Use of Titanium Dioxide Photocatalysis on the Remediation of Model Textile Wastewaters Containing Azo Dyes (original) (raw)
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Photocatalytic Degradation of Textile Dyeing Wastewater Using Titanium Dioxide and Zinc Oxide
Photodegradation of a real textile dyeing wastewater taken from Hilla textile factory in Babylon Governorate, Iraq have been investigated. Photocatalytic degradation was carried out over suspensions of titanium dioxide or zinc oxide under ultraviolet irradiation. Photodegradation percentage was followed spectrophometrically by the measurements of absorbance at λmax equal to 380 nm. The rate of photodegradation increased linearly with time of irradiation when titanium dioxide or zinc oxide was used. A maximum color removal of 96% was achieved after irradiation time of 2.5 hours when titanium dioxide used at 303K and 82% color reduction was observed when zinc oxide used for the same period and at the same temperature. The effect of temperature on the efficiency of photodegradation of dyestuff was also studied. The activation energy of photodegradation was calculated and found to be equal to 21 ± 1 kJ mol -1 on titanium dioxide and 24 ± 1 kJ mol -1 on zinc oxide.
In this study, the photocatalytic degradation of textile wastewater from Gul Ahmad textile industry in Karachi, Pakistan, using TiO 2 , ZnO, and H 2 O 2 as photocatalyst was investigated. The experiments were carried out at 38 o C in astirrerbath reactor by using Ultra-Violet photo oxidation process. The degradation of wastewater using TiO 2 and ZnO under various pH and using TiO 2 and H 2 O 2 were examined. Titanium dioxideand zinc oxide proved to be very effective catalysts in photocatlytic degradation of real textile industrial water. The maximum decolorization achieved was 95.29% by using TiO 2 and 64.41% by using ZnO at 37 o C and pH of 9, within 150minutes of irradiations. At pH of 7.3 the maximum decolorization was 90.48%. When TiO 2 was combined with H 2 O 2 the maximum decolorization was about 86% but surprisingly within 50 minutes of the irradiation time. A higher reaction rate was found for Titanium dioxide. The results indicate that for real textile wastewater, TiO 2 is comparatively more effective than ZnO. This study proves that real textile wastewater reacts differently to catalysts than aqueous solution of azo-dyes, which is associated with surface steps and sensitization of the reaction rate by presence of other contaminants in real textile wastewater.
Decolouration of textile dyes in wastewaters by photocatalysis with TiO2
Solar Energy, 2005
The photocatalytic removal of colour of a synthetic textile effluent, using TiO 2 suspensions under solar radiation, has been studied at pilot plant scale. A synthetic dye solution was prepared by a mix of six commercial textile dyes. A photochemical reactor of parallel CPC reflectors with UV-transparent tubular receivers was used. The study of photodegradation was carried out using the TaguchiÕs parameter design method. Following this methodology, the reaction was conducted under different flow conditions, pH and H 2 O 2 concentrations. The results show that all dyes used in the experiences can be degraded successfully by photo-oxidation. The process shows a significant enhancement when it is carried out at high flows, alkaline media and high H 2 O 2 concentration. Colour removal from the effluent was reached at 55 min operating time.
Optimization of the photocatalytic degradation of commercial azo dyes in aqueous TiO2 suspensions
Reaction Kinetics, Mechanisms and Catalysis, 2014
The photocatalytic degradation of three textile azo dyes, Remazol Yellow Gold RGB, Remazol Blue RGB and Remazol Carbon RGB has been studied in model effluents regarding the variation of parameters as concentration of titanium dioxide (TiO 2 ), concentration of the dyes, effect of hydrogen peroxide (H 2 O 2 ), effect of pH, recycling of TiO 2 . The concentration of 1 g L -1 of TiO 2 degraded around 100 % of Remazol Blue RGB and Remazol Carbon RGB and around 90 % for the Remazol Yellow Gold RGB after 120 min of photodegradation. The remaining concentrations of added TiO 2 were found to be less efficient, except for Remazol Blue RGB, which still reaches about 80 % photodegradation, for 0.1 g L -1 of TiO 2 . The efficiency of photodegradation of all dyes decreased with an increase of the initial dye concentration. For a concentration of 30 mg L -1 , all dyes showed around 100 %. However, upon increasing the concentration of the dye until 150 mg L -1 , the photodegradation becomes very slow, with photodegradation rates off only 11 % for Remazol Yellow Gold RGB and Remazol Blue RGB and 9.7 % for the Remazol Carbon RGB. Photodegradation of the three dyes was found to be pH dependent. The maximum reaction rate was observed with 0.3 9 10 -3 mol L -1 120 min). At higher concentrations of H 2 O 2 , the degradation efficiency decreased significantly for all dyes. In what regards the reuse of the photocatalyst, the first cycle degraded 100 % of the Remazol Carbon RGB after 60 min of irradiation and the second and third cycles degraded 44 and 36 % of the dye. The effect of the simultaneous photodegradation of the three azo dyes in water was further investigated for distilled and natural lake water. It was observed that the degradation rates achieved in mono and three-component system were identical. The degradation yield in lake water observed to be smaller than in distillated water with 75, 72 and 53 % (99, 98 and 88 % in distilled water) of degradation for Remazol Blue RGB, Remazol Carbon RGB and Remazol Yellow Gold RGB, respectively.
Optimised photocatalytic degradation of a mixture of azo dyes using a TiO 2 /H 2 O 2 /UV process
Water Science & Technology, 2012
The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO2-P25. Response surface methodology, based on a 32 full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO2 (0.1–0.9 g/L) and H2O2 (1–100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO2/L and 50 mmol H2O2/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min−1. Based on these results, this photocatalytic process has promise as an alternative f...
Photochemical and photocatalytic degradation of an azo dye in aqueous solution by UV irradiation
Journal of Photochemistry and Photobiology A: Chemistry, 2003
The photochemical and photocatalytic degradation of aqueous solutions of Solophenyl Green (SG) BLE 155%, an azo dye preparation very persistent in heavy colored textile waters, has been investigated by means of ultraviolet (UV) irradiation. The pure photochemical process demonstrated to be very efficient for low initial concentrations of the dyestuff. For higher concentrations the photocatalyitic degradation was carried on using commercial titanium dioxide, and mixtures of this semiconductor with different activated carbons (AC) suspended in the solution. The kinetics of photocatalytic dyestuff degradation were found to follow a first-order rate law. It was observed that the presence of the activated carbon enhanced the photoefficiency of the titanium dioxide catalyst. Differently activated carbon materials induced different increases in the apparent first-order rate constant of the process. The effect was quantified in terms of a synergy factor (R) already described in the literature. The kinetic behavior could be described in terms of a modified Langmuir-Hinshelwood model. The values of the adsorption equilibrium constants for the organic molecules, K C , and for the reaction rate constants, k C , were 0.0923 l mg −1 and 1.58 mg l −1 min −1 for the TiO 2 /UV process and 0.0928 l mg −1 and 2.64 mg l −1 min −1 for the TiO 2 + AC/UV system with highest synergy factor, respectively. The mechanism of degradation was discussed in terms of the titanium dioxide photosensitization by the activated carbon.
Photocatalytic degradation of model textile dyes in wastewater using ZnO as semiconductor catalyst
Journal of Hazardous Materials, 2004
Rhodamine B (RhB), a dye widely used in the textile manufacturing, contributes with other dyes to harm the environment. Here, with the final goal to provide new tools for the removal of dyes from water, visible light activated carbon-doped titanium dioxide was used to investigate on the decolourization and the photocatalytic degradation of RhB dye from water solutions. The photodegradation activity was tested varying the initial concentration of RhB and the amount of carbon-doped titanium dioxide, taking into account the ratio between the amount of catalyst and the amount of RhB (TiO 2 /RhB), thus obtaining a parameter that allows the method to be scaled up without losing its effectiveness. Values of k 2 and t 0.5 were obtained by fitting kinetics data to a second-order kinetic adsorption model. The important role played by doped TiO 2 particles is demonstrated by the highly efficient color removal obtained during the visible light-induced photocatalysis. The presence of different degradation intermediates was demonstrated by means of UV-vis Absorption and Fluorescence spectroscopy. Such results underline that the whole photodegradation process does not end with the decolourization occurrence.
Journal of Photochemistry and Photobiology A: Chemistry, 2006
The degradation of three commercially available textile azo dyes, Solophenyl Green BLE 155% (SG), Erionyl Red B (ER) and Chromotrope 2R (C2R), has been studied by using photochemical and photocatalytic processes under UV irradiation. The adequacy of each process depends on the concentration of dye. At low dye concentration, the neat photochemical degradation is very efficient. The photocatalytic process, using either slurry of Degussa P-25 TiO 2 or a biphasic mixture of TiO 2 and activated carbon (AC), more effectively bleaches heavier colored solutions. The heterogeneous photocatalytic regime was characterized in terms of catalyst load, TiO 2 to AC mass ratio, initial dye concentration and oxygen partial pressure. Catalyst recovery and reuse was also analyzed. Based on the Langmuir-Hinshelwood approach, reaction rates and adsorption equilibrium constants were calculated. A positive effect on the photocatalytic degradation was observed by the addition of AC to TiO 2 catalyst, which was quantified in terms of a synergy factor (R). The efficiencies of different photo-induced degradation processes were compared based on the experimentally determined apparent rate constants, mineralization degrees and initial quantum yields.
Treatment of textile dyehouse wastewater by TiO2 photocatalysis
The oxidative degradation of an actual textile dyehouse wastewater was investigated by means of photocatalysis in the presence of TiO 2 . The UV-A-induced photocatalytic oxidation over TiO 2 suspensions was capable of decolorizing the effluent completely, as well as reducing chemical oxygen demand (COD) sufficiently (COD reduction generally varied between about 40% and 90% depending on the operating conditions) after 4 h of treatment. Two crystalline forms of TiO 2 , viz. anatase and rutile, were tested for their photocatalytic activity and anatase was found to be more active than rutile. The extent of photocatalytic degradation was found to increase with increasing TiO 2 concentration up to 0.5 g/L TiO 2 , above which degradation remained practically constant, reaching a plateau.