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Mechanism of Catalytic Ozonation in Fe2O3/Al2O3@SBA-15 Aqueous Suspension for Destruction of Ibuprofen Jishuai Bing, Chun Hu, Yulun Nie, Min Yang, and Jiuhui Qu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es503729h • Publication Date (Web): 07 Jan 2015 Downloaded from http://pubs.acs.org on January 20, 2015

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Environmental Science & Technology

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Mechanism of Catalytic Ozonation in Fe2O3/Al2O3@SBA-15 Aqueous Suspension for

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Destruction of Ibuprofen

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Jishuai Bing, Chun Hu *, Yulun Nie, Min Yang, Jiuhui Qu

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Key Laboratory of Drinking Water Science and Technology, Research Center for

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Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

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Corresponding author Tel: +86-10-62849628; fax: +86-10-62923541;

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e-mail: [email protected] (Hu C)

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ACS Paragon Plus Environment


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Abstract

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Fe2O3 or/and Al2O3 were supported on mesoporous SBA-15 by wet impregnation and

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calcinations with AlCl3 and FeCl3 as the metal precursor and were characterized by X-ray

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diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared

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spectra (FTIR) of adsorbed pyridine. Fe2O3/Al2O3@SBA-15 was found to be highly effective

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for the mineralization of ibuprofen aqueous solution with ozone. The characterization studies

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showed that Al-O-Si were formed by the substitution of Al3+ for the hydrogen of surface

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Si-OH groups, not only resulting in high dispersion of Al2O3 and Fe2O3 on SBA-15, but also

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inducing the greatest amount of surface Lewis acid sites. By the studies of in situ attenuated

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total reflection FTIR (ATR-FTIR), in situ Raman and electron spin resonance (ESR) spectra,

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the chemisorbed ozone was decomposed into surface atomic oxygen species at the Lewis acid

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sites of Al3+ while it was converted into surface adsorbed •OHads and O2•- radicals at the Lewis

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acid sites of Fe3+. The combination of both Lewis acid sites of iron and aluminium onto

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Fe2O3/Al2O3@SBA-15 enhanced the formation of •OHads and O2•- radicals, leading highest

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reactivity. Mechanisms of catalytic ozonation were proposed for the tested catalysts on the

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basis of all the experimental information.

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Introduction

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Heterogeneous catalytic ozonation has recently gained significant attention as an effective

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process for the degradation and mineralization of refractory organic pollutants in water.1, 2 A

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variety of efficient solid catalysts have been developed for catalytic ozonation, however, these

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successful results are on a laboratory level. Catalytic ozonation has not been applied widely in

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water industry.3 The reason is that the mechanisms of these processes are still unclear,4

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including the process of ozone decomposition on the surface of different catalysts, the

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generation of reactive oxygen species (ROS), key structure factors of catalyst. An in-depth

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understanding of the mechanism is essential to introduce this technique in water treatment at

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an industrial scale.

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The efficiency of catalytic ozonation and the transformation of pollutants predominantly

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depend on the behavior of ozone on the surface of the catalysts. However, there is not still any

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unified mechanism of the process, moreover, many proposed mechanisms are contradictory.4

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Various metal oxides (Al2O3, Fe2O3 and MnO2), metals supported on oxides are claimed to

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catalytic activity in ozonation. Nevertheless, there are full of contradictory reports on their

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catalytic activity, which mainly including two possible mechanisms of catalytic ozonation. The

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one is that ozone is decomposed into ROS to oxidize organic compound in water; the other one

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is that both ozone and organic compounds are adsorbed on the catalyst surface, subsequently

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interact between adsorbed species.3, 4 For example, Al2O3 does not reveal any catalytic activity

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due to not decomposing ozone according to some researches,5, 6 while Al2O3 is an active

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catalyst due to the adsorption of organic compounds and ozone on its surface.7, 8 Even, there

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are four different hypotheses for the adsorption and decomposition of ozone on

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Fe-hydroxyoxides.9 In addition, in most of literatures,10, 11 the high efficiency of catalytic

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ozonation was assigned to the hypothesis of hydroxyl radicals (•OH) generation from ozone

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decomposition. However, the recent researches indicated that catalytic ozonation does not

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necessarily rely on

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understanding of the catalytic ozonation in aqueous phase seems to be very poor.

OH formation.12,

•

13

These examples show irrefutably that our

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The surface of all the oxides, including metal oxides and metals supported on oxides, is

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covered by hydroxyls that can have ion exchange properties and the hydroxyls are considered

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as the main adsorption centers.14, 15 Some of them have Lewis acid sites, while others of them

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have hydrophobic sites. All the above properties depend on the variety of metal in the oxides.

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Single hydroxyl sites for cation exchange and hydrophobic sites are usually found on the

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surface of silica, while ion-exchange bridged hydroxyl sites and Lewis acid sites are usually

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found on the surface of Al2O3 and Fe2O3.16 These factors would have great influence on the

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behavior of ozone on the surface of the oxides, leading to different catalytic activity. However,

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there was no direct evidence to indicate the process of the interaction between these sites with

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ozone and what ROS would be involved in aqueous-phase catalytic ozonation.

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The objective of this study was to investigate the transformation of ozone over supported

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metal oxides with different surface hydroxyls and Lewis acid sites, elucidating catalytic

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ozonation mechanism at the aqueous-solid interface. In the present study, mesoporous SBA-15

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silica was used as support, Al2O3@SBA-15, Fe2O3/SBA-15 and Fe2O3/Al2O3@SBA-15 were

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prepared by impregnation method and characterized by XRD, XPS and Pyridine-FTIR and so

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on. The reaction process of ozone were observed at the aqueous-solid interface of four

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catalysts by in situ attenuated total reflection FTIR (ATR-FTIR) spectroscopy, in situ Raman

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spectra, Electron spin resonance (ESR) spectra and the determination of ozone. Ibuprofen

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(IBU) is anti-inflammatory drug, estimated annual global production of several kilotons,

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which has been detected in surface water and wastewater at range from ng to low µg L-1 levels

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due to its stability for photolysis and biodegradation.17, 18 Some researchers suggested that IBU

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may alter the postembryonic development of anuran species in freshwater environs, where

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IBU is a persistent or seasonal pollutant.19 Therefore, IBU was selected to evaluate the activity

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and properties of the catalysts. A preliminary effort to identify a correlation between

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transformation of ozone onto catalysts and catalytic effect has been undertaken.

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Experimental Section

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Chemicals and Reagents. Ibuprofen (IBU) was obtained from TCI Japan (Tokyo, Japan),

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its molecular structure was shown in Figure S1 Supporting Information. The triblock

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copolymer EO20PO70EO20 (Pluronic P123, MW 5800) was purchased from Sigma-Aldrich.

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Tetraethyl orthosilicate (TEOS), crystallization of aluminumchloride (AlCl3·6H2O), ferric

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chloride hexahydrate (FeCl3·6H2O), deuteroxide (D2O), were purchased from Sinopharm

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Chemical Reagent Beijing Co. Ltd. (Beijing, China). Spin trap 5-tert-butoxycarbonyl

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5-methyl-1-pyrroline N-oxide (BMPO) was purchased from DOJINDO Molecular

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Technologies, Inc. (Shanghai, China). Horseradish peroxidase (POD, specific activity of > 250

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u mg-1) was purchased from Amresco (USA). All chemicals were of analytical grade and used

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as received. Milli-Q water (18.2 MΩ⋅cm in resistivity, Millipore) was used throughout the

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experiments. The solution pH was adjusted with dilute HCl and NaOH solution.

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Catalysts Preparation. SBA-15 was synthesized as described previously using triblock

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copolymer EO20PO70EO20 (Pluronic P123) as organic template.20 Aluminia coated SBA-15

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(Al2O3@SBA-15) was prepared by the incipient wetness impregnation method with

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AlCl3·6H2O as the metal precursor. For example, 0.894 g of AlCl3·6H2O was dissolved in 10

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ml Milli-Q water. 2 g of SBA-15 dried at 100°C for 12 h, was dispersed into this solution with

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stirring vigorously for 60 min. Then the mixture was dried in an oven at 85°C for 10 h. The

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impregnation process was repeated for three times to obtain the Si/Al atomic ratio of 3, and

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finally the obtained product was grinded, and calcined at 550°C for 4 h at a heating rate of 5 °C

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min-1 and then cooled to room temperature naturally. Furthermore, Fe2O3/Al2O3@SBA-15 was

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prepared by an incipient wetness impregnation method with FeCl3·6H2O as the metal precursor.

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Typically, 1.16 g of FeCl3·6H2O was dissolved in 6 ml of distilled water, and 2 g of

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Al2O3@SBA-15 was added to this solution. After ultrasonic vibration for 60 min, the sample

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was dried at 80°C for 10 h and finally calcined in a muffle furnace (exposed to static air) at

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300°C for 30 min and cooled to room temperature naturally. Following this procedure, the

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catalysts containing different Fe amount were prepared with different Fe dosages (3, 6, 12, 15

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wt% Fe with respect to Al2O3@SBA-15), while the catalyst with 12 wt% Fe dosage exhibited

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the highest activity for catalytic ozonation of IBU, designated by Fe2O3/Al2O3@SBA-15, and

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was used for all the experiments. As references, Fe2O3/SBA-15 was prepared under the

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otherwise identified conditions as that of Fe2O3/Al2O3@SBA-15.

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Characterization. Powder X-ray diffraction (XRD) of the catalyst was recorded on a

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Scintag-XDS-2000 diffractometer with Cu Kα radiation (λ = 1.540598 Å). The high-resolution

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transmission electron microscopy (HRTEM) images of the catalysts were obtained using a

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JEOL-2010 TEM with an acceleration voltage of 200 kV. The X-ray photoelectron

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spectroscopy (XPS) data was taken on an AXIS-Ultra instrument (Kratos Analytical, UK)

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using monochromatic Al Kα radiation (225 W, 15 mA, 15 kV). The point of zero charge (pHpzc)

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of the catalysts was measured with a Zetasizer Nano (Malvern, UK) with three consistent

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readings.

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Procedures and Analysis. Semi-batch experiments were carried out with a 1.2 L reactor. The

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reaction temperature was maintained at 20°C. In a typical experiment, 1 L of 10 mg L-1

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aqueous suspensions of IBU and 1.5 g of catalyst powder were added into the reactor under

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continuously magnetically stir. And 30 mg of gaseous O3 L-1 oxygen-zone was bubbled into

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the reactor through the porous plate of the reactor bottom at a 200 mL min-1 flow rate. The

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initial pH of reaction suspensions was about 7. The same procedures were carried out for the

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control experiments of ozone alone and sorption without ozone. Ozone was produced in situ

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from pure oxygen by a 3S-A5 laboratory ozone generator (Tonglin Technology, China). The

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residual ozone in the off-gas was absorbed by a KI solution. At given time intervals, sample

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was withdrawn, subsequently, an aliquot of 0.1 M Na2S2O3 was added to the sample to quench

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the residual aqueous ozone, and filtered through a Millipore filter (pore size 0.45µm) for

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analysis. The gaseous ozone concentration was measured by an IDEAL-2000 ozone

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concentration detector (China). The concentration of ozone dissolved in the aqueous phase was

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determined with the indigo method. IBU was analyzed by means of a 1200 series HPLC

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(Agilent, U.S.A.) equipped with a UV detector at 220 nm and a ZORBAX Eclipse XDB-C18

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column (4.6×150 mm, 5 µm). The mobile phase was a solution of 60/40 (v/v)

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acetonitrile–phosphate buffer solution (20 mM, pH = 2.5) and a flow rate of 1 mL min-1. TOC

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was determined by a Shimadzu TOC-VCPH analyzer. The iron and aluminum contents in the

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whole particle of Fe2O3/Al2O3@SBA-15 after dissolved by concentrated nitric acid, were

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detected by inductively coupled plasma optical emission spectrometry (ICP-OES) on an

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OPTIMA 2000 (Perkin Elmer Co., U.S.A.). Moreover, the released metallic ions from the

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catalysts in reaction process also were determined by ICP-OES. Electron spin resonance (ESR)

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spectra were obtained with a Bruker A300-10/12 ESR spectrometer using BMPO as a spin trap

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agent at room temperature. All information for FTIR, in situ ATR-FTIR, in situ Raman spectra,

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the experiments of O3 decomposition, the determination of H2O2, the surface Fe2+ of the

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catalysts, gas chromatography-mass spectrometry (GC-MS) analysis and the preparation of

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samples are shown in the Supporting Information (SI). Each experiment was run in triplicate.

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Data were the arithmetic mean of three measured values.

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Results and Discussion

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Characterization of Catalysts. The low angle and wide angle XRD patterns of different

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supported SBA-15 were shown in Figure S2 (SI). All the samples exhibited a very strong

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diffraction peak near 1°, which is identified to be the typical pattern of hexagonal structure

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attributed to the diffraction plane (100). The other two weaker patterns were indexed to the

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diffraction plane (110) and (200).20 The results indicated that these samples retained a highly

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ordered structure of SBA-15 after a loading process. No significant diffraction peaks of Al2O3

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were observed in both Al2O3@SBA-15 and Fe2O3/Al2O3@SBA-15, and a weaker peak

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appeared at 35.65 °, which is assigned to α-Fe2O3, in Fe2O3/[email protected] In the contrast,

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several stronger peaks for α-Fe2O3 (JCPDS card 01-073-2234) appeared in Fe2O3/SBA-15.

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TEM images of different samples confirmed this observation (Figure S3, SI). All the catalyst

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samples exhibited well-ordered hexagonal arrays structure with the loading of alumina and

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iron oxide. There is no aggregated alumina phase in Al2O3@SBA-15 (FigureS3B, SI), despite

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the high loading content of Al2O3. The result indicated that Al2O3 layers were homogeneously

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coated on the pore walls of SBA-15. Large particles of iron oxide were found on the outer

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surface of SBA-15, indicating that the iron oxide particles were not well-dispersed. However,

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the large iron oxide nanoparticles were not observed in Fe2O3/Al2O3@SBA-15, suggesting that

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the small sized iron oxide nanoparticles were homogeneously dispersed on the surface of

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Al2O3@SBA-15. By XPS measurement, the surface Al and Fe concentrations were 8.53 and

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7.97 wt%, which were more than those (7.18 and 6.47 wt%) in bulk for Fe2O3/Al2O3@SBA-15,

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indicating that most of Al and Fe were supported on the surface of SBA-15. The Fe 2p spectra

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comprise three peaks with differentiated binding energy values assigned to Fe 2p 3/2 peak

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(∼711 eV), satellite peak (∼718.2 eV) and Fe 2p 1/2 peak (∼724 eV) (Figure S4, SI). The

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energy separation between Fe 2p 3/2 and Fe 2p 1/2 is more than 13 eV, indicating Fe3+

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existence.22 In Fe2O3/Al2O3@SBA-15 sample, the Al 2p XPS spectra exhibit two binding

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energies (BEs) of Al3+ at 73.6 and 74.7 eV, assigned to Al-O-Al and Al-O-Si respectively,23

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whereas the Si 2p XPS spectra also exhibit two BEs 103.4 and 102.3 eV assigned to Si-O-Si

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and Al-O-Si respectively (Figure 1).23 The same results also were observed in the XPS spectra

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of Al2O3@SBA-15 (not data shown). In addition, FTIR spectra also shows that the surface

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Si-OH groups of SBA-15 at 966 cm-1 disappeared with the loading of aluminium oxide (Figure

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S5, SI). These data indicated that Al-O-Si were formed by the substitution of Al3+ for the

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hydrogen of surface Si-OH groups, resulting in aluminium oxide homogeneously highly

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dispersed on the surface of SBA-15, which enhanced the dispersion of iron oxide on the

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surface of Al2O3@SBA-15.

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The acid sites of different catalysts were determined by FTIR of adsorbed pyridine after

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degassing at 200°C (Figure 2). Obviously, no any peak was observed for SBA-15, two weaker

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IR bands appeared at 1450 and 1608 cm-1 for Fe2O3/SBA-15 assigned to pyridine adsorbed

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onto Lewis acid sites.24 Whereas Al2O3@SBA-15 exhibited three strong IR bands at 1452 and

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1620 cm-1 attributed to pyridine adsorbed onto Lewis acid sites and at 1492 cm-1 ascribed to

200

pyridine adsorbed onto both Lewis and Brønsted acid sites.24 Furthermore, the three bands

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became wide and the 1608 cm-1 band remained for Fe2O3/Al2O3@SBA-15. The total and

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strong Lewis acid sites were quantitatively estimated for these catalysts using pyridine

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adsorption followed by degassing at 200 and 350°C according to the described method (Table

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S1, SI).25 The total acid sites and medium/strong acid sites were 21.7 and 19.2 µmol g-1 on the

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surface of Fe2O3/SBA-15, while the total Lewis acid sites were 246.2 and 264.3 µmol g-1, and

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medium/strong acid sites were 184.3 and 193.1 µmol g-1 for Al2O3@SBA-15,

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Fe2O3/Al2O3@SBA-15. The loading of aluminum greatly increased the total acid and

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medium/strong acid site, which was contributed to the substitution of aluminum for the

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hydrogen of surface Si-OH group of SBA-15. Dissociative chemisorption of water molecules

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occurs at Lewis acid sites,26 which was examined by in situ ATR-FTIR experiments in the D2O

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solvent with N2 atmosphere (Figure S6, SI). The stretching vibration of the hydrogen-bonded

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MeO-D was 2499 cm-1, while those ones of the hydrogen-bonded D2O were 2252 and 1064

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cm-1. The peak intensities increased according to the following order: SBA-15, Fe2O3/SBA-15,

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Al2O3@SBA-15 and Fe2O3/Al2O3@SBA-15, indicating that the more surface Lewis acid sites

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resulted in the more chemisorbed water. Besides, the presence of Lewis acid sites increased the

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point of zero charge (pHpzc), increasing the ability of surface hydroxyl groups to dissociate or

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to be protonated in water.16 Expectedly, the pHpzc were 3.1, 3.79, 6.75 and 7.25 for SBA-15,

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Fe2O3/SBA-15, Al2O3@SBA-15 and Fe2O3/Al2O3@SBA-15.

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Catalytic ozonation of IBU. The catalytic activity of various catalysts was evaluated by

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the degradation of IBU (10 mg L-1) with ozone at an initial pH 7. 2.8%, 5.7%, 8.0% and 9.7%

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of the tested IBU were adsorbed on the surface of Fe2O3/Al2O3@SBA-15, Al2O3@SBA-15,

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Fe2O3/SBA-15 and SBA-15 respectively. The degradation of IBU mainly was contributed to

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the catalytic ozonation. The degradation rate of IBU was almost the same with ozone alone and

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catalytic ozonation (Figure S7, SI). Ozone decomposition increased in water at pH more than 7,

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causing more hydroxyl radicals (•OH). tert-Butanol (TBA) is a strong radical scavenger that

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has a reaction rate constant of 6×108 M-1 s-1 with hydroxyl radicals and only 3×10-3 M-1 s-1

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with ozone. In order to examine the role of •OH and ozone in ozonation, TBA was adopted as

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the indicator for the radical type reaction. The addition of TBA markedly reduced the

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degradation of IBU (Figure S8, SI), indicating that •OH radicals also were involved, and the

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removal of IBU predominantly came from the oxidation of ozone and •OH in ozonation at pH

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7. However, the degradation of IBU was less suppressed by the addition TBA in catalytic

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ozonation than ozone alone. At pH 7, only 2.8% of IBU was adsorbed on the surface of

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Fe2O3/Al2O3@SBA-15, the oxidation reaction of IBU occurred mainly in solution. Since there

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was no significant amount of TBA adsorbed on the catalyst in aqueous systems, it

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predominantly scavenged the free •OH radicals in solution. The results suggested that the free

236

•

237

important role in the catalytic ozonation. However, the TOC removal rate was greatly

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enhanced in catalytic ozonation (Figure 3). Only 26% of TOC was removed with ozone alone

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at 60 min, while about 90%, 65%, 48% and 36% of TOC were removed at the same time in

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Fe2O3/Al2O3@SBA-15,

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respectively. The pH of solution great decreased from initial pH 7 to 3.8 (Figure S9, SI) in the

242

process of ozonation indicating the accumulation of organic acids in solution, verifying that

OH radicals in solution were not main, the surface reactive oxygen species might play

Al2O3@SBA-15,

Fe2O3/SBA-15

11


and

SBA-15

suspensions,


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most of organic acids could not be oxidized in ozonation, leading lower TOC removal.

244

Differently, in the process of catalytic ozonation, the pH changed less than 0.3 in

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Fe2O3/Al2O3@SBA-15 suspension, while the pH changed less than 0.7 in other catalysts

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suspensions, which was contributed to the faster removal of produced organic acids (Figure S9,

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SI). The results demonstrated that the catalytic activity predominantly depended on the amount

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of surface Lewis acid sites. There was no Lewis acid sites on the surface of SBA-15, leading to

249

less activity, while the loading of aluminum greatly increased Lewis acid sites, leading to

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higher activity, and the synergism of aluminium and iron resulted in highest activity of

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Fe2O3/Al2O3@SBA-15. The activity of Fe2O3/Al2O3@SBA-15 did not markedly decrease

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after six successive cycles of degradation testing, and the crystalline structure of

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Fe2O3/Al2O3@SBA-15 retained almost the same as the fresh catalyst (Figure S10, SI). During

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the catalytic ozonation, there was not any metallic ion release. These results verified that

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Fe2O3/Al2O3@SBA-15 is a highly efficient catalyst for the mineralization of IBU in the

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ozonation process.

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Catalytic Ozonation Mechanism. Intermediates of IBU Degradation with Ozonation or

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Catalytic Ozonation. GC-MS was used to monitor the generation of reaction intermediates

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during the degradation of IBU in ozonation and catalytic ozonation, respectively. All of the

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identified compounds were unequivocally identified using the NIST98 library database with fit

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values higher than 93%. Table S2 shows the main intermediates from the degradation of IBU at

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reaction time of 5 and 20 min. In ozone alone, at 5 min, 4 intermediates produced , including

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2-methylpropan-1-ol, 2-(3,4-dihydroxyphenyl)-2-hydroxyacetic acid, propane-1,2,3-triol and

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p-hydroxybenzoic acid, indicating that hydroxylation reaction firstly occurred on the aromatic

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ring at para, meta position of 2-methylacetice acid group, and methyl position of acetic acid

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and propyl group by ozone or •OH. At the reaction time of 20 min, p-hydroxybenzoic acid

267

remained,

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2-hydroxy-3-methybutyric acid appeared, which were produced by the hydroxylation and

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carbonylation of aromatic ring at meta position of 2-hydroxyacetic acid group, subsequently

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some aliphatic acids produced. In Fe2O3/Al2O3@SBA-15 suspension with ozone, at the

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reaction

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2-(3,4-dihydroxyphenyl)-2-hydroxyacetic

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propane-1,2,3-triol, succinic acid and p-hydroxybenzoic acid. Meanwhile, 4 organic acids

274

were detected on the surface of the catalyst, such as 2-(3,4-dihydroxyphenyl)-2-hydroxyacetic

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acid, 3,4,5-trihydroxybenzoic acid, 3,4-dihydroxybutanoic acid and p-hydroxybenzoic acid.

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While at the reaction time of 20 min, in solution, these products disappeared, only some

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aliphatic acids, such as 2-hydroxy-propanoic acid, glycolic acid and malonic acid. Moreover,

278

on the surface of the catalyst, other acids disappeared, only p-hydroxybenzoic acid remained,

279

and malonic acid, 3-hydroxy-hexanedioic acid produced. The results demonstrate that the

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catalytic ozonation of IBU proceeds by the simultaneous hydroxylation of different substitute

281

groups, followed by the opening of aromatic rings to form small molecular organic acids or

282

triols into carbon dioxide and water, where the intermediates produced and disappeared more

283

quickly than those ones in ozone alone. The results indicated that catalytic ozonation had more

284

stronger oxidation performance than ozonation for the further degradation of organic acids

285

intermediates, causing more TOC removal. On the other hand, it was found that most of

286

aromatic acids and long-chain aliphatic acids were adsorbed on the surface of the catalyst,

other

time

products

of

5

min

disappeared,

in

while

solution,

5

acid,

2,3-dihydroxy-propanoic

intermediates

acid

appeared,

2-hydroxy-3-methybutyric

13


and

including acid,


287

indicating these intermediates from IBU degradation were oxidized by the surface reaction.

288

The Effect of pH on IBU Degradation. The IBU degradation rate increased with increasing

289

initial pH in ozone alone and Fe2O3/Al2O3@SBA-15 suspension with ozone (Figure S11, SI).

290

For ozonation (Figure S11A, SI), with initial pH increasing, ozone decomposition increased,

291

resulting in more •OH formation. The rate constant of the ozone-IBU reaction is 9.6 M-1s-1,

292

while that one of the •OH-IBU reaction is 7.0×109 M-1s-1. At initial pH 3, ozone was main

293

oxidant, leading to lower IBU degradation; while at initial pH 7 and 9, ozone and •OH were

294

predominant oxidant, causing more IBU degradation. Correspondingly, TOC removal

295

increased with initial pH increasing, however, the maximum TOC removal was only 40%.

296

Oppositely, in Fe2O3/Al2O3@SBA-15 suspension with ozone (Figure S11B, SI), TOC removal

297

increased with increasing initial pH from 3.0 to 7.0, but at pH 9, TOC removal rate greatly

298

decreased. The analysis of intermediates had verified that most of organic acids from IBU

299

degradation were adsorbed and oxidized predominantly on the surface of the catalyst at initial

300

pH 7. Since the pHpzc of Fe2O3/Al2O3@SBA-15 is about 7.25, the surface of the catalyst was

301

positively charged in the range of pH < 7, while the surface exhibited great negative

302

zeta-potential at pH 9. So organic acid can be adsorbed onto the surface of catalyst by

303

electrostatic attraction at pH < 7, while they hardly had any adsorption on the negative charged

304

surface at pH 9 due to repulsive force. At pH = 9, the lower TOC removal indicated that the

305

oxidation of organic acids greatly decreased in bulk solution. These results indicated that

306

organic acid degradation predominantly occurred on the surface of the catalyst, indicating

307

where more •OH and other reactive oxygen species formed.

308

Characterization of Ozone on the Surface of Different Catalysts. The concentrations of

14


Page 14 of 32

Page 15 of 32


309

ozone in bulk water and the surface of the catalysts were determined with different reaction

310

time (Figure 4). The concentration of ozone decreased more rapidly in SBA-15 suspension

311

than other suspensions before 20 min, then tend to steady. In the contrast, the concentration of

312

ozone continuously decreased in other suspensions with reaction time, and the decay rate of

313

ozone was highest, and ozone completely disappeared at 45 min in Fe2O3/Al2O3@SBA-15

314

suspension. The similar changes of ozone concentration occurred on the surface of the

315

catalysts except SBA-15. The concentration of ozone gradually decreased on the surface of

316

Fe2O3/SBA-15, Al2O3@SBA-15 and Fe2O3/Al2O3@SBA-15, and the ozone completely

317

disappeared at 60 min on the surface of Fe2O3/Al2O3@SBA-15. SBA-15 had the maximum

318

adsorption capacity of ozone, and the concentration of ozone on the surface of SBA-15 did not

319

change within 60 min. The results indicated that ozone molecule was direct oxidant over

320

SBA-15 suspension, leading to lower reactivity, while more ROS formed in other suspensions

321

with the ozone decomposition. Fe2O3/Al2O3@SBA-15 showed the highest ozone

322

decomposition efficiency, resulting in the most ROS formation. In situ ATR-FTIR experiments

323

were carried out in different catalysts suspensions with D2O (Figure S12, SI). In SBA-15

324

suspension, with increasing ozone bubbling time, the intensities of peaks at 1064 cm-1, 2252

325

cm-1 and 2499 cm-1 hardly had any change, indicating that the surface hydroxyl site (Si-OH) of

326

SBA-15 could not ion exchange with ozone, the ozone was physical absorption onto SBA-15

327

by hydrogen bond.27 In Fe2O3/SBA-15 suspension, the intensities of peak at 1064 cm-1 did not

328

change, but the intensities of peaks at 2252 cm-1 and 2499 cm-1 decreased gradually, suggesting

329

that the adsorbed water was replaced by ozone. Moreover, in Al2O3@SBA-15 and

330

Fe2O3/Al2O3@SBA-15 suspensions, the three peaks decreased gradually, suggesting that the

15



331

hydroxyl groups in these locations could be ion exchange with ozone. The results indicated

332

that the surface Lewis acid sites were active sites for adsorption and decomposition of ozone

333

on the surface of the catalysts. Figure 5 shows the Raman spectra of Fe2O3/Al2O3@SBA-15

334

and Al2O3@SBA-15 with ozone aqueous solution. Both samples exhibited a new bands

335

appeared at 913 cm-1 and 938 cm-1 respectively, which was assigned to a surface atomic

336

oxygen species.13, 28, 29 Oppositely, no surface atomic oxygen formed on the surface of SBA-15

337

and Fe2O3/SBA-15 with ozone aqueous solution (Figure S13, SI). The results indicated that

338

ozone was decomposed into a surface atomic oxygen when it was adsorbed on stronger Lewis

339

acid sites of Al2O3@SBA-15, while the ozone adsorbed on Lewis acid sites of iron was not

340

converted into the surface atomic oxygen. By ESR spin-trap technique with BMPO, ROS were

341

determined in different catalysts suspensions (Figure 6). Neither O2•-, nor •OH signals were

342

detected in SBA-15 suspension, indicating that the physics-sorbed ozone was stable on the

343

surface of SBA-15, confirming that ozone was direct oxidant. The six characteristic peaks of

344

the

345

Fe2O3/Al2O3@SBA-15 suspensions. When BMPO was added to catalyts-ozone suspension,

346

the •OH species were not detected in the three suspensions (not data shown), while four

347

characteristic peaks of BMPO-•OH, 1:2:2:1 quartet pattern, appeared when ozone-saturated

348

aqueous solution was added to adsorbed BMPO three catalysts suspensions because BMPO

349

possesses positive and negative charge (Figure S14, SI), leading its adsorption onto the surface

350

of the catalysts. The phenomena indicated that the produced •OH from ozone decomposition

351

mainly was adsorbed on the surface of the catalysts, which were coincident with these results

352

from the effects of initial pH values and TBA scavenger. Moreover, these intensities of

BMPO-O2•- adducts were observed

in

Al2O3@SBA-15, Fe2O3/SBA-15 and

16


Page 16 of 32

Page 17 of 32


353

BMPO-•OH and BMPO-O2•- increased according to the following order of Al2O3@SBA-15,

354

Fe2O3/SBA-15 and Fe2O3/Al2O3@SBA-15. The all above results indicated that the adsorbed

355

ozone was decomposed into both O2•- in solution and adsorbed •OH radicals and surface

356

atomic oxygen in Fe2O3/Al2O3@SBA-15 suspension with ozone, verifying most of organic

357

acids were favored to be oxidized on the surface of the catalyst, leading to the lower removal

358

rate of TOC in bulk water at pH 9. Furthermore, the reduction of surface Fe3+ to Fe2+ was

359

observed with ozone decomposition, and it was greatly enhanced with IBU degradation in

360

Fe2O3/SBA-15 and Fe2O3/Al2O3@SBA-15 suspensions, and the produced surface Fe2+

361

concentration increased and reached to the maximum at about 20 min, then decreased to be

362

oxidized to Fe3+ with prolonged reaction time (Figure S15, SI). Under the same conditions, the

363

produced H2O2 in the suspensions exhibited the same changes (Figure S16, curves c and e).

364

The phenomena indicated that the surface multivalent iron took part in the redox reaction of

365

ozone decomposition, enhancing the formation of •OH and O2•- radicals.

366

In light of the experimental data and several reviews of the literature,1, 30-32 a mechanism

367

scheme is proposed for the catalytic decomposition of ozone at the Lewis acids of iron and

368

alumina on SBA-15 (Table S3, SI). In this process, ozone replaced the ≡ Fe3+ -OH groups

369

produced at the surface Lewis acid sites of Fe3+, forming surface adsorbed •OH (•OHads) and

370

O3•- complexing with Fe3+, subsequently, the free electron transferred from O3•- to the surface

371

Fe3+ to generate the surface Fe2+ and HO2•. It has been reported that the complexation of Fe3+

372

with organic acids can decrease the Fe3+/Fe2+ redox potential,33 during the catalytic ozonation

373

of IBU, most of produced organic acids were adsorbed on the surface of

374

Fe2O3/Al2O3@SBA-15, complexing with the surface Fe3+, enhancing the reaction rate of the

17



375

surface Fe3+ with O3•-, resulting in the more surface Fe2+ and HO2• production. The more HO2•

376

reacted with each other, producing more H2O2, causing the consistency of H2O2 and Fe2+

377

concentration. With the adsorbed organic acids degradation, the complexation of Fe3+ with

378

organic acid decreased, leading to the lower the surface Fe2+ and H2O2 formation. Moreover,

379

H2O2 also reacted with the surface Fe2+ to form •OH and the surface Fe3+, leading to the

380

decrease of the Fe2+ and H2O2. On other hand, ozone replaced the ≡ Al3+ -OH groups

381

produced at the surface Lewis acid sites of Al3+ forming surface atomic oxygen, subsequently,

382

the active surface atomic oxygen species could react with water to form •OHads and hydrogen

383

peroxide (H2O2) due to its stronger oxidizing potential 2.43V.32 Expectedly (Figure S16, SI)

384

smaller amount of H2O2 were produced in ozone alone and SBA-15 suspension with ozone,

385

while H2O2 production was greatly increased according to the following order Fe2O3/SBA-15,

386

Al2O3@SBA-15 and Fe2O3/Al2O3@SBA-15 suspensions. The concentration of H2O2

387

increased up to about 20 min when IBU was completely degraded, and then decreased with

388

reaction time, which was contributed to the radical chain reactions. Since most of

389

intermediates from IBU degradation were organic acids, which could not be oxidized by

390

HO2•/O2•-, the excess HO2•/O2•- reacted with H2O2, besides the surface Fe2+, decreasing H2O2

391

concentration in water. The results confirmed that the conjecture about the reaction of surface

392

atomic oxygen with water. The results suggested that the ozone adsorbed onto the Lewis sites

393

of iron was predominantly decomposed into •OHads and O2•- radicals, and the combination of

394

both Lewis sites of iron and aluminium enhanced the formation of •OHads and O2•- radicals in

395

Fe2O3/Al2O3@SBA-15 suspension. Therefore, the main ROS were aqueous O3 and surface

396

adsorbed O3 in SBA-15 suspension; •OHads and O2•- were predominant in Fe2O3/SBA-15

18


Page 18 of 32

Page 19 of 32


397

suspension; while the surface atomic oxygen was ROS, resulting in higher reactivity in

398

Al2O3@SBA-15 suspension. Nevertheless, ROS included surface oxygen atom, •OHads and

399

O2•- leading to highest reactivity in Fe2O3/Al2O3@SBA-15. These finding could supply the

400

evidence for the development of new catalysts and adjusting of catalytic ozonation for water

401

purification.

402 403

Acknowledgments

404

This work was supported by the National Natural Science Foundation of China (Grant

405

Nos.21125731, 51138009, 51278527). The project of Chinese Academy of Sciences (Grant No.

406

YSW2013A02).

407 408

Associated Content

409

Supporting Information Available. Details about the experiments: FTIR measurement, in

410

situ ATR-FTIR Spectroscopy, in situ Raman spectra, the decomposition of ozone in different

411

catalysts suspensions, the determination of H2O2, the determination of the surface Fe2+ of the

412

catalysts, GC-MS analysis and the preparation of samples. The structure of IBU and BMPO,

413

XRD patterns, TEM images, XPS Fe 2p spectra, FTIR and in situ ATR-FTIR spectra, IBU

414

degradation in different processes, stability of Fe2O3/Al2O3@SBA-15 in catalytic ozonation

415

process, effect of initial pH on IBU and TOC removal in ozonation alone and

416

Fe2O3/Al2O3@SBA-15 suspension with ozone, in situ Raman spectra of SBA-15 and

417

Fe2O3/SBA-15 with and without ozone, the concentration of Fe2+ on the surface of

418

Fe2O3/SBA-15 and Fe2O3/Al2O3@SBA-15 under different conditions, the concentration of

19



419

H2O2 formation during the degradation of IBU, intermediates from IBU degradation in ozone

420

alone and Fe2O3/Al2O3@SBA-15 suspensions with ozone detected by GC-MS at different

421

reaction times and a mechanism scheme for the catalytic ozonation in Fe2O3/Al2O3@SBA-15

422

suspension. This material is available free of charge via the Internet at http://pubs.acs.org.

423 424

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425

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426

enhancing molecular ozone reactions in water treatment. Appl. Catal., B 2003, 46, (4),

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2. Legube, B.; Karpel Vel Leitner, N. Catalytic ozonation: a promising advanced oxidation technology for water treatment. Catal. Today 1999, 53, (1), 61-72. 3. Nawrocki, J.; Kasprzyk-Hordern, B. The efficiency and mechanisms of catalytic ozonation. Appl. Catal., B 2010, 99, (1–2), 27-42. 4. Nawrocki, J. Catalytic ozonation in water: Controversies and questions. Discussion paper. Appl. Catal., B 2013, 142–143, 465-471. 5. Kasprzyk, B.; Nawrocki, J. Preliminary Results on Ozonation Enhancement by a Perfluorinated Bonded Alumina Phase. Ozone: Sci. Eng. 2002, 24, (1), 63-68. 6. Lin, J.; Kawai, A.; Nakajima, T. Effective catalysts for decomposition of aqueous ozone. Appl. Catal., B 2002, 39, (2), 157-165.

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7. Álvarez, P. M.; Beltrán, F. J.; Pocostales, J. P.; Masa, F. J. Preparation and structural

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8. Kasprzyk-Hordern, B.; Raczyk-Stanisławiak, U.; Świetlik, J.; Nawrocki, J. Catalytic

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ozonation of natural organic matter on alumina. Appl. Catal., B 2006, 62, (3–4), 345-358.

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9. Sui, M.; Sheng, L.; Lu, K.; Tian, F. FeOOH catalytic ozonation of oxalic acid and the effect

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of phosphate binding on its catalytic activity. Appl. Catal., B 2010, 96, (1–2), 94-100.

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10. Yang, L.; Hu, C.; Nie, Y.; Qu, J. Catalytic Ozonation of Selected Pharmaceuticals over

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Mesoporous Alumina-Supported Manganese Oxide. Environ. Sci. Technol. 2009, 43, (7),

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2525-2529.

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11. Zhao, L.; Sun, Z.; Ma, J. Novel Relationship between Hydroxyl Radical Initiation and

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Surface Group of Ceramic Honeycomb Supported Metals for the Catalytic Ozonation of

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Nitrobenzene in Aqueous Solution. Environ. Sci. Technol. 2009, 43, (11), 4157-4163.

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12. Ikhlaq, A.; Brown, D. R.; Kasprzyk-Hordern, B. Mechanisms of catalytic ozonation: An

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investigation into superoxide ion radical and hydrogen peroxide formation during catalytic

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ozonation on alumina and zeolites in water. Appl. Catal., B 2013, 129, 437-449.

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13. Zhang, T.; Li, W.; Croué, J.-P. Catalytic Ozonation of Oxalate with a Cerium Supported

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Palladium Oxide: An Efficient Degradation Not Relying on Hydroxyl Radical Oxidation.

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Environ. Sci. Technol. 2011, 45, (21), 9339-9346.

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14. Kasprzyk-Hordern, B. Chemistry of alumina, reactions in aqueous solution and its application in water treatment. Adv. Colloid Interface Sci. 2004, 110, (1–2), 19-48.

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15. Panagiotou, G. D.; Petsi, T.; Bourikas, K.; Garoufalis, C. S.; Tsevis, A.; Spanos, N.;

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Kordulis, C.; Lycourghiotis, A. Mapping the surface (hydr)oxo-groups of titanium oxide

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and its interface with an aqueous solution: The state of the art and a new approach. Adv.

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Colloid Interface Sci. 2008, 142, (1–2), 20-42.

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16. Nawrocki, J.; Rigney, M.; McCormick, A.; Carr, P. W. Chemistry of zirconia and its use in chromatography. J. Chromatogr. A 1993, 657, (2), 229-282.

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17. Buser, H.-R.; Poiger, T.; Müller, M. D. Occurrence and Environmental Behavior of the

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Chiral Pharmaceutical Drug Ibuprofen in Surface Waters and in Wastewater. Environ. Sci.

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Technol. 1999, 33, (15), 2529-2535.

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18. Brozinski, J.-M.; Lahti, M.; Meierjohann, A.; Oikari, A.; Kronberg, L. The

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Anti-Inflammatory Drugs Diclofenac, Naproxen and Ibuprofen are found in the Bile of

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Wild Fish Caught Downstream of a Wastewater Treatment Plant. Environ Sci Technol

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2012, 47, (1), 342-348.

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19. Veldhoen, N.; Skirrow, R. C.; Brown, L. L. Y.; van Aggelen, G.; Helbing, C. C. Effects of

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Acute Exposure to the Non-steroidal Anti-inflammatory Drug Ibuprofen on the

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Developing North American Bullfrog (Rana catesbeiana) Tadpole. Environ Sci Technol

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2014, 48, (17), 10439-10447.

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20. Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D.

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Triblock Copolymer Syntheses of Mesoporous Silica with Periodic 50 to 300 Angstrom

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Pores. Science 1998, 279, (5350), 548-552.

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21. Lim, H.; Lee, J.; Jin, S.; Kim, J.; Yoon, J.; Hyeon, T. Highly active heterogeneous Fenton

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catalyst using iron oxide nanoparticles immobilized in alumina coated mesoporous silica.

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Chem. Commun. 2006, (4), 463-465.

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22. Liu, W.-J.; Zeng, F.-X.; Jiang, H.; Zhang, X.-S.; Li, W.-W. Composite Fe2O3 and

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ZrO2/Al2O3 photocatalyst: Preparation, characterization, and studies on the photocatalytic

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activity and chemical stability. Chem. Eng. J. 2012, 180, 9-18.

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23. Parlett, C. M. A.; Durndell, L. J.; Machado, A.; Cibin, G.; Bruce, D. W.; Hondow, N. S.;

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Wilson, K.; Lee, A. F. Alumina-grafted SBA-15 as a high performance support for

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Pd-catalysed cinnamyl alcohol selective oxidation. Catal. Today 2014, 229, 46-55.

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24. Li, Y.; Feng, Z.; Xin, H.; Fan, F.; Zhang, J.; Magusin, P. C. M. M.; Hensen, E. J. M.; van

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Santen, R. A.; Yang, Q.; Li, C. Effect of Aluminum on the Nature of the Iron Species in

490

Fe-SBA-15. J. Phys. Chem. B 2006, 110, (51), 26114-26121.

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25. Emeis, C. A. Determination of Integrated Molar Extinction Coefficients for Infrared

492

Absorption Bands of Pyridine Adsorbed on Solid Acid Catalysts. J. Catal. 1993, 141, (2),

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347-354.

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26. Tamura, H.; Tanaka, A.; Mita, K.-y.; Furuichi, R. Surface Hydroxyl Site Densities on Metal

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Oxides as a Measure for the Ion-Exchange Capacity. J. Colloid Interface Sci. 1999, 209,

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(1), 225-231.

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27. Bulanin, K. M.; Lavalley, J. C.; Tsyganenko, A. A. IR spectra of adsorbed ozone. Colloids Surf., A 1995, 101, (2–3), 153-158.

499

28. Che, M.; Tench, A. J. Characterization and Reactivity of Mononuclear Oxygen Species on

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Oxide Surfaces. In Advances in Catalysis, D.D. Eley, H. P.; Paul, B. W., Eds. Academic

501

Press: 1982; Vol. Volume 31, pp 77-133.

502

29. Che, M.; Tench, A. J. Characterization and Reactivity of Molecular Oxygen Species on

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Oxide Surfaces. In Advances in Catalysis, D.D. Eley, H. P.; Paul, B. W., Eds. Academic

504

Press: 1983; Vol. Volume 32, pp 1-148.

505 506

30. Seinfeld, J. H.; Pandis, S. N. Atmospheric chemistry and physics: from air pollution to climate change. John Wiley & Sons: 2012.

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507

31. Beltrán, F. J.; Rivas, J.; Álvarez, P.; Montero-de-Espinosa, R. Kinetics of Heterogeneous

508

Catalytic Ozone Decomposition in Water on an Activated Carbon. Ozone: Sci. Eng. 2002,

509

24, (4), 227-237.

510 511

32. Hoeben, W. F. L. M. Pulsed corona-iduced degradation of organic materials in water. Technische Universiteit Eindhoven: 2000.

512

33. Strathmann, T. J.; Stone, A. T. Reduction of Oxamyl and Related Pesticides by FeII:

513

Influence of Organic Ligands and Natural Organic Matter. Environ Sci Technol 2002, 36,

514

(23), 5172-5183.

515 516 517 518 519 520 521 522 523 524 525 526 527 528

24


Page 24 of 32

Page 25 of 32


Captions for Figures

529 530 531

Figure 1. Al 2p (A) and Si 2p (B) XPS spectra for Fe2O3/Al2O3@SBA-15.

532

Figure 2. Infrared spectra of adsorbed pyridine for different samples after outgassing at 200°C:

533

(a) SBA-15, (b) Fe2O3/SBA-15, (c) Al2O3@SBA-15, (d) Fe2O3/Al2O3@SBA-15.

534

Figure 3. TOC removal during the degradation of IBU in aqueous dispersions of various

535

catalysts with ozone. (a) Fe2O3/Al2O3@SBA-15, (b) Al2O3@SBA-15, (c) Fe2O3/SBA-15, (d)

536

SBA-15 and (e) without catalyst. (Initial pH = 7.0, initial IBU concentration = 10 mg L-1,

537

catalyst concentration = 1.5 g L-1, gaseous ozone concentration = 30 mg L-1).

538

Figure 4. The changes of ozone concentration in bulk water (A) and the adsorbed ozone onto

539

catalysts (B) during the decomposition of ozone in aqueous dispersions of various catalysts. (a)

540

Fe2O3/Al2O3@SBA-15, (b) Fe2O3/SBA-15, (c) Al2O3@SBA-15, (d) SBA-15 and (e) without

541

catalyst. (Initial pH = 7.0, initial ozone concentration = 10 mg L-1, catalyst concentration (if

542

use) = 1.5 g L-1).

543

Figure 5. Raman spectra of Al2O3@SBA-15 (A) and Fe2O3/Al2O3@SBA-15 (B) aqueous

544

dispersions without (a) and with (b) ozone. (Catalyst concentration = 33.3 g L-1, ozone

545

concentration in water = 4.23 mg L-1, initial pH = 7.0).

546

Figure 6. BMPO spin-trapping ESR spectra recorded in methanol dispersion for

547

BMPO-HO2•/O2•- (A) and aqueous dispersion for BMPO-•OH (B) with ozone. (a) ozone, (b)

548

SBA-15, (c) Al2O3@SBA-15, (d) Fe2O3/SBA-15 and (e) Fe2O3/Al2O3@SBA-15. (Initial pH =

549

7.0, catalyst concentration (if use) = 2 g L-1, initial BMPO concentration = 25 mM, recording

550

time = 3 min).

25



Page 26 of 32

551 552 553

1200

Al 2p

A

Al-O-Si

1000

CPS

800

Al-O-Al

600 400 200 0 68

70

72

74

76

78

80

82

Binding energy (eV) 554

8000

Si 2p

B

Al-O-Si Si-O-Si

CPS

6000 4000 2000 0 98

100

102

104

106

108

Binding energy (eV) 555 556

Figure 1. Al 2p (A) and Si 2p (B) XPS spectra for Fe2O3/Al2O3@SBA-15.

557 558 559

26


Page 27 of 32


560 561 562 563 564 565

1.0 1452

Absorbance (a.u.)

0.8

1492

1620 1608

0.6

d

0.4

c b

0.2

a

0.0

1400

1500

1600

1700

-1

Wavenumbers (cm ) 566 567

Figure 2. Infrared spectra of adsorbed pyridine for different samples after outgassing at 200°C:

568

(a) SBA-15, (b) Fe2O3/SBA-15, (c) Al2O3@SBA-15, (d) Fe2O3/Al2O3@SBA-15.

569 570 571 572 573 574 575 27



Page 28 of 32

576 577 578 579 580 581

1.0 e

0.8

TOC/TOCo

d

0.6

c

0.4

b

0.2

a

0.0

0

10

20

30

40

50

60

Reaction time (min) 582 583

Figure 3. TOC removal during the degradation of IBU in aqueous dispersions of various

584

catalysts with ozone. (a) Fe2O3/Al2O3@SBA-15, (b) Al2O3@SBA-15, (c) Fe2O3/SBA-15, (d)

585

SBA-15 and (e) without catalyst. (Initial pH = 7.0, initial IBU concentration = 10 mg L-1,

586

catalyst concentration = 1.5 g L-1, gaseous ozone concentration = 30 mg L-1).

587 588 589 590

28


Page 29 of 32


4

-1

CO (mg L )

3 e

1

d c b a

3

2

A

0 0

10

20

30

40

50

60

Reaction time (min) 591

1.5 -1

Surface O3 density (mg g )

d

1.0 b

0.5

c a

B

0.0

0

10

20

30

40

50

60

Reaction time (min) 592 593

Figure 4. The changes of ozone concentration in bulk water (A) and the adsorbed ozone onto

594

catalysts (B) during the decomposition of ozone in aqueous dispersions of various catalysts. (a)

595

Fe2O3/Al2O3@SBA-15, (b) Fe2O3/SBA-15, (c) Al2O3@SBA-15, (d) SBA-15 and (e) without

596

catalyst. (Initial pH = 7.0, initial ozone concentration = 10 mg L-1, catalyst concentration (if

597

use) = 1.5 g L-1).

598 599

29



Page 30 of 32

600 601

400

487

A

Intensity (a.u.)

300 808

200

913 962 1064

600

b

100 a

0 400

600

800

1000

1200

-1

Raman Shift (cm ) 602

200 B

801

Intensity (a.u.)

150

446

1042

551 663

100

938

a

50 0 400

b

600

800

1000

1200

-1

Raman Shift (cm ) 603 604

Figure 5. Raman spectra of Al2O3@SBA-15 (A) and Fe2O3/Al2O3@SBA-15 (B) aqueous

605

dispersions without (a) and with (b) ozone. (Catalyst concentration = 33.3 g L-1, ozone

606

concentration in water = 4.23 mg L-1, initial pH = 7.0).

607 608

30


Page 31 of 32


609 610

7

1.5x10

A

Intensity (a.u.)

e 7

1.0x10

d 6

5.0x10

c b a

0.0 3480

3500

3520

3540

3560

Magnetic (G) 611

7

1.5x10

B

Intensity (a.u.)

e 7

1.0x10

d 6

c

5.0x10

b a

0.0 3480

3500

3520

3540

Magnetic (G) 612 613

Figure 6. BMPO spin-trapping ESR spectra recorded in methanol dispersion for

614

BMPO-HO2•/O2•- (A) and aqueous dispersion for BMPO-•OH (B) with ozone. (a) ozone, (b)

615

SBA-15, (c) Al2O3@SBA-15, (d) Fe2O3/SBA-15 and (e) Fe2O3/Al2O3@SBA-15. (Initial pH =

616

7.0, catalyst concentration (if use) = 2 g L-1, initial BMPO concentration = 25 mM, recording

617

time = 3 min).

31



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Al2O3 ... - ACS Publications

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