N.Hadj Salah a,b, M.Bouhelassa a, B.David b, *

Available online at www.sciencedirect.com Physics Procedia 21 (2011) 115 121 Seventh International Conference on Material Sciences (CSM7) Photocatalytic Decoloration of Cibacron Green RG12, on TiO 2 Fixed on Mineral Supports by the PMTP Method N.Hadj Salah a,b, M.Bouhelassa a, B.David b, * a Université Mentouri- Constantine, Dpt. de Chimie Industrielle, Laboratoire LIPE, 25000 Constantine, Algérie b Université de Savoie, LCME, 73376 Le Bourget du Lac, France Abstract The aim of this study was to realize catalytic depositions of commercial titane dioxide on classic glass plates by the PMTP method, Previed Made Titanium Powder, and to characterize these deposits by MEB and DRX. As confirmed by SEM, three successive layers of photocatalyst are obtained on the glass plates in a quite homogeneous phase as well as it is confirmed that the anatase accounts for 75 % after the calcination treatment by the PMTP method. The photocatalytic reactivity is evidenced with the determination of the rate constants of degradation of the dye cibacron green RG12, used as target, on the fixed TiO 2 bed (0.010 min -1 ) compared to the direct photolysis in homogenous aqueous phase 0.001 min -1. Optimization of the process was explored by studying the dependence of the liquid flow rate and the absorption of photon by the photocatalyst on the kinetic rate constants of the dye photodegradation. 2011 Published by Elsevier B.V. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of the Organizer. Keywords : photocatalysis; deposed TiO 2 ; azo-dye. 1. Introduction Among dyes, azoic dyes are very useful chemicals for industrial activities such as paper and textile plants. So, a lot of dyes are ubiquitous in the environment, since about 15-20% of the world production of dye is estimated to be released into the environment [1-2], especially in water because plants use large volumes of water in wet processing operations. The depollution of water contaminated by dyes then remains a great challenge. The photocatalytic treatment is one of the well-known technical possibilities to eliminate the dyes from waters. It consists to the illumination of a photocatalyst solid having a band gap of 3.2 ev, mainly based on anatase TiO 2, which is dispersed in the aqueous phase of concern. A fluidized bed as well as a fixed bed can be used for this operation [3-4]. In the last decade, supported photocatalytic systems based on TiO 2 have been of growing interest for the water decontamination [5]. Works have been especially carried out on the nature of supports for the photocatalyst, on the type of deposition, the nature of the photocatalyst deposited and the design of the reactor. On the other hand fundamentals studies were also investigated. At the laboratory scale, it was shown that whatever the configuration of * Corresponding author. Tel.: +33 (0) 479 758 803; fax: +33 (0) 479 758 674. E-mail address: Bernard.david@univ-savoie.fr 1875-3892 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Organizer. Open access under CC BY-NC-ND license. doi:10.1016/j.phpro.2011.10.017

116 N.Hadj Salah et al. / Physics Procedia 21 (2011) 115 121 the reactor, the aqueous dispersion of the TiO 2 suspension always gives better yields in the photodegradation process than an immobilized TiO 2 on supports [6-7]. This is mainly due to the higher specific surface develops by the photocatalyst in suspension than when fixed on supports. However, this last process is very convenient since it allows to eliminate the constraining filtration step after treatment, inducing a cost decrease for industrial operations. 2. Materials and experimental procedures. 2.1 Chemicals Cibacron green T3G-E or reactive green 12 (C 60 H 29 Cl 3 N 16 NiO 21 S.6Na, molar mass 1837,7g) is a typical azoic dye, and belongs to the phthalocyanine chemicals. The photocatalyst TiO 2 P25 was provided by Degussa (75 % anatase, 25% rutile, 51 m 2 g -1 ) with crystallites of 20 nm diameter. 2.2 Analytical procedure Variation of Cibacron green was followed spectrophotometrically during the time course of the reaction, on a Shimadzu 160A UV-Visible spectrophotometer, at 616 nm, the maximum absorption band of the dye. DRX analysis was performed on a Philips PAN analytical (X Pert PRO-MPD). 2.3 Preparation of the TiO 2 supported material The different steps for the fixation of the photocatalyst on support by the PMTP method appear on scheme 1. Agitation of a TiO 2 suspension (4g/l) in UHQ water during 2h Support : glass plate Ultrasonic bath (2h) Deposition of TiO 2 on glass plate drying in the air (1h) and at 100 C (1h) Calcination at 475 C (4h) Scheme 1. PMTP method for the TiO 2 Degussa P25 fixation on glass plates (Ould-Mame et al., 2000). 2.4 Illumination process Irradiations were performed at 254 nm, with the reactor described on scheme 2, at room temperature. Scheme 2. Reactor with a recirculating bath. (1) UV protection system, (2) UV lamp at 254 nm at 8cm height from the solution to be treated, (3) bath (surface of 182.4 cm²) with the dye irradiated contaminated solution (200 ml), (4) glass plate supporting the TiO 2, (5) buffer volume (250 ml), (6) peristaltic pump.

N.Hadj Salah et al. / Physics Procedia 21 (2011) 115 121 117 3. Results and discussion The main characteristics of the glass plates prepared under calcination are presented in Table1. It is observed that the three successive layers fixed on the support can be considered as equivalent in mass deposited by unit surface. The operation is reproducible. Total number of layer 3 Order of the deposition Mass of TiO 2 fixed (mg) Mass/surface (mg/cm²) Cumulative mass (mg) 1 48 0.25 48 2 50 0.26 98 3 52 0.27 150 Table 1. Amount of TiO 2 fixed after three successive deposits. 3.1 Characterization of deposits 3.1.1. Morphology of the photocatalyst SEM analyses (Fig. 1) show that the homogeneity of the TiO 2 deposit on glass plates increases as the number of layer increases. Nevertheless, the total surface is not fully recovered by TiO 2. Phocatalytic grains appear irregular in form and size (diameter<10 μm). Voids still exist between grains after recovering of plates with three layers. As observed by Szczyrbowski, a thickness of about hundred of angstrom is sufficient to induce a good reactivity [8]. 3.1.2. Photocatalyst composition Fig. 1. Successive deposits of TiO 2 Degussa P25 by the PMTP method, with SEM observation. (a) one layer, (b) two layers, (c) three layers. The rutile titane dioxide is known to be thermodynamically stable, but also to have a low photocatalytic activity compared to the anatase phase [9]. The higher density of hydroxyl functions at the surface of anatase, allow to adsorb a great amount of water molecules inducing a higher photoreactivity towards the production of the very strong and not specific hydroxyl radical HO [10].

118 N.Hadj Salah et al. / Physics Procedia 21 (2011) 115 121 The irreversible transformation of anatase into rutile is got at about 700 C, far away from the calcinations temperature used in this study at 475 C [11]. The anatase phase after the treatment still appears as the predominant one for the TiO 2 P25, as with the starting material at 75%, and, 25% for the rutile phase as observed on Fig. 2. anatase rutile Fig. 2. Diffractogram of the TiO 2 Degussa P25 after deposition on glass plate. 3.2 Photocatalytic treatment of RG12 aqueous solutions First photolysis experiment, carried out without the supported TiO 2 in the reactor, showed that only 2% of the initial dye RG12 amount disappears in 2h. A contrario, 85% of RG12 is degraded within the same duration, in presence of the supported TiO 2 (three layers deposited) according to fig. 3. The efficiency of the fixed bed in then clearly demonstrated. 1 0,9 Photolysis 0,8 0,7 0,6 C/C 0 0,5 0,4 0,3 0,2 Photocatalysis 0,1 0 0 20 40 60 80 100 120 Time (min) Fig. 3. Comparison photolysis/photocatalysis with the TiO 2 Degussa P25 fixed on glass plate. Normalized concentration of RG12 vs time, at ph = 6.3, 25 C and with an initial concentration [RG12] 0 =10 ppm, a flow of 550 ml/min. A mechanical agitation is ensured in the bath at 350 rd/min.

N.Hadj Salah et al. / Physics Procedia 21 (2011) 115 121 119 In addition, the fixation of TiO 2 by means of the PMTP method is very good since 80 % of the initial amount of TiO 2 is recovered on the glass plate at the end of the reaction. The 20% mass loss observed corresponds to the transfer of the photocatalyst into the aqueous solution. These losses are expected to be reduced by decreasing the mechanical agitation speed in the bath. 3.3 Influence of the recirculation rate on the potocatalysis The flow of the dye-contaminated water in the reactor is important in the process since it is in close relationship with the duration time of RG12 exposed to UV radiation. The flows studied were in the range 324 to 787 ml/min. According to the kinetics of RG12 photodegradation, a first apparent order rate was obtained by using the following equation : Ln(C t /C 0 ) = -k.t, where C 0 and C t are the dye concentrations at initial time and time t, and, k is the experimental photocatalytic pseudo-first order rate constant. Results are given on Fig. 4. 0,012 0,01 0,008 k (min -1 ) 0,006 0,004 0,002 0 300 350 400 450 500 550 600 650 700 750 800 Flow (mlmin -1 ) Fig. 4. Pseudo first order rate constant of the RG12 photocatalytic degradation vs the flow rate of the RG12 aqueous solution on fixed bed, at 25 C, ph = 6.3 and with an initial concentration [RG12] 0 =10 ppm. As it can be observed, an optimum flow is got when the flow of the recirculation rate is 550 ml/min. 3.4 Influence of the initial dye RG12 concentration As it is often observed in photochemistry, the rate of photodepletion of pollutants increases as their concentration decreases. For high concentration the reaction rate is of zero order because of the full absorption of the photonic flux by the pollutant, whereas in case of dilute solution, this is a first order rate which occurs. Results listed in Table 1, show that in the concentration range studied (10 to 50 ppm), this is a typical dilute dye solution which is treated. Initial RG12 concentration (ppm) 10 30 40 50 k (min -1 ) 0.010 0.008 0.003 0.002 R² 0.993 0.986 0.983 0.936 Table 1. First apparent order rate constant of the RG12 photocatalytic degradation vs the initial concentration of RG12 in aqueous solution on fixed bed, at 25 C, ph = 6.3 at a optimum liquid flow of 550 ml/min. The classic interpretation of the photocatalytic phenomenon is done via the use of the Langmuir-Hinshelwood model b y plotting 1/k vs 1/[RG12] 0 [12]. Since R² = 0.78 for the previous plot (Fig.5), it means that initial

120 N.Hadj Salah et al. / Physics Procedia 21 (2011) 115 121 hypotheses are not all suitable, especially the fact that one species is adsorded on one kind of adsorption site and that Langmuir adsorption constants depend on dark and under illumination experiments [13]. A competition phenomenon of species formed during the dye degradation is expected to occur at the TiO 2 surface, which fits with the dashed curve of fig. 5 (work in progress). 500 400 1/k (min -1 ) 300 200 L-H model 100 0 0 10 20 30 40 50 60 [RG12] 0 (mgl -1 ) Fig.5. Langmuir-Hinshelwood (L-H) fitting (dashed plot, R²=0.774) leads to a negative intercept at the origin, not allowed by the model. Full layout could correspond to a competitive adsorption model, currently in progress. 4. Conclusion It has been shown that the dye RG12 can be efficiency degraded by means of a photocatalytic process using supported TiO 2 on glass plate. Three successive layers have been deposited by the PMTP method and characterized. No modification of the ratio anatase/rutile was observed after calcination at 475 C. Experimental parameters have been optimized, with a UV-lamp at 254 nm located at 8 cm from the solution to be treated and a optimal flow rate of 550 ml/mn, corresponding to a residence time of 22s for the illuminated dye. Kinetic approach of the dye photodegradation leads to conclude that the Langmuir-Hinshelwood is not well adapted to describe the phenomenon. A work on a competitive adsorption process of species at the TiO 2 surface is currently in progress in order to understand the kinetic behavior. References [1] A.A. Vaidya and K.V. Datye : Environmental pollution during chemical processing of synthetic fibers. In : Colourate 14 (1982), pp. 3-10 [2] J. T. Spadaro, L. Isabelle, V. Renganathan : Hydroxyl radical mediated degradation of azo dyes: evidence for benzene generation. In : Environ. Sci. Technol. 28 (1994), pp 1389-1393 [3] M.R. Hoffmann, S.T. Martin, W. Choi, D.W. Bahnemann : Environmental Applications of Semiconductor Photocatalysis. In : Chemical Reviews, 95, 1 (1995), pp 69-96 [4] D.F. Ollis, E. Pelizzetti, N. Serpone : Destruction of water contaminants. In : Environ. Sci. Technol. 25 (1991), pp 1523-1529 [5] S.M. Ould-Mame, O. Zahraa et M. Bouchy : Photocatalytic degradation of salicylic acid on fixed TiO 2 - Kinetic studies. In : Int. J. Photoenergy 2 (2000), pp 59-66 [6] M. Bideau, B. Claudel, C. Dubien, L. Faure and H. Kazouan : photocatalytic oxidation of spent waters. In : J. Photochem. Photobiol. A 91 (1995), pp 137-144 [7] Roberto L. Pozzo, Miguel A. Baltanás and Alberto E. Cassano : Supported titanium oxide as photocatalyst in water decontamination: State of the art. In : Catalysis Today, 39, 3 (1997), pp 219-231

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