The photocatalytic degradation of Toluidine Blue dye (TB) in aqueous solution was investigated under UV light in the presence of magnesium oxide (MgO) as a photocatalyst at different operating parameters. The operating conditions were photocatalyst dose, initial dye concentration and the pH of the solution. Increasing of photocatalyst dose from 10 to 70 mg enhanced the degradation rate of TB dye. However, the increasing of TB dye concentration from 2 to 8 mg/L negatively affected the degradation rate. It was found that the percent of dye removal reached the maximum value at high acidic medium. In dark condition, 15 % of dye was adsorbed by MgO. Furthermore, the kinetics involved in the degradation of TB dye was examined and the degradation was found to follow pseudo first order kinetic model.

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Zinc oxide (ZnO) has been used as heterogeneous catalyst for the degradation of Acid Alizarin Black S dye (AAB) in aqueous solutions using UV light irradiation. Experiments were conducted at various operating parameters. The operating parameters were amount of catalyst (50 mg, 100 mg and 150 mg), initial concentration of dye (30 mg/L, 50 mg/L and 70 mg/L), the pH of solution (2, 4, 6, 8, 10 and 12) and the UV light intensity (6 watt and 12 watt). The progress of the degradation reaction was monitored spectrophotometrically. It was found that the degradation process of AAB solution was accelerated with increased catalyst dosage and decreased initial concentration of AAB. It was also found that the removal efficiency of AAB significantly depend on pH value of solution. The results show that the degradation percent reaches the highest values with pH close to neutral. The data proved that removal percent of dye decreased when 6 watt lamp used instead of 12 watt lamp. The kinetic study confirmed that photocatalytic degradation of AAB dye follows a pseudo first order reaction rate.