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Fenton-Like Catalysis and Oxidation/Adsorption Performances of Acetaminophen and Arsenic Pollutants in Water on a Multimetal Cu− Zn−Fe-LDH Hongtao Lu,† Zhiliang Zhu,*,† Hua Zhang,† Jianyao Zhu,† Yanling Qiu,‡ Linyan Zhu,§ and Stephan Küppers§ †

State Key Laboratory of Pollution Control and Resource Reuse and ‡Key Laboratory of Yangtze River Water Environment, Ministry of Education, Tongji University, Shanghai 200092, China § ZEA-3, Research Center Jülich, Jülich 52425, Germany S Supporting Information *

ABSTRACT: Acetaminophen can increase the risk of arsenicmediated hepatic oxidative damage; therefore, the decontamination of water polluted with coexisting acetaminophen and arsenic gives rise to new challenges for the purification of drinking water. In this work, a three-metal layered double hydroxide, namely, Cu−Zn−Fe-LDH, was synthesized and applied as a heterogeneous Fenton-like oxidation catalyst and adsorbent to simultaneously remove acetaminophen (Paracetamol, PR) and arsenic. The results showed that the degradation of acetaminophen was accelerated with decreasing pH or increasing H2O2 concentrations. Under the conditions of a catalyst dosage of 0.5 g·L−1 and a H2O2 concentration of 30 mmol·L−1, the acetaminophen in a water sample was completely degraded within 24 h by a Fenton-like reaction. The synthesized Cu−Zn−Fe-LDH also exhibited a high efficiency for arsenate removal from aqueous solutions, with a calculated maximum adsorption capacity of 126.13 mg·g−1. In the presence of hydrogen peroxide, the more toxic arsenite can be gradually oxidized into arsenate and adsorbed at the same time by Cu−Zn−Fe-LDH. For simulated water samples with coexisting arsenic and acetaminophen pollutants, after treatment with Cu−Zn−Fe-LDH and H2O2, the residual arsenic concentration in water was less than 10 μg·L−1, and acetaminophen was not detected in the solution. These results indicate that the obtained Cu−Zn−FeLDH is an efficient material for the decontamination of combined acetaminophen and arsenic pollution. KEYWORDS: layered double hydroxides, heterogeneous catalysis, acetaminophen, arsenic, adsorption

1. INTRODUCTION The coexistence of pharmaceuticals and arsenic in water environments and their possible effects on human health have attracted more attention in recent years, as coexisting arsenic and pharmaceuticals are found in different natural water bodies such as Taihu Lake and Dianchi Lake in China and the Columbia River at Warrendale, OR, in the United States.1−4 This gives rise to new challenges in the purification of polluted water. Pharmaceutical contamination in water environments is a public concern.5 Many studies and evaluations have shown that chemicals with pharmaceutical activities are widely found in natural surface water and groundwater systems the serve as sources of drinking water.6−8 As a common antipyretic and analgesic medicine, acetaminophen (Paracetamol) is used all over the world.9 Usually, it cannot be completely metabolized and is excreted through urine and stool, after which it enters into the wastewater system. It can also be discharged during manufacturing or discarded in the form of unused and expired medicines. After the conventional biological treatment process © 2016 American Chemical Society

for water, acetaminophen cannot be completely removed, and a certain amount of acetaminophen will still remain in the water as a pollutant. 10 Acetaminophen is well-known as a pharmaceutically active compound (PAC);11 its continuous release poses potential dangers to animals and people even in very low concentrations;12 and its presence is likely to cause aquatic toxicity, genotoxicity, and endocrine disruption.13 Advanced oxidation processes (AOPs), such as photocatalysis, ozonation, and Fenton oxidation, are important technologies for the degradation of refractory contaminants in water and wastewater. 14−16 Various AOPs such as photocatalytic oxidation,9,17,18 electrochemical oxidation,19 and the Fenton process20 have been employed to remove acetaminophen from polluted water. The advantage of a suitable heterogeneous catalyst is that it can be easily separated from the stream and does not cause disposal problems.21 Among AOPs, the Received: July 20, 2016 Accepted: September 2, 2016 Published: September 2, 2016 25343

DOI: 10.1021/acsami.6b08933 ACS Appl. Mater. Interfaces 2016, 8, 25343−25352

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ACS Applied Materials & Interfaces

arsenic in drinking water and that acetaminophen was not detected.

heterogeneous Fenton method is an attractive technique for removing various organic substances from aqueous solutions.22 Arsenic (As) is both toxic and carcinogenic. Control of arsenic pollution ia a great concern throughout the world. Ingestion of arsenic can lead to seriously detrimental influences on human health including cancers, neurological disorders, and muscular weakness.23 The World Health Organization has set a limit of 10 μg·L−1 for arsenic in drinking water.24 In natural water environments, inorganic arsenic usually occurs in oxidation states of As(III) and As(V).25−27 As(V) species predominate in oxygen-enriched environments, but As(III) is more stable in groundwater systems because of the prevailing anoxic and near-neutral pH conditions.28 Arsenite [As(III)] species have been found to have higher toxicity than arsenate [As(V)] species.29 Many possible technologies for removing arsenic from contaminated water have been investigated, for instance, sedimentation and coagulation,30,31 filtration,32 phytoremediation,33 and adsorption.34−36 Among the many available methods, adsorption is considered to be an promising and practical approach. Usually, As(V) species are easier to adsorbe on the surfaces of adsorbent materials than As(III) species. Several studies have focused on the use of adsorption after oxidation to remove As(III) substances.37 Several methods of oxidation have been reported such as use of O2/O3,38 manganese oxides,39 iron oxides,40 and H2O241,42 and photochemical and photocatalytic oxidations.43,44 In recent years, the study of the toxicology of arsenic and acetaminophen has attracted scientists’ attention.45−48 Several investigations have indicated that acetaminophen can increase the risk of arsenic-mediated hepatic oxidative damage,49,50 which gives rise to new challenges for the purification of drinking water. However, to the best of our knowledge, the simultaneous decontamination of water with coexisting arsenic and acetaminophen has not been reported. Considering the characteristics of arsenic and acetaminophen, the most likely way to simultaneously remove the organic pollutant and arsenic is to use a catalytic/adsorption method. Layered double hydroxide (LDH) materials are useful multifunctional anionic clays with the general form represented by [MII1−xM IIIx(OH)2 ]x+(A n−)x/n·mH2 O. Here, M II and MIII represent ions of divalent and trivalent metals, respectively. The intercalated anion is represented by An−. The number of interlayer waters is denoted as m, and the ratio of MIII/(MII + MIII) is represented by x.51 In recent years, more studies on the synthesis and application of different functional LDHs and related composite materials have been reported.52,53 The main purpose of this study was to find an efficient way to decontaminate the combined water pollution of acetaminophen and arsenic. In this work, a multimetal Cu−Zn−Fe-LDH material with a layer composition including three transitionmetal ions and intercalation of sulfate was developed and used to study the catalytic oxidation and adsorption performances for single and mixed pollutants of acetaminophen and arsenic in water. Based on preliminary experimental results for the catalysis efficiency of the synthesized Cu−Zn−Fe-LDH, further studies on the heterogeneous Fenton process of acetaminophen in aqueous solution, identification of the major degradation intermediates, and possible catalysis mechanism were performed. Then, the catalytic oxidation/adsorption of arsenite was studied. Finally, the Cu−Zn−Fe-LDH material was successfully applied to treat simulated water samples containing coexisting acetaminophen and arsenite pollutants, and it was found that the treated water can meet the requirements for

2. MATERIALS AND METHODS 2.1. Chemicals. Acetaminophen (Paracetamol, PR) was purchased from Sinopharm Chemical Regent Co. with >98% purity and used for test samples. Acetaminophen (purity >99.5%) was purchased from Sigma-Aldrich and used for preparing a standard solution of the compound. Acetaminophen-d4 standard solution, arsenic salt Na2HAsO4·7H2O, and NaAsO2 (purity >98%) were purchased from Sigma-Aldrich. A stock solution with an As(V) concentration of 1000 mg·L−1 was prepared with the pure water from a Milli-Q device (18.2 MΩ·cm at 25 °C). All experimental solutions were made from the stock solution through dilution with deionized water. The experimental solutions of As(III) were freshly made. Other chemicals were all of analytical grade with no further purification before use. 2.2. Synthesis of Cu−Zn−Fe-LDH Material. The Cu−Zn−FeLDH material with intercalation of sulfate ions was synthesized using the coprecipitation method in aqueous solution. First, 1 mol·L−1 NaOH and 100 mL of a mixed solution containing Cu(SO4)2·5H2O (2.49 g), Fe(SO4)2·7H2O (8.34 g), and Zn(SO4)2·7H2O (17.25 g) were slowly dropped into a glass reactor that contained 100 mL of deionized water. The pH value of the mixed solution was controlled at about 7 by addition of dilute sulfuric acid or sodium hydroxide solution. After completion of the reaction, the resulting suspensions were aged at 313 K for 24 h. The suspensions were filtered, and the solid part was washed with deionized water. Then, the obtained material was dried at 313 K to obtain the final product Cu−Zn−FeLDH that was used in the subsequent experiments. 2.3. Characterization of Cu−Zn−Fe-LDH Material. The synthesized Cu−Zn−Fe-LDH material was dissolved in hydrogen nitrate to prepare the chemical analysis solution. The analysis method and instruments for characterization of the materials were the same as described in detail in our previous publications,54,55 and included inductively coupled plasma optical emission spectrometry (ICP-OES; Agilent 720, Palo Alto, CA), X-ray diffraction (XRD; Bruker D8 ADVANCE), Fourier transform infrared (FTIR) spectroscopy (Nicolet Instrument Corporation, Madison, WI), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS; Hitachi S-4800, Tokyo, Japan), transmission electron microscopy (TEM; JEOL JEM-2011, Tokyo, Japan), and X-ray photoelectron spectroscopy (XPS; PHI, Chanhassen, MN). 2.4. Determination of Acetaminophen and Arsenic Concentrations. The acetaminophen concentrations in solution were measured by ultraperformance liquid chromatography (UPLC) with a UV−vis photodiode array detector and an ACQUITY UPC2 BEH (C18), 100 × 3.0 mm, 1.7-μm particle size column. Acetonitrile and water were used as the mobile phases in an acetonitrile/water ratio of 10:90. The flow rate was 0.35 mL·min−1. The sample injection volume and retention time were 5.00 μL and 0.7 min, respectively. The degradation intermediates were determined by high-performance liquid chromatography−time-of-flight mass spectrography (HPLC− TOFMS), using a Waters ACQUITY UPLC I-Class instrument equipped with an ACQUITY UPLC BEH (C18), 100 × 3.0 mm, 1.7μm particle size column. The mobile phases were acetonitrile and water with 0.1% formic acid. The concentrations of arsenic were determined by inductively coupled plasma mass spectrometry (ICPMS) and atomic fluorescence spectrometry (AFS). 2.5. Catalytic Activity Tests. 2.5.1. Degradation of Acetaminophen by Cu−Zn−Fe-LDH with H2O2. Experiments on the catalytic oxidation of acetaminophen degradation were conducted in an Erlenmeyer flask (250 mL). The catalyst material of Cu−Zn−FeLDH was added to 100 mL of aqueous acetaminophen solution (pH 7.0), unless otherwise specified. The pH value of the solution was not adjusted during the experiments. The initial acetaminophen concentration was taken as C0. A solution of H2O2 was added under dark conditions to initiate the reaction of degradation, and the flask was shaken in a thermostatic shaker at 25 °C and 150 rpm. The required samples were removed and filtered with 0.22-μm membranes 25344


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ACS Applied Materials & Interfaces at set time intervals during the reaction to remove the solid material. The residual acetaminophen concentration in the supernatant was then determined by UPLC. A blank test without the addition of H2O2 was carried out at the same time. 2.5.2. Adsorption and Oxidation of Arsenic. Adsorption experiments were conducted using the batch equilibrium sorption method at 298 K. The experiments were performed in triplicate, and the average results are reported. The effects of the original solution pH, sorption isotherm, and kinetics on arsenic adsorption were studied. After the Cu−Zn−Fe-LDH material had been added to the system, the flask was shaken at 150 rpm in a thermostatic shaker for a set time. Then, the solution was filtered with a 0.22-μm membrane and analyzed. The kinetics of As(III) oxidation and the adsorption process were investigated at 298 K and pH 7.0. The initial concentrations of hydrogen peroxide and arsenite were 0.4 mmol·L−1 and 1 mg·L−1, respectively. The amount of Cu−Zn−Fe-LDH material added was in the range of 0.1−0.4 g·L−1.

3.1.3. FTIR Spectroscopy Analysis. Figure 1b shows the FTIR spectrum of the LDH material. The broad and strong absorbance peak at about 3412 cm−1 is related to the hydrogenbond stretching vibrations of the hydroxide layers and interlayer waters. The absorbance peak at 1624 cm−1 is due to the vibration of adsorbed waters.57 The peaks appearing in the range of 450−650 cm−1 can attributed to metal−hydrogen or metal−oxygen bonds.58 The Zn−O lattice vibrations are presented at 513 cm−1.59 The peak at about 1113 cm−1 is attributed to sulfate and is consistent with the results of similar XRD analyses.60,61 3.1.4. Specific Surface Area and Zero Potential Analysis. The N2 adsorption−desorption isotherm of the synthesized material is shown in Figure S1. The isotherm data were in accordance with a type IV adsorption isotherm of the IUPAC classification. The isotherm exhibited an H3 type hysteresis loop, which is relevant for wedge-shaped pores. It can be generated with the packing of plate-like particles. These results indicate that the material had a layer structure and are consistent with another report.62 The specific surface area was 29.7 m2·g−1 [calculated by the multipoint Brunauer−Emmett− Teller (BET) method, C = 472.51]. The pore size distribution based on adsorption data was determined by the Barrett− Joyner−Halenda (BJH) method. The total pore volume was 0.439 cm3·g−1, and the average pore diameter was 33.4 nm. These results indicate that the material belonged to the category of mesoporous materials. The point of zero charge (pHpzc) of the Cu−Zn−Fe-LDH material was 9.6, which was determined from the zeta potential of its dispersions in the pH range from 4 to10 (Figure S2). 3.1.5. Surface Morphology Analysis. A TEM image of Cu− Zn−Fe-LDH is shown in Figure 2a. The as-synthesized Cu− Zn−Fe-LDH was generally hexagonal and schistose. This result is consistent with the XRD index. An SEM image of Cu−Zn− Fe-LDH is presented in Figure 2b. It can be seen that the material aggregated in a lamellar structure. The irregular accumulation of sheet lamina produced pores, in accordance with the pore size analysis. A selected-area electron diffraction (SAED) pattern of the material is shown in Figure 2c, where the crystal plane indices are consistent with the XRD patterns of (110), (300), and (302) (d(110) = 0.2705 nm, d(300)= 0.1545 nm, and d(302) = 0.1500 nm). Figure 2d a high-resolution transmission electron microscopy (HRTEM) image of Cu− Zn−Fe-LDH. It can be seen that the interplanar spacing was about 0.254 nm, which is in agreement with the crystal structure data for the (113) lattice plane determined from the XRD pattern. It also supports the conclusion that the Cu−Zn− Fe-LDH material has a layered structure. An energy-dispersive spectrum of Cu−Zn−Fe-LDH is shown in Figure 3. The

3. RESULTS AND DISCUSSION 3.1. Characterization. 3.1.1. Chemical Composition of Cu−Zn−Fe-LDH. From the chemical analysis results, the metal ratio of the synthesized Cu−Zn−Fe-LDH was determined, and it is reported in Table 1. According to the general structure and Table 1. Chemical Composition of the Cu−Zn−Fe-LDH parameter

chemical analysis result

M(Cu/Zn/Fe)a m(Cu)b (%) m(Zn)b (%) m(Fe)b (%)

1:4.09:2.89 5.68 23.95 14.43

a

Cu/Zn/Fe molar ratio. bMass content of Cu, Zn, or Fe in the material.

composition of LDHs, a chemical formula of [Cu0.13Zn0.51Fe0.36(OH)2](SO4)0.18·mH2O was assumed. This shows that the molar ratio of the metals in the synthesized material was similar to the ratio of the starting reactants. 3.1.2. XRD Analysis. The XRD pattern of the Cu−Zn−FeLDH material is shown in Figure 1a. The reflection of the LDH material’s characteristic peaks was of high intensity. It was found that the material was in a highly crystalline state. The peaks of (001), (002), (003), (110), and (113) were clearly observed, and no peaks of other crystalline phases were found. The FULLPROF program was used to analyze the structure.56 Based on the diffraction data, the sample of Cu−Zn−Fe-LDH was indexed as a hexagonal lattice, with unit-cell parameters of a = 0.5410 nm and c = 1.0914 nm. The spacing of the basal lamina (d(001)) was 1.0914 nm, which is similar to those of SO42−-intercalated LDHs from a previous report.51

Figure 1. (a) XRD pattern and (b) FTIR spectrum of Cu−Zn−Fe-LDH. 25345


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Figure 2. (a) TEM image, (b) SEM image, (c) selected-area electron diffraction (SAED) pattern, and (d) high-resolution transmission electron microscopy (HRTEM) image of Cu−Zn−Fe-LDH.

Figure 3. EDS spectrum of Cu−Zn−Fe-LDH.

from 0.5 to 50 mmol·L−1. Without the addition of the Cu−Zn− Fe-LDH catalyst material, as the H2O2 concentration was increased, the degradation rate of acetaminophen remained nearly unchanged, with almost no degradation occurring, as shown in Figure 4a,b. In the presence of Cu−Zn−Fe-LDH, the acetaminophen degradation rate increased gradually with increasing H2O2 concentration. When the catalyst dosage was

presence of sulfur peaks further confirms the results of the XRD and FTIR analyses. 3.2. Heterogeneous Fenton Degradation Test. 3.2.1. Effect of Hydrogen Peroxide Dosage on Acetaminophen Degradation. A 0.1 mmol·L−1 aqueous solution of acetaminophen was prepared, and then the required amount of Cu−Zn− Fe-LDH (0.5 g·L−1) added. The H2O2 dosage range ranged 25346


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Figure 4. (a,b) Effects of hydrogen peroxide dosage on acetaminophen (PR) degradation ([PR]0 = 0.1 mmol·L−1, [Cu−Zn−Fe-LDH] = 0.5 g·L−1 , T = 25 °C). (c) Effects of catalyst dosage on acetaminophen (PR) degradation ([PR]0 = 0.1 mmol·L−1, [H2O2] = 30 or 50 mmol·L−1 , T = 25 °C). (d) Effects of pH on acetaminophen (PR) degradation ([PR]0 = 0.1 mmol·L−1, [H2O2] = 20 mmol·L−1 , [Cu−Zn−Fe-LDH] = 0.5 g·L−1 , T = 25 °C).

0.5 g·L−1 and the initial H2O2 concentration was 30 mmol·L−1 (mM), after 10 h, the degradation rate of acetaminophen reached 99%. Iron and copper ions were not detected in the solution after the degradation reaction. These results show that Cu−Zn−Fe-LDH can be used as an effective catalyst for the heterogeneous oxidation of acetaminophen. 3.2.2. Effect of Catalyst Dosage on Acetaminophen Degradation. The effect of catalyst dosage on acetaminophen degradation is shown in Figure 4c. The initial concentration of acetaminophen in aqueous solution was 0.1 mmol·L−1. The dosages of the catalyst were set as 0.25, 0.5, and 1.0 g·L−1, respectively. Initial H2O2 concentrations of 30 and 50 mmol· L−1 were used. For a given hydrogen peroxide concentration, it was found that the degradation rate of acetaminophen was obviously enhanced as the catalyst dosage was increased. 3.2.3. Effect of pH on Acetaminophen Degradation. The effect of the solution pH on acetaminophen degradation was studied for different initial pH values in range of 6.0−9.0. The results are shown in Figure 4d. It can be seen that, under weakly acidic conditions, the degradation efficiency of acetaminophen was higher. This behavior is related to the relationship between the redox potential of H2O2 and the hydrogen ion concentration. A higher concentration of hydrogen ions will increase the redox potential of H2O2. 3.3. Adsorption and Heterogeneous Oxidation of Arsenic. 3.3.1. Effect of Solution pH. The effect of the initial solution pH on As(V) adsorption by Cu−Zn−Fe-LDH was studied. The pH values were in the range from 3.0 to 10.0. As shown in Figure S3, high removal efficiencies of As(V) were observed in the pH range of 3−8. Nevertheless, the removal efficiency declined when the initial solution pH was greater than 8. This behavior can be explained in terms of the different forms of As(V) species in aqueous solution at various pH values. H2AsO4− is a major species at pH values in the range from 2.1 to 6.7. However, when the pH value of the aqueous solution was higher than 6.7, the divalent negative ion form

(HAsO42−) will be the dominant.26 Because the pHpzc of Cu− Zn−Fe-LDH is 9.6, the surface was negatively charged fror pH > 9.6. The electrical rejection might be stronger than under low-pH conditions between the negatively charged sites of the surface and the species of HAsO42−. 3.3.2. Adsorption Kinetics. Two kinetics models (pseudofirst-order and pseudo-second-order) were used to fit the batch experimental data. These two models can be expressed by the equations Pseudo-first-order model ln(Q e − Q t ) = ln Q e − K1t

(1)

Pseudo-second-order model t 1 t = + 2 Qt Q K 2Q e e

(2)

where Qe and Qt are the equilibrium adsorption capacity and the amount adsorbed in time t, respectively, and K1 and K2 are the pseudo-first-order and pseudo-second-order rate constants, respectively. As shown in Figure S4, the adsorption was fast in the initial 8 h and then slowed and finally reached equilibrium after 24 h. The kinetics parameters of the fitting curves are presented in Table S1. These results show that the experimental data can be excellently described by the pseudo-second-order model with a value of the correlation coefficient close to 1. 3.3.3. Adsorption Isotherms. The Langmuir, Freundlich, and Sips isotherms models were applied to the analysis of the adsorption data of arsenite and arsenate on the Cu−Zn−FeLDH material. These models can be expressed by the equations Langmuir isotherm

Qe = 25347

Q mKLCe 1 + KLCe

(3) DOI: 10.1021/acsami.6b08933 ACS Appl. Mater. Interfaces 2016, 8, 25343−25352

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Figure 5. Kinetics of As(III) oxidation and adsorption (T = 298 K, pH = 7.0, [H2O2] = 0.4 mmol·L−1). The concentration of As(III) was 1 mg·L−1, and the dosages of catalyst Cu−Zn−Fe-LDH were in the range from 0.1 to 0.4 g·L−1. Changes in (a) As(III) and (b) As(V) concentrations with time in solution.

the coexisting arsenic and acetaminophen is shown in Figure S6. In addition, Figure S7 presents the chromatogram of acetaminophen as a function of time during the treatment of coexisting arsenic and acetaminophen. 3.5. Cyclic Utilization and Stability of Cu−Zn−Fe-LDH. Cu−Zn−Fe-LDH materials before and after the adsorption of arsenic were used to study the cyclic utilization and stability of the LDH as a Fenton catalyst for six cycles. The initial concentration of acetaminophen was 15 mg·L −1. The concentration of hydrogen peroxide was 50 mmol·L−1, and the catalyst dosage was 0.5 g·L−1. The reaction time for each cycle was 24 h. The concentrations of acetaminophen, arsenic, copper, and iron in the solution were detected after each cycle of the reaction. It was found that no arsenic was released into the solution during each cycle. After each cycle, no copper or iron species were found leaching into the solution. As shown in Figure S8, the degradation efficiency of acetaminophen remained almost unchanged in six cycles. These results indicate that the Cu−Zn−Fe-LDH material as a heterogeneous Fenton catalyst can be reused. Arsenic adsorbed on the material had no effect on the catalytic degradation of acetaminophen, and the process of degradation did not cause the release of arsenic. 3.6. Mechanism of Catalytic Oxidation and Adsorption. As stated in section 3.2, the Cu−Zn−Fe-LDH material exhibited good activity for the catalytic oxidation of acetaminophen by H2O2. This is a Fenton-like reaction, where the LDH material acts as the source of Fe2+ ions. Because the Zn−Fe-LDH material without copper exhibited little catalytic activity for the degradation of acetaminophen in our experiments, it can be inferred that Cu2+ might activate and enhance the catalytic activity of the material.63,64 Generally, hydrogen peroxide is believed to have an inclined chain structure. According to the bond energies, it can be speculated that the O−O bond is more likely broken. The layered structure of Cu−Zn−Fe-LDH is shown in Figure S9. The surface of Cu−Zn−Fe-LDH might experience a cyclic process of iron or copper, and active species such as •OH that play a role of oxidation are produced in that process. The H2O2 molecules might form Cu(II)−OOH species with Cu2+ and transfer electrons to produce Cu(I)−OH and •OH.51,65,66 To understand the mechanism more clearly, the surface states of the Cu−Zn−Fe-LDH material before and after the reactions were determined by the XPS analysis method. The XPS full-range spectra are shown in Figure S10. Further details of the S 2p, As 3d, O 1s, Cu 2p, and Fe 2p XPS spectra before and after oxidation/adsorption are shown in Figure 6a, Figure

Freundlich isotherm

Q e = KFCe1/ n

(4)

Sips isotherm Qe =

K sQ mCe m 1 + K sCe m

(5)

where Ce is the equilibrium concentration of the adsorbate; Qm is the maximum adsorption capacity; and KL, KF, and Ks are the Langmuir, Freundlich, and Sips adsorption constants, respectively. In the Sips isotherm, m is an index of heterogeneity. Figure S5 shows the adsorption isotherms of arsenate and arsenite on the Cu−Zn−Fe-LDH material and the fits determined by nonlinear regression. The obtained parameters and constants of the isotherm models are summarized in Table S2. According to the R2 (correlation coefficient) values, the adsorption data of As(V) better conform to the Sips isotherm equation than the others. The maximum adsorption capacity for arsenate was found to be 126.13 mg·g−1. The adsorption data of As(III) can be described well by the Langmuir isotherm equation. The maximum adsorption capacity for arsenite was found to be 51.56 mg·g−1. These results indicate that this synthesized Cu−Zn−Fe-LDH is an efficient material for arsenic decontamination by adsorption from aqueous solutions. 3.3.4. Heterogeneous Oxidation of As(III). The kinetics of arsenite oxidation and adsorption are shown in Figure 5. The concentration of As(III) in solution gradually decreased with time, but the concentration of As(V) species increased in the first 1 h and then decreased and remained stable at a very low level. This indicates that the arsenite was gradually oxidized into arsenate and adsorbed at the same time onto the Cu−Zn−FeLDH. When the material dosage was 0.4 g·L−1, , the residual arsenic in solution after 8 h was less than 10 μg·L−1, which can meet the demands for arsenic in drinking water set by WHO. 3.4. Simultaneous Removal of Acetaminophen and Arsenic. Batch experiments for the removal of coexisting arsenic and acetaminophen in simulated water samples were carried out in an aqueous solution at pH 7.0 that contained As(III) (5 mg·L−1) and acetaminophen (15 mg·L−1). The Cu− Zn−Fe-LDH material dosage was 0.5 g·L−1, and the hydrogen peroxide concentration was 50 mmol·L−1. The result showed that, after 24 h, the remaining concentration of arsenic was less than 10 μg·L−1 and no acetaminophen was detected in the solution by UPLC. The AFS spectra for As after treatment of 25348


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positive level after oxidation/adsorption, and a similar oxygen state of the Cu−Zn−Fe-LDH material surface was found after the oxidation/adsorption of arsenite and the catalytic degradation of acetaminophen. After As(III) oxidation/ adsorption and acetaminophen degradation, the Cu 2p and Fe 2p spectra for the Cu−Zn−Fe-LDH also exhibited little change, as shown in Figure S12. The change in the Cu 2p binding energy after the catalytic oxidation of acetaminophen is more obvious, which indicates that the activity of the copper ions is related. For Fe 2p, the shift from 716.2 to 715.8 eV related to the catalytic oxidation of acetaminophen occurred mainly at about 716 eV. The degradation intermediates of acetaminophen were also identified in our experiments and are shown in Table 2. On the basis of the determined intermediates, a degradation reaction mechanism was speculated. At the beginning of the reaction, HPLC-TOFMS analysis showed the presence of N(3,4-dihydroxyphenyl)acetamide and acetamide. These results indicate that the attack of OH radicals on the aromatic ring proceeds through an addition mechanism.67 A schematic diagram of the possible degradation reaction mechanism of acetaminophen is shown in Figure 7. Based on the above results, the possible removal mechanism of acetaminophen and arsenite by the Cu−Zn−Fe-LDH material could be described as depicted in Figure 8.

Figure 6. (a) S 2p XPS spectra of Cu−Zn−Fe-LDH before and after oxidation/adsorption. (b) As 3d XPS spectra of Cu−Zn−Fe-LDH after oxidation/adsorption of arsenite and coexisting acetaminophen (PR) and arsenite.

6b, Figure S11, and Figure S12, respectively. As shown in Figure 6a, ions exchanged between arsenate and sulfate species lead to the shift of binding energy of S 2p to a less negative level after oxidation and sorption of arsenite. As shown in Figure 6b, the binding energy peaks of As 3d after the oxidation and adsorption of As(III) are 47.6 and 46.4 eV, respectively. This is attributed to the bonding of As(V)−O, revealing that the arsenic species existing on the surface of the material were As(V) only after the oxidation/adsorption of As(III) in a single or coexistence system. Figure S11 shows the O 1s spectra of the material. The binding energy of O 1s has moved to a less

4. CONCLUSIONS A multimetal Cu−Zn−Fe-LDH material was synthesized and used as a heterogeneous Fenton-like oxidation catalyst and adsorbent. The degradation of acetaminophen (PR) and the

Table 2. Identified Intermediates during Degradation of Acetaminophen

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Specific surface area and zeta potential analysis figures, adsorption performances of arsenic on the materials (effects of pH, isotherm, and kinetics), AFS spectra for arsenic, UPLC chromatogram for acetaminophen, cyclic reutilization of Cu−Zn−Fe-LDH, XPS characterization spectra, and diagram of the material’s layered structure (PDF)

AUTHOR INFORMATION

Corresponding Author

*Address: State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, 1239 Siping Road, Shanghai, 200092, China. E-mail: [email protected]. Phone: +86-21-6598 2426. Fax: +86-21-6598 4626. Notes

Figure 7. Schematic diagram of the degradation reaction of acetaminophen.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 41372241).

Figure 8. Diagrammatic sketch of the mechanism for the simultaneous removal of acetaminophen and arsenite by Cu−Zn−Fe-LDH.

oxidation/adsorption of arsenic were studied in aqueous solutions. The degradation of acetaminophen was accelerated by decreasing pH or increasing H2O2 concentration. When the catalyst dosage was 0.5 g·L−1 and the H2O2 dosage of 30 mmol· L−1 (mM), the degradation of acetaminophen reached 99%. The Cu−Zn−Fe-LDH is also a potentially efficient adsorbent for the removal of arsenic from water, with a maximum adsorption capacity of 126.13 mg·g−1. In the presence of hydrogen peroxide, arsenite was gradually oxidized into arsenate and adsorbed by Cu−Zn−Fe-LDH at the same time. For simulated water samples with coexisting arsenic and acetaminophen, after treatment with Cu−Zn−Fe-LDH and H2O2, the remaining concentration of arsenic was less than 10 μg·L−1, and acetaminophen was not detected in the solution. The Cu−Zn−Fe-LDH material obtained in this work might be useful for the simultaneous efficient removal of acetaminophen and arsenic [As(III)/As(V)]. This study focused only on the coexistence of acetaminophen and arsenic. For the wider application of catalytic oxidation and adsorption processes to treat other coexisting pollutants, further research is needed and could expand the application of this functional material in the decontamination of complex pollution systems.

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REFERENCES

(1) Morace, J. L. Water-Quality Data, Columbia River Estuary, 2004− 05; USGS Data Series 213; U.S. Geological Survey: Reston, VA, 2006. (2) Miller, K. J.; Meek, J. Helena Valley Ground Water: Pharmaceuticals, Personal Care Products, Endocrine Disruptors (PPCPs), and Microbial Indicators of Fecal Contamination; Montana Bureau of Mines and Geology Open-File Report 532; Montana Department of Environmental Quality: Helena, MT, 2006. (3) Zhang, N.; Wei, C.; Yang, L. Occurrence of Arsenic in Two Large Shallow Freshwater Lakes in China and a Comparison to Other Lakes around the World. Microchem. J. 2013, 110, 169−177. (4) Lin, T.; Yu, S. L.; Chen, W. Occurrence, Removal and Risk Assessment of Pharmaceutical and Personal Care Products (PPCPs) in an Advanced Drinking Water Treatment Plant (ADWTP) around Taihu Lake in China. Chemosphere 2016, 152, 1−9. (5) Kaplan, S. Review: Pharmacological Pollution in Water. Crit. Rev. Environ. Sci. Technol. 2013, 43, 1074−1116. (6) Murray, K. E.; Thomas, S. M.; Bodour, A. A. Prioritizing Research for Trace Pollutants and Emerging Contaminants in the Freshwater Environment. Environ. Pollut. 2010, 158, 3462−3471. (7) Bu, Q. W.; Wang, B.; Huang, J.; Deng, S. B.; Yu, G. Pharmaceuticals and Personal Care Products in the Aquatic Environment in China: A Review. J. Hazard. Mater. 2013, 262, 189−211. (8) Kasprzyk-Hordern, B.; Dinsdale, R. M.; Guwy, A. J. The Occurrence of Pharmaceuticals, Personal Care Products, Endocrine Disruptors and Illicit Drugs in Surface Water in South Wales, Uk. Water Res. 2008, 42, 3498−3518. (9) Yang, L.; Yu, L. E.; Ray, M. B. Photocatalytic Oxidation of Paracetamol: Dominant Reactants, Intermediates, and Reaction Mechanisms. Environ. Sci. Technol. 2009, 43, 460−465. (10) Jones, O. A. H.; Voulvoulis, N.; Lester, J. N. The Occurrence and Removal of Selected Pharmaceutical Compounds in a Sewage Treatment Works Utilising Activated Sludge Treatment. Environ. Pollut. 2007, 145, 738−744. (11) Santos, J. L.; Aparicio, I.; Alonso, E.; Callejón, M. Simultaneous Determination of Pharmaceutically Active Compounds in Wastewater Samples by Solid Phase Extraction and High-Performance Liquid Chromatography with Diode Array and Fluorescence Detectors. Anal. Chim. Acta 2005, 550, 116−122. (12) Feng, L.; van Hullebusch, E. D.; Rodrigo, M. A.; Esposito, G.; Oturan, M. A. Removal of Residual Anti-Inflammatory and Analgesic Pharmaceuticals from Aqueous Systems by Electrochemical Advanced Oxidation Processes. A Review. Chem. Eng. J. 2013, 228, 944−964. (13) Rakic, V.; Rajic, N.; Dakovic, A.; Auroux, A. The Adsorption of Salicylic Acid, Acetylsalicylic Acid and Atenolol from Aqueous

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Research Article

ACS Applied Materials & Interfaces Solutions onto Natural Zeolites and Clays: Clinoptilolite, Bentonite and Kaolin. Microporous Mesoporous Mater. 2013, 166, 185−194. (14) Yang, X.-j.; Xu, X.-m.; Xu, J.; Han, Y.-f. Iron Oxychloride (FeOCl): An Efficient Fenton-Like Catalyst for Producing Hydroxyl Radicals in Degradation of Organic Contaminants. J. Am. Chem. Soc. 2013, 135, 16058−16061. (15) Liu, W.; Wang, Y.; Ai, Z.; Zhang, L. Hydrothermal Synthesis of FeS2 as a High-Efficiency Fenton Reagent to Degrade Alachlor Via Superoxide-Mediated Fe(II)/Fe(III) Cycle. ACS Appl. Mater. Interfaces 2015, 7 (51), 28534−28544. (16) Zhou, L.; Shao, Y.; Liu, J.; Ye, Z.; Zhang, H.; Ma, J.; Jia, Y.; Gao, W.; Li, Y. Preparation and Characterization of Magnetic Porous Carbon Microspheres for Removal of Methylene Blue by a Heterogeneous Fenton Reaction. ACS Appl. Mater. Interfaces 2014, 6 (10), 7275−7285. (17) Ziylan-Yavas, A.; Mizukoshi, Y.; Maeda, Y.; Ince, N. H. Supporting of Pristine TiO2 with Noble Metals to Enhance the Oxidation and Mineralization of Paracetamol by Sonolysis and Sonophotolysis. Appl. Catal., B 2015, 172−173, 7−17. (18) Moctezuma, E.; Leyva, E.; Aguilar, C. A.; Luna, R. A.; Montalvo, C. Photocatalytic Degradation of Paracetamol: Intermediates and Total Reaction Mechanism. J. Hazard. Mater. 2012, 243, 130−138. (19) Arredondo Valdez, H. C.; García Jimenez, G.; Gutiérrez Granados, S.; Ponce de Leon, C. Degradation of Paracetamol by Advance Oxidation Processes Using Modified Reticulated Vitreous Carbon Electrodes with TiO2 and CuO/TiO2/Al2O3. Chemosphere 2012, 89, 1195−1201. (20) de Luna, M. D. G.; Briones, R. M.; Su, C. C.; Lu, M. C. Kinetics of Acetaminophen Degradation by Fenton Oxidation in a FluidizedBed Reactor. Chemosphere 2013, 90, 1444−1448. (21) Pignatello, J. J.; Oliveros, E.; MacKay, A. Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry. Crit. Rev. Environ. Sci. Technol. 2006, 36, 1−84. (22) Neyens, E.; Baeyens, J. A Review of Classic Fenton’s Peroxidation as an Advanced Oxidation Technique. J. Hazard. Mater. 2003, 98, 33−50. (23) Saha, K. C. Review of Arsenicosis in West Bengal, India - a Clinical Perspective. Crit. Rev. Environ. Sci. Technol. 2003, 33, 127− 163. (24) Guidelines for Drinking-Water Quality: First Addendum to Third Edition. Volume 1, Recommendations; World Health Organization: Geneva, Switzerland, 2006; Vol. 1. (25) Guo, H. M.; Wen, D. G.; Liu, Z. Y.; Jia, Y. F.; Guo, Q. A Review of High Arsenic Groundwater in Mainland and Taiwan, China: Distribution, Characteristics and Geochemical Processes. Appl. Geochem. 2014, 41, 196−217. (26) Smedley, P. L.; Kinniburgh, D. G. A Review of the Source, Behaviour and Distribution of Arsenic in Natural Waters. Appl. Geochem. 2002, 17, 517−568. (27) Wu, B.; Song, J.; Li, X. Distribution and Chemical Speciation of Dissolved Inorganic Arsenic in the Yellow Sea and East China Sea. Acta Oceanol. Sin. 2015, 34, 12−20. (28) Mohan, D.; Pittman, C. U. Arsenic Removal from Water/ Wastewater Using Adsorbents - a Critical Review. J. Hazard. Mater. 2007, 142, 1−53. (29) Hughes, M. F. Arsenic Toxicity and Potential Mechanisms of Action. Toxicol. Lett. 2002, 133, 1−16. (30) Jia, Y. F.; Zhang, D. N.; Pan, R. R.; Xu, L. Y.; Demopoulos, G. P. A Novel Two-Step Coprecipitation Process Using Fe(III) and Al(III) for the Removal and Immobilization of Arsenate from Acidic Aqueous Solution. Water Res. 2012, 46, 500−508. (31) Sun, Y. K.; Zhou, G. M.; Xiong, X. M.; Guan, X. H.; Li, L. N.; Bao, H. L. Enhanced Arsenite Removal from Water by Ti(SO4)2 Coagulation. Water Res. 2013, 47, 4340−4348. (32) Waypa, J. J.; Elimelech, M.; Hering, J. G. Arsenic Removal by RO and NF Membranes. J. Am. Water Works Assoc. 1997, 89, 102− 114.

(33) Chen, Y. S.; Xu, W. Z.; Shen, H. L.; Yan, H. L.; Xu, W. X.; He, Z. Y.; Ma, M. Engineering Arsenic Tolerance and Hyperaccumulation in Plants for Phytoremediation by a PvACR3 Transgenic Approach. Environ. Sci. Technol. 2013, 47, 9355−9362. (34) Liu, W.; Zhao, X.; Borthwick, A. G. L.; Wang, Y.; Ni, J. DualEnhanced Photocatalytic Activity of Fe-Deposited Titanate Nanotubes Used for Simultaneous Removal of As(III) and As(V). ACS Appl. Mater. Interfaces 2015, 7 (35), 19726−19735. (35) Wen, T.; Wu, X.; Tan, X.; Wang, X.; Xu, A. One-Pot Synthesis of Water-Swellable Mg−Al Layered Double Hydroxides and Graphene Oxide Nanocomposites for Efficient Removal of As(V) from Aqueous Solutions. ACS Appl. Mater. Interfaces 2013, 5 (8), 3304−3311. (36) Cheng, W.; Ding, C.; Wang, X.; Wu, Z.; Sun, Y.; Yu, S.; Hayat, T.; Wang, X. Competitive Sorption of As(V) and Cr(VI) on Carbonaceous Nanofibers. Chem. Eng. J. 2016, 293, 311−318. (37) Bissen, M.; Frimmel, F. H. Arsenic - a Review. Part II: Oxidation of Arsenic and Its Removal in Water Treatment. Acta Hydrochim. Hydrobiol. 2003, 31, 97−107. (38) Kim, M. J.; Nriagu, J. Oxidation of Arsenite in Groundwater Using Ozone and Oxygen. Sci. Total Environ. 2000, 247, 71−79. (39) Driehaus, W.; Seith, R.; Jekel, M. Oxidation of Arsenate(III) with Manganese Oxides in Water Treatment. Water Res. 1995, 29, 297−305. (40) Wen, Z.; Zhang, Y.; Dai, C.; Sun, Z. Nanocasted Synthesis of Magnetic Mesoporous Iron Cerium Bimetal Oxides (MMIC) as an Efficient Heterogeneous Fenton-Like Catalyst for Oxidation of Arsenite. J. Hazard. Mater. 2015, 287, 225−233. (41) Kim, D.-h.; Bokare, A. D.; Koo, M. s.; Choi, W. Heterogeneous Catalytic Oxidation of As(III) on Nonferrous Metal Oxides in the Presence of H2O2. Environ. Sci. Technol. 2015, 49, 3506−3513. (42) Pettine, M.; Campanella, L.; Millero, F. J. Arsenite Oxidation by H2O2 in Aqueous Solutions. Geochim. Cosmochim. Acta 1999, 63, 2727−2735. (43) Xu, J.; Ding, W.; Wu, F.; Mailhot, G.; Zhou, D.; Hanna, K. Rapid Catalytic Oxidation of Arsenite to Arsenate in an Iron(III)/ Sulfite System under Visible Light. Appl. Catal., B 2016, 186, 56−61. (44) Zou, J.-P.; Wu, D.-D.; Bao, S.-K.; Luo, J.; Luo, X.-B.; Lei, S.-L.; Liu, H.-L.; Du, H.-M.; Luo, S.-L.; Au, C.-T.; Suib, S. L. Hydrogen Evolution from Water Coupled with the Oxidation of As(III) in a Photocatalytic System. ACS Appl. Mater. Interfaces 2015, 7 (51), 28429−28437. (45) Alam, Md. A.; Uddin, R.; Haque, S. Protein Binding Interaction of Warfarin and Acetaminophen in Presence of Arsenic and of the Biological System. Bangladesh J. Pharmacol. 2008, 3, 49−54. (46) Ingawale, D. K.; Mandlik, S. K.; Naik, S. R. Models of Hepatotoxicity and the Underlying Cellular, Biochemical and Immunological Mechanism(s): A Critical Discussion. Environ. Toxicol. Pharmacol. 2014, 37, 118−133. (47) Vijayakaran, K.; Kannan, K.; Kesavan, M.; Suresh, S.; Sankar, P.; Tandan, S. K.; Sarkar, S. N. Arsenic Reduces the Antipyretic Activity of Paracetamol in Rats: Modulation of Brain COX-2 Activity and CB1 Receptor Expression. Environ. Toxicol. Pharmacol. 2014, 37, 438−447. (48) Vijayakaran, K.; Kesavan, M.; Kannan, K.; Sankar, P.; Tandan, S. K.; Sarkar, S. N. Arsenic Decreases Antinociceptive Activity of Paracetamol: Possible Involvement of Serotonergic and Endocannabinoid Receptors. Environ. Toxicol. Pharmacol. 2014, 38, 397−405. (49) Manimaran, A.; Nath Sarkar, S.; Sankar, P. Toxicodynamics of Subacute Co-Exposure to Groundwater Contaminant Arsenic and Analgesic-Antipyretic Drug Acetaminophen in Rats. Ecotoxicol. Environ. Saf. 2010, 73, 94−100. (50) Majhi, C. R.; Khan, S.; Leo, M. D. M.; Prawez, S.; Kumar, A.; Sankar, P.; Telang, A. G.; Sarkar, S. N. Acetaminophen Increases the Risk of Arsenic-Mediated Development of Hepatic Damage in Rats by Enhancing Redox-Signaling Mechanism. Environ. Toxicol. 2014, 29, 187−198. (51) Cavani, F.; Trifirò, F.; Vaccari, A. Hydrotalcite-Type Anionic Clays: Preparation, Properties and Applications. Catal. Today 1991, 11, 173−301. 25351


Research Article

ACS Applied Materials & Interfaces (52) Zou, Y.; Wang, X.; Ai, Y.; Liu, Y.; Li, J.; Ji, Y.; Wang, X. Coagulation Behavior of Graphene Oxide on Nanocrystallined Mg/Al Layered Double Hydroxides: Batch Experimental and Theoretical Calculation Study. Environ. Sci. Technol. 2016, 50, 3658−3667. (53) Li, J.; Fan, Q.; Wu, Y.; Wang, X.; Chen, C.; Tang, Z.; Wang, X. Magnetic Polydopamine Decorated with Mg-Al LDH Nanoflakes as a Novel Bio-Based Adsorbent for Simultaneous Removal of Potentially Toxic Metals and Anionic Dyes. J. Mater. Chem. A 2016, 4, 1737− 1746. (54) Lu, H.; Zhu, Z.; Zhang, H.; Zhu, J.; Qiu, Y. Simultaneous Removal of Arsenate and Antimonate in Simulated and Practical Water Samples by Adsorption onto Zn/Fe Layered Double Hydroxide. Chem. Eng. J. 2015, 276, 365−375. (55) Lu, H.; Zhu, Z.; Zhang, H.; Qiu, Y. In Situ Oxidation and Efficient Simultaneous Adsorption of Arsenite and Arsenate by Mg− Fe−LDH with Persulfate Intercalation. Water, Air, Soil Pollut. 2016, 227, 125. (56) Rodriguez-Carjaval, J. FULLPROF: A Program for Rietveld Refinement and Profile Matching Analysis of Complex Powder Diffraction Patterns; Laue-Langevin Institute: Grenoble, France, 1994. (57) Rodrigues, E.; Pereira, P.; Martins, T.; Vargas, F.; Scheller, T.; Correa, J.; Del Nero, J.; Moreira, S. G. C.; Ertel-Ingrisch, W.; De Campos, C. P.; Gigler, A. Novel Rare Earth (Ce and La) Hydrotalcite Like Material: Synthesis and Characterization. Mater. Lett. 2012, 78, 195−198. (58) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds. In Handbook of Vibrational Spectroscopy; Chalmers, J. M., Griffiths, P. R., Eds.;John Wiley & Sons, Ltd.: New York, 2006; Vol. 3. (59) Carbajal Arizaga, G. G. Intercalation Studies of Zinc Hydroxide Chloride: Ammonia and Amino Acids. J. Solid State Chem. 2012, 185, 150−155. (60) Miller, F. A.; Wilkins, C. H. Infrared Spectra and Characteristic Frequencies of Inorganic Ions. Anal. Chem. 1952, 24, 1253−1294. (61) Zhang, H.; Wen, X.; Wang, Y. X. Synthesis and Characterization of Sulfate and Dodecylbenzenesulfonate Intercalated Zinc-Iron Layered Double Hydroxides by One-Step Coprecipitation Route. J. Solid State Chem. 2007, 180, 1636−1647. (62) Carja, G.; Nakamura, R.; Aida, T.; Niiyama, H. Textural Properties of Layered Double Hydroxides: Effect of Magnesium Substitution by Copper or Iron. Microporous Mesoporous Mater. 2001, 47, 275−284. (63) Kuan, C.-C.; Chang, S.-Y.; Schroeder, S. L. M. Fenton-Like Oxidation of 4-Chlorophenol: Homogeneous or Heterogeneous? Ind. Eng. Chem. Res. 2015, 54, 8122−8129. (64) Kim, S.; Ginsbach, J. W.; Lee, J. Y.; Peterson, R. L.; Liu, J. J.; Siegler, M. A.; Sarjeant, A. A.; Solomon, E. I.; Karlin, K. D. Amine Oxidative N-Dealkylation Via Cupric Hydroperoxide Cu-OOH Homolytic Cleavage Followed by Site-Specific Fenton Chemistry. J. Am. Chem. Soc. 2015, 137, 2867−2874. (65) Zhu, K.; Liu, C.; Ye, X.; Wu, Y. Catalysis of Hydrotalcite-Like Compounds in Liquid Phase Oxidation: (I) Phenol Hydroxylation. Appl. Catal., A 1998, 168, 365−372. (66) Arends, I. W. C. E.; Sheldon, R. A. Activities and Stabilities of Heterogeneous Catalysts in Selective Liquid Phase Oxidations: Recent Developments. Appl. Catal., A 2001, 212, 175−187. (67) Andreozzi, R.; Caprio, V.; Marotta, R.; Vogna, D. Paracetamol Oxidation from Aqueous Solutions by Means of Ozonation and H2O2/ UV System. Water Res. 2003, 37, 993−1004.

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