Dye-containing wastewater generated from textile industries is a major source of environmental pollution. Azo dyes, which are the largest group of coloring agents, are widely used in industry.
Advanced Oxidative Processes are very promising for effluent treatment mainly due to their high efficiency and simplicity of operation. Our group became interested on photocatalytic methods (included in the AOP’s), using TiO2, for degradation of dyes, started with simpler structures and continued with commercial dyes. 
Titanium dioxide (TiO2) has proven to be the most effective and suitable catalyst for photocatalytic reaction due to its low cost economical, chemical stability, and insolubility.
In this paper, the effects of UV light irradiation in the presence of TiO2 particles at various pH’s (3, 6, 8 and 10) on the photodegradation of an azo dye, Reactive Red 158, were investigated. The photocatalytic degradation was carried out either in aqueous solutions or in a synthetically prepared dyebath effluent, under UV irradiation, in the presence of Degussa P25 TiO2 as the catalyst. Reactive dyes of the pyrimidinyl type partly hydrolyse during dyeing in basic medium; RR 158 was hydrolysed and this solution was also irradiated. The fastest degradation was obtained with an acid solution (14 minutes, 95.53% loss of colour), but the hydrolysed dye took longer to be decolourised

Campos, Ana M. F. Oliveira

Hrdina, Radim

Miranda, Teresa

Oldrich, Machalicky

Universidade do Minho: RepositoriUM

Photodegradation studies on C. I. reactive red 158

3rd INTERNATIONAL TEXTILE, CLOTHING & DESIGN CONFERENCE – Magic World of Textiles October 08th to 11th 2006, DUBROVNIK, CROATIA   1                                   PHOTODEGRADATION STUDIES ON C.I. REACTIVE RED 158  Teresa MIRANDA; Rosa ALVES; Lumir LICHY; Oldrich MACHALICKY; Radim HRDINA & Ana OLIVEIRA-CAMPOS    Departamento de Engenharia Têxtil, Universidade do Minho, Campus de Azurém, 4800-058, Guimarães   Portugal    Centro de Química, Universidade do Minho, 4710-057, Braga, Portugal    E-mail: tmiranda@det.uminho.pt  Abstract:   Dye-containing wastewater generated from textile industries is a major source of environmental pollution. Azo dyes, which are the largest group of coloring agents, are widely used in industry.  Advanced Oxidative Processes are very promising for effluent treatment mainly due to their high efficiency and simplicity of operation. Our group became interested on photocatalytic methods (included in the AOP’s), using TiO2, for degradation of dyes, started with simpler structures and continued with commercial dyes.  Titanium dioxide (TiO2) has proven to be the most effective and suitable catalyst for photocatalytic reaction due to its low cost economical, chemical stability, and insolubility.  In this paper, the effects of UV light irradiation in the presence of TiO2 particles at various pH’s (3, 6, 8 and 10) on the photodegradation of an azo dye, Reactive Red 158, were investigated. The photocatalytic degradation was carried out either in aqueous solutions or in a synthetically prepared dyebath effluent, under UV irradiation, in the presence of Degussa P25 TiO2 as the catalyst. Reactive dyes of the pyrimidinyl type partly hydrolyse during dyeing in basic medium; RR 158 was hydrolysed and this solution was also irradiated. The fastest degradation was obtained with an acid solution (14 minutes, 95.53% loss of colour), but the hydrolysed dye took longer to be decolourised.   Keywords: Photodegradation, Titanium dioxide, Decolourisation, Azo dye, Reactive dye, C. I. Reactive Red 158.  1. Introduction  More than 30.000 commercial dyes based on ca 8.000 different chemical structures are used in textile, food, pharmaceutical, paper and ink industries, and usually they are discharged in waste water [1].  The textile industry is the largest consumer of dyes (60%), using them in conjunction with a wide range of auxiliary reagents for various dyeing, printing and finishing processes. Irrespective of dye or fibre class, mill effluents are invariably deeply coloured by unabsorbed dyes, the extent of which varies according to the dye-fibre system [2]. Azo dyes, represent the most common dyes actually employed in textile industries, and a relevant problem is related to the presence of these products in the environment. By the year 2004, the forecast is that the use of reactive dyes will increase to about 50%. As a result of the chemical reactions involved in the fixation of reactive dyes to fabrics, as much as 20 to 50 % of the reactive dye can be released into waterways depending upon dyestuff type, the application route and depth of shade required.  Waste water derived from industrial plants that use dyes in their processes needs suitable treatments before its release in order to avoid dangerous increase of BOD and COD in rivers or in drainage areas. Moreover, effluent streams coming from textile plants contain toxic or carcinogenic residues together with their by-products. The treatments are focussed not only to solve the environmental impact but also to allow water and dyes reuse.  The effluents are usually treated by physico-chemical, oxidative or, most commonly, active sludge biochemical processes. The main drawback of the above processes is that they generally produce secondary pollution due to the introduction of chemicals and/or the possible accumulation of other bio-resistant species in the environment.   3rd INTERNATIONAL TEXTILE, CLOTHING & DESIGN CONFERENCE – Magic World of Textiles October 08th to 11th 2006, DUBROVNIK, CROATIA   2   Since azo dyes are intentionally designed to resist degradation, traditional methods such as flocculation, carbon adsorption, reverse osmosis and activated sludge process have low mineralization (i.e. conversion to inorganic species) efficiency for this class of xenobiotics. These alternative methods, such as activated carbon adsorption and dissolved air flotation, are not only costly, but result in phase transfer of pollutants.  As an alternative or an integration to the conventional processes, advanced oxidation technologies have been proposed. Bleaching of dyes has been carried out by using ozone [3], photo-Fenton type reactions [4] or a reduction followed by a photo-oxidation process [5]. They are generally referred to as advanced oxidation processes (AOP) [6]. The AOP processes involve the oxidation of organic pollutants by the combination of ultraviolet light, oxidants (H2O2, O3, etc) and/ or a catalyst (such as TiO2) and in most cases imply the generation of hydroxyl radicals and their subsequent reactions with pollutant molecules. This will remove the organic impurities by converting them into harmless inorganic products (CO2, H2O, etc). The combination of UV irradiation with photocatalysts such as TiO2 is one of such methods which has attracted considerable attention in recent years, due to its effectiveness in mineralization of organic compounds [1, 2, 6, 7]. TiO2 semiconductor is  a very good photocatalyst for the elimination of pollutants from air and water due to its low cost, chemical stability, nontoxicity, high photocatalytic reactivity and insobility. A further important advantage is the fact that the process can be powered by natural sunlight [8,9], thus reducing significantly the electrical power requirements and operating costs. It should be noted that with visible light, the photodegradation processes proceed by different routes, involving for example electron transfer from the excited state of the dye molecules adsorbed on the TiO2 surface into the conduction band of TiO2. Such processes are less efficient than those occurring with UV light [2].  For the photocatalytic oxidation (TiO2/UV) the semiconductor absorbs UV light and OH. radicals are generated mainly from the absorbed H2O and hydroxide ions. The mechanism of the TiO2/UV degradation has been described using the band-gap model [10]. It is well established that by irradiation of an aqueous TiO2 suspension with light energy greater than the band gap energy of the semiconductor conduction band, electrons and valence band holes are generated [6]. These will act as strong oxidising agents that can easily attack any organic molecules adsorbed on, or located close to, the surface of the catalyst, thus leading to their complete degradation into small inorganic species (Figure 1).                 TiO2 + hν              TiO2 (h+ + e-) (hν ≥ Eg = 3.2 eV; λ< 390 nm)              (1)                                 O2 + e-                 O2. -                                                                                                (2)                                    H2O  +    h+                  H+   +   OH.                                                                              (3)                                 OH.    +   RH                  H2O   +    R.                                                     (4)                                 R.       +   O2                             ROO.                                  CO2                                 (5)   Figure 1: Mechanism of the TiO2-catalysed UV oxidative degradation of organic species.  Our group became interested on photocatalytics methods for degradation of dyes, started with simpler azo dye structures (model dyes) [11], and continued with commercial dyes such as C.I. Reactive Red 2 [12], and C. I. Reactive Orange 4 in the last case studying a simulated dyeing bath as well [2].  Our previous studies on photocatalytic degradation of dyes with TiO2 [13], have now been extended to include the   important  reactive dye C. I. Reactive Red 158 (6). This dye is applied to cotton at about 50 ºC in the presence of common salt (sodium chloride or sulfate), and sodium carbonate (final pH 10,5-11). The present paper describes the effects of UV light irradiation in the presence of TiO2 particles on the photodegradation of an azo dye, Reactive Red 158 at various pH values (3, 6, 8 and 10). The photocatalytic degradation was carried either in aqueous solutions or in a synthetically prepared dyebath (only for cotton dyeing) effluent, under UV irradiation, in the presence of TiO2 as the catalyst. Reactive dyes of the pyrimidinyl type partly hydrolyse during dyeing in basic medium; RR 158 was hydrolysed and this solution was also irradiated.    3rd INTERNATIONAL TEXTILE, CLOTHING & DESIGN CONFERENCE – Magic World of Textiles October 08th to 11th 2006, DUBROVNIK, CROATIA   3                                                                                                                                               (6)  2. Experimental  2.1. Materials  A commercial sample of C.I. Reactive Red 158 (from Dystar) was used in this study, without further purification. The catalyst employed was technical grade TiO2 Degussa P-25. Additives for the preparation of simulated dyebath effluent were from Bayer (Diadavin ANE) and all other chemicals were of technical grade.  2.2. Apparatus  UV-vis spectra were recorded on a Unicam UV2 spectrophotometer.  UV irradiation experiments were carried out using an annular laboratory immersion UV Reactor System 2, Heraeus Noblelight was equipped with medium pressure arc mercury lamp Heraeus TQ 150 (efficiency ca 150 W).  2.3. Irradiation of dye solutions  The photocatalysis of Reactive Red 158 (0.2 g/L) was carried out in a UV reactor in the presence of TiO2 (0.4 g/L) in media of different pH (3, 6, 8 and 10) with a maximum irradiation time of 150 minutes at room temperature. The reaction mixture (800 mL) was vigorously stirred during irradiation. The starting reaction mixture was ca 20 min sonicated before use and kept 30 min conditioned in the dark under stirring to equilibrate. Samples of reaction mixtures (1 mL) were withdrawn diluted to 10 mL flasks, centrifuged and the absorption at 512 nm determined. For the rate determinations, calibration curves for the dye in water were obtained at λ max (512 nm) at pH values of 3, 6 (pH of distilled), 8, 10 and 11.2.     Table 1: Composition of the simulated dyebath effluent.  Component Concentration  Function Dye 0.019 g/L ----- NaCl 5 g/L Promotes exhaustion of  the dye onto cotton Na2CO3 1.5 g/L Adjustment of the final dyeing pH (10.5-11.0) to cause further ionisation of the cellulose and dye-fibre reaction Diadavin ANE 0,15 mL/L Detergent for washing off  Blank experiments were also conducted (without TiO2) under UV light irradiation.  Conversion of the reactive dye into its hydrolysed form was ensured by heating the solution at 50 ºC for 2 hours, in the presence of NaOH (0.03 M). The composition of the simulated dyebath (only for cotton dyeing) effluent and the function of the additives in the mixture are described in Table 1.    NNFFClHNNSO-OONSHNOSO- OOHOO-OO+Na+Li+Na3rd INTERNATIONAL TEXTILE, CLOTHING & DESIGN CONFERENCE – Magic World of Textiles October 08th to 11th 2006, DUBROVNIK, CROATIA   4  3.  Results and discussion  3.1. Influence of pH on decolourization of Reactive Red 158  Reactive dyes of the pyrimidinyl type partly hydrolyse during dyeing in basic medium, reacting with water or hydroxide ions, thus being part of the waste.   The degradation studies were performed in aqueous solutions of the dye, as marketed, at different pH values.   The pH dependence of the rate of decolourization for the dye solutions was examined by carrying out UV-irradiated experiments with TiO2 catalyst (0.4 g/L), at pH values of 3, 6, 8 and 10. The influence of pH on degradation of hydrolysed dye was also studied. The kinetic results are summarised in Figure 2.  0204060801001200 50 100 150 200Irradiation time (min.)Decolouration (%)pH=3pH=6pH=8pH=10pH=11.2, hydrolysed dye  Figure 2: Influence of pH on UV-induced decolourisation of dye in the presence of TiO2 (0,4 g/L).  The fastest degradation was obtained with an acid solution (14 minutes, 95.53% loss of colour), but the hydrolysed dye took longer to be decolourised. In the case of the pH=6, after the photolysis it was obtained a value of pH=2.2, which suggest that possibly acids, had already formed. In the case of the photocatalytic degradation of dye-only solution, without TiO2, at pH=6, the behaviour is similar, that is, after the photolysis it was obtained a value of pH=3.4.   3.2. Kinetic analysis  Initial decolourisation rate constants were determined from the slope of ln(C0/C) vs t (min) plots, where C0 and C are the dye concentration at zero time and time t, respectively.   In the experiments the degradation of the dye during the first 14 minutes of irradiation followed pseudo first order kinetics. Relevant first order rate constants are indicated in Table 2.  Table 2: Pseudo first order rate constants for the degradation of solutions of Reactive Red 158 (0.2 g/L).  Solutiona pH R2b K (min-1)c Aqueous 3 0.9405 0.3294 Aqueous 6 0.9853 0.0454 Aqueous 8 0.9806 0.0532  a “Aqueous” refers to a solution of the dye in water with no other additives. b Correlation coefficient of the straight line. C Pseudo first order rate constant determined for the first 14 minutes of irradiation.    3rd INTERNATIONAL TEXTILE, CLOTHING & DESIGN CONFERENCE – Magic World of Textiles October 08th to 11th 2006, DUBROVNIK, CROATIA   5  3.3. Photodegradation of simulated dyebath effluent  In an attempt to relate our present study to the real situation arising with effluent from the commercial dyeing of cotton with Reactive Red 158, it was decided to formulate a simulated spent dyebath and to test its response to photocatalytic decolourisation.  The rinsing and soaping processes which follow the reactive dyeing of cotton (namely the reactive red 158) result in a considerable dilution of the dyehouse effluent [14].  The results for the photocatalysed degradation reaction are presented in Figure 3.  01020304050607080901000 10 20 30 40Irradiation timeDecolouration (%)Simulated dyebath  Figure 3: Decolourisation (%) of the simulated dyebath effluent (pH=10,74, Dye 19mg/L, TiO2 0,4 g/L).  The simulated dyebath effluent shows to degrade reasonably fast. However it may be remembered that the relative concentration dye /catalyst is, in this case, lower than in the studies previously carried out.   3.  Conclusion  We have shown that photodegradation using UV light in conjunction with TiO2 is a promising method for degrading C. I. Reactive Red 158 either alone in water, or in it hydrolysed form in spent dyebath liquor.   The fastest degradation was obtained with an acid solution (14 minutes, 95.53% loss of colour), but the hydrolysed dye took longer to be decolourised. It may concluded that the photocatalytic method is feasible for dyehouse wastewater treatment. However further experiments must be carried out in order to obtain the best results.   References  [1] Molinari, R., Pirillo, F., Falco, M., Loddo V. & Palsimano, L.: Photocatalytic degradation of dyes by using a membrane reactor, Chemical Engineering and Processing, 43 (2004), pp.1103-1104. [2] Gonçalves, M., Pinto, E., Nkeonye, P. & Oliveira-Campos A.: Degradation of C. I. Reactive Orange 4 and its simulated dyebath wastewater by heterogeneous photocataysis, Dyes and Pigments, 64 (2005), pp.135-139. [3] Chen L.: Effects of factors and interacted factors on the optimal decolorization process of methyl orange by ozone, Water Res., 34 (2000), pp. 974-982.   [4] Bandara, J., Morrison, C. et al.: Degradation/decoloration of concentrated solutions of Orange II, Photochem. Photobiol., 99 (1996), pp. 57-66. 3rd INTERNATIONAL TEXTILE, CLOTHING & DESIGN CONFERENCE – Magic World of Textiles October 08th to 11th 2006, DUBROVNIK, CROATIA   6 [5] Feng, W., Nansheng, D.& Helin, H.: Degradation mechanism of azo dye C. I. reactive red 2 by iron powder reduction and photoxidation in aqueous solution, Chemosphere, 41 (2000), pp.1233-1238. [6] Hoffman, M. R., Martin, S. T. et al.: Environmental applications of semiconductor photocatalysis. Chem. Rev., 95 (1995), pp. 69-96. [7] Legrini, O., Oliveros, E. et al.: Photochemical processes for water treatment, Chem. Rev., 93 (1993) pp. 671-698. [8] Saquib, M. & Munner, M.: Semiconductor mediated photocatalysed degradation of an anthraquinone dye, Remazol Brilliant  Blue R under sunlight and artificial light source, Dyes and Pigments, 53 (2002), pp.237-249. [9] Augugliaro, V., Baiocchi, C. et al.: Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation, Chemosphere, 49 (2002), pp.1223-1230. [10] Bockelmann, D. & Shugui D.: Solar Thermal Energy Utilization, Springer-Verlag, Berlin, 1992. [11] Gonçalves M., S., T., Oliveira-Campos A.M. F. et al.: Photochemical treatment of solutions of azo dyes containing TiO2, Chemosphere, 39 (1999), pp. 781-786. [12] Gonçalves M., S., T., Oliveira-Campos A., M., F. et al.: Photocatalytic Treatment of C. I. Reactive Red 2, Sci. Pap. Univ. Pardubice Ser. A, 10 (2004), pp. 253-269. [13] Soares, G.M.B., Miranda T. M. et al.: Current Situation and Future Perpesctives for Textile Effluent Decoulorization, Proceedings ofThe Textile Institute 83rd World Conference, College of textiles, Donghua University (Ed.) pp. 745-749, ISBN 1870372611, Donghua University , May, Shanghai,  (2004). [14] Arlan, I. & Balcioglu, I. A.: Degradation of Remazol Black B dye and its simulated dyebath wastewater by advanced oxidation processes of heterogeneous and homogeneous media, Color Technol., 117 (2001), pp. 38-42.     Prof. Teresa MIRANDA, Ph.D.; Rosa AlLVES University of Minho, Textile Department Campus of Azúrem, 4800 Guimarães, Portugal Phone: +351253510272  Fax: +351253510293 E-mail: tmiranda@det.uminho.pt Prof. Ana Oliveira-Campos, Ph.D. University of Minho, Chemistry Department Campus of Azúrem, 4800 Guimarães, Portugal Phone: +(351)253604377  Fax:  E-mail: amcampos@quimica.uminho.pt  Prof. Radim HRDINA, Ph.D.; Oldrich MACHALICKY, Ph.D; Lumir LICHY University of Pardubice, Faculty of Chemical Studentská 95, 53210, Pardubice, Czech Republic Phone:  Fax:  radim.hrdina@upce.cz; oldrich.machalicky@seznaam.cz                       3rd INTERNATIONAL TEXTILE, CLOTHING & DESIGN CONFERENCE – Magic World of Textiles October 08th to 11th 2006, DUBROVNIK, CROATIA   7                

Photodegradation studies on C. I. reactive red 158

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Universidade do Minho: RepositoriUM

Universidade do Minho: RepositoriUM