Combined heterogeneous and homogeneous photodegradation of a dye using immobilized TiO ₂ nanophotocatalyst and modified graphite electrode with carbon nanotubes

In this paper, the efficiency of photoelectro-Fenton (PEF) combined with photocatalytic process was studied for decolorization of C.I. Acid Yellow 36 (AY36) as a model textile dye. The investigated photocatalyst was TiO ₂ nanoparticles (Degussa P25) immobilized on glass plates. The efficiency of three cathode materials (i.e. bare graphite, activated carbon immobilized onto graphite surface (AC/graphite) and carbon nanotubes immobilized onto graphite surface (CNT/graphite)) was investigated for H ₂O ₂ electrogeneration and dye removal. The CNT/graphite electrode fed with air had the best efficiency for H ₂O ₂ production and decolorization of AY36 solution. A comparison of electro-Fenton (EF), UV/TiO ₂, PEF, photolysis and PEF/TiO ₂ processes for dye removal was performed. Results showed that decolorization followed the decreasing order: PEF/TiO ₂ > PEF > EF > UV/TiO ₂ > photolysis. Central composite design (CCD) was employed to model and optimize the decolorization of dye solution using combined process. The variables for CCD optimization were initial concentration of Fe (III) and dye, reaction time and applied current. Analysis of variance (ANOVA) showed high coefficient of determination value (R ² = 0.9867 and adjusted-R ² = 0.9751). The degradation pathway of AY36 was proposed based on the identified compounds by GC-Mass technique. The unit energy demand (UED) and operating cost for photoelectrocatalytic process was evaluated.