Photocatalytic Degradation of Solophenyl Red 3 BL in an Aqueous

Ashdin PublishingJournal of Advanced Chemical Engineering Vol. 1 (2011), Article ID A110301, 8 pages doi:10.4303/jace/A110301 Research Article Photocatalytic Degradation of Solophenyl Red 3 BL in an Aqueous Suspension of Titanium Dioxide A. Boukhennoufa,1 M. Bouhelassa,1 and A. Zoulalian2 1 LIPELaboratory, Department of Industrial Chemistry, Faculty of Engineering Sciences, University Mentouri Constantine, 25000 Constantine, Algeria 2 Wood-Material Study and Research Laboratory (LERMAB), Faculty of Science, Henri Poincaré University, Nancy I, BP 70239, 54506 Vandoeuvre lès Nancy Cédex, France Address correspondence to A. Zoulalian, [email protected] Received 8 March 2011; Revised 26 August 2011; Accepted 29 August 2011 Abstract The wastewater from the textile industry gener- decontamination, since it involves very oxidizing species ates a serious problem for environment by the presence of such as hydroxyl radicals [15, 16, 21, 26]. The photocatalytic compounds such as dyes, resistant to the natural and con- degradation rate of different compounds depends on ventional treatment. In this work, the photocatalytic degra- various parameters (concentration of semiconductor, initial dation of aqueous solution of an azo-dye as Solophenyl red concentration of the pollutant, initial pH, temperature, light 3 BL was investigated, using a semiconductor (TiO2 ) and a intensity, addition of salts and oxidants, partial pressure of UV lamp. The decolorization of dye aqueous solution was oxygen, etc.) [5, 13]. Since the azo-dyes are considered the controlled by spectrophotometry. Photolysis is enhanced by most common dyes present in textile industry wastewater the addition of TiO2 particles. The degradation rate depends [20], we are interested, in this work, in the decolorization on the initial pH of the suspension and it goes through a min- of an aqueous solution containing this type of dyes such imum at neutral pH. For a fixed concentration of dye, degra- as Solophenyl red 3 BL which was previously investigated dation rate increases with the oxygen concentration and tem- [8, 9]. Effects of some parameters such as initial pH, perature. The influence of temperature on the rate constant temperature, light intensity and addition of H2 O2 on the corresponds to activation energy of 31.9 kJ/mol. Intensity photodegradation of this direct dye were investigated. and geometry of UV radiation and the addition of hydro- A photocatalytic process is based on the action of light gen peroxide, are significant parameters whose influence is on the surface of a semiconductor, which causes a jump directly related to changes in the concentrations of OH• and of electrons from the valence band to the conduction band O−• 2 radicals. (electronically) within the superficial atoms of semi driver. This process can be summarized, in brief, in three steps: Keywords azo-dye; solophenyl red 3 BL; photocatalytic degradation; titanium dioxide (1) the production of pairs of electron-positive holes: under the effect of UV irradiation, provided that the photon 1 Introduction energy is greater than or equal to the difference in energy between the valence band and conduction band (band Dyes are usually resistant compounds that can be found in gap) [10], an electron can move from the valence band industrial wastewater, producing important environmental to a vacant orbital of the conduction band as follows: problems [4]. Different biological treatments [3] and + traditional methods like ultrafiltration, extraction and TiO2 + hν −→ e− CB + hVB ; (1) carbon adsorption [19] have been applied to remove such compounds. A disadvantage of most of these processes (2) the separation of electrons and holes: the lifetime of the + is that they are non-destructive; they simply transfer the pairs (e−CB /hVB ) is a few nanoseconds and recombina- pollutant from one phase to another [24]. Over the past few tion is accompanied by heat: years, several advanced oxidation processes (AOPs) have + e− CB + hVB −→ heat. (2) been proposed as alternative routes for water purification. Among them, oxidation via ozonation or hydrogen peroxide Recombination of electrons and holes is the main factor was one method [6, 14]. Nevertheless, the photocatalytic limiting the rate of oxidation of organic substrates [11]. process seems to be the most successful one for water The recombination should be avoided, for an efficient (5) In addition. 2. type of the titania is d = 3. 100 W. λmax = 366 nm) and Lamp HPK 125 (lamp 2: immersed lamp. temperature constant. sam. 5. For example. 4. Pyrex vessel. 2 Materials and methods Figure 3: Relative spectral distribution. we used a complex mixture of a solution TiO2 and dye. at regular time intervals. Its tocatalysis) was contained in the Pyrex vessel (200 mL) and chemical structure is presented in Figure 1. L = 12. photocatalyst. envelope and with respective values of diameter and height The data of luminous intensity of two lamps were (di = 5. react and produce free Spectral irradiance radicals OH• . adsorbed on the surface of titanium. The distance between the free area of azo dye tor represented by a cylindrical Pyrex vessel with a double aqueous solution and the lamp 1 is 10 cm. To verify the quantum yield is known and is constant in wavelength adsorption capacity of the azo dye on TiO2 particles. mainly the anatase form.1 Chemicals The dye chosen as a model molecule in this work is a water In case of photolysis and photocatalysis processes. 2. the hydroxyl groups OH. Thus. λmax = 366 nm). Lamp HPK 125 (immersed lamp). Irradiation of this solu- was supplied by Sigma and the manufacturer’s values are tion is made (separately) from two different monochromatic minimum 99. of oxalic acid (5 · 10−2 M) and a solution of uranyl sulfate . Spot.e. reducing). forming superoxide radicals: −• e− CB + O2 (adsorbed) −→ O2 . TiO2 powder was subjected to a magnetic stirring. water was flowing through the double The principle of the actinometry is based on irradiation of envelope from a Lauda RC6 thermostatic bath. 3. To maintain the obtained experimentally using the actinometry method.9 g/cm3 .8 cm).2 Journal of Advanced Chemical Engineering Figure 1: Chemical structure of Solophenyl red 3 BL. electrons (i. the electron trapping occurs at sites of defective Ti3+ (instead of Ti4+ ) or molecular oxygen adsorbed. the main reactions are [27] as follows: h+ • + VB + H2 O (adsorbed) −→ OH + H . not immersed projection lamp. Bi-distilled a reference substance called chemical actinometer whose water was used throughout the experiments. ples were collected on an aqueous dispersion of particles of In this work.0%. respectively. 18]. All the experiments were performed in a batch photoreac. emitted by the lamp.2 Experimental device Light spectra of the two lamps are shown in Figures 3 and 4. hydrogen peroxide can be formed in the solution or at the solid-liquid interface [12.e.4 cm. and the density UV lamps: Lamp Wood (lamp 1: B-100AP. 2. in an aqueous medium. These are oxidation or reduc- tion substances which are interesting for remediation. In fact. Magnetic agitator. the soluble azo-dye: Solophenyl red 3 BL which is used with- aqueous dye solution (in the presence of TiO2 in case of pho- out further purification (manufactured by COLOREY). see Figure 2. (3) the oxidation and reduction: the charges created migrate to the surface of the catalyst and react with adsorbed sub. Figure 2: Experimental setup for photocatalytic process in stances likely to accept electrons (i. Thermostatic bath. Lamp wood (not immersed projection lamp). (4) h+ − • VB + OH (surface) −→ OH . This is made possible by the transfer and trapping of free charges to intermediate energy levels (irregularities of structure or adsorbed molecules). characteristic of light to lamp 1 (lamp wood). oxidizing) or give the presence of two different lamps (used separately). (3) 1. All reagents were analytical grade.42 · 10−9 and 7. In the range of initial that the absorption spectrum of Solophenyl red 3 BL is pH between 2 and 12. The acidic solution (pH = 1) and strongly basic solution (pH = pH has been changed by adding to the solution different 14) of Solophenyl red 3 BL. for lamps 1 and 2 are 4. with their remains similar to that obtained for the water solution maxima located at 531 nm and 380 nm. The absorbance bands at wood (lamp 1). The UV-visible strongly basic solution takes on a dark purple color and spectrum of Solophenyl red 3 BL dye (C0 = 30 mg/L) shows a larger effect bathochrome and a very remarkable consists of many absorption bands. However. respectively. the solution Figure 5 shows the electronic absorption spectra of changes color and takes on a dark blue one. intense band centered around 380 nm is due to the partly experiments are carried out in the presence of UV lamp forbidden n → π ∗ transition. the suspension was sampled (3 mL) at regular intervals irradiation time and then filtered through a millipore membrane filter (pore size. At pH = 1. It has been noticed disappearance of the dye molecules.82). In different cases. Figure 7 displays the illumination of dye 220 nm and 280 nm are due to the benzene and naphthalene in three cases: adsorption.82). the decoloriza- tion of solution was monitored by absorbance measurements at the wavelength of 531 nm by using a spectrophotometer Figure 6: UV-visible absorption spectrum of both highly (Shimadzu 160 A).2 Photocatalytic degradation chromophore containing azo linkage. in the ultraviolet region located at 220 nm and 280 nm. It seems that the less To examine the photodegradation feasibility of dye solution.30 · 10−9 Einstein/s.3 Experimental procedure After 30 min of agitation (average speed) and adsorption of dye on TiO2 particles. (10−2 M). characteristic of Figure 5: UV-visible absorption spectrum of Solophenyl light to lamp 2 (lamp HPK 125 Philips). In . see Figure 6. and are assigned to a π → π ∗ oxygen through a tube in the Pyrex vessel. The absorbance bands in the visible region are due to the 3. transition. the Solophenyl red 3 BL in water (pH = 6.Journal of Advanced Chemical Engineering 3 Figure 4: Relative spectral distribution.20 μm) to remove the residual powder of TiO2 . photoreaction is derived from the direct contact of the sus- pension with atmospheric air or by introducing the air or the rings of 3 BL. in water (C0 = 100 mg/L. 0. amounts of H2 SO4 or NaOH. The absorption spectra of Solophenyl red 3 BL were 3 Results and discussion determined about highly acidic (pH = 1) and highly basic 3. This mixing leads to the formation of complexes of uranyl oxalate: UO2 (C2 O4 )−2 2 and UO2 C2 O4 . the appearance of absorption spectra characterized by two bands in the visible region. respectively.1 UV-visible spectra of solopheny red 3 BL solution solutions (pH = 14). 2. optical path of cell (l = 1 cm)). photolysis and photocatalysis. red 3 BL in water (C0 = 30 mg/L. The oxygen needed for the optical path of cell (l = 1 cm)). The lumi- nous intensity values found. and by two bands (pH = 6. photochemical process is a very difficult task. CTiO2 = 1 g/L. in the presence of pH = 6.4 Journal of Advanced Chemical Engineering Figure 7: Temporal evolution of normalized residual Figure 8: Temporal evolution of normalized residual concentration of Solophenyl red 3 BL. with absence of light.82 been studied in the pH of 2–14 under UV irradiation (Lamp are lower for those corresponding to the runs carried out Wood) for 60 min with particles of TiO2 (1 g/L). the kinetic rate values at pH < 6. as shown in Figure 9 [23]. This result is due to the increase of OH• and The initial kinetic rate values of dye degradation O−• 2 radicals in the solution. in the presence of concentration of dye for various initial pH (lamp 1.2% at the end of 2 h. T = 25 °C. at acidic pH values the particle the dye at various initial pH. [1] on the there is a strong dependence between the pH of the solution degradation of a common azo-dye (orange II). Tang et al. Figure 7 shows Figure 9: Changing the surface charge of TiO2 as a function a negligible decrease of the residual dye concentration. The pH of the solution presence of polycrystalline TiO2 irradiated by sunlight. aggregate it forms.82. a certain decolorization of the solution of the red solophenyl 3 BL was noted. 100 mg/L. T = 25 °C. [25] have noticed surface is positively charged and at basic pH values it is that the interpretation of pH effects on the efficiency of the negatively charged. contact of the liquid surface). in the presence of atmospheric air with direct atmospheric air with direct contact of the liquid surface). photocatalytic process improves the rate of decolorization of the azo-dye. In case of TiO2 . Gouvêa et al. The rate of decolorization increased from 14. These rate tions of oxidizing free radicals.3 Effect of pH decreases with the increase of initial pH until pH = 6. The photoreactivity 3. case of the direct photolysis (in absence of semiconductor particles). However. the zero point charge pH Although it is not easy to fully explain the behavior of (pHzpc ) is at pH 6. The influence of adsorption of Solophenyl red 3 BL on TiO2 particles is also examined in this study.82 The photocatalytic degradation of the dye (100 mg/L) has (natural pH). The result at the initial pH > 6. The addition of a certain quantity of TiO2 (1 g/L) in the irradiated medium clearly improved the rate of decolorization of the solution colored by the red Solophenyl 3 BL. [7] noted the same effect of the ing place on the surface of the TiO2 particles as it revealed pH on the degradation of a reactive dye (Remazol Brillant by the charge on the particles surface and the size of the Blue R).82. an experiment was carried out in the same Pyrex vessel. because three . Subsequently. C0 = lamp 1 (C0 = 100 mg/L. The of pH. Hence. CTiO2 = 1 g/L. A similar behavior was obtained is depicted in Figure 8 and the observation indicates that in the study carried out by Augulgliaro et al. in the and the heterogenous photon process. In is an important parameter in the photocatalytic reactions tak. we will examine obtained by performing photodegradation reactions under various operating parameters for changing the concentra- different initial pH are reported in Figure 10. the same way. values indicate that the reaction rate is high at strong acidic pH for Solophenyl red (pH = 2). under the same operating conditions. in the presence of ZnO as a photocatalyst.7% to 32. 3. if the increase of tempera- possible reaction mechanisms can contribute to dye degra.6 cates that the oxygen concentration in the liquid phase is C/CL0 very important in the photodegradation process. direct oxidation by bates. namely. the positive hole and direct reduction by the electron in the With the chosen operating conditions.82 and 14 has been observed. which can be highly fostered by the high concentra- tion of adsorbed hydroxyl groups at high pH values. hydroxyl radical attack.8 of bubbling the pure O2 . interacting with the positively charged CL0 catalyst surface. the reactional steps are favored. C0 = the oxygen concentration in the liquid phase on the pho- 100 mg/L. C0 = 100 mg/L. The importance of each one depends on tal values of the degradation of the dye show that there is the substrate nature and on the pH. The decolorization was studied in three cases: the first case was performed in the presence of atmospheric air by direct contact of the liquid surface with the atmosphere. These figures show that an 25 °C.4 rate of production of O−•2 radicals is favored. the experimen- conducting band. atmospheric air with direct contact of the liquid surface). solution at time t of illumination. The results of the reduced Figure 11: Temporal evolution of normalized residual pollutant concentration versus irradiation time are shown concentration of dye for various dissolved concentrations in Figure 12. over the range 15 °C to 55 °C. The third case consists 0. in the presence of todegradation process.0 increasing temperature [2]. The relationship (7) shows that CL0 − C30 the kinetic law of degradation of the dye is of first-order R(%) = ∗ 100. In fact.Journal of Advanced Chemical Engineering 5 where CL0 and C30 are the initial dye concentration and the dye concentration after 30 min of adsorption process (with- out irradiation).2 without bubbling of atmospheric air 3. This is confirmed by a better dye adsorption where Ct represents the concentration of the substrate in onto the catalyst surface observed at pH = 2 (see Figure 10). This behavior was probably due to the fact that the main reaction is represented by the hydroxyl radical attack. Con- sequently.0 second case by bubbling the atmospheric air through a tube that is introduced in the dye solution. . 45 and 55 °C) under the same other operating conditions.5 Effect of temperature with bubbling of atmospheric air with bubbling of pure O 2 Generally. The results of the initial rate versus temper- of oxygen (lamp 1. a linear relationship between the natural logarithm of the The significantly higher reaction rate found at pH = 2 Ct /CL0 ratio and time (see Figure 14): corresponding to the substrates disappearance can suggest Ct the occurrence of fast primary attacks by oxidant species − Ln = kt. T = ature are shown in Figure 13. Figure 11 shows that the bubbling of dye solution by pure O2 gives the best results and indi- 0. 0. (7) to the dyes strongly. In this work. the rates of photocatalytic reactions increase with 0. the yield of photocatalytic degradation is mostly affected by the pH value. a significant enhancement on the decolorization process of Solophenyl red at pH between 6. increase of the temperature leads to an increase in the rate of photocatalytic degradation of Solophenyl red 3 BL. CTiO2 = 1 g/L. we examine five values of temperature (15. ture increases the desorption of physical and chemical adsor- dation. the 1. T = 25 °C.4 Effect of oxygen Figure 10: Effect of initial pH on the initial rate of Experiments were carried out to determining the effect of decolorization of Solophenyl red 3 BL (lamp 1. the 0. CTiO2 = 1 g/L. (6) CL0 kinetics with respect to the concentration of the dye. 25. pH = 6. CL0 is the initial residual The adsorption ratio R is determined by expression (6): concentration (after adsorption) and k represents the appar-   ent rate constant (min−1 ).82). 35. Same. Also. 125 W) directly immerged T is the temperature [K] and k is the rate constant [M/s].82. pH = 6. while the rate of decolorization passes for 1. with continuous 1 g/L. and the lamp 2 (type HPK 125. C0 = 100 mg/L. the curve ln(k) versus 1/T (Figure 15) is estimated to Figure 16 shows that the efficiency of photocatalysis Ea = 31. from 24% (lamp 1) to 83% (lamp 2).6 Sensitive parameters for the growth of the degradation assumes that this variation obeys the Arrhenius relationship: rate of the dye 3.5 μE/s. C0 = 100 mg/L. (8) The influence of light intensity is determined by using two different lamps: the lamp 1 (Lamp Wood. CTiO2 = 1 g/L. Ea is the type Spot.6 Journal of Advanced Chemical Engineering C/CL0 Irradiation time (min) Figure 12: Temporal variation of normalized residual Figure 14: Variation of − Ln(C/C0 ) versus irradiation time concentration of dye for various temperatures (lamp 1.42 · 10−9 and 7. Figure 15: Variation of − Ln(k) versus inverse of tempera- with continuous bubbling of atmospheric air).6. Let us 3.1 Effect of light intensity k = k0 exp(−Ea/RT).521 mg/L·min in case of the first ties. the luminous The value of the activation energy deduced from intensity values of 4. Figure 13: Variation of initial rate versus different tempera- tures (lamp 1. R is the gas constant [J/mol.K]. The initial rate of photodegradation of Solophenyl tion energies obtained under different illumination intensi. and 18. C0 = for different temperatures (lamp 1. ture (lamp 1.82.8 kJ/mol lamp (lamp 2).30 · 10−9 Einstein/s. in the liquid in the vessel with.82. 13. reaction increases with increasing the incident light This value of the activation energy is higher than activa. air).566 mg/L·min in case of the second illumination was carried out with 4. C0 = 100 mg/L. 90 kJ/mol. CTiO2 = 1 g/L.82). pH = 6. CTiO2 = 100 mg/L. intensity. pH = 6. [2] when lamp (lamp 1) to 2.5 μE/s. at the end of . 100 W. where k0 represents the pre-exponential factor. red 3 BL goes from 0. B-100AP.6 kJ/mol was obtained by Bahnemann et al. The rate constant k increases with temperature. pH = 6. CTiO2 = 1 g/L. respectively. projection lamp) set at the outside of the reactor activation energy [J/mol]. with continuous bubbling of atmospheric bubbling of atmospheric air). The influence of temperature is noticeable H2 O2 is considered as having two functions in the pho- between 15 °C and 55 °C. the rate by varying the temperature level and addition of hydrogen of decolorization decreases due to its hydroxyl radical peroxide to increase the kinetics of degradation of the dye. of an aqueous suspension of anatase TiO2 . considera- 2 −→ OH + OH + O2 . Finally. the concentration of hydrogen peroxide it also forms OH• : should be optimized so as not to favoring the production of TiO2(e−) + H2 O2 −→ TiO2 + OH− + OH• . Experiments were conducted to evaluate the effect of addi- tion of H2 O2 (0. with oxygen concentration (for O−• 2 radicals formation) and nation (relation (2)).Journal of Advanced Chemical Engineering 7 Figure 16: Temporal variation of normalized residual Figure 17: Effect of addition of H2 O2 on the initial rate concentration for two different photoreactor systems. with temperature. The enhancement of decolorization by to the arrangement and geometry of the radiation to respect the addition of H2 O2 is due to an increase in the hydroxyl + to the irradiated solution. in the presence of the HPK 125 lamp.6. . hBV recombi. 60 min of photocatalytic process. T = 25 °C. CTiO2 = 1 g/L. When the H2 O2 concentration is higher.5 · 10−2 –5 · 10−2 mol/L) on the Solophenyl red photodegradation. (11) red 3 BL is dependent not only by the luminous intensity HO•2 + OH• −→ H2 O + O2 . The light intensity on scavenging effect. with continuous continuous bubbling of atmospheric air). the great difference obtained between the two lamps shows that the photocatalytic process of Solophenyl H2 O2 + OH• −→ H2 O + HO•2 . (12) but also by the geometry of optical field received by the dye solution. OH• : Moreover. T = 25 °C.83. the degra- H2 O2 also reacts with superoxide anion to form OH radical: dation rate is favored in acidic medium. bubbling of atmospheric air). However. (C0 = of decolorization of Solophenyl red 3 BL (lamp 2. (10) tion should be given to the deterioration in the natural state. the reported the beneficial effect of H2 O2 on the photocatalytic influence of radiation is not limited to the intensity but also degradation [17. The rate of degradation can be sig- tocatalytic degradation: it accepts a photogenerated conduc- nificantly increased by adding in the middle of the hydrogen tion band electron that promotes the charge separation and peroxide. the addition of the hydrogen peroxide can be 3. on the environmental plan. The degradation rate increases radical concentration since it inhibits the e− CB . however. (9) HO−• • 2 radicals at the expense of OH radicals whose oxida- tive activity is higher than the previous. The degradation Several researchers have obtained the same results and have rate depends on the intensity of UV radiation. with 100 mg/L. 4 Conclusions The results are shown in Figure 17 and indicate that decol- The study confirms that the degradation of Solophenyl red orization efficiency increases notably as the concentration 3 BL dye can be achieved by photocatalysis in the presence of H2 O2 increases and reaches an optimum at 10−2 mol/L. C0 = 100 mg/L. the semiconductor is favorable for creating positive hole the formed HO•2 is significantly less reactive than the formed and electron (relation (1)).10−2 mol/L) of H2 O2 . but in the case of H2 O2 + O−• − • industrial discharges. At high concentration (2. Ultimately. 22].2 Effect of the addition of H2 O2 very favorable provided to adjust its concentration in the production of hydroxyl radicals relatively to HO•2 radicals. CTiO2 = 1 g/L. pH = 6. Bianchi. and P. vol. Ollis. Pramauro. N. Duran. 881–886. Hoffmann. 280 (2004). 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