Photodegradation of Hazardous Dye Naphthol Yellow S Over Titanium Dioxide

The present study involves the photocatalytic degradation of a hazardous dye Naphthol Yellow S, employing heterogeneous photocatalytic process. Photocatalytic activity of semiconductor such as anatase titanium dioxide (TiO2) has been investigated. An attempt has been made to study the effect of process parameters viz., amount of catalyst, concentration of dye, temperature, electron acceptor hydrogen peroxide (H2O2) and pH on photocatalytic degradation of Naphthol Yellow S. The experiments were carried out by irradiating the aqueous solutions of dyes containing photocatalysts with ultraviolet (UV) light. The rate of decolorization was estimated from residual concentration spectrophotometrically. The degradation rate of Naphthol Yellow S was high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. The results obtained from the experiments after adding H2O2/TiO2 show that maximum decolorization rate is achieved by the combination of (UV+TiO2+H2O2). The decolorization efficiencies are 2.6%, 34.8%, 70.2%, and 95.3% in the runs UV, UV+H2O2, UV+TiO2, and (UV+TiO2+H2O2) after approximately 40 minutes illumination periods, respectively. The optimum experimental conditions for the degradation of the dye are dye concentration 8 x 10(-5) M, pH 5.4, and 12 mg catalyst dose. At the used experimental conditions the substrate photooxidation rate follows pseudo-first order kinetics. The adsorption trends of Naphthol Yellow S at various initial concentrations followed the Langmuir isotherm trend. Measuring chemical oxygen demand (COD) also monitors the toxicity of the degraded dye solution and a significant decrease is observed, which implies the photodegradation through TiO2 a safer technique. Results show that the employment of efficient photocatalysts and the selection of optimal operational parameters may lead to complete decolorization and to substantial decrease of the chemical oxygen demand (COD) of the dye solutions.