the field of heterogeneous EF.3-5 The EF cathode material of Fe3O4-NP@ carbon nanofiber (CNF) textile has been synthesized to removal carbamazepine in wastewater.5 The synergistic

3



effect of Fe3O4-NP@CNF textile achieved a higher removal rate of pollutants. In addition, ironbased element modified reduced graphene oxide had been proved to have the synergistic effect of EF and filtration processes and have high stability and antifouling property.4 And the removal rate of antibiotic florfenicol was as high as 90%. Compared with above carbon-based materials, carbon felt (CF) has the advantages of convenient modification, low cost and has been widely used in the field of EF degradation of pollutants.6,7 Cretin and co-workers synthesized hierarchical CoFelayered double hydroxide (CoFe-LDH) grown on CF for heterogeneous EF system by using in situ solvothermal growth.7 It is found that the CoFe-LDH/CF cathode not only ameliorated the applicable pH range of catalytic degradation, but also improved the formation of H2O2, which was mainly due to the combination of CoFe-LDH and CF. Therefore, CF is a promising and versatile alternative to heterogeneous EF for PAM removal. Iron-based catalyst is distinguished as an effective Fenton reagent, which has vital effects on the activation of hydrogen peroxide in Fenton reaction. However, the effective reduction of Fe3+ is the rate-limiting step of H2O2 decomposition, which restricts the wide applications of Fenton reaction in the field of pollutant degradation.8 Therefore, increasing the decomposition rate of H2O2 by using catalyst is an effective way to improve the degradation efficiency of organic pollutants.9 Ceria (CeO2) has been widely used in the field of environmental catalysis because of its excellent redox performance.10 In recent years, CeO2 has received widespread attentions. Well accepted that Ce-based mixed oxides with transition metal oxides, such as Fe3O4/CeO2, have greatly improved catalytic performance.11 Furthermore, CeO2 is considered to be an effective thermocatalyst in the presence of precious metal, which can effectively remove volatile organic compounds, mainly due to its reducibility.12 On the other hand, CeO2 has the ability to activate H2O2 similar to iron-based catalyst and can decompose it into OH.13,14 Other studies have shown

4


Page 4 of 32

Page 5 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


that the formation of a ceria–zirconia solid solution by doping Zr into CeO2 lattice would enhance the redox properties and the oxygen mobility.15 Hence, in this work, we fabricated a Fe-doped Ce0.75Zr0.25O2 solid solution (Fe-Ce0.75Zr0.25O2)/CF composite cathode for heterogeneous EF process and the performance of Fe-Ce0.75Zr0.25O2/CF for the degradation of PAM was detailedly investigated. 2. Materials and Methods Chemicals. Ferric chloride hexahydrate (FeCl3·6H2O; CAS: 10025-77-1, 99%), Cerium nitrate hexahydrate (Ce(NO3)3·6H2O; CAS: 13093-17-9(51523), 99%), Zirconium nitrate pentahydrate (Zr(NO3)4·5H2O; CAS: 13746-89-9(51064), 99%), Sodium formate (HCOONa; CAS: 141-53-7, 99%), Sodium hydroxide (NaOH; CAS: 1310-73-2(82001), 96%), Sulfuric acid (H2SO4; CAS: 7664-93-9(81007), 98%) and Sodium sulfate (Na2SO4; CAS: 7757-82-6, 99%) were purchased from Shanghai Aladdin Industrial Co. Bromine (Br2; CAS: 7726-95-6(81021), >3%) and Polyacrylamide (PAM; CAS: 9003-05-8, 500 kDa) were obtained from Shanghai Macklin biochemical technology Co. Ltd. Analytical-grade Cadmium iodide (CdI2; CAS: 7790-80-9, 99%) was purchased from Meryer (Shanghai) Chemical Technology Co. Ltd. All of the reagents aforementioned were analytical grade and used directly. The CFs were supplied by Shanghai Qijie carbon material Co. Ltd. Materials preparation and cathode fabrication. The cathode material was obtained by using coprecipitation method. Firstly, 34.40 mg Ce(NO3)3·6H2O, 11.33 mg Zr(NO3)4·5H2O and 14.27 mg FeCl3·6H2O (molar ratio of 3:1:2) dissolved in 50 mL beaker with 20 mL deionized water. Then the pretreatment CF (5 cm×3 cm×0.5 cm) was immerged into the aforementioned solution.16 When the CF was completely soaked, 0.1 mol·L-1 NH3·H2O was added to the solution until the yellowish-brown precipitation was formed. In order to disperse the precipitation adequately on the

5



surface of CF, the ultrasonic treatment was carried out for 30 min. The precursor of FeCe0.75Zr0.25O2/CF cathode was obtained. Afterward, the Fe-Ce0.75Zr0.25O2/CF was dried at 65 °C overnight. Finally, the 3.13 wt% Fe-Ce0.75Zr0.25O2/CF cathode was heated to 500 °C at 10 °C·min-1 under a flow of N2 (99.999%) for 5 h. Similarly, different amount of Fe-Ce0.75Zr0.25O2 loading on CF and different molar ratios of Fe-Ce0.75Zr0.25O2/CF were prepared by using similar method. Heterogeneous EF process for PAM degradation. The degradation experiments of PAM were performed in an electrolytic tank (100 mL) equipped with two-electrode system. The prepared FeCe0.75Zr0.25O2/CF was employed as cathode, and the platinum electrode (2 cm×1 cm) was used as anode. The distance between the two electrodes was 1 cm. Then 200 mg PAM was dissolved in 50 mmolL-1 Na2SO4 solution which served as simulated wastewater, and the concentration of PAM in all experiments was 200 mg·L-1, which was no longer specified below. At last, 0.5 mol·L-1 sulfuric acid and 0.5 mol·L-1 sodium hydroxide were employed to adjust pH value. In heterogeneous EF process, the compressed O2 (99.998%) was persistently pumped into the supporting electrolyte at a rate of 100 mL·min-1. Analytical procedures. The concentration of PAM was detected by Starch-cadmium iodine method, the standard curve of UV absorbance versus PAM concentration shown in Figure S1.17 The concentration of H2O2 produced in heterogeneous EF process was quantified by potassium iodide spectrophotometry (λ = 352 nm, εmax = 26400 M-1cm-1).18 Surface morphology was monitored by using scanning electron microscopy (SEM) coupled with mapping analysis (JEOL6700 FESEM, Japan). Brunauer-Emmett-Teller (BET) and density functional theory (DFT) methods were used to figure out the total surface area and pore size distribution of different materials, employing the surface area and pore-size analyzer (Quantachrome Autosorb iQ-MP) by the nitrogen adsorption-desorption isotherm at 77 K. X-ray photoelectron spectroscopy (XPS) was

6


Page 6 of 32

Page 7 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


collected on an ESCALAB 250Xi spectrometer (Thermo Scientific, UK) with a monochromatic Al Kɑ source (1486.6 eV), and all binding energies were referenced to the C 1s peak at 284.8 eV. The X-ray diffraction (XRD) patterns of different materials were performed with Rigaku D/max 2500 v/pc instrument employing Cu Kɑ source (λ=1.5406 Ǻ), over a 2θ range of 10° - 80°. The electron paramagnetic resonance (EPR) spectrometer (Magnettech MiniScope 400, Germany) was executed to identify free radical produced in degradation process. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and electrochemical active surface area (ECSA) were used to detect the electrochemical behavior of electrode in typical three-electrode system. Fe-Ce0.75Zr0.25O2/CF was used as the working-electrode. Pt plate (1 cm×1 cm) and saturated calomel electrode (SCE) were used as the counter electrode and the reference electrode, respectively. The dissolved PAM was freeze-dried to get the solid power. The structures of cathode materials and PAM were identified by Fourier transform infrared spectrometry (FT-IR). TOC was measured on a Shimadzu VCSH TOC analyzer. Acute toxicity tests were carried out at multi-mode microplate readers (SynergyTM H4, BioTek, USA). Molecular mass change of PAM during the heterogeneous EF process was detected by gel permeation chromatography (GPC; 1515, Waters Co., USA). The structures of PAM and its degradation products were identified by nuclear magnetic resonance spectrometry (NMR; AVANCE III HD, Bruker Co., Germany). Rheological property change of PAM solution during the heterogeneous EF process was monitored by Discovery DHR-2 rheometer. 3. Results and Discussion Optimization of parameters for heterogeneous EF treatment of PAM. In order to improve the degradation efficiency of PAM, we explored influence factors in heterogeneous EF process by using Fe-Ce0.75Zr0.25O2/CF cathode. The molar ratio of elements was rather vital in the degradation

7



Page 8 of 32

process of organic pollutants.19 In our previous work, we found that the optimal degradation efficiency was obtained when the molar ratio of Ce/Zr was 3:1, so the iron content was discussed detailedly in this work.20 As shown in Figure 1a, the degradation efficiency of PAM increased initially and followed a decrease with the increase of the iron content. When the molar ratio of Ce/Zr/Fe increased from 3:1:1 to 3:1:2, the degradation efficiency increased from 69% to 86% at 120 min. However, with the continuous increase of iron content, the degradation efficiency of PAM decreased to 75%, 66% and 64% which corresponded to the molar ratio of Ce/Zr/Fe at 3:1:4, 3:1:8 and 3:1:10, respectively. So it was confirmed that the optimal molar ratio of Ce/Zr/Fe was 3:1:2 in this work. The result showed that Fe-Ce0.75Zr0.25O2 had more excellent heterogeneous catalytic performance and superior oxidative degradation of PAM. As a classical Fenton reagent, iron had a profound effect on the degradation efficiency. Under the condition of lower iron content, the reduction amount of H2O2 to ·OH (Equation 1) was not enough, which was the limiting factor of ·OH production. Herein, the degradation efficiency was limited due to the inadequate active ·OH. When Fe content was too high, excessive Fe2+ might consume ·OH and made it into OH− (Equation 2) instead of producing active ·OH.21 Fe2 + + H2O2 + H + → Fe3 + + ·OH + H2O Fe2 + + ·OH → Fe3 + + OH -

(1) (2)

The optimal loading amount of Fe-Ce0.75Zr0.25O2/CF composite in heterogeneous EF process was evaluated. As shown in Figure 1b, when the amount of Fe-Ce0.75Zr0.25O2 loaded on CF was 3.13 wt%, the degradation efficiency was the highest and reached 86% at 120 min. Nevertheless, the degradation efficiency was successive 77%, 68%, 67%, 65% and 60% at 120 min corresponded to 4.90 wt%, 1.87 wt%, 6.18 wt%, 8.91 wt% and 1.08 wt% Fe-Ce0.75Zr0.25O2 loaded on CF, respectively. Modified Fe-Ce0.75Zr0.25O2 on CF could improve electron transport properties and

8


Page 9 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


produce more active sites. Therefore, the increasing loading amount of Fe-Ce0.75Zr0.25O2 gave a good rise to degradation efficiency. However, excessive loading of Fe-Ce0.75Zr0.25O2 (4.90 wt% or above) might cause the aggregation of Fe-Ce0.75Zr0.25O2 and the decline of the degradation efficiency due to the block of Fe-Ce0.75Zr0.25O2 particles on CF. Therefore, the active sites on the surface of Fe-Ce0.75Zr0.25O2/CF would be covered, which would hinder the electron transfer and reduce reaction sites.22

Figure 1. Degradation efficiency of PAM for different cathodes under different conditions (a) molar ratio of Ce/Zr/Fe, (b) loading amount of Fe-Ce0.75Zr0.25O2, (c) pH and (d) current value. The value of pH was investigated in PAM degradation process when 3.13 wt% FeCe0.75Zr0.25O2/CF was used as cathode and applied current was 200 mA. As shown in Figure 1c, the degradation efficiency of PAM was the highest and reached 86% at pH = 3. It indicated that Fe-Ce0.75Zr0.25O2/CF might had better oxidative degradation efficiency at pH = 3 and produced 9



Page 10 of 32

abundant high activity ∙OH as shown in Equation 1-4. When pH was 2, the degradation efficiency of PAM decreased rapidly, reaching only 52%. The possible reason was that the ion spalling and the active sites decreased in the catalyst which caused by strongly acidic environment. Furthermore, excess H+ had a undesired side reaction that eventually overflowed in the form of H2 (Equation 5), resulting in forming a competitive side reaction with two electron oxygen reduction reactions as depicted in Equation 6.23 As the initial pH was 5 or higher, the degradation efficiency of PAM decreased, especially at pH = 6, and the degradation efficiency was 68%. The reason was the catalyst deactivation that the Ce4+ and Fe3+ in heterogeneous EF system easily formed Fe(OH)3 and Ce(OH)4, respectively.24 The synergistic electrocatalytic cycles of Ce4+/Ce3+ and Fe3+/Fe2+ were broken. Therefore, the value of pH could affect the degradation process of PAM, and unsuited value led to competitive side reactions. When the initial pH was 3, the Fe-Ce0.75Zr0.25O2 catalyst could in situ generate H2O2 continuously.25 That was an important intermediate step to achieve oxidative fragmentation of PAM molecular chains. Ce3 + + H2O2 + H + →Ce4 + + ·OH + H2O Ce4 + + Fe2 + → Ce3 + + Fe3 +

(3) (4)

2H + +2e - → H2(g)

(5)

O2(g) +2H + +2e - → H2O2

(6)

The effect of applied current was also investigated in heterogeneous EF process as shown in Figure 1d. The results showed that 200 mA was the optimal current for the degradation of PAM and the degradation efficiency reached 86% at 120 min. Nevertheless, the degradation efficiency decreased greatly whether the current went up or down. Hence, the applied current was of particular importance to the degradation of PAM in heterogeneous EF process.26 Excessive current would induce the undesired side reactions, such as over-reduction of metal ions and the reduction

10


Page 11 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of H2O2 to H2O as shown in Equation 7.27 Inversely, the Fe3+ and Ce4+ couldn’t be reduced due to insufficient electron, so Ce3+ and Fe2+ could not be recovered in time. Only when the applied current reached about 200 mA, the reactive metal ion would have a benignant circle to keep the Fenton reaction proceeding continuously.20 2H2O2 → O2(g) +2H2O

(7)

Furthermore, in order to find the effect of Fe-Ce0.75Zr0.25O2/CF on the degradation of PAM in heterogeneous EF system, blank measurement for the adsorption of PAM by CF was carried out in Figure 1 and Figure S2. It showed that CF had a strong adsorption capacity for PAM and it is up to about 59%. The degradation efficiency increased to 72% in EF process with Fe2+ and CF (Fe2+/CF) system. The degradation efficiency of PAM was the lowest in anodic oxidation process, and the degradation efficiency was only 4% at 120 min. What’s more, the best degradation efficiency was obtained in heterogeneous EF process, and the degradation efficiency reached 86% at 120 min. Structural and textural characterizations of the electrode. The different magnification SEM images of CF and Fe-Ce0.75Zr0.25O2/CF electrode were shown in Figure 2a and 2b. The SEM images of pure CF showed that carbon fibers interlace with each other to form a complex threedimensional network structure. And the carbon fiber of Fe-Ce0.75Zr0.25O2/CF was evenly coated with Fe-Ce0.75Zr0.25O2 particles. The elemental mapping analysis of Fe-Ce0.75Zr0.25O2/CF electrode (Figure 2c-g) provived strong evidence that the Fe-Ce0.75Zr0.25O2 composition uniformly distributed on the surface of CF. From above results, we could find that Fe-Ce0.75Zr0.25O2 uniformly distributed on the surface of CF, which would increase the percentage of surface atoms and catalytic activity sites on CF.

11



To further understand the composition of three-element composite electrode, the FT-IR spectroscopy of CF and Fe-Ce0.75Zr0.25O2/CF was employed by using KBr pellet pressing method as shown in Figure S3. For comparison, CeO2, ZrO2, and Fe3O4 were also discerned by FT-IR spectroscopy. Comparison of FT-IR spectra before and after Fe-Ce0.75Zr0.25O2 loading on CF, the absorption peaks at 586.07 cm-1(Zr-O-Zr), 529.09 cm-1 (Fe-O), 510.02 cm-1 (Ce-O), 410.83 cm-1 (Zr-O) were all in the infrared spectrum of Fe-Ce0.75Zr0.25O2/CF.28-30 While the absorption peak strength of the carbon-carbon triple bond or cumulative double bond functional group was weakened, and the stretching vibration absorption peaks of the C-O bond at 1082 cm-1 and 1022.81 cm-1 were also presented for CF after loading Fe-Ce0.75Zr0.25O2. Results indicated that the FeCe0.75Zr0.25O2 catalyst had been successfully loaded on the surface of CF.

Figure 2. The different magnification SEM images of CF (a), Fe-Ce0.75Zr0.25O2/CF electrode (b) with the elemental mapping analysis (c-g).

12


Page 12 of 32

Page 13 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In order to clearly verify the constitution of composite electrode, the XRD patterns were shown in Figure S4. As shown in Figure S4, the XRD patterns of Fe-Ce0.75Zr0.25O2 matched well with the standard data for the Ce0.75Zr0.25O2 (111), (200), (220), (400) and (331), which could be attributed to the cubic structure of Ce0.75Zr0.25O2 (JCPDS no. 28-0271). And there were no characterization peaks of Fe element could be observed in the XRD patterns of Fe-Ce0.75Zr0.25O2 and the diffraction peaks shifted slightly to higher angle in comparison to the Ce0.75Zr0.25O2, indicating the formation of ternary metal composite oxide Fe-Ce0.75Zr0.25O2 and phase structure of the Ce0.75Zr0.25O2 nanocomposite was unchanged.31,32 The XRD patterns of Fe-Ce0.75Zr0.25O2/CF shown above indicated that the Fe-Ce0.75Zr0.25O2/CF composite cathode was successfully obtained, which was in accordance with the FT-IR spectroscopy of Fe-Ce0.75Zr0.25O2/CF.

Figure 3. Nitrogen adsorption-desorption isotherm curve (a) and pore diameter distribution (b) of Fe-Ce0.75Zr0.25O2/CF. The N2 adsorption-desorption isotherm and pore diameter distribution curve were shown in Figure 3 and Figure S5. Clearly, this isotherm presented the type IV curve with hysteresis loop. As listed in Table S1, the specific surface area of Fe-Ce0.75Zr0.25O2/CF was 64.5 m2·g-1, the pore volume was 0.1 cm3·g−1 and the average pore size was 7.2 nm, which could better adsorb organic molecules and produce H2O2 by two-electron reduction of dissolved oxygen. The formation of

13



Page 14 of 32

mesoporous structure and specific surface area provided more active sites for the degradation of PAM. Therefore, in situ formation of ·OH was occurred on the electrode interface as showed in Equation 1. The active radical of ·OH would directly oxidize the target molecules on the surface of Fe-Ce0.75Zr0.25O2/CF, so that the reaction distance was shortened and the reaction rate was accelerated.

Figure 4. C 1s spectrum of Fe-Ce0.75Zr0.25O2/CF (a). O 1s spectra of Fe-Ce0.75Zr0.25O2/CF and FeCe0.75Zr0.25O2 (b, c). Ce 3d spectrum of Fe-Ce0.75Zr0.25O2/CF (d). Table 1. XPS analysis results of samples Samples

O

O

Fe-Ce0.75Zr0.25O2.

37.50 %

62.50 %

α

14


β

Page 15 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fe-Ce0.75Zr0.25O2/CF

45.36 %

54.64 %

The XPS measurements could reveal the composition and the surface electronic structure of the Fe-Ce0.75Zr0.25O2/CF cathode. The C 1s XPS spectrum for Fe-Ce0.75Zr0.25O2/CF (Figure 4a) could be deconvoluted into two peaks at 284.8 eV (sp2 carbon of graphitic C=C) and 286.1 eV (C-O-M, C atoms of the CF bonding to the deprotonated hydroxyl groups).33,34 The formation of the C-OM was beneficial to combine the CF and metallic element of Fe-Ce0.75Zr0.25O2, which was better to accelerate electronic transmission in heterogeneous EF system. On the other hand, the FeCe0.75Zr0.25O2/CF had more chemisorbed oxygen species such as O- or O2- compared with FeCe0.75Zr0.25O2 catalyst, which corresponded to hydroxyl-like group or defect-oxide at 532.0 eV (denoted as Oα) (Figure 4b and 4c), whereas the peak with a lower binding energy around 529.9 eV was ascribed to the lattice oxygen species (denoted as Oβ) (See Table 1).35 As shown in Table 1, the relative ratio of Oα / (Oα+ Oβ) for Fe-Ce0.75Zr0.25O2/CF (45.36 %) was higher than that of FeCe0.75Zr0.25O2 (37.50 %), suggesting that the content of adsorption oxygen increased due to the formation of Fe-Ce0.75Zr0.25O2/CF composite material. Generally, it is considered that Oα has higher activity than Oβ in the oxidation reaction.36 Therefore, the adsorption and activation of oxygen molecules formed active oxygen species, which improved the degradation efficiency of PAM for Fe-Ce0.75Zr0.25O2/CF. In Figure 4d, the Ce 3d XPS spectrum showed two main peaks at 885.2 eV for Ce 3d5/2 and 904.6 eV for Ce 3d3/2 peak, respectively. The peaks were labeled as V, V', V'', V''', U, U', U'' and U''' locating at the binding energy peaks of 882.9 eV, 886.2 eV, 889.6 eV, 898.6 eV, 901.6 eV, 905.6 eV, 910.0 eV and 917.0 eV, respectively. The binding energy of V, V'', V''', U, U'' and U''' were the fingerprints of Ce4+ (3d104f0), while V' and U' were characteristic peaks of the presence

15



of Ce3+ (3d104f1). Figure S6a depicted the XPS spectrum of Fe 2p for Fe-Ce0.75Zr0.25O2/CF composite. There were two dissociated peaks at 710.54 eV and 724.04 eV corresponding to Fe2+. And two characteristic peaks locating at 712.76 eV and 726.26 eV were identified as Fe3+ with a satellite peak of Fe 2p3/2 at 718.03 eV.37 The proportion of ferrous iron (63.18%) in the composite cathode was more than the content of ferric iron (Table S2), which could be a promotion for the decomposition of H2O2. The XPS spectrum of Zr 3d was shown in Figure S6b. And it showed three primary dissociated peaks located at 182.0 eV (3d5/2), 184.8 eV (3d3/2) and 186.7eV (3d3/2) by curve fitting. All of them corresponded to the oxidation state of Zr4+, which could catch reactive oxygen species.38 The doping of Fe with Ce0.75Zr0.25O2 might produced large numbers of oxygen vacancies in the lattice of CeO2, which was beneficial to the generation of H2O2 in heterogeneous EF system.39 The XPS results interpreted that Fe-Ce0.75Zr0.25O2 catalyst integrated the virtues of ternary metal oxides, leading to the increase of the degradation efficiency.

Figure 5. (a) Cyclic voltammogram of 3.13 wt% and pure CF electrodes in 0.1 mol·L-1 K4[Fe(CN)6] solution at scan rate of 0.04 V·s-1. All scans were performed from the negative potential to positive potential. (b) Nyquist plots of Fe-Ce0.75Zr0.25O2/CF and pure CF electrodes under a potential of 0.8 V in 0.1 molL-1 K4[Fe(CN)6] solution.

16


Page 16 of 32

Page 17 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The electrochemical behavior of Fe-Ce0.75Zr0.25O2/CF was investigated by CV, EIS and ECSA. From Figure 5a, it was found that the redox peak current and peak area values of the FeCe0.75Zr0.25O2/CF increased compared with pure CF, which indicated the Fe-Ce0.75Zr0.25O2/CF had better electrochemical activity due to the faster electron transmission rate of Fe-Ce0.75Zr0.25O2. Figure 5b exhibited the Nyquist plots for CF and Fe-Ce0.75Zr0.25O2/CF electrodes. And the charge transfer resistance at the electrode surface could be represented by the effective diameter of a semicircle.40 The radius of the semicircle of Fe-Ce0.75Zr0.25O2/CF was smaller than that of CF, which indicated that the composite electrodes had better charge transfer ability due to the loading of Fe-Ce0.75Zr0.25O2. To evaluate the electrochemical activity of the electrode, the ECSAs of different electrodes were obtained by measuring the double layer capacitance of the electrode (Figure S7).41 And the ECSA of Fe-Ce0.75Zr0.25O2/CF was 397 cm2, which was higher than that of CF (335 cm2), which potently proved Fe-Ce0.75Zr0.25O2 would accelerate mass transport rates of the reaction (Table S3). Discussion of the degradation process of PAM. In view of PAM is a polymer, GPC chromatogram was performed to better evaluate the degradation effect. From Table 2, it could be seen that molecular mass reduction rate of PAM reached more than 90%. Furthermore, the GPC chromatogram of PAM demonstrated one peak at retention time of 25.73 min after the heterogeneous EF process, while the retention time of untreated PAM was 25.58 min (Figure 6a). As we all know, the polymers were separated according to their relative molecular mass by GPC. The larger molecules had shorter retention time, while the smaller molecules had longer retention time. According to the shift of the peak and the changes of molecular mass during the heterogeneous EF process, we could conclude that PAM happened the chain scission reaction.17

17



Page 18 of 32

To clearly evaluate the degradation process of PAM in heterogeneous EF system, TOC analysis was conducted to monitor the disappearance of PAM during 300 min of treatment. As shown in Figure 6b, CF reached adsorption saturation for PAM within 120 min in the adsorption process, and the corresponding TOC removal rate remained about 10% and made a negligible difference. However, heterogeneous EF process using Fe-Ce0.75Zr0.25O2/CF had the ability to degrade PAM continuously, and the TOC removal rate reached about 79% within 300 min, which fully demonstrated that PAM was catalytically degraded during heterogeneous EF process. In addition, the TOC removal rate was only 38% in the case of Fe2+/CF system. The phenomenon could be account for the superior absorption ability and favourable catalytic activity of the FeCe0.75Zr0.25O2/CF for PAM and its intermediate products. Combined with SEM, XPS, XRD and BET analysis, the Fe-Ce0.75Zr0.25O2/CF had better redox ability and formed more active sites, improving the transmission rate of electrons, the effective decomposition of H2O2 and the formation of ·OH. In comparsion with Fe2+/CF system, Fe-Ce0.75Zr0.25O2/CF had continuous and efficient mineralization level for PAM in heterogeneous EF system. Table 2. Molecular mass changes during heterogeneous EF process Time

Mn/g·mol-1

Mw/g·mol-1

Mz/g·mol-1

0h

4.0 × 106

4.8 × 106

5.5 × 106

1h

3.7 ×106

3.8 × 106

3.8 × 106

2h

1.9 × 106

2.4 × 106

3.2 × 106

3h

6.5 × 105

7.9 × 105

9.8 × 105

4h

5.4 × 105

6.1 × 105

6.8 × 105

5h

3.7 × 105

3.8 × 105

3.9 × 105

Molecular mass reduction rate (%)

90.7

92.0

92.9

18


Page 19 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The acute toxicity test of luminous bacteria is based on the negative correlation between the luminous intensity of bacteria and toxic substances, and the luminous inhibition rate (LIR) reflects the comprehensive toxicity of wastewater.42 The toxicity of the PAM and its intermediate products was determined by monitoring the LIR of marine bacteria Vibrio fischeri after 5 min and 15 min of exposure.43 As shown in Figure S8, PAM itself was not a hazardous pollutant for marine bacteria Vibrio fischeri. At the beginning of the heterogeneous EF process, the toxicity of solutions increased relatively little, reaching a maximum of 30.0%. As degradation proceeded, the toxicity decreased obviously. The toxicity of degradation products after 300 min of treatment was about 5%. These results showed that the heterogeneous EF process was environmentally friendly and the degradation products were almost non-toxic.

19



Figure 6. (a) GPC chromatograms of PAM and its polymeric products obtained at different treatment time. (b) TOC removal of PAM by different degradation systems (c) 1H NMR spectra of untreated PAM and its degradation products in heterogeneous EF process. (d) Changes of storage modulus of PAM solution in heterogeneous EF process. (All the experiments were under conditions of 200 mA, pH = 3 and 3.13 wt% Fe-Ce0.75Zr0.25O2/CF). As shown in Figure S9, the infrared peak at 1405 cm-1 attributed to C−N stretching vibration in amido bond was disappeared after the heterogeneous EF process. Furthermore, the peak at 3450 cm-1 attributed to N-H stretching vibrationa which was weakened and suggested that the number of amido bond decreased.44 The FT-IR spectrum implied the amido bond was the most vulnerable in PAM molecule. So we could conclude that the chain scission started at amido bonds. 1H NMR analysis revealed the similar results. Two characteristic peaks located at δ = 2.08 and 1.52 ppm in 1H

NMR spectrum of untreated PAM pointed to −CH (II) and −CH2 (I) (Figure 6c).44 The

degradation products showed no −CH (II) and −CH2 (I), while the –CH3 at 1.0 ppm appeared a stronger peak. These results indicated that the amido bond was oxidized easily, then the carbon backbone cleaved into shorter alkyl chain. As we all know, PAM is widely used in industry mainly because of its high viscosity and interface elasticity.45 Rheological property was an important indicator to characterize polymer solution, and the rheological property of PAM products in degradation process was shown in Figure 6d and Figure S10. As degradation progressed, both the complex viscosity and elasticity modulus of PAM solution were decreased nearly 50% at 300 min. The above results showed that heterogeneous EF process had tremendous application potential in pretreatment of PAM, expecially in oilfield produced fluid treatment.

20


Page 20 of 32

Page 21 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. (a) EPR spectra of DMPO-·OH in 3.13 wt% Fe-Ce0.75Zr0.25O2/CF and Fe2+/CF systems. (b) Effect of radical scavengers on the degradation of PAM. With the aim of speculating the essential mechanism of PAM degradation in the heterogeneous EF process of Fe-Ce0.75Zr0.25O2/CF, DMPO trapped EPR experiments were carried to explore reactive oxygen species generated in different systems. Figure 7a exhibited the DMPO-·OH peak intensity by using Fe2+/CF and Fe-Ce0.75Zr0.25O2/CF cathode, respectively.46 The heterogeneous EF process of Fe-Ce0.75Zr0.25O2/CF showed stronger characteristic signals than that of Fe2+/CF system, which certified that the chain scission reaction of PAM caused by the produced ·OH. For one thing, the Fe2+ could activate H2O2 to generate OH. For another, Ce3+ caused Fenton-like reaction, which could activate H2O2 to OH as well. In addition, Fe3+/Fe2+ and Ce4+/Ce3+ could occur a thermodynamically spontaneous redox reaction as shown in Equation 4, which would promote the electron transfer of cathode.20 Radical quenching experiments were employed to further confirm reactive oxygen species generated in heterogeneous EF system (Figure 7b). After adding different kinds of excess scavengers (ethanol for both ·OH and ferryl ion, isopropanol for ·OH and p-benzoquinone (PBQ) for ·O2-), the degradation efficiency was monitored to identify the reactive oxygen species.9,47 From Figure 7b, we could see that the PAM degradation efficiency decreased mostly after adding

21



ethanol and isopropanol while the PAM degradation efficiency occurred a slight decline after adding PBQ. It indicated that ·OH was the most significant active species for the degradation of PAM. On the other hand, the contribution of ·O2- to the degradation efficiency was about 4%, suggesting the involvement of ·O2- produced by single-electron reduction of oxygen in the PAM degradation.48 Furthermore, as shown in Figure S11, the H2O2 concentration was 8.2 mg·L-1 at the beginning of the degradation process for Fe2+/CF system, then the H2O2 concentration decreased until it reached 2.0 mg·L-1. Compared to Fe2+/CF system, the concentration of H2O2 produced by Fe-Ce0.75Zr0.25O2/CF was much lower than that of Fe2+/CF system, which demonstrated the better degradation efficiency of Fe-Ce0.75Zr0.25O2/CF due to the quick conversion from H2O2 to ·OH by the heterogeneous EF reaction between H2O2 and Fe2+ or Ce3+. According to above results, the chain scission of PAM induced by active species ·OH in the heterogeneous EF process could be verified. As shown in Scheme 1, the effective adsorption of PAM molecules was attributed to the high specific surface area and large pore size distribution of Fe-Ce0.75Zr0.25O2/CF. On the other hand, Fe-Ce0.75Zr0.25O2 distributed on CF could rapidly reduce dissolved oxygen in the solution to H2O2 on the surface of the electrode. Furthermore, the H2O2 produced on the surface of Fe-Ce0.75Zr0.25O2/CF instantly converted into ·OH by Ce3+ and Fe2+, which was beneficial to the catalytic oxidation of PAM. PAM was then decomposed into shortchain alkyl groups and further decomposed into CO2 and H2O by the oxidation of ·OH.

22


Page 22 of 32

Page 23 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Schematic of heterogeneous EF process and mechanism for PAM degradation by using the Fe-Ce0.75Zr0.25O2/CF cathode. The stability and reusability of the catalyst are the most concerned points in the catalytic reaction. Therefore, we detected the ion leaching concentration of Fe-Ce0.75Zr0.25O2/CF under the optimal degradation conditions. It is found that the leaching ions of the catalyst accumulated continuously during the whole reaction process. After the reaction, the concentrations of Ce, Zr and Fe ions in the electrolyte were 3.9 mg·L-1, 0.2 mg·L-1 and 1.0 mg·L-1, respectively (Figure S12). Although the leaching ion concentrations of metal elements in the catalyst were very low, the leaching of the catalyst was still unfavourable for the heterogeneous EF reaction to a certain degree.6 This was because the surface catalytic effect of the solid catalyst mainly occurred on the surface of the catalyst, and ion leaching might lead to the disappearance of the catalytic site of the catalyst and deactivate the catalyst.7 4. Conclusion

23



Heterogeneous EF process by using Fe-Ce0.75Zr0.25O2/CF cathode was a promising approach for degradation of PAM in environmental water from oil and other chemical industries. It showed that degradation efficiency of Fe-Ce0.75Zr0.25O2 for PAM was up to 86% within 120 min under optimal conditions of applied current 200 mA, pH 3 and 3.13 wt% of Fe-Ce0.75Zr0.25O2/CF. Meanwhile, the molecular mass of PAM was reduced above 90% and the removal rate of TOC was nearly 79%. The high degradation efficiency benefited from the good adsorption capacity, and efficient catalytic performance of Fe-Ce0.75Zr0.25O2/CF. The possible pathway and reaction mechanism were suggested. This work achieved the goal of efficient and rapid treatment of PAM-containing sewage, which opened new avenues for industrial treatment of PAM and provided further understanding for removal process of organic contaminant. Associated Content Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. Supporting information includes Figure S1-S12 and Table S1-S3. Standard curve of UV absorbance versus PAM concentration, detailed characterization of catalysts and degradation products and comparative trial by using different degradation system are included. Author Information Corresponding Author *E-mail: [email protected] *E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

24


Page 24 of 32

Page 25 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Notes The authors declare no competing financial interest. Acknowledgment This project was supported by the National Natural Science Foundation of China (Grant No. 21722702 and 21874099), National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2016ZX05058-003-004), the Tianjin Commission of Science and Technology as key technologies R&D projects (Grant No. 15JCZDJC41200, 16YFXTSF00440, and 16ZXGTSF00020), Innovation and Entrepreneurship Training Program of Tianjin for College Students (Grant No. 201910056072) and the Ministry of Public Security of the PRC (Grant No. 2016JSYJD04). References (1) Al-Sabahi, J.; Bora, T.; Claereboudt, M.; Al-Abri, M.; Dutta, J., Visible Light Photocatalytic Degradation of HPAM Polymer in Oil Produced Water Using Supported Zinc Oxide Nanorods. Chem. Eng. J. 2018, 351, 56-64. (2) Mousset, E.; Frunzo, L.; Esposito, G.; van Hullebusch, E. D.; Oturan, N.; Oturan, M. A., A Complete Phenol Oxidation Pathway Obtained during Electro-Fenton Treatment and Validated by a Kinetic Model Study. Appl. Catal., B 2016, 180, 189-198. (3) Huong Le, T. X.; Bechelany, M.; Cretin, M., Carbon Felt Based-Electrodes for Energy and Environmental Applications: A Review. Carbon 2017, 122, 564-591. (4) Jiang, W.-L.; Xia, X.; Han, J.-L.; Ding, Y.-C.; Haider, M. R.; Wang, A.-J., Graphene Modified Electro-Fenton Catalytic Membrane for in Situ Degradation of Antibiotic Florfenicol. Environ. Sci. Technol. 2018, 52 (17), 9972-9982.

25



(5) Liu, K.; Yu, J. C.-C.; Dong, H.; Wu, J. C. S.; Hoffmann, M. R., Degradation and Mineralization of Carbamazepine Using an Electro-Fenton Reaction Catalyzed by Magnetite Nanoparticles Fixed on an Electrocatalytic Carbon Fiber Textile Cathode. Environ. Sci. Technol. 2018, 52 (21), 12667-12674. (6) Ganiyu, S. O.; Huong Le, T. X.; Bechelany, M.; Oturan, N.; Papirio, S.; Esposito, G.; van Hullebusch, E.; Cretin, M.; Oturan, M. A., Electrochemical Mineralization of Sulfamethoxazole over Wide Ph Range Using FeIIFeIII LDH Modified Carbon Felt Cathode: Degradation Pathway, Toxicity and Reusability of the Modified Cathode. Chem. Eng. J. 2018, 350, 844-855. (7) Ganiyu, S. O.; Huong Le, T. X.; Bechelany, M.; Esposito, G.; van Hullebusch, E. D.; Oturan, M. A.; Cretin, M., A Hierarchical Cofe-Layered Double Hydroxide Modified Carbon-Felt Cathode for Heterogeneous Electro-Fenton Process. J. Mater. Chem. A 2017, 5 (7), 3655-3666. (8) Sun, M.; Ru, X.-R.; Zhai, L.-F., In-Situ Fabrication of supported iron oxides from Synthetic Acid Mine Drainage: High Catalytic Activities and Good Stabilities towards Electro-Fenton Reaction. Appl. Catal., B 2015, 165, 103-110. (9) Dai, C.; Tian, X.; Nie, Y.; Lin, H.-M.; Yang, C.; Han, B.; Wang, Y., Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2 Activation in Fenton-Like Reaction and Organic Pollutant Degradation. Environ. Sci. Technol. 2018, 52 (11), 6518-6525. (10) Zhan, W.; Yang, S.; Zhang, P.; Guo, Y.; Lu, G.; Chisholm, M. F.; Dai, S., Incorporating Rich Mesoporosity into a Ceria-Based Catalyst via Mechanochemistry. Chem. Mater. 2017, 29 (17), 7323-7329. (11) Xu, L.; Wang, J., Magnetic Nanoscaled Fe3O4/CeO2 Composite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of 4-Chlorophenol. Environ. Sci. Technol. 2012, 46 (18), 10145-10153.

26


Page 26 of 32

Page 27 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12) Zeng, M.; Li, Y.; Mao, M.; Bai, J.; Ren, L.; Zhao, X., Synergetic Effect between Photocatalysis on TiO2 and Thermocatalysis on CeO2 for Gas-Phase Oxidation of Benzene on TiO2/CeO2 Nanocomposites. ACS Catal. 2015, 5 (6), 3278-3286. (13) Zang, C.; Yu, K.; Hu, S.; Chen, F., Adsorption-Depended Fenton-Like Reaction Kinetics in CeO2-H2O2 System for Salicylic Acid Degradation. Colloids Surf. A 2018, 553, 456-463. (14) Heckert, E. G.; Seal, S.; Self, W. T., Fenton-Like Reaction Catalyzed by the Rare Earth Inner Transition Metal Cerium. Environ. Sci. Technol. 2008, 42 (13), 5014-5019. (15) Mansingh, S.; Acharya, R.; Martha, S.; Parida, K. M., Pyrochlore Ce2Zr2O7 Decorated over rGO: a Photocatalyst that Proves to be Efficient towards the Reduction of 4-nitrophenol and Degradation of Ciprofloxacin under Visible Light. Phys. Chem. Chem. Phys. 2018, 20 (15), 98729885. (16) Li, Y.; Han, J.; Mi, X.; Mi, X.; Li, Y.; Zhang, S.; Zhan, S., Modified Carbon Felt Made Using Cexa1−Xo2 Composites as a Cathode in Electro-Fenton System to Degrade Ciprofloxacin. RSC Adv. 2017, 7 (43), 27065-27078. (17) Sang, G.; Pi, Y.; Bao, M.; Li, Y.; Lu, J., Biodegradation for Hydrolyzed Polyacrylamide in the Anaerobic Baffled Reactor Combined Aeration Tank. Ecol. Eng. 2015, 84, 121-127. (18) Huang, L.; Szewczyk, G.; Sarna, T.; Hamblin, M. R., Potassium Iodide Potentiates BroadSpectrum Antimicrobial Photodynamic Inactivation Using Photofrin. ACS Infect. Dis. 2017, 3 (4), 320-328. (19) Li, X.; Ao, Z.; Liu, J.; Sun, H.; Rykov, A. I.; Wang, J., Topotactic Transformation of Metal– Organic Frameworks to Graphene-Encapsulated Transition-Metal Nitrides as Efficient Fenton-like Catalysts. ACS Nano 2016, 10 (12), 11532-11540.

27



(20) Li, Y.; Li, Y.; Xie, B.; Han, J.; Zhan, S.; Tian, Y., Efficient mineralization of Ciprofloxacin Using a 3D CexZr1−xO2/RGO Composite Cathode. Environ. Sci.: Nano 2017, 4 (2), 425-436. (21) Borras, N.; Arias, C.; Oliver, R.; Brillas, E., Anodic Oxidation, Electro-Fenton and Photoelectro-Fenton Degradation of Cyanazine using a Boron-Doped Diamond Anode and an Oxygen-Diffusion Cathode. J. Electroanal. Chem. 2013, 689, 158-167. (22) Li, Y.; Zhang, S.; Han, Y.; Cheng, S.; Hu, W.; Han, J.; Li, Y., Heterogeneous Electrocatalytic Degradation of Ciprofloxacin by Ternary Ce3ZrFe4O14-X/CF Composite Cathode. Catal. Today 2019, 327, 116-125. (23) Ding, S.; Liu, X.; Shi, Y.; Liu, Y.; Zhou, T.; Guo, Z.; Hu, J., Generalized Synthesis of Ternary Sulfide Hollow Structures with Enhanced Photocatalytic Performance for Degradation and Hydrogen Evolution. ACS Appl. Mater. Interfaces 2018, 10 (21), 17911-17922. (24) Brillas, E.; Martínez-Huitle, C. A., Decontamination of Wastewaters Containing Synthetic Organic Dyes by Electrochemical Methods. An updated review. Appl. Catal., B 2015, 166, 603643. (25) Yu-xuan, Y.; Shan, C.; Zhang, X.; Liu, H.; Wang, D.; Lv, L.; Pan, B.-C., Water decontamination from Cr(III)-organic complexes based on Pyrite/H2O2: Performance, mechanism, and validation. Environ. Sci. Technol. 2018, 52 (18), 10657-10664. (26) Annabi, C.; Fourcade, F.; Soutrel, I.; Geneste, F.; Floner, D.; Bellakhal, N.; Amrane, A., Degradation of enoxacin antibiotic by the Electro-Fenton Process: Optimization, Biodegradability Improvement and Degradation Mechanism. J. Environ. Manage. 2016, 165, 96-105. (27) Wang, Y.; Liu, Y.; Wang, K.; Song, S.; Tsiakaras, P.; Liu, H., Preparation and Characterization of a Novel KOH Activated Graphite Felt Cathode for the Electro-Fenton Process. Appl. Catal., B 2015, 165, 360-368.

28


Page 28 of 32

Page 29 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Grewal, J. K.; Kaur, M., Effect of Core-Shell Reversal on the Structural, Magnetic and Adsorptive Properties of Fe2O3-GO Nanocomposites. Ceram. Int. 2017, 43 (18), 16611-16621. (29) Ponnaiah, S. K.; Periakaruppan, P.; Vellaichamy, B.; Nagulan, B., Efficacious Separation of Electron–Hole Pairs in CeO2-Al2O3 Nanoparticles Embedded GO Heterojunction for Robust Visible-Light Driven Dye Degradation. J. Colloid Interf. Sci. 2018, 512, 219-230. (30) Reddy, A. S. S.; Kityk, I. V.; Kumar, V. R.; Jedryka, J.; Ozga, K.; Venkatramaiah, N.; Veeraiah, N., Third Order Nonlinear Optical Effects of ZnO–ZrO2–B2O3 Glass Ceramics Embedded with ZnZrO3 Perovskite Crystal Phases. J. Mater. Sci.-Mater. Electron. 2017, 28 (21), 16403-16414. (31) Cai, S.; Zhang, D.; Zhang, L.; Huang, L.; Li, H.; Gao, R.; Shi, L.; Zhang, J., Comparative Study of 3D Ordered Macroporous Ce0.75Zr0.2M0.05O2−δ (M = Fe, Cu, Mn, Co) for Selective Catalytic Reduction of NO with NH3. Catal. Sci. Technol. 2014, 4 (1), 93-101. (32) Ajumobi, O. O.; Muraza, O.; Bakare, I. A.; Al Amer, A. M., Iron- and Cobalt-Doped Ceria– Zirconia Nanocomposites for Catalytic Cracking of Naphtha with Regenerative Capability. Energy Fuels 2017, 31 (11), 12612-12623. (33) Lyu, L.; Yan, D.; Yu, G.; Cao, W.; Hu, C., Efficient Destruction of Pollutants in Water by a Dual-Reaction-Center Fenton-like Process over Carbon Nitride Compounds-Complexed Cu(II)CuAlO2. Environ. Sci. Technol. 2018, 52 (7), 4294-4304. (34) Li, H.; Gan, S.; Wang, H.; Han, D.; Niu, L., Intercorrelated Superhybrid of AgBr Supported on Graphitic-C3N4-Decorated Nitrogen-Doped Graphene: High Engineering Photocatalytic Activities for Water Purification and CO2 Reduction. Adv. Mater. 2015, 27 (43), 6906-6913.

29



(35) Zhang, L.; Shi, L.; Huang, L.; Zhang, J.; Gao, R.; Zhang, D., Rational Design of HighPerformance DeNOx Catalysts Based on MnxCo3–xO4 Nanocages Derived from Metal–Organic Frameworks. ACS Catal. 2014, 4 (6), 1753-1763. (36) Liu, F.; He, H., Structure−Activity Relationship of Iron Titanate Catalysts in the Selective Catalytic Reduction of NOx with NH3. J. Phys. Chem. C 2010, 114 (40), 16929-16936. (37) Jin, H.; Tian, X.; Nie, Y.; Zhou, Z.; Yang, C.; Li, Y.; Lu, L., Oxygen Vacancy Promoted Heterogeneous Fenton-like Degradation of Ofloxacin at pH 3.2–9.0 by Cu Substituted Magnetic Fe3O4@FeOOH Nanocomposite. Environ. Sci. Technol. 2017, 51 (21), 12699-12706. (38) Zhang, Y.; Davenport, A. J.; Burke, B.; Vyas, N.; Addison, O., Effect of Zr Addition on the Corrosion of Ti in Acidic and Reactive Oxygen Species (ROS)-Containing Environments. ACS Biomater. Sci. Eng. 2018, 4 (3), 1103-1111. (39) Gupta, A.; Kumar, A.; Waghmare, U. V.; Hegde, M. S., Activation of Oxygen in Ce2Zr2O7+x across Pyrochlore to Fluorite Structural Transformation: First-Principles Analysis. J. Phys. Chem. C 2017, 121 (3), 1803-1808. (40) Divyapriya, G.; Thangadurai, P.; Nambi, I., Green Approach To Produce a Graphene Thin Film on a Conductive LCD Matrix for the Oxidative Transformation of Ciprofloxacin. ACS Sustain. Chem. Eng. 2018, 6 (3), 3453-3462. (41) Trellu, C.; Chaplin, B. P.; Coetsier, C.; Esmilaire, R.; Cerneaux, S.; Causserand, C.; Cretin, M., Electro-oxidation of Organic Pollutants by Reactive Electrochemical Membranes. Chemosphere 2018, 208, 159-175. (42) Le, T. X. H.; Nguyen, T. V.; Yacouba, Z. A.; Zoungrana, L.; Avril, F.; Petit, E.; Mendret, J.; Bonniol, V.; Bechelany, M.; Lacour, S.; Lesage, G.; Cretin, M., Toxicity Removal Assessments

30


Page 30 of 32

Page 31 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Related to Degradation Pathways of Azo Dyes: Toward an Optimization of Electro-Fenton Treatment. Chemosphere 2016, 161, 308-318. (43) Le, T. X. H.; Nguyen, T. V.; Amadou Yacouba, Z.; Zoungrana, L.; Avril, F.; Nguyen, D. L.; Petit, E.; Mendret, J.; Bonniol, V.; Bechelany, M.; Lacour, S.; Lesage, G.; Cretin, M., Correlation between Degradation Pathway and Toxicity of Acetaminophen and Its By-Products by Using the Electro-Fenton Process in Aqueous Media. Chemosphere 2017, 172, 1-9. (44) Sun, M.; Qiao, M.-X.; Wang, J.; Zhai, L.-F., Free-Radical Induced Chain Degradation of High-Molecular-Weight Polyacrylamide in a Heterogeneous Electro-Fenton System. ACS Sustain. Chem. Eng. 2017, 5 (9), 7832-7839. (45) Venkataraman, P.; Tang, J.; Frenkel, E.; McPherson, G. L.; He, J.; Raghavan, S. R.; Kolesnichenko, V.; Bose, A.; John, V. T., Attachment of a Hydrophobically Modified Biopolymer at the Oil–Water Interface in the Treatment of Oil Spills. ACS Appl. Mater. Interfaces 2013, 5 (9), 3572-3580. (46) Lyu, L.; Yu, G.; Zhang, L.; Hu, C.; Sun, Y., 4-Phenoxyphenol-Functionalized Reduced Graphene Oxide Nanosheets: A Metal-Free Fenton-Like Catalyst for Pollutant Destruction. Environ. Sci. Technol. 2018, 52 (2), 747-756. (47) Tang, J.; Wang, J., Metal Organic Framework with Coordinatively Unsaturated Sites as Efficient Fenton-like Catalyst for Enhanced Degradation of Sulfamethazine. Environ. Sci. Technol. 2018, 52 (9), 5367-5377. (48) Zhang, Y.; Li, J.; Bai, J.; Li, L.; Xia, L.; Chen, S.; Zhou, B., Dramatic Enhancement of Organics Degradation and Electricity Generation via Strengthening Superoxide Radical by Using a Novel 3D AQS/Ppy-GF Cathode. Water Res. 2017, 125, 259-269.

31



Table of Contents (TOC) Graphic

32


Page 32 of 32

Highly Efficient Degradation of Polyacrylamide by an Fe-Doped Ce0

Recommend Documents