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A detailed investigation of photocatalytic degradation of Acid Yellow 36 (AY36) has been carried out in aqueous heterogeneous medium containing ZnO as photocatalyst in a batch reactor. The effects of some parameters such as pH, catalyst loading, and ethanol concentration were examined. Solutions with initial concentration of 50 mg L−1 of dye, within the range of typical concentration in textile wastewaters, were treated at natural pH of 6.93 and catalyst concentration of 1 g L−1 after 180 min irradiation. Investigations on the active species indicated that hydroxyl radicals play the major role in the process. Experiments showed that the most efficient pH on the removal of the dye with photocatalytic degradation process was 8; however, acidic pH was favored for the dark surface adsorption. Electrical energy consumption per order of magnitude for photocatalytic degradation of AY36 has been also determined.

A detailed investigation of photocatalytic degradation of m-cresol purple (mCP) dye has been carried out in aqueous heterogeneous medium containing zinc oxide (ZnO) as the photocatalyst in a batch reactor. The effects of some parameters such as amount of photocatalyst, dye concentration, initial pH of solution, ethanol concentration and temperature were examined. The most efficient pH in removal of the dye with photocatalytic degradation and dark surface adsorption processes was observed to be 8. The adsorption constant calculated from the linear transform of the Langmuir isotherm model was similar to that obtained in photocatalytic degradation at pH = 8; hence, the Langmuir–Hinshelwood model was found to be accurate for photocatalytic degradation at this pH. Dark surface adsorption and degradation efficiency were increased by enhancement in the temperature at the optimum pH of 8 and the apparent activation energy (Ea) for the photocatalytic degradation of mCP was determined as 14.09 kJ/mol at this pH. The electrical energy consumption per order of magnitude (EEO) for photocatalytic degradation of mCP was also determined.

In this study, the photocatalytic degradation of azo dye “Food Black 1” (FB1) was investigated using TiO2 and ZnO nanoparticles under ultraviolet (UV) light. The performances of the two photocatalysts were evaluated in terms of key parameters (e.g., decolorization, dearomatization, mineralization, and detoxification of dye) in relation to variables including pre-adsorption period, pH, and temperature. Under acidic conditions (pH 5), the ZnO catalyst underwent photocorrosion to increase the concentration of zinc ions in the system, thereby increasing the toxic properties of the treated effluent. In contrast, TiO2 efficiently catalyzed the degradation of the dye at pH 5 following the Langmuir–Hinshelwood (L–H) kinetic model. The overall results of this study indicate that the decolorization rate of TiO2 on the target dye was far superior to ZnO (i.e., by 1.5 times) at optimum catalyst loading under UV light.

The present investigation showed that the indicator dye m-cresol purple (mCP) was degraded in a laboratory scale, undivided electrolysis cell system. A platinum anode was used for generation of chlorine in the dye solution. The influence of supporting electrolyte, applied voltage, pH, initial dye concentration and temperature were studied. The ultraviolet-visible spectra of samples during the electrochemical oxidation showed rapid decolorization of the dye solution. During the electrochemical degradation process, dye concentration and current were measured to evaluate the energy consumption and current efficiency. After 10 minutes of electrolysis, a solution containing 20 mg/L mCP showed complete color removal at a supporting electrolyte concentration of 1 g/L NaCl, initial pH 6.7, temperature 25 °C and applied voltage 5 V; however, when pH was kept at 6.7, a higher rate constant was observed. There was good fit of the data to pseudo-first-order kinetics for dye removal in all experiments. Dependence of the decolorization rate on the initial mCP concentration can be described as roα[mCP]o−0.98. The apparent activation energy for the electrochemical decolorization of mCP was determined to be −6.29 kJ/mol.

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