S. Sakthivel

SOLAR PHOTOCATALYTIC DEGRADATION OF AZO DYE: COMPARISON OF PHOTOCATALYTIC EFFICIENCY OF ZNO AND TIO2

Abstract The photocatalytic activity of commercial ZnO powder has been investigated and compared with that of Degussa P25 TiO2. Laboratory experiments with acid brown 14 as the model pollutant have been carried out to evaluate the performance of both ZnO and TiO2 catalysts. Solar light was used as the energy source for the photocatalytic experiments. These catalysts were examined for surface area, particle size and crystallinity. The effect of initial dye concentration, catalyst loading, irradiation time, pH, adsorption of acid brown 14 on ZnO and TiO2, intensity of light and comparison of photocatalytic activity with different commercial catalysts were studied. The progress of photocatalytic degradation of the acid brown 14 has been observed by monitoring the change in substrate concentration of the model compound employing HPLC and measuring the absorbance in UV–Visible spectrophotometer for decolourisation. The photodegradation rate was determined for each experiment and the highest values were observed for ZnO suggesting that it absorbs large fraction of the solar spectrum and absorption of more light quanta than TiO2. The complete mineralisation was confirmed by total organic carbon (TOC) analysis, COD measurement and estimation of the formation of inorganic ions such as NH4+, NO3−, Cl− and SO42−.

Solar/UV-induced photocatalytic degradation of three commercial textile dyes

The photocatalytic degradation of three commercial textile dyes with different structure has been investigated using TiO(2) (Degussa P25) photocatalyst in aqueous solution under solar irradiation. Experiments were conducted to optimise various parameters viz. amount of catalyst, concentration of dye, pH and solar light intensity. Degradation of all the dyes were examined by using chemical oxygen demand (COD) method. The degradation efficiency of the three dyes is as follows: Reactive Yellow 17(RY17) > Reactive Red 2(RR2) > Reactive Blue 4 (RB4), respectively. The experimental results indicate that TiO(2) (Degussa P25) is the best catalyst in comparison with other commercial photocatalysts such as, TiO(2) (Merck), ZnO, ZrO(2), WO(3) and CdS. Though the UV irradiation can efficiently degrade the dyes, naturally abundant solar irradiation is also very effective in the mineralisation of dyes. The comparison between thin-film coating and aqueous slurry method reveals that slurry method is more efficient than coating but the problems of leaching and the requirement of separation can be avoided by using coating technique. These observations indicate that all the three dyes could be degraded completely at different time intervals. Hence, it may be a viable technique for the safe disposal of textile wastewater into the water streams.

Solar light induced and TiO2 assisted degradation of textile dye reactive blue 4.

Aqueous solutions of reactive blue 4 textile dye are totally mineralised when irradiated with TiO2 photocatalyst. A solution containing 4 x 10(-4) M dye was completely degraded in 24 h irradiation time. The intensity of the solar light was measured using Lux meter. The results showed that the dye molecules were completely degraded to CO2, SO4(2-), NO3-, NH4+ and H2O under solar irradiation. The addition of hydrogen peroxide and potassium persulphate influenced the photodegradation efficiency. The rapidity of photodegradation of dye intermediates were observed in the presence of hydrogen peroxide than in its absence. The auxiliary chemicals such as sodium carbonate and sodium chloride substantially affected the photodegradation efficiency. High performance liquid chromatography and chemical oxygen demand were used to study the mineralisation and degradation of the dye respectively. It is concluded that solar light induced degradation of textile dye in wastewater is a viable technique for wastewater treatment.

Photocatalytic decomposition of leather dye: Comparative study of TiO2 supported on alumina and glass beads

Abstract TiO 2 supported on alumina and glass beads were prepared and their photocatalytic activities were determined by photo-oxidation of commercial leather dye, Acid brown 14 in aqueous solution illuminated with solar light. The progress of photocatalytic degradation of the Acid brown 14 was studied by monitoring the change in the concentration of the dye employing HPLC and measuring the absorbance with UV–Vis spectrophotometer for decolourisation. The photodegradation rate was determined for each experiment and the highest efficiency was observed for TiO 2 supported on alumina beads suggesting that the dye molecules are adsorbed on the alumina supports to make high concentration environment around the loaded TiO 2 . The effect of pH on the rate of degradation was followed in the pH range 3–11. Acidic pH range was found to favour the degradation rate. Comparative study of different advanced oxidation methods applied to degrade Acid brown 14 in aqueous solution was made and solar light/TiO 2 /Fenton system was found to be very effective.

Degradation of textile dye by solar light using TiO2 and ZnO photocatalysts

Abstract The photocatalytic degradation of a textile dye, reactive red 2 in presence of sunlight using TiO2 and ZnO as photocatalysts is reported. The experimental studies have indicated complete decolourisation of the dye in a short period and degradation within 8 hr of irradiation. ZnO was found to be more effective in the removal of colour than TiO2, but the degradation efficiency was found to be more with TiO2. ZnO decomposes on prolonged irradiation while TiO2 is not photocorrosive. The percent degradation of the dye is high for both the catalysts at an optimum concentration of the catalysts. The first order rate constant is found to increase with decreasing dye concentration.

Photocatalytic degradation of textile dye commonly used in cotton fabrics

UV light induced degradation of textile dye, reactive red M5B has been carried out on TiO2 and ZnO semiconductor particles. Spectrophotometer and COD techniques have been used to elucidate the details of dye decolourisation and degradation. The experiments have been carried out with different amount of catalyst, various concentration of dye solution, different irradiation time and in the presence of air. The reactive red M5B has been degraded to colourless end products. The results suggest that the photocatalytic degradation of textile dye may be a viable method for the safe disposal of wastewater.

KINETICS OF PHOTOCATALYTIC DEGRADATION OF REACTIVE YELLOW 17 DYE IN AQUEOUS SOLUTION USING UV IRRADIATION

In this paper photoinduced degradation of reactive yellow 17 (RY 17) dye has been studied employing TiO2 in the form of slurry in a batch reactor. UV lamps were used as the source for irradiation. The disappearance of the dye in the solution follows approximately pseudo-first order kinetics. The apparent rate constant decreases with increase in initial concentration of the dye. The addition of oxygen, hydrogen peroxide and persulphate ion influences the degradation rate of the dye. The formation of CO2, SO4 2−, NO3− and NH4+ions have been identified in the mineralisation process. The decolourisation and mineralisation were followed by UV-Visible spectrophotometer and high performance liquid chromatography respectively. The results reveal that photocatalytic degradation may be a useful technique in the removal of reactive dyes in wastewater from textile industries.