Vol. 05 INTERNATIONAL JOURNAL OF PHOTOENERGY 2003

Photocatalytic degradation of reactive yellow17 dye in aqueous solution in the presence

of TiO2 with cement binder

B. Neppolian,1 S. R. Kanel,1 H. C. Choi,1,† M. V. Shankar,2

Banunathi Arabindoo,2 and V. Murugesan2

1 Department of Environmental Science and Engineering Kwangju Institute of Science and Technology (K-JIST),

Kwangju - 500 712, South Korea2 Department of Chemistry, Anna University, Chennai - 600 025, India

Abstract. This study examined the photocatalytic degradation of common textile dye, reactive yellow 17 byphotocatalysis over TiO2 (Degussa P25) photocatalyst coated on the glass plates (reactor) using cement as abinder. Sunlight was used as an energy source. The degradation efficiency was found to be the high at aroundneutral pH values. The influence of additives such as H2O2, K2S2O8, Na2CO3 or NaCl, on the degradationefficiency of the dye in the presence of cement binder was systematically studied. Both Na2CO3 and NaClwere hindering the rate of photocatalytic degradation. Whereas, increase the initial concentrations of bothH2O2 and K2S2O8, increased the rate of degradation of the dye. UV-vis spectrophotometer and chemicaloxidation demand were used to study decolourisation and degradation of dye, respectively. From this study,degradation of textile dye reactive yellow 17 with TiO2 photocatalyst coated on the glass plate using cementas a binder employing solar energy may emerge as a cost-effective method for textile dye wastewater of lowconcentration.

1. INTRODUCTION

The discharge of wastewater that contains high concen-tration of reactive dyes is a well-known problem as-sociated with dye stuff activities. Some of these dyeshave documented health hazards [1]. There are dif-ferent physico-chemical and biological methods forthe treatment of reactive dyes in wastewater. How-ever, these processes have high operating cost and areof limited applicability. If not removed, would causedisturbance to the ecological system of the receivingwaters [2–4]. Hence, the necessity of investigating newalternatives for the adequate treatment of the dyepresent in wastewater is inevitable.

Thus many processes have been proposed overthe years and are currently employed to destroy toxicchemicals discharged along with textile wastewater.Photocatalytic detoxification (AOPs) has been focussedas an alternative method to clean up polluted water.This technique adopts the possibility of combiningthe heterogeneous catalysis with solar light to achievemineralisation of toxic pollutants present in textilewastewater [5]. In the past few years many catalystslike TiO2, ZnO, WO3, SnO2, ZrO2, CeO2, CdS and ZnShave been attempted for photocatalytic oxidation ofwater borne environmental contaminants [1, 6]. In thepresent study, TiO2 assisted photocatalytic degrada-tion of reactive yellow 17 dye coated on the glass plate(reactor) using cement as a binder is reported. Theeffects of the concentrations of H2O2, K2S2O8, Na2CO3

†E-mail: hcchoi@kjist.ac.kr

and NaCl in the degradation of reactive yellow 17 dyewere studied.

2. EXPERIMENTAL

2.1. Materials. The textile dye reactive yellow 17(C21H20O10N4S3) purchased from Vanavil (India) lim-ited. The Titanium dioxide (Degussa P-25) obtainedfrom Germany. The titania particles are a mixtureof both anatase and rutile crystalline phase (mostlyanatase) with an average particle size of 30 nm and sur-face area of 50 m2/g were used without any pretreat-ment. Portland cement is used in this study as a binderfor the TiO2 on glass surface, mainly consists of 45% tri-calcium silicate and 25% dicalcium silicate and remain-ing is metal oxides and sulphates. Required concentra-tion of solutions were prepared by dissolving the dyein distilled water (17 MΩ).

2.2. Thin-film coated photocatalytic reactor.The photocatalyst powder (TiO2) was thoroughly mixedwith Portland cement in the ratio 1 : 1 by grinding.The mixture was then transformed into a semisolidmass with suitable addition of distilled water. Thesemisoild mass was applied physically to the innersurface of the Petri dish as a thin coating. It was thenallowed to set for 2 h. The dye solution was taken in thedish and exposed to direct sunlight. The Petri dish inthis study is 15.5 cm× 1.8 cm (diameter× height). Theprogress of photocatalytic degradation of the dye wasmonitored by withdrawing definite quantity of aliquots

46 B. Neppolian et al. Vol. 05

at regular intervals and measuring the absorbance inthe UV-visible spectrophotometer for decolourisationand degradation using COD method.

2.3. Analysis. The decolorisation of reactive yel-low 17 was measured with UV-vis spectrophotometer(Model Hitachi UV-2000, doble beam, Japan) at 596 nm.The chemical oxygen demand (COD) was measured bythe closed reflux method [7]. The dye solution with cat-alyst in the reactor were withdrawn at periodic intervalsand analyzed after centrifugation for decolorizationand degradation. CO2 was tested by bubbling throughlime water, sulphate by turbidimetry and NH4

+ andNO3

− ions by spectrophotometic method.

3. RESULTS AND DISCUSSION

Reactive Yellow 17 dye was degraded in the presenceof TiO2 (coated on the glass plates using cement asa binder) by irradiation with solar light. A blank ex-periment in the absence of irradiation illustrated therapid attainment of adsorption equilibrium of the dyeon to TiO2. Another experiment in the absence ofTiO2 with irradiation showed no significant degrada-tion. This clearly indicates that this reaction followsphotocatalytic degradation.

0 2 4 6 8 10

Irradiation time (h)

0

10

20

30

40

50

60

70

80

90

100

Deg

rad

atio

n(%

)

0.8× 10−4 M0.9× 10−4 M1.0× 10−4 M1.2× 10−4 M1.3× 10−4 M

Figure 1. Influence of different initial concentrations of re-

active yellow 17 dye (TiO2 and Cement: 200 mg (1:1)).

3.1. Influence of initial concentration of dye.Figure 1 illustrates the degradation of different initialconcentration of the dye (0.8–1.3 × 10−4 M) by pho-tocatalysis in the presence of TiO2. It is found that1.2 × 10−4 M dye degraded to 84% by photocatalysisin the presence of 200 mg each of TiO2 and cement in8 hours. So we fixed the initial concentration of dye as1.2 × 10−4 M. After fixing the initial concentration ofdye, experiments were carried out by varying differentconcentrations of cement and TiO2.

0 2 4 6 8 10

Irradiation time (h)

0

10

20

30

40

50

60

70

80

90

Deg

rad

atio

n(%

)

100 mg (1:1)150 mg (1:1)200 mg (1:1)250 mg (1:1)300 mg (1:1)

Figure 2. Influence of different amounts of TiO2 and ce-

ment (1 : 1) in the degradation of reactive yellow 17 dye

(1.2× 10−4 M).

3.2. Influence of titanium dioxide catalyst and ce-ment (1 : 1). The results of photodegradation of thedye (1.2 × 10−4 M) over different amounts of TiO2 andcement (100, 150, 200, 250, 300 mg, i.e. 1:1 ratio) are il-lustrated in Figure 2. With an increase of TiO2 dosages,the rate was enhanced due to the increase of activesite for the production of OH radicals. The degrada-tion reached maximum at an optimum concentration ofTiO2 (200mg). Further increasing the dosage, degrada-tion of dye decreased due to increase of turbidity, whichreduces the light transmission through solution. Whilebelow this optimum level, it is assumed that the cata-lyst surface and adsorption of light by the catalyst arelimited. Particle interaction becomes significant as thenumber of particles in solution increases. This reducesthe site density for surface holes and electrons [8]. Sim-ilar result was observed by Reutergarth & Langphasuk(1997), [1] during the degradation of reactive dye usingTiO2.

3.3. Influence of pH. The effect of another impor-tant parameter in photodegradation, pH, experimentwere conducted at different initial pH values varyingfrom 5 to 12 and results are shown in Figure 3. Thepercent degradation of the dye was unchanged with in-creasing of pH up to 10 and further increasing of pH,the degradation was decreased. The inhibitory effectseems to be more pronounced at alkaline range. At highpH values, the OH radical concentration is high andhence the chances of recombination is also high. The pHaffects not only the surface properties of TiO2 but alsothe dissociation of the dye and formation of hydroxylradicals. In the present case, it can be presumed thatthe main reaction is presented by the hydroxyl radicalattack, which can be favored by the high concentrationof the hydroxyl radicals at around neutral pH [9].

Vol. 05 Photocatalytic degradation of reactive yellow 17 dye in aqueous solution … 47

5 7 9 10 11 12

pH

0

10

20

30

40

50

60

70

80

90D

egra

dat

ion

(%)

Figure 3. Influence of pH in the degradation of reactive

yellow dye 17 dye (1.2× 10−4 M).

−3.5

−3

−2.5

−2

−1.5

−1

−0.5

0

Ln(C

/C0)

0 0.5 1 1.5 2 2.5

Irradiation time (h)

1× 10−2 M

2× 10−2 M

3× 10−2 M4× 10−2 M

Figure 4. Kinetics of degradation of reactive yellow 17 dye

(1.2× 10−4 M) with different concentration of H2O2.

3.4. Influence of hydrogen peroxide. Figure 4shows the influence of H2O2 dosage on the degradationefficiency of the dye in the light/TiO2-cement system.Since reactive hydroxyl radicals are easily generated bythe breakdown of hydrogen peroxide (eqs. (2)–(4)), thepresence of hydrogen peroxide in the reaction mixturewill play key role in the photocatalytic process [10].The dye degradation with hydrogen peroxide indicatedthat the reaction followed the pseudo-first order kinet-ics with respect to different H2O2 concentrations. Rateconstant of dye degradation was calculated from theslope of the plot of the dye concentration in logarith-mic scale with time and listed in Table 1.

The increase of H2O2 concentration, resulted in afaster degradation of the dye was observed. This is dueto photolysis of H2O2 to produce OH radical (H2O2 +hν → 2OH•) and H2O2 is suitable for trapping elec-trons [11] by preventing the recombination of e− andh+ pairs, thus increasing the chance of the formation

Table 1. Rate constant of degradation of Reactive Yellow

17 dye.

H2O2 × 10−2 M Rate constant (k/sec) ×10−4 R2

1 3.508 0.98

2 3.500 0.98

3 4.161 0.97

4 3.198 0.99

of OH radical and O2− on the surface of the catalyst.

The percent degradation has been found to be very highin the presence of hydrogen peroxide in comparisonto the results in the absence of hydrogen peroxide. Itwas noted that 100% degradation was achieved with 4 hin the presence of hydrogen peroxide (3 × 10−3 M) in-stead of 84% degradation in the absence of hydrogenperoxide in 8 h. It has been widely reported that the ad-dition of small amount of hydrogen peroxide greatlyenhances the oxidation of organic pollutants mediatedby TiO2 catalyst [10]. The enhanced photodegradationefficiency in the presence of hydrogen peroxide maybe either directly via conduction band electrons or in-directly via superoxide radical anion which produceshydroxyl radicals [12]. The degradation of the dye in-creased rapidly up to H2O2 concentration of 3×10−2 M.The further increase of H2O2 concentration (4×10−2 M),considerably decreased the rate of the degradation ofdye. This is due to quenching of OH radical by H2O2

(eq. (1)). Perhydroxide radical is significantly less re-active than OH radical with respect to organic oxida-tion [11], (eq. (1))

H2O2 +OH• −→ HO2• +H2O, (1)

H2O2 + e− −→ •OH+OH−, (2)

H2O2 +O2−• −→ •OH+OH− +O2, (3)

H2O2 −→ 2•OH, (4)

H2O2 −→ O22− + 2H+. (5)

3.5. Influence of potassium persulphate. In thisstudy, the effect of persulphate ion on the photocat-alytic degradation of the dye was investigated (con-centration of K2S2O8 : 25 to 200 mg/100 ml dye so-lution, 4 h). The data are presented in Figure 5. Thepercentage degradation of the dye increased with in-creasing amount of persulphate ion concentration andachieved 98% degradation within 4 h irradiation timewith 200 mg persulphate ion concentration instead of84% degradation in the absence persulphate ion at 8 h.It is a beneficial oxidising agent in photocatalytic detox-ification because SO4

−• is formed from the oxidant byreaction (eqs. (6) and (7)) with the semiconductor gen-erated electrons (e−cb)

S2O82− + e−aq −→ SO4

−• + SO42−, (6)

S2O82− + e−cb −→ SO4

−• + SO42−. (7)

48 B. Neppolian et al. Vol. 05

0

20

40

60

80

100

120D

egra

dat

ion

(%)

0 mg 25 mg 50 mg 100 mg 200 mg

Concentration of persulphate ion (100 mL of dye/4h)

Figure 5. Influence of K2S2O8 in the degradation of reactive

yellow dye 17 (1.2× 10−4 M).

The sulphate radical anion (SO4−•) is a strong ox-

idant (E0 = 2.6 eV) and engages in the following threepossible modes of reactions with organic compounds.(i) by abstracting a hydrogen atom from saturated car-bon. (ii) by adding to unsaturated or aromatic carbonand (iii) by removing one electron from the carboxylateanion and from certain neutral molecules [13]. In addi-tion, it can trap the photogenerated electrons and/orgenerated hydroxyl radical [13–15]

SO4−• + e−cb −→ SO4

2−, (8)

SO4−• +H2O −→ •OH+ SO4

2− +H+. (9)

The formation of hydroxyl radical and sulphate rad-ical anion (eqs. (10) and (11)) are powerful oxidants thatcan degrade the dye molecules at faster rate. The SO4

−•

has the unique nature of attacking the dye molecule atvarious positions and hence the fragmentation of thedye molecules is rapid [5]

SO4−• + dye −→ SO4

2− + dye+• (intermediate), (10)

SO4−• + dye+• (intermediate)

−→ SO42−+ CO2+HNO3+ other inorganics. (11)

3.6. Influence of sodium carbonate. Sodium car-bonate is the common auxiliary chemical employedin textile processing operations. Sodium carbonate ismainly used in the dyeing bath in order to adjust thepH of the bath as it plays an important role in the fixingof dye on the fabrics and in the fastness of color. There-fore the wastewater from the dyeing operation will con-tain considerable amount of carbonate ion. Hence it isimportant to study the influence of carbonate ion inthe treatment efficiency. Experiments were performedwith sodium carbonate, the percent degradation grad-ually decreased with increasing carbonate ion concen-tration as shown in Figure 6 [16]. The decrease in the

0

10

20

30

40

50

60

70

80

90

Deg

rad

atio

n(%

)

0 mg 25 mg 50 mg 100 mg 200 mg

Concentration of Sodium carbonate (100 mL dye/8h)

Figure 6. Influence of Na2CO3 in the degradation of reac-

tive yellow dye 17 (1.2× 10−4 M).

degradation of the dye in the presence of carbonateions is due to the hydroxyl scavenging property of car-bonate ions, which can be accounted from the followingreaction (eqs. (12) and (13))

•OH+ CO32− −→ OH− + CO3

•−, (12)•OH+HCO3

− −→ H2O+ CO3•−. (13)

This type of trend was also observed in the pho-tocatalytic degradation of reactive dyes [17]. Beharet al., (1970) [18], reported the possibility of gener-ating carbonate radicals (CO3

•−) with the help of hy-droxyl radicals. Thus the free hydroxyl radical whichis a primary source (oxidant) for the photocatalyticdegradation found to decrease gradually with increasein carbonate ions and ultimately significant decrease inthe percent degradation of the dye [5].

3.7. Influence of sodium chloride. Sodium chlo-ride usually comes out in the effluent along with sec-tional wastes in textile mills. Hence studies have beencarried out with sodium chloride in the range 25–200 mg/100 mL dye solution.

The percent degradation of the dye decreased withincrease of the amount of chloride ion. The resultsshown in the Figure 7 are in good agreement with thosepublished by Abdullah et al., (1990) [19], who reported astrong inhibiting effect of chloride and phosphate ionswhen they studied the photocatalytic degradation ofsalicylic acid, aniline and ethanol. The decrease in thedegradation of dye in the presence of chloride ion isdue to the hole scavenging properties of chloride ion asshown in the following equations 14 and 15 [20]. Thisis a typical example for competitive inhibition. The re-action of dye molecules with the holes will have to com-pete with reaction

TiO2 −→ TiO2(h+vb, e−cb), (14)

Vol. 05 Photocatalytic degradation of reactive yellow 17 dye in aqueous solution … 49

0

10

20

30

40

50

60

70

80

90D

egra

dat

ion

(%)

0 mg 25 mg 50 mg 100 mg 200 mg

Concentration of Sodium chloride (100 mL dye/8h)

Figure 7. Influence of NaCl in the degradation of reactive

yellow dye 17 (1.2× 10−4 M).

Cl− + h+vb −→ Cl•, (15)

Cl• + Cl− −→ Cl2•−. (16)

While chlorine atoms are forming slowly, they areinstantaneously converted into chloride radical anion(eq. (16)). Alternatively, surface sites normally availableat the TiO2/dye solution interface for the adsorptionand electron transfer from the dye can be blocked byanions such as chloride and phosphate which are notreadily oxidisable but yet very effective inhibitors forthe detoxification process. However reversible by wash-ing the catalyst with pure water to fully restore its pho-tocatalytic activity when chloride ions were present inthe wastewater.

4. CONCLUSION

From the foregoing discussions, it is seen that TiO2

catalyzed (with cement binder) photodegradation usingsolar irradiation is a suitable technique for removal ofcolored wastewater from textile industries. The oxidiz-ing agents such as hydrogen peroxide and persulphateion have major role in the degradation efficiency of thereactive yellow 17 dye. The additives such as sodiumcarbonate and sodium chloride are hindering the rateof photocatalytic degradation but it can be removed bydiluting the dye solution to appropriate concentrationand washing the catalyst. Hence the photodegradationof textile dyes employing solar energy may emerge as aviable method because of its eco-friendliness and costeffective.

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[3] Wang Yizhong, Wat. Res. 34(3) (2000), 990.[4] S. K. Chaudhari and Sur Babita, J. of Environmental

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[15] C. Minero, E. Pelizzetti, S. Malato, and J. Blanco,Chemosphere 26 (1993), 2103.

[16] G. V. Buxton, C. C. Greenstock, W. P. Helman, andA. B. Ross, J. Phy. Chem. 17 (1988), 513.

[17] D. Nansheng, F. Tao, and T. Shizhong, Chemo-sphere 33 (1996), 547.

[18] D. Behar, G. Czapki, and I. Duchovny, J. Phy. Chem.74(10) (1970), 2206.

[19] M. Abdullah, G. K. C. Low, and R. W. Matthws, J.Phys. Chem. 94 (1990), 6820.

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