Scholarly article on topic 'Kinetic modeling of BB41 photocatalytic treatment in a semibatch flow photoreactor using a nano composite film'

Kinetic modeling of BB41 photocatalytic treatment in a semibatch flow photoreactor using a nano composite film Academic research paper on "Chemical sciences"

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{"Kinetic modeling" / "Photocatalytic degradation" / "Semibatch flow photoreactor" / COD / "Basic Blue 41"}

Abstract of research paper on Chemical sciences, author of scientific article — S. Mohammadi-Aghdam, R. Marandi, M.E. Olya, A.A. Mehrdad Sharif

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 electron 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 K app = 436.6517 2.1927 1 + 2.1927 [ BB 41 ] 0 0.1937 FR 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 experimental 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.

Academic research paper on topic "Kinetic modeling of BB41 photocatalytic treatment in a semibatch flow photoreactor using a nano composite film"

Journal of Saudi Chemical Society (2013) xxx, xxx-xxx

King Saud University Journal of Saudi Chemical Society

www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Kinetic modeling of BB41 photocatalytic treatment in a semibatch flow photoreactor using a nano composite film

S. Mohammadi-Aghdam a *, 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, Iran b Department of Environmental Engineering, Faculty of Engineering, North Tehran Branch, Islamic Azad University, Tehran, Iran c Department of Environmental Research, Institute for Color Science and Technology, Tehran, Iran

d Department of Analytical Chemistry, Faculty of Chemistry, North Tehran Branch, Islamic Azad University, Tehran, Iran

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 electron 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 (2040 °C). The following equation was obtained by kinetic modeling Kapp = 436.6517

(1+2 29272BB41]0) (^FFHexpff). Calculated data from the model are in good agreement with the experimental results. Electrical energies per order (EEO) estimated from the calculated and experimental 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.

© 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

* 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.

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 cause several ecological problems. Wastewater containing these dyes is harmful to the environment because of their stability and

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carcinogenic effects. Therefore it is very important to remove or degrade these dyes before discharging them into the environment. 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 standards are becoming more stringer (ISO 14001, October 1996, EPA, CCL 3 lists, September 2009), technological systems for the removal of organic pollutants, such as dyes have been recently developed but are often very costly and ineffective methods for complete degradation of some disobedient organic dyes or only transfer the contaminant from one phase to another in some cases like coagulation, electrocoagulation, precipitation and filtration [5,19,34,38,41]. Advanced oxidation process (AOPs) is the most effective method for degradation 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 applications because of its strong oxidizing abilities for decomposition of organic pollutants, superhydrophilicity, chemical stability, long durability, non-toxicity, low-cost and biocompatible [17,39,42,43]. In AOPs, photocatalytic property of TiO2 is based on the formation of photogenerated charge carries (electron-hole pairs) which occurs upon absorption of UV light to the band gap. These pairs are able either to take part in the oxidation and reduction reactions at the TiO2 surface or recombine together and produce heat. Electrons in the conduction band participate in the reduction processes and reduce the dye or react with electron acceptors such as molecular oxygen in the air to produce O^", HO2~ and OH' radicals. Meanwhile, photogenerated holes in the valance band disperse over the TiO2 surface and oxidize water and organic molecules adsorbed at the surface, directly or through the formation of radicals [36]. Generally, literature reports have shown that a photocatalyst may be used as a suspension in an aqueous solution or immobilized onto a supporting substrate. There are advantages for slurry reactors such as high surface area, high degradation rate, no mass transfer limitation and simple reactor structure. Despite all of the mentioned benefits above, there is a significant drawback for the suspended system that needs to separate the TiO2 nanoparticles after the photocatalytic reaction and their reuse [3,14]. Because of this problem, recently considerable interest has been focused on sol-gel derived 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] and carbon nanotube [26] considered as effective photocata-lysts.The sol-gel dip-coating method has attracted more attention due to low cost, homogeneity, low working temperature, producing films with good photocatalytic properties and coating on large area substrates [6,16,20,27,31]. Moreover the most important benefit of this method is the managing of particle size, properties and morphology according to the target applications [15,44]. For instance, with adding TiO2 nanoparticles as nanofillers into titanium alkoxide solution nano composite films would be formed with promising perspectives for different kinds of requests like water and air treatment [9]. At first the focus of this work was to design a semibatch flow photore-actor with immobilized nano composite TiO2 films with a digital heater thermometer for studying of photocatalytic degradation of azo dyes. The influence of various operational parameters including initial concentration of BB41, flow rate

(FR) and temperature (T), on photocatalytic degradation of BB41was investigated. Then a kinetic model was proposed for the prediction of kapp. Eventually, the obtained model was utilized to evaluate the required electrical energies per order (Eeo) for the UV/TiO2 process at various operational conditions.

2. Materials and methods

2.1. Materials

Titanium tetraisopropoxide (TTIP), Isopropanol (IPA), Acetyl acetone (AcAc), Polyethylene glycol 4000 (PEG) and Hydrogen peroxide H2O2 were purchased from Merck. Degussa P25 TiO2 nano powders (average primary particle size around 20 nm, purity >97%, 80:20 anatase:rutile ratio and specific BET surface area of 50±15 m2/g) were provided by Degussa Company. BB41 was purchased from Alvan Sabet chemical company (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 typical procedure [11,16,30]. TTIP (5 mL), AcAc (3.5 mL) and IPA (10 mL) were serially added into a Pyrex reactor under constant stirring for 15 min; then deionized water (20 mL) was added to the mixture and stirred for 20 min at the room temperature. Prepared suspension, containing titanium hydroxide Ti(OH)4 was filtered by vacuum distillation and washed with deionized water two times to yield a white paste. H2O2 (2030 mL) deionized water (100 mL) and PEG (0.3 g from an aqueous solution of PEG 10 wt.%) were added step by step and agitated for 40 min to form orange yellowish titanium peroxide sol. After that it was left overnight at room temperature to complete hydrolysis reaction and to obtain a sol with good viscosity. Finally 10 g/L TiO2 nano powders were slowly added in sol under vigorous stirring to avoid the formation of larger titanium agglomerates in the sol.

2.3. Preparation of nano composite films

Before dip coating the substrates with dimensions of 400 mm x 45 mm x 3 mm were carefully washed with detergent, then rinsed with deionized water. Afterward they were ultrason-ically cleaned in mixture 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 then withdrawn at same velocity. Subsequently, all supports were dried, first at 100 0C for 60 min, and then the temperature of the oven was increased at a ramp rate of 5 0C/min to 500 0C and was held at this value for 30 min [49,51]. Eventually, the films were cooled naturally at room temperature. Dip coating process was carried out three times to generate a three 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

^mxLx. (nm) Molecular weight color index(C.I)

CH,OCSOT

482grmol"1 41; 11, 105

30 40 50 26(degree)

Figure 1 (a) X-ray diffraction pattern (b) transmission electron microscopy image of the nano composite TiO2 film.

The information of the crystalline and the average crystallite size of TiO2-sol were determined by X-ray diffraction (PW 1800 philips). From Fig. 1a, the broadening of XRD peak at 2h = 25° for anatase, and 2h = 27.5° for rutile nano composite TiO2, was used to calculate the crystallite size according to the well-known Scherer equation Eq. (1) [44] as 34 nm.

D — -

where D is the average crystallite size (nm), k is a constant equal 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 half diffraction 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 (Philips XL 30). Fig. 1b, shows that the majority of nano composite TiO2 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 was well-immobilized on the glass support. The N2 adsorption-desorption analysis is a very reliable technique commonly employed to investigate the mesoporous structure of any powder sample. Because it was difficult to obtain enough amounts of TiO2 particle samples (i.e., 0.1 g) scraped from the photocata-lytic films, TiO2 nano powders prepared at the "same" conditions were analyzed by N2 adsorption. Quantachrome Nova 2200 Gas Adsorption Analyzer was employed for the analysis of BET surface area and pore structure of these photocatalytic films. The results are shown in Fig 3. A reversible type IV-adsorption/desorption isotherm with hysteresis loop was observed, 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 PEG in 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 during heat treatment [30]. The textural properties of the investigated TiO2 nanocomposite are as follow: a BET surface area of 88.36 m2/g, average pore diameter of 23.7 nm and total pore volume 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 s and resolution 5000 im/sample. As shown in Fig. 4 the maximum 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 x 150 mm x 150 mm, which consisted a Pyrex reactor with a high-pressure mercury lamp (15 W, UV-C, manufactured by Osram) encircled by a quartz tube (outer diameter = 32 mm and inner diameter = 30 mm) at the center of it. For measuring UV light intensity, 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 was equal to the distance between the outer surface of the quartz tube and the inner surface of the Pyrex photoreactor. Photore-

a 350 300 250

« 200

¡3 150

ä 100 50

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

280 240

J 160 5

§ 120 I

o 80 l/l T3

* 40 0

-Desorbtion Adsorbtion

0.2 0.4 0.6

Relative Pressure, P/P0

Figure 3 N2 adsorption-desorption isotherm of nano composite TiO2 powders.

s =

1 » ....... 1 1 1 ■ 11111 1 1 1 1 1 1 1 1 t

¡000 2000 3000 4000 (urn)

Figure 4 Thickness spectra of the nano composite TiO2 film.

actor was covered with the metallic protection to prevent from diffusion of the harmful UV irradiation to the laboratory. The nano composite TiO2 films were placed in the inner wall of reactor. In each set-up prior to irradiation, 1200 mL of BB41 solution with a desired initial concentration over the catalyst was circulated by a water pump (PASSEO QC, 8 W, QMAX = 650 L/h), located below the reactor in the dark for 30 min to obtain an adsorption-desorption equilibrium. A liquid flow meter (LZB-4; Guanshan) was used to adjust the FR. The reactor was equipped with a digital heater-

Scheme 1 Experimental setup for the photocatalytic degradation 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.

thermometer which was inserted into the feed tank to maintain the reaction temperature at a constant value with accuracy of ±0.5 0C. The UV lamp and the pump were switched on at the beginning of each experiment. Air was entered to the reaction system 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 concentration of the dye between 200.0-800.0 nm. COD evolution was studied to investigate the mineralization of the BB41 based on APHA standard method [4]. Also FT-IR spectra changes were studied using FT-IR instrument (NICOLET 8700 FTIR) in the mid IR region of 400-4000 cm-1. Samples were taken at the start (control) after 60 min and 120 min. To prepare pellets the samples were dried at 50 0C for 2 h, mixed with KBr and then pulverized in an agate mortar. The background obtained

from KBr disks was automatically subtracted from the sample disks spectra.

3. Result and discussion

Degradation kinetic of many organic compounds has often been observed to follow pseudo-first order kinetics and according to the previous studies established photocatalytic oxidation reactions follow Langmuir-Hinshelwood model [7,12,46]. We studied 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)-

d[BB41] kL_HKR[BB41]

1 + Kr[BB41]0

= kapp [BB41 ]

k _ kL-HKR

kapp ~ 1 + Kr [BB41]

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

[BB41]0

kL HKR KL

[BB41]o t [BB41] kqpp

where r is the reaction rate (mg/L min), kL_H the reaction rate constant (mg/L min), t photocatalysis time (min), KR

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

0 10 20 30 40 50 60

[BB41] mg/L

Figure 6 Modified Langmuir plot (T = 298 K, natural pH and FR = 9 L/h).

adsorption equilibrium constant (L/mg), [BB41] and [BB41]0 are initial dye concentration and dye concentration at t (min), respectively, and kapp apparent pseudo-first-order rate constant [7]. Fig. 5a-c, shows the semi-logarithmic graphs of degradation of BB41 in mentioned conditions versus irradiation time during UV/TiO2 process. In all graphs, straight lines with correlation coefficients of more than 0.99 proved the suggested kinetics, and the apparent rate constants were calculated from the slope of the plots (Scheme 1).

(5) 3.1. The effect of initial dye concentration

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

Figure 5 The effect of (a) initial concentration, (b) temperature, (c) and flow rate of dye on degradation of BB41: ([BB41]0 = 25 mg/L T = 298 K, natural pH and FR = 9 L/h).

g 3.75 «

y = 825.95x + 1.0169 R2 = 0.9931

0.00315 0.0032 0.00325 0.0033 0.00335 0.0034 0.00345 1/T

Figure 7 Arrhenius plot for photocatalytic degradation of BB41 ([BB41]0 = 25 mg/L, natural pH and FR = 9 L/h).

& 0.02 fei

0.01 0.005

y = 0.1937x + 0.0016 R2 = 0.9976

0.03 0.05 0.07 0.09 0.11 0.13 0.15 0.17 0.19 1/(FR)

Figure 8 Plot of kapp versus 1/FR ([BB41]0 = 25 mg/L, natural pH and T = 298 K).

1 0.05 в

^ 0.03 ■a

.S 0.02

3 0.01 0

y = 0.9945x + 0.0002 R2 = 0.9947

Table 2 Experimental and calculated Eeo at different operational conditions for the photocatalytic degradation of BB41.

Л 20 -

Co (mg L-1) FR (L h-1) T (K) Eeo (kWhm- 3 order ')

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

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).

species (OH',O^") needed for degradation on the catalyst surface are constant, therefore the available hydroxyl radicals are inadequate for the degradation of the dye at high concentration [29].

Experimental Kapp (min-1)

Figure 9 Comparison between the experimental and calculated apparent pseudo-first-order rate constants of the UV/TiO2 process.

[12]. According to the Fig 6 and Eq. (4) kL_H and KR were estimated as 0.58544 mg/L min and 2.1927 (L/mg), respectively. The finding shows that the photocatalytic degradation efficiency slightly decreases with an increase in the initial amount of BB41. This trend may be described by several factors. (1) At high concentration of dye, interferences would be provided which prevent degradation. (2) Dye molecules inhabit all the active sites of photocatalyst surface and this leads to a decrease in degradation efficiency. (3) At the same operational conditions, for a constant light intensity the formation of reactive

3.2. The effect of reaction temperature

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

- ln kapp = -]n A + (6)

where kapp is apparent pseudo-first-order rate constant 1/min T temperature (K), Ea the activation energy and R the gas constant 8.314 J (K mol)-1. The results shown in Fig. 7, indicates that the reaction rate increases when the photocatalytic reaction temperature rises. Most of the previous investigations stated that an increase in photocatalytic reaction temperature promotes the recombination of charge carriers and demotes the adsorption of organic compounds onto the TiO2 surface [35].Ea value was calculated from the slope of line -ln kapp

200 300 400 500 600 700 800

Wavelenth (nm)

Figure 11 UV-Vis spectra changes of BB41 during the photocatalytic process at different irradiation times; ([BB41]0 = 25 mg/ L, T = 295 K natural pH and FR = 9 L/h).

vs. 1/T, as 6.859 kJ mol-1 in the temperature range of 293.15313.15 K, which is consistent with other studies and the activation energies were measured between 5.5 and 8.24kJmol~1 [12,50].

3.3. The effect of flow rate

A linear relationship between the kapp and 1/FR shown in Fig. 8 might be in agreement with Eq. (7), which indicates a slight improvement in decolorization efficiency with decreasing flow rate from 15 to 6 L/h.

kaPP = 0.193/FR

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. Hence a simple model was designed for prediction of kapp as a function of [BB41]0, 1/FR and T(K) is as follows:

v — v

Kapp k

1 + Kr [BB41]0

fr) lexp rt

Ea, and KR were estimated by nonlinear regression analysis and then with known values of T, FR, and [BB41]0, k was calculated. With replacement of these values into Eq. (8), the following equation was obtained:

kapp = 436.6517 ( 1

2.1927

2.1927[BB41](

0.1937 FR

This equation can determine kapp in the various ranges of operational conditions.

3500 3000 2500 2000 1500 Ю00 500

Wavenunibers (cm1)

Figure 12 FT-IR spectra of BB41 during the photocatalytic process at times: (a) 0 min, (b) 60 min, (c) 120 min under the optimized conditions.

3.5. Model evaluation

For evaluation of the model mentioned above a comparison between 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 plot the experimental data are in good agreement with estimated data by the model.

3.6. Electrical energy determination

Among several important factors in selecting a waste-treatment technology like flexibility, safety, economical of scale etc., economics is a paramount. Since electric energy can represent a major fraction of the operating costs in photodegradation process, evaluation of it can be performed by the Eeo for the first-order kinetics regime, which was observed in this study as well. EEO has been accepted by IUPAC and defined as the required amount of electric energy (kW h) to eliminate 90% of a pollutant in one liter of contaminated water [13]. EEO can be measured as following:

38.4 Pd

Eeo — "

where Pel is the sum of the input power (kW) from UV lamps to the UV/TiO2 system and water pump, and V is the volume of solution (L). The experimental and predicted EEO values are summarized in Table 2. It can be concluded that the kinetic model can be used successfully for prediction of EEO values at different operational conditions.

after 120 min irradiation time shows that degradation of dye molecules was done successfully by hydroxyl radicals attacks. The FT-IR spectra in our study were in agreement with the results obtained by Khataee et al. [28].

4. Conclusions

The kinetic characteristics of the photocatalytic degradation of BB41 using immobilized TiO2 nano composite were experimentally 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 operational parameters. The apparent pseudo-first-order rate constant decreases with increasing the initial concentration of BB41, decreases with the enhancement of FR and increases with the enhancement of temperature. Eeo was evaluated based on the experimental and theoretical kapp, which were calculated from the model. The results indicated that the model can properly predict the values of kapp at various operational conditions. The results of COD measurement, UV-Vis and FT-IR spectra changes indicated that this process can be used for complete decolorization and mineralization of BB41.

Acknowledgements

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

3.7. Mineralization of BB41

References

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 and irradiation 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 the end of photocatalytic process. COD disappearance results presented in Fig. 10 show that the rectangular semibatch-flow photoreactor with TiO2 immobilized plates can degrade and mineralize organic pollutants. The changes in the UV-Vis absorption spectra of BB41 during the photocatalytic process at different irradiation times, are shown in Fig. 11. The decrease in the absorption peaks of the dye at the maximum absorption wavelength (605 nm) indicates photocatalytic destruction of BB41. Fig. 12 displays the FT-IR obtained from BB41 during photocatalytic degradation process before irradiation 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 vibrations of C-H in the benzene rings, respectively. In addition, the peak 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 of BB41. The FT-IR spectra of BB41 after 60 min irradiation time shows the same peaks with the FT-IR spectra of BB41 before removal with less intensity. The FT-IR spectra of BB41

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