Kinetic study for photocatalytic degradation of Direct Red 23 in UV–LED/nano-TiO2/S2O82− process: Dependence of degradation kinetic on operational parameters

Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

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JIEC-1798; No. of Pages 8

Kinetic study for photocatalytic degradation of Direct Red 23 inUV–LED/nano-TiO2/S2O8

2� process: Dependence of degradationkinetic on operational parameters

Mohammadhossein Rasoulifard a,*, Mostafa Fazli b,**, Mohammadreza Eskandarian b

a Laboratory of Water & Wastewater Treatment, Department of Chemistry, Faculty of Sciences,University of Zanjan, Zanjan, Iranb Department of Applied Chemistry, Faculty of Chemistry, University of Semnan, Semnan, Iran

A R T I C L E I N F O

Article history:

Received 26 October 2013

Accepted 25 December 2013

Available online xxx

Keywords:

Kinetic study

Photodegradation

Photocatalysis

UV–LED

Direct Red 23

A B S T R A C T

Present work involves the prospects of the kinetic study for photocatalytic degradation of Direct Red 23

using UV–LED/nano-TiO2/S2O82� procedure. Advantageously usages of UV–LEDs as illumination sources

were collected to the advanced oxidation process in presence of immobilized nano-TiO2. Additionally,

kinetic approach for various parameters in different conditions for decolorization has been studied.

Results demonstrated that kinetic model of UV–LED/nano-TiO2/S2O82� process can effectively degrade

DR23 dye with optimum conditions. A new kinetic model was suggested on the basis of intrinsic element

reactions. The proposed kinetic model fairly resembled that dye decolorization was followed by the first

order reaction.

� 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights

reserved.

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec

1. Introduction

Undoubtedly, decontamination of water supplies and resourceshas become a threatened menace for recent days. Among the vastmajority of procedures proposed to water and wastewatertreatment, advanced oxidation processes (AOPs) has the uniqueposition between other routes [1]. In the last years, removal of thedyes from waste water has been given much attention by adoptingdifferent amenable traditional technologies. Mentioned aspectsinvolve physical, chemical and biological treatment and also someother methods which are based on UV light have been utilized [2–5]. Simultaneous utilizing of UV light and advanced oxidationprocesses (AOPs) have been suggested as a prominent alternativeto traditional technologies for the removal of contaminants inwater treatment [6–10]. AOPs are based on the formation of thehighly reactive hydroxyl radicals �OH provided by UV irradiationon S2O8

2� or TiO2 and are based on the traditional lamps. Advancedoxidation processes (AOPs), especially heterogeneous photocata-lysis with UV-irradiated TiO2 is the most effective method for thedegradation of various organic compounds and dyes has beenreported because of its high chemical stability, inexpensive, high

* Corresponding author. Tel.: +982415152591; fax: +982415152477.** Corresponding author. Tel.: +982313333752, Fax: +982313338847.

E-mail addresses: [email protected] (M. Rasoulifard),

[email protected] (M. Fazli).

Please cite this article in press as: M. Rasoulifard, et al., J. Ind. Eng.

1226-086X/$ – see front matter � 2013 The Korean Society of Industrial and Engineer

http://dx.doi.org/10.1016/j.jiec.2013.12.068

photocatalytic activity and non-toxicity of the TiO2 which is usedas a photocatalyst in the reactions [11,12]. Newly investigated lightemitting diodes (LEDs) have been commercialized for decades withrecent developments of the technology permitting LEDs to emit UVlight down to very low wavelengths (240 nm) [13]. Moreover,some characteristics of UV–LED light sources have been presentedin (Table 1).

However, due to the very high cost and low output power at thisstage of development, UV–LEDs have mostly been tested for waterdisinfection [10,13] and for photocatalysis using UV-A light(k > 365 nm) [13–17]. The main aim of present research wasprimarily to characterize the kinetic approach of the UV–LED/TiO2

system. The work utilizes models formerly developed in severalresearch studies [18,19] and predictions given by LED supplierscoupled with experimental data determined in this study to evaluatethe critical parameters which need to be improved for UV–LED basedAOPs to be economically competitive compared to traditional UVlamps. Controlled pulse illumination (CPI) which is based on a seriesof alternate light and dark periods (TON/TOFF) has been previouslyreported as a means of increasing the photonic efficiency andimproving the conversion rate of reactants or formation of productsin TiO2 photocatalysis [20–24]. It was previously suggested thatperiodically illuminating the TiO2 particle at short intervals wouldinhibit the build-up of intermediates and reduce the rate ofrecombination reactions. A transient kinetic model by Upadhyaand Ollis suggested rapid oxidation of the organic substrate duringlight on periods (TON) was responsible for the high photonic

Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.068

ing Chemistry. Published by Elsevier B.V. All rights reserved.


mailto:[email protected]

mailto:[email protected]


http://www.sciencedirect.com/science/journal/1226086X

http://dx.doi.org/www.elsevier.com/locate/jiec


Table 1UV lamps properties. Adapted from Ibrahim [19].

Low pressure lamp Medium pressure lamp Light emitting diode (prediction 2020)

Typical wavelength(nm) Monochromatic 254 Polychromatic 200–500 Any from 240

Wall plug efficiency (%) 35–38 10–20 75

Lifetime (h) 8000–10,000 4000–8000 100,000

Electrical input (W) 8–100 100–60,000 1

Operating temperature (8C) 40 600–900 20

M. Rasoulifard et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx2

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efficiencies under CPI [22]. This study investigates the kineticallyeffect of light and dark time periods on photonic efficiency of DirectRed 23 degradation removal. The procedure is composed of thecollective controlled experiment approach using a novel UV–LEDilluminated photoreactor followed by an AOP (S2O8

2�) in presence ofTiO2 nanoparticles. The study involves impact of photonic efficiencyunder CPI at different maximum intensity, Imax, and continuousillumination in view point of reaction kinetic. The dependence of thedegradation rate to the illumination and current intensity is relatedto the TiO2 photocatalyst activation. Many researches have beenstudied on the dependencies of the photocatalysis kinetic either onthe initial concentration at a given irradiation intensity or on thelight intensity at a given initial concentration [25]. Although, veryfew of these works involves interdependence of the decolorizationrate on both initial concentration and the illumination intensity inliquid phase [26]. Emeline et al. were suggested a kinetic modelingusing concentration and also irradiation strength as follow [27]:

rðCR; IÞ ¼ bICR

gIþxCR(1)

where r is the photocatalytic decolorization rate, I is theillumination intensity, CR is the concentration of the reagent, b,g and x are the coefficients of the equation which are independentof the initial concentration and the light intensity. Furthermore, ithas been previously showed that expression (1) could beconsistently used to highlight the interdependence of theconcentration and the light intensity on the reaction rate [26].Additionally, the first-order kinetic expression Eq. (2), has oftenbeen used due to its simplicity with good fitness for a certain initialcontaminant concentration in photocatalytic procedure in whichkapp is the apparent first-order rate constant (with the samerestriction of [Dye] = [Dye]0 at t = 0, with [Dye]0 being the initial

Table 2Characteristics of Direct Red 23.

Color Index C.I. Direct Red 23

Color index number 29160

Number of Azo group Two

Molecular structure

Type Dianionic

Molecular formula C35H25N7Na2O10S2

Solubility in water(19 8C) 50–100 mg/l

lmax (nm) 507

Molecular weight (g/mol) 813.72


content in the bulk solution after dark adsorption and t the reactiontime). The kinetic behavior in which kapp of the first-order kineticsis affected by the initial dye concentration, could be commonlydescribed in terms of a modified L–H model. This modified modelhas been used for heterogeneous photocatalytic degradation todetermine the relationship between the apparent first-order rateconstant and the initial content of the organic substrate which iscommonly expressed as Eq. (2) [28].

r ¼ � dC

dt¼ kapp½Dye�

r ¼ � dC

dt¼ kobsKR½Dye�

1 þ KR½Dye�0¼ kapp½Dye�

1

kapp¼ 1

kobsKRþ ½Dye�0

kobs

(2)

where [Dye]0 is the initial organic content, kobs is the reaction rateconstant and KR is the adsorption rate constant. Present workinvolves kinetic study for degradation of DR23 dye using nano-TiO2/S2O8

2� in an UV–LED photoreactor. The influence of the dyeconcentration and pulsed illumination on the photocatalyticdecolorization of DR23 has been considered. A three dimensionalfitting of kinetic study for removal efficiency has been presented [29].

2. Materials and methods

2.1. Chemicals and instruments

Direct Red 23 with 99% purity was obtained from Alvan Sabet Co.,Tehran, Iran. The dye was used without any further purification andsolution was prepared using double distilled water. The molecularstructure and chemical properties of DR23 are given in (Table 2).



Fig. 1. Schematic drawing of batch reactor: (1) DC power supplier; (2) magnetic

stirring; (3) beaker; (4) UV LEDs; (5) cooling system; (6) clamp.

M. Rasoulifard et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx 3

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Potassium peroxydisulfate was obtained from Merck Co.,(Germany). Its solution was unhesitatingly prepared before themeasurements to avoid the change of concentration due to self-decomposition. TO-18 UV–LEDs was purchased from SeoulOptodevice Co., Ltd., and the power of each UV–LED was3 W(l = 385 nm). After electrical connection, the UV–LEDs wereput into plastic covers to increase the lifespan of UV–LEDs. UV–LEDs and cooling system were attached using a 5 cm clamp abovethe beaker. Current and voltage was adjusted by a DC power supplywith galvanostatic operational options (Fig. 1). Titanium dioxidenanoparticles (Degussa P-25, Fluka) with determined surface area(BET: 50 m2/g) and nanoparticle size of 21 nm which immobilizedon glass beads (diagonal = 0.5 cm), has been applied in thisinvestigation.

Fig. 2. Schematic diagram of TiO2 photocatalyst position and performance in UV–LED pho

(4) UV–LED unit; (5) magnetic stirrer; (6) glass beads supported by TiO2 nanoparticles


2.2. Photoreactor

The photoreactor was operated and solutions were prepared bydissolving the necessary quantity of the dye and S2O8

2� in distilledwater and fed into the photoreactor. Peroxydisulfate and dyeconcentrations were varied from 0 to 150 mM and 5 ppm to75 ppm, respectively. Moreover, a control circuit has used togenerate periodic pulses with 0.1 s changes. The On/Off periodswere varied between 0.1/0.9, 0.2/0.8, 0.3/0.7, 0.4/0.6, 0.5/0.5, 0.6/0.4, 0.7/0.3, 0.8/0.2 and 0.9/0.1 s. In order to use of TiO2

nanocatalyst, TiO2 nanoparticles immobilized on glass beads havebeen inserted to experiment container after washing and dryingprocesses. Taking into consideration of using the photocatalyticproperties of TiO2 nanoparticles, glass beads should placed on theexposure of UV–LED illumination. So a setup which is presented inFig. 2 was applied.

The solution in the beaker was continuously stirred with astirrer to prepare uniform mixing of the degrading dye solution sixUV–LEDs (3 W) were turned on at room temperature (258C � 28C)and the dye solution samples were taken at desired time intervals andanalyzed on a UV–Visible spectrophotometer (Shimadzu 160, Japan)at lmax = 514 nm with a calibration curve based on the Beer–Lambert’s law. For each experiment, operating conditions aresummarized in the corresponding figure legends.

2.3. Procedure

To probe the dependence of the kinetic characteristics of thephotocatalytic degradation upon light intensity and initial organiccontent, a series of experiments were carried out at differentphotocatalytic conditions. Peroxydisulfate and dye concentrationswere varied from 0 to 150 mM and 5 to 75 ppm, respectively.Moreover, a control circuit has used to generate periodic pulseswith 0.1 s changes. The On/Off periods were varied between 0.1/0.9, 0.2/0.8, 0.3/0.7, 0.4/0.6, 0.5/0.5, 0.6/0.4, 0.7/0.3, 0.8/0.2 and 0.9/0.1 s. In order to use of TiO2 nanocatalyst, TiO2 nanoparticlesimmobilized on glass beads have been inserted to experimentcontainer after washing and drying processes. The solution in thebeaker was continuously stirred with a stirrer to prepare uniform

toreactor; (1) photoreactor; (2) UV–LED configuration setup; (3) aluminum radiator;

; (7) TiO2 nanoparticles; (8) LED power supply; (9) pulsed radiation controller.



Table 3Kinetic parameters for the removal of DR23 in UV–LED/nano-TiO2/S2O8

2 process in different temperatures; [DR23]0 = 20 ppm, UV = 18 W, [S2O82�] = 10 mM, pH = 6.7.

1/[T (k)] ln[r(ppm/min)] ln[C(ppm)] r (ppm/min) [DR23] (ppm) Temperature (8C) Time (min)

0.0035316 �2.63443 2.85871 0.07176 17.43902439 10 0

�2.73815 2.839292 0.06470 17.10365854 5

�2.83512 2.81949 0.058712 16.76829268 10

�2.92211 2.802991 0.053820 16.49390244 15

�2.99561 2.786215 0.050006 16.2195122 20

�3.05167 2.77297 0.047280 16.00609756 25

�3.08697 2.759547 0.045640 15.79268293 30

�3.09907 2.743982 0.045092 15.54878049 35

0.0034112 �1.97217 2.826736 0.139154 16.06707 20 0

�2.04463 2.786215 0.129428 14.72561 5

�2.12276 2.745941 0.119701 13.5061 10

�2.20751 2.710081 0.109974 12.80488 15

�2.30012 2.672886 0.100246 11.92073 20

�2.40219 2.640798 0.090519 11.12805 25

�2.51587 2.60989 0.080792 10.33537 30

�2.64415 2.580309 0.071065 9.634146 35

0.003299 �1.56446 2.793706 0.209201 16.34146341 30 0

�1.63938 2.706016 0.1941003 14.9695122 5

�1.72037 2.64297 0.178999 14.05487805 10

�1.8085 2.605396 0.163899 13.53658537 15

�1.90515 2.554577 0.148801 12.86585366 20

�2.01208 2.490986 0.133710 12.07317073 25

�2.13191 2.444466 0.118611 11.52439024 30

�2.26809 2.384502 0.103509 10.85365854 35

0.003193 �1.56514 2.81767 0.209058 15.45732 40 0

�1.59046 2.753738 0.203832 12.71341 5

�1.61643 2.683358 0.198606 11.06707 10

�1.6431 2.616594 0.1986064 9.847561 15

�1.6705 2.547442 0.1881153 8.658537 20

�1.69867 2.473151 0.182927 7.804878 25

�1.72766 2.390104 0.177699 6.585366 30

�1.75751 2.305629 0.172474 5.54878 35


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mixing of the degrading dye solution six UV–LEDs (3 W) wereturned on at room temperature (258C � 28C) and the dye solutionsamples were taken at desired time intervals and analyzed on a UV–Visible spectrophotometer (Shimadzu 160, Japan) at lmax = 514 nmwith a calibration curve based on the Beer–Lambert’s law. For eachexperiment, operating conditions are summarized in the correspond-ing figure legends. The samples were taken from the reactor atscheduled times, and the removal of color was followed by using UV–Vis spectrophotometer.

3. Results and discussion

3.1. Kinetic modeling of photocatalytic degradation in UV–LED/nano-

TiO2/S2O82� process

Due to the practical evaluation, kinetic study for degradation ofDR23 was investigated in UV–LED/nano-TiO2/S2O8

2� processunder of S2O8

2� 30 mM concentration, natural pH and thetemperature range of 10–60 8C. Another thing worthy ofmentioning, about the mechanism of the procedure, sulfateradicals produced by irradiation of UV light beams on perox-ydisulfate ions and also using interaction of sulfate radicals withconductive bond electrons (e�Cb) which resulted form thecollision of UV light beams to TiO2 nanoparticles (Eq. (3)).Additionally, hydroxyl radicals generated from the reaction ofsulfate radicals with water molecules. Positive electron holesproduced in the surface of TiO2 nanoparticles could producehydroxyl radicals by the use of interactions of UV light and TiO2

nanoparticles with water molecules. Moreover, supplementaryinteractions took place according to the following equations(Eqs. (4)–(11)).

S2O2�8 þ e�Cb! SO2�

4 þ SO�4 (3)


S2O2�8 þ hy ! 2SO

��4 (4)

SO��4 þ RH2! SO2�

4 þ Hþ þ RH�

(5)

RH� þ S2O2�

8 ! R þ SO2�4 þ Hþ þ SO

��4 (6)

SO��4 þ RH ! R

� þ SO2�4 þ Hþ (7)

2R� ! RRðdimerÞ (8)

SO��4 þ H2O ! HSO�4 þ OH

�ðk ¼ 500 � 60 S�1Þ (9)

HSO�4 ! Hþ þ SO2�4 (10)

OH�þ S2O2�

8 ! HSO�4 þ SO��4 þ

1

2O2 (11)

Here, a preliminary power law kinetic model was chosen formodeling the experimental data, as [30–34]:

r ¼ � dC

dt¼ kCn (12)

Was employed for correlating data, where r, C, t, k and n are therate of degradation, concentration of DR23, time, rate constant andorder of the reaction, respectively. As it is well known, the rateconstant is related to temperature by Arrhenius equation:

k ¼ k0e�Ea=RT (13)

where k0, Ea and R are frequency factor, activation energy and theuniversal constant of gases, respectively. Combining Eqs. (12) and(13) and applying logarithmic function leads to:

lnr ¼ lnk0 �Ea

R

1

Tþ nln½C� (14)



Fig. 3. Kinetics of DR23 photodegradation (ln([Dye]0/[Dye])) in photocatalytic

experiments using nanoparticles of TiO2 for different concentration of DR23.

Fig. 4. Dependence of K (min�1) on the initial dye concentration, UV = 18 W,

pH = 6.7, [S2O82�] = 80 mM.


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The differential method of analysis, based on the data ofconcentration versus time, was used to find the rates. Tempera-tures of 10, 20, 30, 40 8C (around ambient temperature) wereconsidered. Equations resulted form these temperatures are shownin Eqs. (15)–(18).

C ¼ 17:440506 � 0:071762292t þ 0:000761134t2

� 7:2382362 � 10�6 T

¼ 10 �C (15)

C ¼ 16:887703 � 0:13915505t þ 0:00097270616t2 T

¼ 20 �C (16)

C ¼ 16:338923 � 0:20920441t þ 0:0015098722t2 T

¼ 30 �C (17)

C ¼ 16:722561 � 0:20905923t þ 0:00052264808t2 T

¼ 40 �C (18)

In these equations C and t are in terms of ppm and minrespectively. Results of the Eq. (14) have been considered in orderto finding kinetic of the photooxidation process which isrepresented in Table 3.

Additionally, results illustrate effect of different amount ofS2O8

2� on to the rate constant (Table x). Even though the120 mM amount of S2O8

2� has the most rate constant for thereaction, but results shows that taking into the optimum

Table 4Dependence of K (min�1) on S2O8

2� concentration, current and pulsed-illumination, U

Parameter Rate constant Parameter

[S2O82�] (mM) K (min�1) Current (A)

0 0.0002 0.36

5 0.006 0.72

10 0.0098 1.44

20 0.0143 2

30 0.0217

40 0.02777

80 0.0483

120 0.0958


conditions 80 mM of S2O82� would be more logical which

approve our previous selection. In addition, effect of dyeconcentration is so important factor. Figs. 3 and 4 show theeffect of dye concentration on to the rate constant of degradationreaction. Accordingly, increasing the dye concentration resultedin the decrease of the rate constant which is an endorsement toabove mentioned results.

Same assessment for analysis of the influence of current intensityvs. rate constant has been done. Results are presented in (Table 4). Asclearly seen from (Table 4) rate constant of 1.4 and 2 A is relativelyequal which, for the sake avoid high energy consumption the 1.4 Ahas been chosen. Moreover, effects of pulsed-illumination on to thedegradation kinetic are shown in Table 4.

Meanwhile, effect of dye concentration, peroxydisulfateconcentration and also, periodic-based illuminations (pulsedillumination) on the electric energy consumption is presented inFigs. 5–7.

By the way, the same evaluation for the pulse efficiencyamounts has been utilized. Clearly, the more illumination, thefaster removal, but in present method lower energy consumptionwas required and as can be seen in Fig. 8, by the use of 0.6 On-0.4Off, proper dye removal and also appropriate rate constant hasbeen achieved (Figs. 7 and 8).

As a result, it would be so interesting which we have acomparison between the above mentioned procedures. Due totestify the DR23 dye degradation efficiency under UV, UV/TiO2, UV/S2O8

2� and UV/TiO2/S2O82� methods we compare the kinetic

dependency of these routes. Outcomes, with a good certaintyapproved our previously discussed results (Figs. 9 and 10). As canbe seen obviously in Figs. 9 and 10, the rate constant for the UV/TiO2/S2O8

2� process is more than other methods.Finally, the three dimensional fitting of kinetic study for the

removal efficiency of DR23 was performed which is illustrated in(Fig. 11).

V = 18 W, pH = 6.7, [S2O82�] = 80 mM, [DR23]0 = 20 ppm.

Rate constant Parameter Rate constant

K (min�1) Pulse (tON-s) K (min�1)

0.0136 0.1 0.0071

0.0228 0.2 0.011

0.034 0.3 0.0163

0.0368 0.4 0.0168

0.5 0.032

0.6 0.0344

0.7 0.0311

0.8 0.031

0.9 0.0357



Fig. 6. Effect of dye concentration on electric energy consumption in the removal of

DR23, UV = 18 W, [S2O82�] = 20 mg/l, pH0 = natural, T = 25 8C, glass bead nano-

TiO2.

Fig. 7. Effect of periodic illumination on electric energy consumption in the removal

of DR23, UV = 18 W, [S2O82�] = 80 mg/l, [DR23]0 = 20 mg/l, pH0 = natural, T = 25 8C,

glass bead Nano-TiO2.

Fig. 8. Dependence of K (min�1) on the photonic efficiency, UV = 18 W, pH = 6.7,

[S2O82�] = 80 mM.

Fig. 9. Dependence of the dye removal kinetic (min�1) on UV, UV/TiO2, UV/S2O82�

and UV/TiO2/S2O82�.

Fig. 5. Effect of peroxydisulfate concentration on electric energy consumption in the

removal of DR23, UV = 18 W, [DR23]0 = 20 mg/l, pH0 = natural, T = 25 8C, glass bead

nano-TiO2.


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The goodness of fitting in agreement with Eq. (14) is shown inFig. 11. In this figure experimental data has been marked with bolddots and the fitted 3D equation with a meshed plane. Variables z, x

and y are attributed to the ln r, ln C and 1=T respectively and fromthe coefficients of a, b and c, kinetic parameters can be obtained.The estimated coefficient of determination (R2) for this fitting is0.919. Amounts for the kinetic parameters, Activation energy and


also thermodynamic parameters for photocatalytic degradationare provided in Table 5. The kinetic parameters appropriate toUV–LED/nano-TiO2/S2O8

2� process i.e. activation energy andreaction order are 39.01787 kJ/mol and 1.001, respectively.

As it can be clearly seen from Table 5 using the optimizedcondition for photocatalytic process, reaction order for UV–LED/nano-TiO2/S2O8

2� process is first order. Consequently, reaction



Fig. 10. Comparison of dye removal kinetic (min�1) between UV, UV/TiO2, UV/

S2O82� and UV/TiO2/S2O8

2�.

Fig. 11. The three dimensional fitting of kinetic study for removal efficiency of DR23

based on the concentration and temperature in UV–LED/nano-TiO2/S2O82� system,

[DR23]0 = 20 ppm, [S2O82�] = 30 mM pH0 = 6.7.

Table 5Kinetic and thermodynamic parameters for photocatalytic removal of DR23 in UV–LED/nano-TiO2/S2O8

2.

DH (kJ/mol) DG (kJ/mol) DS (kJ/mol/K) k (min�1) Ea (kJ/mol) k0 (min�1) n t (8C)

36.539 �134.398 0.5733 0.46303 39.01787 3.174131 � 106 1.001 25

Fig. 12. Comparison of predicted kinetic model with experimental data for the

removal of DR23 in UV–LED/nano-TiO2/S2O82� system.


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rate of the DR23 dye during 35 min is given by Eq. (19):

r ¼ 52902:189exp�39:01787

RT

� �C1:001 (19)

In above equation C and t are in terms of ppm and min,respectively.

3.2. Assessment of kinetic model

As it can be seen from Fig. 12, proper good fitting betweenamong predicted kinetic model and experimental data isestablished. All plots of ln([Dye]0/[Dye]) versus t and otherparameters confirm the consistency of our kinetic model.Moreover, regression analysis for the kinetic studies presentsvaluable amounts which support validity of the experimental data.


4. Conclusion

Kinetic characteristics for photodegradation of DR23 in UV–LED/nano-TiO2/S2O8

2� system were experimentally investigatedconsidering influences of dye initial concentration, photonicefficiency and pulsed-illumination. Results showed that it waseffectual and safe technique with almost 89.9% color removal.Degradation rate is illustrated to be dependent on the irradiationpulse, current and peroxydisulfate concentration. Moreover, it waslogical that the more concentration of dye, the lower decoloriza-tion would be. In order to importance of photonic efficiency incolor destruction process, in whole investigation by increasing ordecreasing K the photonic efficiency is increased or decreased,respectively. Kinetic approach of DR23 removal showed that thefirst order equation was verified with photodegradation of DR23.Furthermore, the three dimensional fitting of kinetic study forremoval efficiency of DR23 has been illustrated an excellent fittingbetween predicted kinetic model with experimental data. Thevalidity of the model was accordingly proved by three dimension-ally fitting of the experimental data with theoretical data. Theregression analysis (R2 > 0.919) indicated that the kinetic modelwas rationally deduced on the basis of the considered assumptions.

In het rijk van de ideeen hangt alles af van het enthousiasme . . .

in de echte wereld alle rust op doorzettingsvermogen. . .[[nl]]Inthe realm of ideas everything depends on enthusiasm . . . in thereal world all rests on perseverance... (J.W. von Goethe (1749–1832)).

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Documents

Kinetic study for photocatalytic degradation of Direct Red 23 in UV–LED/nano-TiO2/S2O82− process: Dependence of degradation kinetic on operational parameters