Optimised photocatalytic degradation of a mixture of azo dyes using a TiO2/H2O2/UV process

The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO2-P25. Response surface methodology, based on a 32 full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO2 (0.1–0.9 g/L) and H2O2 (1–100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO2/L and 50 mmol H2O2/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min−1. Based on these results, this photocatalytic process has promise as an alternative for the treatment of textile effluents.