Optimization and Modeling of Photocatalytic Removal of Norfloxacin

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Optimization and Modeling of Photocatalytic Removal of Norfloxacin Using Tungsten Bismuth Loaded Carbon Iron Complexes Based on Response Surface Methodology Shijie Chen, Yingjie Li, Renjiang LÜ, Jiping Jiang, Guangshan Zhang, and Peng Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 10 Jun 2014 Downloaded from http://pubs.acs.org on June 11, 2014

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Industrial & Engineering Chemistry Research

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Optimization and Modeling of Photocatalytic

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Removal of Norfloxacin Using Tungsten

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Bismuth Loaded Carbon Iron Complexes

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Based on Response Surface Methodology

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Shijie CHENa,b, Yingjie LIb, Renjiang LÜb, Jiping JIANGa, Guangshan ZHANG a, Peng

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WANGa,c,*

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a

School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin, 150090, China

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b

College of Chemistry and Chemical Engineering, Qiqihar University ,Qiqihar,161006, China

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c

State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, China

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ACS Paragon Plus Environment


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ABSTRACT

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Photocatalytic degradation of norfloxacin (NOR) (10 mg/L) was studied using tungsten

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bismuth loaded carbon iron complexes (C/Fe-Bi2WO6) under simulated solar light (SSL)

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irradiation in a cylindrical reactor. Three experimental parameters were chosen as

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independent variables: pH, C/Fe-Bi2WO6 concentration, and H2O2 concentration. A

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central composite experimental design (CCD) was used to establish a quadratic model as

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a functional relationship between the removal efficiency of NOR and three independent

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variables. The optimal values of operation parameters under the related constraint

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conditions were found at pH 7.10, C/Fe-Bi2WO6 concentration of 0.78 g/L and H2O2

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concentration of 227 mg/L. In optimal conditions, the removal efficiency of NOR

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reached 91.66%. The regression analysis with R2 value of 0.9728 indicated a good

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correlation between the experimental results and the predictive values.

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1. INTRODUCTION

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In recent years, pharmaceuticals and personal care products (PPCPs), as one kind of

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emerging micropollutants, causes extensive concerns, and are gradually and widely

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detected in most water bodies.1-4 Among medicines, antibiotics possibly receive the most

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attentions because of a wide usage around the world.5-7 NOR is an important

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fluoroquinolone antibiotic and commonly used in human and veterinary medicines. It was

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found in many surface water bodies around the world.8,

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treatment technologies hardly remove them from wastewater completely.10 Their health

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and ecological effects are receiving widely interests in the field of wastewater

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treatment.11-13

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Traditional wastewater

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Hence, there is a need to develop suitable methods to effectively remove NOR. More

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and more researchers have proposed and are studying various physical, chemical and

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biological processes.14-17 However, these techniques have certain disadvantages of high

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cost or secondary pollution of sludge. Advanced oxidation process (AOP) offers a

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promising solution, which adopts semiconductor as photocatalyst to mineralize toxic

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organic chemicals. It has been demonstrated that heterogeneous photocatalysis based on


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TiO2 as photocatalyst had the high efficiency. However, further practical application of


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TiO2 was restricted due to the wide band gap of 3.2 eV. This limitation hinders its

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application, most expected, in the visible-light region.18 Therefore, many efforts have

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been made to find out or compose photocatalytic materials which are active under solar

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light. Among these materials, Bi2WO6 has great advantages owing to the excellent

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photocatalytic activity under visible light irradiation.19-23




3



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In addition, Fenton-like and photo-Fenton were also outstanding AOPs approaches.

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Fenton-like system employs Fe2+ or Fe3+ and H2O2 as a source of hydroxyl radicals (•OH),

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and one of the most powerful oxidants known (E◦ = 2.80 V) and therefore of interest for

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treating waters containing micropollutants like antibiotics. Indeed, Fenton-like catalysts

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have been widely adopted in many application of AOPs.24-27 Photo-Fenton reaction has

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been widely used in the some organic compound degradation.28,

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additional reactions occur in the presence of light that produce •OH or increase the

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production rate of •OH, 30, 31 so increasing the efficiency of this process.

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In this process,

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It is also known that light utilization efficiency in photocatalytic AOPs is very low if a

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catalyst only has semiconductor property or Fenton-like property.32 The system coupling

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semiconductor and Fenton-like oxidation property is able to enhance the light utilization

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dramatically.

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Based on the conventional method in the previous works, a parameter is changed,

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while the other parameters are acted as the constants, and so this method does not

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consider the interaction of the parameters combination. Optimization approach, such as

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response surface methodology (RSM), can be employed to maximize the process

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performance. Literatures have reported that RSM to optimize some photocatalytic

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removal process.33-37

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To our knowledge, there is no such information available in literature for the

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RSM-based optimization on operation parameters of NOR photocatalysis using

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C/Fe-Bi2WO6 as a photocatalyst.

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In this study, we optimized the design parameters of the NOR removal efficiency and

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investigated the interaction effects between the tested variables. Therefore, the present

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work focused on pH, C/Fe-Bi2WO6 concentration and H2O2 concentration which were

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considered as independent factors and RSM was used to study their effects on and to

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optimize the removal efficiency of NOR. Furthermore, a proposed mechanism of

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photocatalytic removal of NOR is also discussed.

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2. MATERIAL AND METHODS

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2.1. Chemicals. Norfloxacin (C16H18FN3O3, MW 319.33) was provided by Chinese

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National Institute for the Control of Pharmaceutical and Biological Products. Its structure

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is shown (Figure S1, Supporting Information). All other chemicals were of reagent grade

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and used without further purification. Double distilled water was used to prepare

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experimental solutions.

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2.2. Catalysts Preparation. The catalyst used, i.e. C/Fe-Bi2WO6 was prepared via a

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two-step method involving resin carbonization and hydrothermal process and then

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calcined at 500 °C for 2 h before used in treating the NOR in aqueous solution under

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simulated sunlight irradiation. The detail procedure for preparing the catalyst was

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described in the previous work.38

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2.3. Catalyst Characterization. Crystalline structure of the sample was examined using

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an X-ray diffraction meter with a Cu Kα radiation (λ=0.15418 nm) (D/max-IIIA, Rigaku

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Corporation, Japan). Scanning electron microscopy (SEM) was recorded with a field

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emission scanning electron microscopy (Hitachi S-4300, Japan) with primary electron 5





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energy of 10 kV. The specific surface area of the sample was measured by N2 adsorption

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at -196 °C on chemisorption-physisorption analyzer (Autosorb-1, Kontakl Company,

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USA). The surface charge of the sample in aqueous solution was measured by a zeta

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potential analyzer (Zeta-sizer Nano series, Malvern Instruments, UK).

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2.4. Removal Experiments. The photocatalytic removal experiments were conducted in

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a cylindrical reactor (Figure S2, SI). SSL irradiation was provided by a 500 W xenon

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lamp, which was positioned in the cylindrical quartz cold trap. The system was cooled by

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circulating water and maintained at room temperature (20 °C). Air was bubbled

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continuously into the solution by an aquarium pump to ensure a constant supply of

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oxygen in the reaction period. Before the irradiation, the suspension was magnetically

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stirred in the dark for 30 min to ensure adsorption equilibrium of NOR on the catalysts.

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The initial pH value of NOR solution was measured by a digital pH meter. The solution

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of 0.1 M HCl and 0.1 M NaOH was used to adjust the pH level. Approximately 3.0 mL of

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reaction solution was taken at given time intervals and was centrifuged to separate the

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catalyst powder for NOR analysis. All the removal experiments were carried out at fixed

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radiation time of 60 min. These experiments were repeated three times to check the

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reproducibility of experimental results.

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2.5. Analytical Procedures. The variation in the NOR concentration was observed

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from its characteristic absorption band at 272 nm using a UV-Visible spectrophotometer.

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Because a linear dependence between the concentration of NOR and the absorption at

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272 nm was observed, the concentration of NOR was determined at this wavelength 6


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during the experimental process. The photocatalytic activity of the C/Fe-Bi2WO6

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photocatalyst was evaluated by degradation of NOR solution under simulated sunlight

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irradiation. The decrease in total organic carbon (TOC) was determined with a TOC

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analyzer (Shimadzu TOC-VCPN). Separation of the catalyst before TOC was done by

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filtering the sample solution using a 0.2 µm Millipore membrane filter. The determination

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of •OH was conducted by means of terephthalic acid (TA) fluorescence (FL) probe

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method.39, 40 In this method, the TA is a non-fluorescent compound, but once combining

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with

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2-hydroxyterephthalic acid (HTA). The fluorescence signal from HTA was measured in a

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1.0 cm quartz cell at λex= 315 nm, λem= 425 nm on a Perk in Elmer (LS55) fluorescence

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spectrophotometer.

a

•OH,

it

becomes

the

only

highly

fluorescent

hydroxy

2.6. Experimental Design and Optimization by Response Surface Methodology. In

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the optimization, RSM was utilized to optimize the three parameters (pH value,

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C/Fe-Bi2WO6 concentration and H2O2 concentration). Three parameters were chosen as

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independent variables, and the removal efficiency of NOR as output response variable.

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Range and level of independent variables are shown in Table 1. The central composite

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experimental design (CCD) was adopted to evaluate the combined effect of three

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independent variables by 20 sets of experiments.41 The fundamental assumption and

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experimental implication of RSM have been discussed elsewhere.42 An empirical

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second-order polynomial regression model for three parameters was expressed as Eq. (1):

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y=β0+β1x1+β2x2+β3x3+β11x12+β22x22+β33x32+β12x1x2+β13x1x3+β23x2x3

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where, y represents response variable (removal efficiency of NOR) (%); β0 is interception



product

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7


(1)



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coefficient, β11, β22 and β33 are quadratic terms, β12, β13 and β23 are interaction coefficients,

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and x1, x2 and x3 are independent variables studied (pH, C/Fe-Bi2WO6 concentration and

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H2O2 concentration). Regression analysis and optimization process were performed by

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Design Expert V.8.0.6 software (Stat-Ease Inc., USA). Data were analyzed by the

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analysis of variance (ANOVA), and the mean values were considered the significant

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difference when p-value

Optimization and Modeling of Photocatalytic Removal of Norfloxacin

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