Application of Ni-doped ZnO rods for the degradation of an azo dye from aqueous solutions

Ni-doped ZnO rods were applied as a photocatalyst for the degradation of an azo dye (Reactive Black 5). Effects of solution pH, catalyst dosage, initial RB5 concentration, H2O2 concentration, different purging gases, and type of organic compounds on the removal efficiency of RB5 were studied. Ni-doped ZnO rods were synthesized by co-precipitation method. Neutral pH was selected as an optimal pH condition due to a photo-corrosion of ZnO in acidic and basic conditions. Photocatalytic degradation efficiency of RB5 was increased as the catalyst dosage increased up to 1 g/L, while it was decreased by increasing initial RB5 concentration. Pseudo-first-order rate constant (k (obs) ) decreased from 0.122 to 0.0051 min(-1) and electrical energy per order (E (Eo) ) increased from 39.34 to 941.18 (kWh/m(3)) by increasing RB5 concentration from 5 to 100mg/L, respectively. Photocatalytic degradation efficiency of RB5 increased by increasing H2O2 concentration, but this trend was not observed above 10 mM. Photocatalytic degradation efficiency of RB5 increased in the presence of folic acid and citric acid while interference was observed in the presence of humic acid, EDTA, oxalic acid, and phenol. Photocatalytic activity was maintained even after five successive cycles.