Photoelectrocatalytic decolorization of diazo dye by zinc oxide nanophotocatalyst and carbon nanotube based cathode: Determination of the degradation products

Response surface methodology (RSM) involving five-level central composite design (CCD) was employed to model and optimize the decolorization of a dye solution containing C.I. Direct Yellow 12 (DY12) using photoelectro-Fenton (PEF) combined with photocatalytic process. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was ZnO nanoparticles, having specific surface area (BET) 32.23 m²/g, and mean crystal size 15nm, immobilized on glass plates. The variables for CCD optimization were initial amount of Fe(III), initial concentration of the dye, reaction time and applied current in PEF/ZnO process. Analysis of variance (ANOVA) showed a high coefficient of determination value (R²=0.962 and adjusted-R²=0.929) and satisfactory prediction second-order regression. Graphical response surface and contour plots were used to locate the optimum point. The result of optimization showed that color removal efficiency presented the maximal result (98%) at the optimal condition of initial amount of Fe(III) 0.2mM, initial dye concentration 50mg/l, reaction time 70min and applied current 400mA. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 96.7% mineralization of 50mg/l dye at 6h using PEF/ ZnO process. GC-MS analysis verified the identity of intermediates.