Journal of Saudi Chemical Society (2014) 18, 317–326

King Saud University

Journal of Saudi Chemical Society

www.ksu.edu.sawww.sciencedirect.com

ORIGINAL ARTICLE

Kinetic modeling of BB41 photocatalytic treatment

in a semibatch flow photoreactor using a nano

composite film

* Corresponding author. Tel.: +98 914 442 9804; fax: +98 21

22977861.E-mail addresses: sarvin_s108@yahoo.com, sarvins108@gmail.com

(S. Mohammadi-Aghdam).

Peer review under responsibility of King Saud University.

Production and hosting by Elsevier

1319-6103 ª 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

http://dx.doi.org/10.1016/j.jscs.2013.09.012

Open access under CC BY-NC-ND license.

Open access under CC BY-NC-N

S. Mohammadi-Aghdama,*, R. Marandi

b, M.E. Olya

c, A.A. Mehrdad Sharif

d

a Department of Applied Chemistry, Faculty of Chemistry, North Tehran Branch, Islamic Azad University, Tehran, Iranb Department of Environmental Engineering, Faculty of Engineering, North Tehran Branch, Islamic Azad University, Tehran, Iranc Department of Environmental Research, Institute for Color Science and Technology, Tehran, Irand Department of Analytical Chemistry, Faculty of Chemistry, North Tehran Branch, Islamic Azad University, Tehran, Iran

Available online 17 October 2013

KEYWORDS

Kinetic modeling;

Photocatalytic degradation;

Semibatch flow photoreac-

tor;

COD;

Basic Blue 41

Abstract In this study, photocatalytic degradation of Basic Blue 41 (BB41) was investigated using

TiO2 nano composite films stuffed with definite dosage of TiO2 nanopowder, immobilized on glass

substrates using the sol–gel dip-coating method, in a semibatch rectangular photoreactor (irradiated

with a UV light). The coatings were characterized by X-ray diffraction (XRD), transmission elec-

tron microscopy (TEM), scanning electron microscopy (SEM), N2 adsorption–desorption isotherm

analysis and coating thickness gauge. The kinetic of the degradation of the BB41 was described with

the Langmuir–Hinshelwood kinetic model. Experimental results indicate that the degradation rate

of BB41 follows pseudo-first-order kinetics. A model was developed with nonlinear regression, for

prediction of pseudo first-order rate constants (kapp) as a function of operational parameters,

including initial concentration of BB41 (10–50 mg/L), flow rate (6–15 L/h) and temperature (20–

40 �C). The following equation was obtained by kinetic modeling Kapp ¼ 436:6517

2:19271þ2:1927½BB41�0

� �0:1937FR

� �exp 6859

RT

� �. Calculated data from the model are in good agreement with the

experimental results. Electrical energies per order (EEO) estimated from the calculated and experi-

mental data show that EEO depends on the operational parameters, considerably. Photocatalytic

mineralization of BB41 was monitored by chemical oxygen demand (COD) decrease, changes in

UV–Vis spectra and FT-IR spectra.ª 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

D license.

1. Introduction

Synthetic dyes are released into the environment mainly in the

form of wastewater effluents through textile, leather, paper,hair dye production, rubber and plastics industries that causeseveral ecological problems. Wastewater containing these dyes

is harmful to the environment because of their stability and

318 S. Mohammadi-Aghdam et al.

carcinogenic effects. Therefore it is very important to removeor degrade these dyes before discharging them into the envi-ronment. A necessary criterion for the using of these dyes is

that they must be highly stable in light and during washing;meanwhile, they must be resistant to microbial attack[1,23,25,38,40,43,45]. As international environmental stan-

dards are becoming more stringer (ISO 14001, October 1996,EPA, CCL 3 lists, September 2009), technological systemsfor the removal of organic pollutants, such as dyes have been

recently developed but are often very costly and ineffectivemethods for complete degradation of some disobedient organ-ic dyes or only transfer the contaminant from one phase to an-other in some cases like coagulation, electrocoagulation,

precipitation and filtration [5,19,34,38,41]. Advanced oxida-tion process (AOPs) is the most effective method for degrada-tion of pollutants and bacteria on wall surface, air and water

[8,18,21,22,37,42]. Among different kinds of photocatalysts,TiO2 has been the most widely studied and used in many appli-cations because of its strong oxidizing abilities for decomposi-

tion of organic pollutants, superhydrophilicity, chemicalstability, long durability, non-toxicity, low-cost and biocom-patible [17,39,42,43]. In AOPs, photocatalytic property of

TiO2 is based on the formation of photogenerated charge car-ries (electron–hole pairs) which occurs upon absorption of UVlight to the band gap. These pairs are able either to take part inthe oxidation and reduction reactions at the TiO2 surface or

recombine together and produce heat. Electrons in the conduc-tion band participate in the reduction processes and reduce thedye or react with electron acceptors such as molecular oxygen

in the air to produce O��2 ;HO��2 and OH� radicals. Meanwhile,photogenerated holes in the valance band disperse over theTiO2 surface and oxidize water and organic molecules ad-

sorbed at the surface, directly or through the formation of rad-icals [36]. Generally, literature reports have shown that aphotocatalyst may be used as a suspension in an aqueous solu-

tion or immobilized onto a supporting substrate. There areadvantages for slurry reactors such as high surface area, highdegradation rate, no mass transfer limitation and simple reac-tor structure. Despite all of the mentioned benefits above, there

is a significant drawback for the suspended system that needsto separate the TiO2 nanoparticles after the photocatalyticreaction and their reuse [3,14]. Because of this problem, re-

cently considerable interest has been focused on sol–gel de-rived nanocomposite films using different kinds of substrates,e.g., glass, [10] mesoporous clays, [24] zeolite, [32] polymeric

material, [36] non-woven paper, [2] sackcloth fiber, [47] andcarbon nanotube [26] considered as effective photocata-lysts.The sol–gel dip-coating method has attracted more atten-tion due to low cost, homogeneity, low working temperature,

producing films with good photocatalytic properties and coat-ing on large area substrates [6,16,20,27,31]. Moreover the mostimportant benefit of this method is the managing of particle

size, properties and morphology according to the target appli-cations [15,44]. For instance, with adding TiO2 nanoparticlesas nanofillers into titanium alkoxide solution nano composite

films would be formed with promising perspectives for differ-ent kinds of requests like water and air treatment [9]. At firstthe focus of this work was to design a semibatch flow photore-

actor with immobilized nano composite TiO2 films with a dig-ital heater thermometer for studying of photocatalyticdegradation of azo dyes. The influence of various operationalparameters including initial concentration of BB41, flow rate

(FR) and temperature (T), on photocatalytic degradation ofBB41was investigated. Then a kinetic model was proposedfor the prediction of kapp. Eventually, the obtained model

was utilized to evaluate the required electrical energies per or-der (EEO) for the UV/TiO2 process at various operationalconditions.

2. Materials and methods

2.1. Materials

Titanium tetraisopropoxide (TTIP), Isopropanol (IPA), Acetyl

acetone (AcAc), Polyethylene glycol 4000 (PEG) and Hydro-gen peroxide H2O2 were purchased from Merck. DegussaP25 TiO2 nano powders (average primary particle size around

20 nm, purity >97%, 80:20 anatase:rutile ratio and specificBET surface area of 50±15 m2/g) were provided by DegussaCompany. BB41 was purchased from Alvan Sabet chemicalcompany (Iran). Table 1 illustrates some characteristics of

BB41. All chemicals and dyestuffs were used as received.

2.2. Preparation of nano composite TiO2 sol

Preparation of nano composite TiO2 sol prepared by typicalprocedure [11,16,30]. TTIP (5 mL), AcAc (3.5 mL) and IPA(10 mL) were serially added into a Pyrex reactor under con-

stant stirring for 15 min; then deionized water (20 mL) wasadded to the mixture and stirred for 20 min at the room tem-perature. Prepared suspension, containing titanium hydroxide

Ti(OH)4 was filtered by vacuum distillation and washed withdeionized water two times to yield a white paste. H2O2 (20–30 mL) deionized water (100 mL) and PEG (0.3 g from anaqueous solution of PEG 10 wt.%) were added step by step

and agitated for 40 min to form orange yellowish titanium per-oxide sol. After that it was left overnight at room temperatureto complete hydrolysis reaction and to obtain a sol with good

viscosity. Finally 10 g/L TiO2 nano powders were slowly addedin sol under vigorous stirring to avoid the formation of largertitanium agglomerates in the sol.

2.3. Preparation of nano composite films

Before dip coating the substrates with dimensions of

400 mm · 45 mm · 3 mmwere carefully washed with detergent,then rinsed with deionized water. Afterward they were ultrason-ically cleaned inmixture of acetone and ethanol (1:1) for 15 min.Finally they were rinsed several times with deionized water and

dried. Glass plates were dipped into the sol at a rate of 1 mm/s,kept there for 60 min, and thenwithdrawn at same velocity. Sub-sequently, all supports were dried, first at 100 �C for 60 min, and

then the temperature of the oven was increased at a ramp rate of5 �C/min to 500 �C and was held at this value for 30 min [49,51].Eventually, the filmswere cooled naturally at room temperature.

Dip coating process was carried out three times to generate athree ply film with high adherence.

2.4. Characterization of nano composite TiO2 films

Nano composite TiO2 films were characterized by XRD,TEM, SEM. and N2 adsorption–desorption isotherm analysis

Table 1 Characteristics of Basic Blue 41.

Structure Molecular weight color index(C.I)

S

N+

N

N

MeO

CH3

N

OH

OH

605 41; 11, 105

a

b

0

50

100

150

200

250

300

350

10 20 30 40 50 60 70 80

Inte

nsity

(a.u

.)

2 (degree)

Figure 1 (a) X-ray diffraction pattern (b) transmission electron

microscopy image of the nano composite TiO2 film.

Kinetic modeling of BB41 photocatalytic treatment 319

The information of the crystalline and the average crystallite

size of TiO2-sol were determined by X-ray diffraction (PW1800 philips). From Fig. 1a, the broadening of XRD peak at2h = 25� for anatase, and 2h = 27.5� for rutile nano compos-

ite TiO2, was used to calculate the crystallite size according tothe well-known Scherer equation Eq. (1) [44] as 34 nm.

D ¼ kkbCosh

ð1Þ

where D is the average crystallite size (nm), k is a constantequal to 0.89, k is the X-ray wavelength equal to 0.154056 nm,b is the full width at half maximum intensity and h is the halfdiffraction angle. The result exhibits a mixing of anatase and

rutile, that according to prior publications a nano photocata-lyst with mixing of anatase and rutile has a higher photoreac-tivity than anatase or rutile alone [15]. Also, the grain size of

nano composite TiO2 was investigated by the TEM (PhilipsXL 30). Fig. 1b, shows that the majority of nano compositeTiO2 sizes are between 20 and 40 nm, which is consistent with

the XRD result. Film morphology was investigated by SEM(LEO 1445 VP). Fig. 2 shows that TiO2 nano composite waswell-immobilized on the glass support. The N2 adsorption–desorption analysis is a very reliable technique commonly em-

ployed to investigate the mesoporous structure of any powdersample. Because it was difficult to obtain enough amounts ofTiO2 particle samples (i.e., 0.1 g) scraped from the photocata-

lytic films, TiO2 nano powders prepared at the ‘‘same’’ condi-tions were analyzed by N2 adsorption. Quantachrome Nova2200 Gas Adsorption Analyzer was employed for the analysis

of BET surface area and pore structure of these photocatalyticfilms. The results are shown in Fig 3. A reversible type IV-adsorption/desorption isotherm with hysteresis loop was ob-served, indicating the presence of pores in the mesoporous

range (2–50 nm) according to the classification of IUPAC[6,30]. Increasing Degussa P25 TiO2 nano powders and PEGin TiO2 sol–gel can lead to a remarkable enhancement in

BET surface area and pore volume of photocatalytic films[16,48]. This is due to PEG completely decomposing duringheat treatment [30]. The textural properties of the investigated

TiO2 nanocomposite are as follow: a BET surface area of88.36 m2/g, average pore diameter of 23.7 nm and total porevolume of 0.3954 cc/g. Thickness measurement of the film

was done with a needle coating thickness gauge (Styluse profi-lometer, VEECO DEK TAK 3) with medium scan speed 25 sand resolution 5000 lm/sample. As shown in Fig. 4 the maxi-mum thickness of the film was around 252.9 nm.

2.5. Photoreactor and experimental procedure

All experiments were performed in a rectangular semibatch-

flow photoreactor (Scheme 1) measured by 400 mm · 150 mm ·150 mm, which consisted a Pyrex reactor with a high-pressuremercury lamp (15 W, UV–C, manufactured by Osram) encir-

cled by a quartz tube (outer diameter = 32 mm and innerdiameter = 30 mm) at the center of it. For measuring UV lightintensity, the UV lamp was centered in a quartz tube and the

light intensity of 0.9 mW cm�2 was measured by a UV-Lux-IR meter (Leybold Co.) at the distance of 18 mm, which wasequal to the distance between the outer surface of the quartztube and the inner surface of the Pyrex photoreactor. Photore-

Figure 2 Scanning electron microscopy images of the nano composite TiO2 film. (a) 10·; (b) 21·.

Figure 3 N2 adsorption–desorption isotherm of nano composite

TiO2 powders.

Figure 4 Thickness spectra of the nano composite TiO2 film.

Scheme 1 Experimental setup for the photocatalytic degrada-

tion of BB41: (1) TiO2 nano-photocatalyst film; (2) Pyrex reactor;

(3) Quartz sleeve with UV lamp in the center of it; (4) Aeration

pump; (5) Flow meter; (6) Solution tank; (7) digital heater-

thermometer; (8) Water pump; (9) Control value.

320 S. Mohammadi-Aghdam et al.

actor was covered with the metallic protection to prevent fromdiffusion of the harmful UV irradiation to the laboratory. Thenano composite TiO2 films were placed in the inner wall of

reactor. In each set-up prior to irradiation, 1200 mL of BB41solution with a desired initial concentration over the catalystwas circulated by a water pump (PASSEO QC, 8 W,

QMAX= 650 L/h), located below the reactor in the darkfor 30 min to obtain an adsorption–desorption equilibrium.A liquid flow meter (LZB-4; Guanshan) was used to adjustthe FR. The reactor was equipped with a digital heater-

thermometer which was inserted into the feed tank to maintainthe reaction temperature at a constant value with accuracy of±0.5 �C. The UV lamp and the pump were switched on at the

beginning of each experiment. Air was entered to the reactionsystem at the constant flow rate using a micro-air pump (AP-500). Sampling was carried out at regular time intervals during

irradiation and analyzed by a double beam UV–Vis spectro-photometer (VARIAN, CARY 100 BIO) to measure the con-centration of the dye between 200.0–800.0 nm. COD evolution

was studied to investigate the mineralization of the BB41 basedon APHA standard method [4]. Also FT-IR spectra changeswere studied using FT-IR instrument (NICOLET 8700 FTIR)

in the mid IR region of 400–4000 cm�1. Samples were taken atthe start (control) after 60 min and 120 min. To prepare pelletsthe samples were dried at 50 �C for 2 h, mixed with KBr andthen pulverized in an agate mortar. The background obtained

1/Kapp = 1.7081[BB41]+ 0.779R² = 0.9988

1/K

app

(min

)

[BB41] mg/L

Figure 6 Modified Langmuir plot (T = 298 K, natural pH and

FR = 9 L/h).

Kinetic modeling of BB41 photocatalytic treatment 321

from KBr disks was automatically subtracted from the sampledisks spectra.

3. Result and discussion

Degradation kinetic of many organic compounds has oftenbeen observed to follow pseudo-first order kinetics and accord-

ing to the previous studies established photocatalytic oxidationreactions follow Langmuir–Hinshelwood model [7,12,46]. Westudied three essential operational parameters (C0dye, T, FR)

to develop and evaluate a simple kinetic model. For a semi-batch-flow photoreactor we can use the well-known Eqs. (2)–(4).

r ¼ d½BB41�dt

¼ kL�HKR½BB41�1þ KR½BB41�0

¼ kapp½BB41� ð2Þ

which

kapp ¼kL�HKR

1þ KR½BB41�0ð3Þ

Whit transforming Eq. (3) to a straight-line equation is asfollows:

1

kapp¼ 1

kL�HKR

þ ½BB41�0KL�H

ð4Þ

ln½BB41�0½BB41� ¼ kqppt ð5Þ

where r is the reaction rate (mg/L min), kL�H the reaction rateconstant (mg/L min), t photocatalysis time (min), KR

Figure 5 The effect of (a) initial concentration, (b) temperature, (c) a

T = 298 K, natural pH and FR = 9 L/h).

adsorption equilibrium constant (L/mg), [BB41] and [BB41]0are initial dye concentration and dye concentration at t(min), respectively, and kapp apparent pseudo-first-order rateconstant [7]. Fig. 5a–c, shows the semi-logarithmic graphs ofdegradation of BB41 in mentioned conditions versus irradia-

tion time during UV/TiO2 process. In all graphs, straight lineswith correlation coefficients of more than 0.99 proved the sug-gested kinetics, and the apparent rate constants were calcu-

lated from the slope of the plots (Scheme 1).

3.1. The effect of initial dye concentration

A correlation between kapp and [BB41]0 could be concludedfrom the modified Langmuir–Hinshelwood equation (Eq. (4))

nd flow rate of dye on degradation of BB41: ([BB41]0 = 25 mg/L

y = 825.95x + 1.0169R² = 0.9931

3.6

3.65

3.7

3.75

3.8

3.85

0.00315 0.0032 0.00325 0.0033 0.00335 0.0034 0.00345

-Ln(

Kap

p)

1/T

Figure 7 Arrhenius plot for photocatalytic degradation of BB41

([BB41]0 = 25 mg/L, natural pH and FR = 9 L/h).

y = 0.1937x + 0.0016R² = 0.9976

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.03 0.05 0.07 0.09 0.11 0.13 0.15 0.17 0.19

Kap

p

1/(FR)

Figure 8 Plot of kapp versus 1/FR ([BB41]0 = 25 mg/L, natural

pH and T = 298 K).

y = 0.9945x + 0.0002R² = 0.9947

0

0.01

0.02

0.03

0.04

0.05

0.06

0 0.01 0.02 0.03 0.04 0.05 0.06

Cal

cula

ted

Kap

p(m

in-1

)

Experimental Kapp (min-1)

Figure 9 Comparison between the experimental and calculated

apparent pseudo-first-order rate constants of the UV/TiO2

process.

Table 2 Experimental and calculated EEO at different oper-

ational conditions for the photocatalytic degradation of BB41.

Co (mg L�1) FR (L h�1) T (K) EEO (kW h m�3 order�1)

Experimental Calculated

10.668 9 298 13.68 13.88

19.362 9 298 25.73 24.73

25.26087 9 298 32.71 32.09

29.0438 9 298 36.26 36.81

38.405 9 298 48.42 48.50

50.608 9 298 64.56 63.72

25.405 9 293 35.05 33.83

25.26 9 298 32.71 32.09

25.261 9 303 30.67 30.66

24.811 9 308 28.31 28.82

24.8406 9 313 26.29 27.65

24.6377 6 298 21.58 20.88

25.1449 9 298 32.71 31.95

24.9565 12 298 41.58 42.28

24.956522 15 298 49.73 52.85

0

10

20

30

40

50

60

70

0 20 60 100 120

Rem

oval

per

cent

irradiation time (min)

Figure 10 COD removal of BB41 aqueous solution during the

UV/TiO2 process ([BB41]0 = 25 mg/L, T = 298 K, natural pH

and FR = 9 L/h).

322 S. Mohammadi-Aghdam et al.

[12]. According to the Fig 6 and Eq. (4) kL�H and KR were esti-mated as 0.58544 mg/L min and 2.1927 (L/mg), respectively.The finding shows that the photocatalytic degradation effi-

ciency slightly decreases with an increase in the initial amountof BB41. This trend may be described by several factors. (1) Athigh concentration of dye, interferences would be provided

which prevent degradation. (2) Dye molecules inhabit all theactive sites of photocatalyst surface and this leads to a decreasein degradation efficiency. (3) At the same operational condi-tions, for a constant light intensity the formation of reactive

species ðOH�;O��2 Þ needed for degradation on the catalyst sur-face are constant, therefore the available hydroxyl radicals areinadequate for the degradation of the dye at high concentra-

tion [29].

3.2. The effect of reaction temperature

As we described in our last work [36], a correlation betweenkapp and the process temperature (T) can be expressed by theArrhenius equation:

� ln kapp ¼ � lnAþ Ea

R

1

T

� �ð6Þ

where kapp is apparent pseudo-first-order rate constant 1/min Ttemperature (K), Ea the activation energy and R the gas con-

stant 8.314 J (K mol)�1. The results shown in Fig. 7, indicatesthat the reaction rate increases when the photocatalytic reac-tion temperature rises. Most of the previous investigations sta-

ted that an increase in photocatalytic reaction temperaturepromotes the recombination of charge carriers and demotesthe adsorption of organic compounds onto the TiO2 surface[35].Ea value was calculated from the slope of line –ln kapp

0.00

0.50

1.00

1.50

2.00

200 300 400 500 600 700 800

Abc

Wavelenth (nm)

0 min102030405060708090

100110120

Figure 11 UV–Vis spectra changes of BB41 during the photo-

catalytic process at different irradiation times; ([BB41]0 = 25 mg/

L, T = 295 K natural pH and FR = 9 L/h).

Kinetic modeling of BB41 photocatalytic treatment 323

vs. 1/T, as 6.859 kJ mol�1 in the temperature range of 293.15–313.15 K, which is consistent with other studies and the activa-

tion energies were measured between 5.5 and 8.24 kJ mol�1

[12,50].

3.3. The effect of flow rate

A linear relationship between the kapp and 1/FR shown inFig. 8 might be in agreement with Eq. (7), which indicates a

slight improvement in decolorization efficiency with decreasingflow rate from 15 to 6 L/h.

kapp ¼ 0:193=FR ð7Þ

Figure 12 FT-IR spectra of BB41 during the photocatalytic process

conditions.

It can be because of increase in residence time of the reac-tant beside photocatalyst with decreasing system turbulence.Several previous studies have been indicated a similar trend

like ours [7,33].

3.4. Kinetic model development

According to the found results in previous parts, degradation

of BB41 is estimated to be a pseudo-first order reaction. Hencea simple model was designed for prediction of kapp as a func-tion of [BB41]0, 1/FR and T(K) is as follows:

Kapp ¼ k0KR

1þ KR½BB41�0

� �1

FR

� �exp�Ea

RT

� �ð8Þ

Ea, and KR were estimated by nonlinear regression analysisand then with known values of T, FR, and [BB41]0, k

0 was cal-

culated. With replacement of these values into Eq. (8), the fol-lowing equation was obtained:

kapp ¼ 436:65172:1927

1þ 2:1927½BB41�0

� �0:1937

FR

� �exp

6859

RT

� �

ð9Þ

This equation can determine kapp in the various ranges of

operational conditions.

at times: (a) 0 min, (b) 60 min, (c) 120 min under the optimized

324 S. Mohammadi-Aghdam et al.

3.5. Model evaluation

For evaluation of the model mentioned above a comparisonbetween experimental and theoretical kapp for degradation of[BB410] at different operational conditions was done which

has been presented in Fig. 9. As can be seen from this plotthe experimental data are in good agreement with estimateddata by the model.

3.6. Electrical energy determination

Among several important factors in selecting awaste-treatment technology like flexibility, safety, economical

of scale etc., economics is a paramount. Since electric energycan represent a major fraction of the operating costs in photo-degradation process, evaluation of it can be performed by the

EEO for the first-order kinetics regime, which was observed inthis study as well. EEO has been accepted by IUPAC and de-fined as the required amount of electric energy (kW h) to elim-

inate 90% of a pollutant in one liter of contaminated water[13]. EEO can be measured as following:

EEO ¼38:4 Pel

Vkapp

ð10Þ

where Pel is the sum of the input power (kW) from UV lampsto the UV/TiO2 system and water pump, and V is the volumeof solution (L). The experimental and predicted EEO values are

summarized in Table 2. It can be concluded that the kineticmodel can be used successfully for prediction of EEO valuesat different operational conditions.

3.7. Mineralization of BB41

The mineralization of BB41 was evaluated by COD decay,changes in UV–Vis and FT-IR spectra during the process with

25 mg/L of BB41 aqueous solution at FR, temperature andirradiation time of 9 L/h, 295 K and 120 min respectively.COD values have been related to the total oxygen demand

for the oxidation of organics to CO2 and H2O in the solution.Decreasing of COD expresses the degree of degradation at theend of photocatalytic process. COD disappearance results pre-

sented in Fig. 10 show that the rectangular semibatch-flowphotoreactor with TiO2 immobilized plates can degrade andmineralize organic pollutants. The changes in the UV–Vis

absorption spectra of BB41 during the photocatalytic processat different irradiation times, are shown in Fig. 11. The de-crease in the absorption peaks of the dye at the maximumabsorption wavelength (605 nm) indicates photocatalytic

destruction of BB41. Fig. 12 displays the FT-IR obtained fromBB41 during photocatalytic degradation process before irradi-ation and after 60 and 120 min. The FT-IR spectrum of BB41

before removal showed the specific peaks in fingerprint region(500–3500 cm�1). The peaks at 1640.21 cm�1 and 670.49 –774.47 cm�1 belong to the C‚C stretching and bending vibra-

tions of C–H in the benzene rings, respectively. In addition, thepeak at 1090.3 cm�1 is for the C–OH stretching vibrations.The broad and strong vibration around 3000–3500 cm�1 is

indicative of the presence of –OH groups on the surface ofBB41. The FT-IR spectra of BB41 after 60 min irradiationtime shows the same peaks with the FT-IR spectra of BB41 be-fore removal with less intensity. The FT-IR spectra of BB41

after 120 min irradiation time shows that degradation of dyemolecules was done successfully by hydroxyl radicals attacks.The FT-IR spectra in our study were in agreement with the re-

sults obtained by Khataee et al. [28].

4. Conclusions

The kinetic characteristics of the photocatalytic degradation ofBB41 using immobilized TiO2 nano composite were experi-mentally investigated with respect to the initial BB41 content,

FR and temperature in rectangular semibatch-flow photoreac-tor. A new kinetic model was proposed on the basis of opera-tional parameters. The apparent pseudo-first-order rate

constant decreases with increasing the initial concentrationof BB41, decreases with the enhancement of FR and increaseswith the enhancement of temperature. EEO was evaluated

based on the experimental and theoretical kapp, which were cal-culated from the model. The results indicated that the modelcan properly predict the values of kapp at various operationalconditions. The results of COD measurement, UV–Vis and

FT-IR spectra changes indicated that this process can be usedfor complete decolorization and mineralization of BB41.

Acknowledgements

The authors thank the Department of Applied Chemistry,Faculty of Chemistry, Islamic Azad University, North TehranBranch, Tehran, Iran and Iranian Nano Technology InitiativeCouncil for financial and other supports.

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