MCM-41 as a Highly Stable and pH-insensitive

Mar 28, 2007 - A heterogeneous catalyst was synthesized by supporting copper metal on MCM-41 by chemical vapor deposition (CVD). The usage of oxygen ...
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Copper/MCM-41 as a Highly Stable and pH-insensitive Heterogeneous Photo-Fenton-like Catalytic Material for the Abatement of Organic Wastewater Frank L. Y. Lam, Alex C. K. Yip, and Xijun Hu* Department of Chemical Engineering, Hong Kong UniVersity of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

A heterogeneous catalyst was synthesized by supporting copper metal on MCM-41 by chemical vapor deposition (CVD). The usage of oxygen as a carrier gas and oxidizing agent is found to be very important in producing a stable and effective Cu/MCM-41 catalyst. This MCM-41-supported copper catalyst is evaluated in the photo-Fenton-like degradation of a dye pollutant, Orange II. Results show that the Cu/MCM-41 catalyst is effective in mineralizing total organic carbon (TOC) of 80%, 78%, and 70% at pH 3, 5.5, and 7, respectively, successfully overcoming the low efficiency problem of the conventional Fenton reaction at high pH. Moreover, the synthesized catalyst is proved to be durable with a stable TOC removal efficiency after four consecutive cycles. The kinetic study of pollutant degradation using Cu/MCM-41 is also conducted. Introduction Due to the limited amount of accessible clean water in the world, water remediation, particularly treating the organic polluted wastewater caused by industrial effluents, has become an important issue of environmental control. Among all methods, cleaning polluted water with the aid of catalysis has drawn much attention and research interest. To date, numerous catalytic processes have been reported as feasible methods in solving the organic pollutant problems. These processes are often referred to as advanced oxidation processes (AOPs).1 Photo-Fenton oxidation is one of the AOPs that can effectively eliminate the organic compounds in wastewater. Its superior performance is attributed to the utilization of ultraviolet irradiation (UV) and Fenton’s reagents (Fe2+ and H2O2). By using Fenton’s reagents, hydroxyl radical, which is nonselective but highly oxidative to organic compounds, can be generated. The mechanism is illustrated in eq 1.2-4

Fe2+ + H2O2 f Fe3+ + OH• + OH-

(1)

The hydroxyl radical can be continuously produced in the system by means of UV irradiation to reduce Fe3+ back to Fe2+, as described in eq 2.

Fe3+ + hν f Fe2+

(2)

This photoassisted homogeneous Fenton system has been used for nearly a decade due to its high catalytic activity in the abatement of organic pollutants. However, there are some drawbacks to this system. First, the ferric ion remaining in the treated wastewater requires a separation system which complicates the overall process and makes it uneconomical. Second, Fenton’s reagents work well within only a narrow pH range (pH 3-4), which greatly limits the catalytic performance of photo-Fenton oxidation systems because most organic wastewater has pH values ranging from 5 to 7. To tackle this problem, some researchers5 suggested another catalyst, copper, which behaves similarly to Fenton’s reagents (eqs 3 and 4)6 and is therefore called a Fenton-like catalyst. An * To whom correspondence should be addressed. Tel.: (852) 23587134. Fax: (852) 23580054. E-mail: [email protected].

advantage of a Fenton-like catalyst is its characteristics of a wide-working pH range (pH 3-7) compared to the conventional Fenton catalyst.

Cu+ + H2O2 f Cu2+ + OH• + OH-

(3)

Cu2+ + hν f Cu+

(4)

Nevertheless, it is well-known that copper is a toxic heavy metal. For this reason, using homogeneous copper in the liquidphase-oxidation process is often thwarted because it is hazardous to both marine animals and humans. This is also the reason copper catalyst is merely used in gas-phase reactions.7 To overcome this problem, copper has been suggested to be supported on a porous solid substrate. Conventionally, there are various methods for coating a metal catalyst onto a substrate such as the sol-gel hydrothermal method,8 coprecipitation,9 impregnation,10 and vapor deposition.11 Until now, less research has been done in applying metallorganic chemical vapor deposition (MOCVD) to the preparation of a heterogeneous metal catalyst supported on porous material. Substrate-supported metal catalysts are generally suggested for gas-phase reactions and seldom for liquid phase because the leaching of metal catalyst from the substrate is usually regarded as a crucial problem in liquid-phase oxidation.12 Severe metal leaching would cause heavy metal ion left over in the treated wastewater and also degrade the catalytic performance, which results in poor durability. In this work, our objective is to synthesize a “clean” and effective MCM-41-supported copper catalyst via an MOCVD technique for the photo-Fenton-like oxidation of organic dye. The developed catalysts were characterized and evaluated in different categories, including catalytic performance at different pH environment, catalyst stability, and durability. Kinetic parameters are also determined to describe the degradation mechanism. By using the proposed model, the activation energy of reaction and the rate constants of the governing equations can be determined. Theory Equations 5 and 6 give the disappearance rate of TOC and the consumption rate of H2O2, having the rate constants of kT

10.1021/ie061436b CCC: $37.00 © 2007 American Chemical Society Published on Web 03/28/2007

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and kH, respectively. [TOC], [H2O2], W, and V represent the

d[TOC] W ) -kT[TOC]m[H2O2]n dt V

(5)

d[H2O2] W ) -kH[H2O2]y dt V

(6)

concentration of the total organic carbon, concentration of hydrogen peroxide, amount of catalyst, and reactor volume, accordingly. The order of the reaction with respect to the H2O2 concentration in the H2O2 disappearance rate equation is denoted as y, while m and n are the orders of the reaction with respect to TOC and H2O2 concentrations in the TOC disappearance rate equation, respectively. Several assumptions have been made for both suggested equations: (1) The order of the reaction with respect to the TOC concentration, m, is assumed to be 1. (2) The order of the reaction with respect to the H2O2 concentration in eq 6, y, is assumed to be 1. (3) The source of photon energy is kept constant throughout the reaction. Assumption 1 is widely accepted by other researchers in both homogeneous and heterogeneous oxidation systems.8,13,14 It should be emphasized that the proposed kinetic model eqs 5 and 6 are power law/empirical equations, without any phenomenological meaning. Since the amount of catalyst used and the reactor volume are constant, eqs 5 and 6 can be rewritten as eqs 7 and 8, correspondingly.

d[TOC] ) -kT′[TOC][H2O2]n dt

(7)

d[H2O2] ) -kH′[H2O2] dt

(8)

The solution for eq 8 is

ln

(

[H2O2]t

)

[H2O2]0

) -kH′t

(9)

The new constant kH′ can be simply obtained from eq 9 with a plot of ln([H2O2]t/[H2O2]0) against time, where kH′ is the slope of the plotted straight line. By substituting eq 9 into eq 7, the disappearance rate of TOC can be obtained. Moreover, the activation energy of the oxidation process can be determined by applying the Arrhenius equation to the kinetic data at different temperatures. Experimental Section The MCM-41-supported copper catalyst was synthesized by an MOCVD technique. Copper(II) acetylacetonate was chosen as the copper precursor because it was relatively cheap and had a low sublimation temperature compared to other precursors. MCM-41 was selected as the substrate support for immobilization of copper catalyst due to its high accessible surface area. The corresponding preparation protocol was described elsewhere in the literature.15 A rotated CVD system was built for the deposition process, as shown in Figure 1. The CVD system can be divided into four sections: a gas supply system, a rotated tubular reactor, a condenser, and a vacuum pump. First, oxygen was used as a carrier gas to deliver the sublimed precursor onto the substrate surface and at, the

Figure 1. Schematic diagram of rotated CVD reactor system.

same time, it acted as an oxidant to build up the linkage between copper element and MCM-41 substrate.16 Second, the rotated tubular reactor was designed to have two characteristic zones, viz., evaporation and deposition zones, for holding the precursor and the substrate, respectively. Third, the condenser was installed at the reactor outlet to immediately condense the unwanted byproducts and prevent them from entering the pump. Finally, the vacuum pump was used to provide a vacuum condition in order to increase the volatility of the cupric precursor. For each deposition, 0.05-1 g of cupric precursor and 1 g of MCM-41 were placed inside the evaporation and deposition zones, respectively. Vacuum (0.5 in.Hg) was first applied and oxygen was then introduced to the system at a flow rate of 0.25 mL/s (normal conditions). The tubular reactor was heated to 280 °C at a heating rate of 5 °C/min. The deposition was expected to start as soon as the target temperature (280 °C) was attained. The deposition lasted for 60 min. During the investigation, the presence of oxygen was found to be a crucial factor in the catalyst stability. Therefore, a sample of Cu/M411-550 °C, which was deposited at 280 °C in the MOCVD process without using oxygen as carrier gas but postcalcined in air at 550 °C, was also synthesized for comparison, which can be seen in the Supporting Information. A washing process was conducted for the prepared Cu/MCM41 catalyst to remove the loosely attached deposited precursor and copper particles. The purpose of this test is to determine the adhesion between the deposited copper element and MCM41 substrate. The washing process was done by soaking 2 g of Cu/MCM-41 with 2 L of 2% HNO3 solution for 6 h. The washed Cu/MCM-41 was filtered, was dried at 50 °C, and was ready for characterization and evaluation. Characterization of Cu/MCM-41 (Cu/M41) was done by several analyses including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma with optical emission spectroscopy (ICP-OES), and nitrogen physisorption. For the analysis of X-ray diffraction, Cu KR irradiation having a wavelength of 1.54 Å was used. The valent state of copper could be determined by the blueprints of XRD spectra. XPS was used to determine the surface copper loading of Cu/MCM-41. The copper loading on the substrate was determined using the ICP-OES technique by dissolving the prepared Cu/MCM-41 into concentrated nitric acid. The physical properties of Cu/MCM-41, such as the specific BET surface area, were determined by nitrogen physisorption. The washed and characterized Cu/MCM-41 was evaluated for organic pollutant degradation. An acidic azo dye, Orange II, was selected as the model pollutant because its nonbiodegradable nature has prevented it from being treated efficiently with biological means. Therefore, it is of great interest to apply a catalytic chemical process, namely, photo-Fenton degradation to this type of organic pollutant. A total of 0.2 g of Cu/MCM-

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Table 1. Specific BET Surface Area and Bulk and Surface Copper Loadings of Developed Cu/MCM-41 sample

BET area, m2/g

Cu loading after CVDa, wt %

XPS after CVD, wt %

Cu loading after washinga, wt %

XPS after washing, wt %

blank MCM-41 Cu/M41-1 Cu/M41-2 Cu/M41-3 Cu/M41-4

1210 1112 1089 1122 1034

0 0.84 1.95 2.83 3.81

0 1.21 2.23 3.22 4.82

0.82 1.79 2.51 3.27

1.23 2.15 3.01 4.32

a

Cu loading is determined by dissolving Cu/M41 into concentrated HNO3 and finally analyzing the Cu concentration in the filtrate by ICP-OES analysis.

41 was put into a photoreactor17 containing 0.2 L of 0.3 mM Orange II solution which was adjusted to pH 3 by adding 0.1 M H2SO4. An 8 W UV-C disinfection lamp was used as the ultraviolet (UV) irradiation source and was inserted in the concentric position of the photoreactor. Both Cu/MCM-41 and Orange II solution were well mixed by the continuous nitrogen flow from the bottom of the photoreactor. Several components of the treated wastewater were analyzed, including total organic carbon (TOC) and Cu2+ ion concentration. Such measurement can reflect the degree of mineralization and the copper leaching. These measurements were done by a TOC analyzer (Shimadzu, TOC 5000A) and ICP-OES (PerkinElmer 3000), respectively. For the kinetic study, determination of H2O2 concentration at each time interval was required. Titanium(IV) oxysulfate (TiOSO4), which was purchased from Sigma Aldrich, was used for measuring H2O2 concentration.18 First, titanium salt solution was prepared by dissolving titanium(IV) oxysulfate into sulfuric acid solution with a ratio of 0.5 g of TiOSO4:20 mL of H2SO4 (98%):200 mL of H2O. In each sampling, 2 mL of titanium salt solution was added into the sample (2 mL) followed by the addition of 2 mL of water. The titanium salt solution would react with the remaining hydrogen peroxide to form a titanyl complex which has a maximum absorbance at 420 nm. By means of the UV-vis spectrophotometer, the concentration of H2O2 can be quantified. Because Orange II also has significant absorbance at 420 nm, its interference has to be corrected. This is done by subtracting the absorbance reading of Orange II at 420 nm (which is obtained at the same time when measuring Orange II concentration at 485 nm) from the sample mixed with TiOSO4. Results and Discussion All developed catalysts were thoroughly washed with acidic solution as mentioned in the Experimental Section. The washing test is to remove unstable substances such as partially decomposed precursors and loosely attached copper particles. The results are shown in the Supporting Information. The washed MCM-41-supported catalysts were then characterized to determine their specific BET surface areas and bulk and surface copper loadings, as listed in Table 1. A total of four MCM41-supported copper catalysts with different copper loadings, denoted as Cu/M41-x (x ) 1-4), were examined. The results show that the specific BET surface areas of the developed catalysts are slightly smaller than that of the blank MCM-41. This implies that the copper was deposited on the external surface and pore walls of MCM-41 as a thin layer without changing its pore structure. A comparison between the ICP and XPS results illustrates that the Cu loadings on the surface (by XPS) are larger than that on the bulk (by ICP). This finding confirms that more copper is deposited on the external MCM41 surface than on the pore walls. This distribution is advantageous for photooxidation due to the efficient contact between

Figure 2. XRD spectra of Cu/M41 catalysts with different copper loadings.

the metal catalyst and UV irradiation. It is also noted that the copper loadings of Cu/M41 after the washing process do not vary much in magnitude. Therefore, it is possible to tune the copper loading even though the washing step is introduced. Figure 2 shows the XRD spectra of the washed Cu/M41. No characteristic peaks of copper or copper oxides are observed for Cu/M41 catalysts having copper loadings from 1.79 to 3.27 wt %. However, characteristic peaks of cuprous oxide (Cu2O) are observed with strong intensities at 36.42°, 42.30°, and 61.34° when the copper loading is around 6 wt %. At a low copper loading, the deposited copper element is mainly distributed at the outermost MCM-41 surface and it can be coated as a thin layer. At a deposition temperature of 280 °C, the oxygen supplied as the carrier gas can chemically react with the MCM41 surface and the deposited copper to form stable Si-O-Cu bonding. Therefore, a thin layer of copper was strongly bonded to the MCM-41 surface. This layer is reasonably evenly distributed over the MCM-41 support due to the rotational motion of the tubular reactor. Further deposition of copper on MCM-41 results in the formation of crystalline Cu2O. This phenomenon agrees well with the findings of Xie and Tang, that the metal loading and crystallinity are closely related in catalyst preparation.19 As mentioned before, the major disadvantage of the conventional photo-Fenton reaction is that the catalytic performance is highly dependent on the solution pH. The activity of Fenton’s reagents (ferric ion and hydrogen peroxide) deteriorates quickly as pH increases above 4. Therefore, poor degradation efficiency is observed at pH higher than this value. This problem was solved in this study by using the developed MCM-41-supported copper catalyst (Fenton-like catalyst). Figure 3 shows the mineralization of Orange II at different pH values and media catalyzed by the developed washed Cu/M41s. In the current study, the term mineralization is defined as the degree of TOC removal in the dye-containing wastewater, which is the organic carbon content in Orange II in this case. For all experiments, unless specified, the developed Cu/M41s are evaluated in the

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Figure 3. Mineralization of Orange II by Cu/M41 and Fe/M41 at different pH values, where their corresponding copper and iron loadings are 2.5 and 3.5 wt %.

Figure 5. Leaching phenomenon of different Cu-loaded catalysts.

Figure 4. TOC degradation of Orange II using different copper-loaded catalysts.

conditions of 0.3 mM Orange II, 1 g/L catalyst concentration (0.2 g of Cu/M41:0.2 L of pollutant solution), 8 W UV-C irradiation, and pH 5.5, which is the natural pH value of 0.3 mM Orange II solution. The hydrogen peroxide concentration is 14.4 mM, which is the theoretical amount to completely oxidize 0.3 mM Orange II. The catalytic efficiencies at 2 h reaction time of Cu/M41 (77% at pH 5.5 and 70% at pH 7) are much better than those of Fe/M41 (60% at pH 5.5 and 40% at pH 7), although Fe/M41 gives a better TOC removal at pH 3 (83%) than Cu/M41 (80%). These results affirmed that our developed Cu/M41 is a promising solution to the narrow working pH range problem faced by the conventional photoFenton reaction. Therefore, Cu/M41 is considered to be more applicable than Fe/M41 in real applications because most wastewater is slightly acidic in nature, i.e., pH slightly less than 7, in which Fe/M41 often losses its activity. The effect of copper loading on the catalytic performance of Orange II degradation has been studied. Figure 4 displays the effect of copper loading on the TOC mineralization of Orange II. It shows that the higher the copper loading, the higher the TOC removal achieved within the examined range between 0.82 and 3.27 wt % Cu, but the difference is small. The mineralization efficiency at 2 h reaction time is reported to be 75% at 0.82 wt % (open circle line), 77% at 1.79 wt % (open square line), 78% at 2.51 wt % (open triangle line), and 80% at 3.27 wt % (open inverted triangle line). It is noted that the degradation rates of TOC slightly increase as the copper loading on MCM-41 increases. The effects of UV irradiation and dosage

Figure 6. (a) Stability test on the catalytic performance of Cu/M41-3 for repeated runs. (b) Leaching profile of Cu/M41-3 during repeated runs.

of H2O2 on the catalyst’s performance of Orange II degradation have also been studied, which can be found in the Supporting Information. The metal leaching is another concern when applying heterogeneous metallic catalysts in wastewater remediation. Figure 5 illustrates the copper leaching of Cu/M41 versus reaction time. The leached copper concentrations varied with different loadings of copper, resulting in copper leachings at 2 h reaction time of 0.08 mg/L at 0.82 wt %, 0.22 mg/L at 1.79 wt %, 0.3 mg/L at 2.51 wt %, and 0.5 mg/L at 3.27 wt %. These leached copper concentrations are far below the discharge standard (∼1 mg/L) suggested by the Environmental Protection Agency (EPA).20 The leached copper amount from the catalyst is further compared to the total copper amount of that catalyst, which is defined as leaching percent and shown in Figure 5.

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Figure 7. Decomposition rate of H2O2 in Orange II mineralization at different reaction temperatures using Cu/M41-3.

Figure 8. Model fitting of TOC values to experimental data using Cu/ M41-3 as catalyst. Table 2. Calculated Kinetic Parameters and Activation Energy of TOC Disappearance Rate Equation for Cu/M41-3 reaction temp, °C

kT, (mol of H2O2)-0.65 L0.65 s-1

n

Eact, kJ/mol

35 45 55

0.519 0.679 0.872

0.65

21.8

For all four catalysts, the leached copper is very small, only around 1%. Therefore, it can be claimed that the deposited copper is kept stable during the degradation process by strongly attaching to the substrate surface. It is also beneficial to the catalyst durability as no active copper is lost during the process, allowing it to be reused for another cycle of pollutant treatment. Stability is always an important issue for a catalyst to be applied in a plant-scale process from both catalytic and economic perspectives. By repeating the Orange II mineralization for a number of runs, the lifespan of Cu/M41-3 can be estimated. Figure 6a illustrates the catalytic efficiencies of Cu/M41-3 during four repeated runs. It clearly shows that approximately 78% of TOC removal can be achieved for each run at 2 h reaction time in the stability test. This is consistent with the results obtained in Figure 6b, in which the leaching of metal catalyst is insignificant (about 0.3 mg/L). This level of metal leaching is even smaller when the number of runs increases. Therefore, it is proved that the catalyst immobilized on MCM41 is sustainable and stable for multiple runs. In the study of reaction kinetics, 0.2 L of 0.3 mM Orange II solution, 0.2 g of catalyst, a hydrogen peroxide concentration of 14.4 mM, an irradiation of 8 W UV-C source, and pH 5.5

were used as standard experimental conditions, unless specified. Reactions at different temperatures (35, 45, and 55 °C) are conducted in order to determine the activation energy. The change of H2O2 concentration is measured as a function of reaction time, from which the corresponding values of ln([H2O2]t/[H2O2]0) can be obtained, which are symbolized with open circles, open squares, and open triangles in Figure 7. The model fittings determined from eq 9 using the reaction temperatures of 35, 45, and 55 °C are illustrated as solid, dashed, and dotted lines, respectively. By comparing the experimental and fitted H2O2 concentrations, a linear relationship with R2 g 0.996 is obtained, which proves that the assumption of y ) 1 in eq 6 is correct. The values of kH′ can be obtained from the slopes of the straight lines and were found to be 0.0123, 0.0153, and 0.0216 s-1 at reaction temperatures of 35, 45, and 55 °C, respectively. Figure 8 shows the experimental values of TOC removal at reaction temperatures of 35, 45, and 55 °C, which are symbolized as solid circles, open circles, and solid triangles, respectively, while for the theoretical values calculated from eq 7, solid, dotted, and dashed-dotted lines are used, correspondingly. It is found that the experimental TOC removals agree very well with the calculated values of TOCs at 35 °C (solid line), 45 °C (dotted line), and 55 °C (dashed-dotted line). This shows that the proposed model is valid for the measured experimental data. There is a small deviation between the model and experimental data when the reaction time is longer than 90 min. This can be explained as that at this time there may be a small amount of stable intermediate organic products such as acetic acid formed which are difficult to be oxidized by the hydroxyl radicals. By fitting the model equations to the experimental data, the modified reaction rate constants at different temperatures, the reaction order of TOC disappearance with respect to [H2O2], and the activation energy can be determined, which are shown in Table 2. It is noted that the value of kT′ increases from 0.519 to 0.872 (mol of H2O2)-0.65 L0.65 s-1 as the reaction temperature increases from 35 to 55 °C. This is expected because the higher the temperature, the more the kinetic energy is supplied to the reaction system. The calculated activation energy is 21.8 kJ/ mol, which is rather low. Conclusions Copper catalysts supported on MCM-41 (Cu/M41) have been successfully synthesized by an MOCVD technique. Characterizations by ICP-AES, XPS, XRD, and nitrogen adsorption show that copper catalysts were loaded on the MCM-41 substrate and mainly distributed on the exterior of MCM-41. The introduction of oxygen as carrier gas and oxidizing agent during the CVD process is found to be very important to obtain a highly stable Cu/MCM-41 catalyst. Various copper-loaded MCM-41s (0.823.27 wt % Cu) were evaluated in the photo-Fenton-like degradation of a dye pollutant, Orange II. Results showed that Cu/M41 has a high catalytic activity not only at a pH 3 but also at pH 5.5 and 7, giving TOC removals at 2 h reaction time of 80% (pH 3), 78% (pH 5.5), and 70% (pH 7). This performance is a significant breakthrough to the conventional photo-Fenton catalysts (Fe3+ and H2O2) which have poor activity for pH >4. The photooxidation system was also optimized with three major parameters: the loadings of copper catalyst, the source of UV irradiation, and the dosage of hydrogen peroxide. The results revealed that the catalytic efficiency of Orange II degradation can be promoted by using higher copper loadings, using higher H2O2 dosage, and conducting the reaction under UV-C irradiation. Most importantly, the leaching of the

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developed catalyst is insignificant, below 0.5 mg/L for all synthesized Cu-loaded MCM-41s. A stability test of Cu/M41 was also conducted to demonstrate the catalyst lifespan. A study consisting of four consecutive reaction runs shows that Cu/M41 is durable and is able to keep the TOC removal efficiency at 78%. The reaction kinetics of Cu/M41 on Orange II degradation was also studied. It was found that the proposed theoretical model agrees well with the experimental data of TOC removal within the experimental range studied. The calculated activation energy was found to be 21.8 kJ/mol. In summary, it is claimed that Cu/M41 is a promising catalytic material for the photoFenton-like degradation of dye pollutant, especially in high pH reaction medium. Acknowledgment This project was supported by the Research Grants Council of Hong Kong Government under Grant 601703 and the Innovation Technology Commission under the GuangdongHong Kong Technology Cooperation Funding Scheme (TCFS) of GHP/031/05. Supporting Information Available: Discussion of the washing test on Cu/M41, effect of UV irradiation on the catalytic performance of Orange II degradation using Cu/M41, and effect of hydrogen peroxide dosage on the catalytic performance of Orange II degradation using Cu/M41. This material is available free of charge via the Internet at http://pubs.acs.org. Nomenclature [H2O2] ) concentration of hydrogen peroxide, mol/L kH ) rate constant of H2O2 consumption rate equation, L/(s g of catalyst) kH′ ) modified rate constant of H2O2 consumption rate equation, s-1 kT ) rate constant of TOC disappearance rate equation, [L/(s g of catalyst)](mol of H2O2)-n Ln kT′ ) modified rate constant of TOC disappearance rate equation, (mol of H2O2)-n Ln s-1 m ) order of reaction with respect to TOC concentration in TOC disappearance rate equation n ) order of the reaction with respect to H2O2 concentration in TOC disappearance rate equation t ) reaction time, s [TOC] ) concentration of total organic carbon, mol/L W ) amount of catalyst used in the reactor, g y ) order of reaction with respect to H2O2 concentration in H2O2 consumption rate equation Literature Cited (1) Oppenlander, T. Photochemical Purification of Water and Air; WileyVCH: Weinheim, 2003.

(2) Fenton, H. Oxidation of Tartaric Acid in the Presence of Iron. J. Chem. Soc. 1894, 65, 899. (3) Katsumata, H.; Kawabe, S.; Kaneco, S.; Suzuki, T.; Ohta, K. Degradation of Bisphenol A in Water by the Photo-Fenton Reaction. J. Photochem. Photobiol., A: Chem. 2004, 162, 297. (4) Fukushima, M.; Tatsumi, K.; Nagao, S. Degradation Characteristics of Humic Acid during Photo-Fenton Processes. EnViron. Sci. Technol. 2001, 35, 3683. (5) Neamtu, M.; Yediler, A.; Siminiceanu, I.; Kettrup, A. Oxidation of Commercial Reactive Azo Dye Aqueous Solutions by the Photo-Fenton and Fenton-like Processes. J. Photochem. Photobiol., A: Chem. 2003, 161, 87. (6) Luzzatto, E.; Cohen, H.; Stockheim, C. Reactions of Low-Valent Transition-Metal Complexes with Hydrogen-Peroxide-Are they Fenton-like or not. 4. The Case of Fe(II)L, L ) EDTA, HEDTA, and TCMA. Free Radical Res. 1995, 23, 453. (7) Long, R. Q.; Yang, R. T. Selective Catalytic Reduction of Nitric Oxide with Ethylene on Copper Ion-Exchanged Al-MCM-41 Catalyst. Ind. Eng. Chem. Res. 1999, 38, 873. (8) Feng, J.; Hu, X.; Yue, P. L.; Zhu, H. Y.; Lu, G. Q. A Novel Laponite Clay-based Fe Nanocomposite and Its Photo-catalytic Activity in Photoassisted Degradation of Orange II. Chem. Eng. Sci. 2003, 58, 679. (9) Pinna, F. Supported metal catalysts preparation. Catal. Today 1998, 41, 129. (10) Hu, X.; Lam, F. L. Y.; Cheung, L. M.; Chan, K. F.; Zhao, X. S.; Lu, G. Q. Copper/MCM-41 as catalyst for photochemically enhanced oxidation of phenol by hydrogen peroxide. Catal. Today 2001, 68, 129. (11) Dossi, C.; Psaro, R.; Bartsch, A.; Brivio, E.; Galasco, A.; Losi, P. Organometallics-chemical vapor deposition: A new technique for the preparation of non-acidic, zeolite-supported Pd and Pt catalysts. Catal. Today 1993, 17, 527. (12) Yip, A. C. K.; Lam, F. L. Y.; Hu, X. A novel heterogeneous acidactivated clay supported copper catalyst for the photobleaching and degradation of textile organic pollutant using Photo-Fenton-like reaction. Chem. Commun. 2005, 3218. (13) Dhananjeyan, M. R.; Kiwi, J.; Albers, P.; Enea, O. Photo-assisted Immobilized Fenton Degradation up to pH 8 of Azo Dye Orange II Mediated by Fe3+/Nafion/Glass Fibers. HelV. Chim. Acta 2001, 84, 3433. (14) Kiwi, J.; Lopez, A.; Nadtochenko, V. Mechanism and Kinetics of the OH-Radical Intervention during Fenton Oxidation in the Presence of a Significant Amount of Radical Scavenger (Cl-). EnViron. Sci. Technol. 2000, 34, 2162. (15) Lam, F. L. Y.; Hu, X. A New System Design for the Preparation of Copper/Activated Carbon Catalyst by Metalorganic Chemical Vapor Deposition Method. Chem. Eng. Sci. 2003, 58, 687. (16) Lam, F. L. Y.; Hu, X. In-situ Oxidation for Stabilization of Fe/ MCM-41 Catalyst Prepared by Metal Organic Chemical Vapor Deposition. Catal. Commun. 2007, in press, http://dx.doi.org/10.1016/j.catcom.2007.02.009. (17) Ding, Z.; Hu, X.; Lu, G. Q.; Yue, P. L.; Greenfield, P. F. Novel Silica Gel Supported TiO2 Photocatalyst Synthesized by CVD Method. Langmuir 2000, 16, 6216. (18) Richardson, E. Some Studies on Inorganic Peroxy-Acids II. Peroxy Complexes of Titanium. J. Less-Common Met. 1960, 2, 458. (19) Xie, Y. C.; Tang, Y. Q. Spontaneous Monolayer Dispersion of Oxides and Salts onto Surface of Supports: Application to Heterogeneous Catalysis. AdV. Catal. 1990, 37, 1. (20) http://www.epa.com.hk.

ReceiVed for reView November 9, 2006 ReVised manuscript receiVed March 6, 2007 Accepted March 6, 2007 IE061436B