Rate of Photocatalytic Degradation of Acid Orange 7 Azo Dye on TiO2 Coated Layers: Role of pH and Initial Dye Concentration

Abstract

This paper examined the role of pH and initial dye concentration on the rate of Acid Orange 7 photocatalytic degradation. A batch mode plate photocatalytic reactor fitted with a TiO2 coated layer of dimensions (10cmí—15cm) immobilized on microscopic glass was used. The coated layer was prepared by sedimentation from an aqueous suspension of 5 g.L-1 phase and annealed at 300°C. Polychromatic sun beds lamps were used as a source of Ultra Violet (UV) light with maximum intensity at wavelength λ= 365 nm. An appropriate dye solution flow rate of 50 lit/hr was used. A UV-Vis spectrophotometer monitored changes in dye concentrations at λ_max= 485 nm. From changes in dye concentration during irradiation the rate of photocatalytic degradation was determined. The findings reveal that pH range 5 to 9 the degradation rate is almost constant, for pH values lower than 5 it marginally increases while for pH values above 9 it significantly decreases. Additionally the degradation rate increased significantly with increasing initial dye concentration in the range from (1í—10-5 mol.L-1 to 8í—10-5 mol. L-1). The amount of adsorbed Acid Orange 7 increases with increased dye concentration, however for concentrations greater than 1í—10-4 mol. L-1 it was observed that the increase was marginal. The findings confirm a direct correlation between the amount of dye adsorbed and resultant degradation rate. The optimum pH and initial dye concentration were determined ;[( pH= 3, r=1.6í—10-7 mol.m-2.s-1); (initial concentration = 8í—10-5 mol.L-1 to 1í—10-4 mol.L-1, r= 3í—10-7 mol.m-2.s-1)]. A shift in dye solution pH from acidic to basic in the range 3 to 11.5 reduced photocatalytic degradation rates by 56.3%.