Due to their extensive range of applications, the existence of notable amounts of reactive dyes in wastewater raises the need for more efficient treatment techniques. The present work investigates the removal of Reactive Black 5 (RB5) azo dye by homogeneous advanced oxidation processes (photo-Fenton) and heterogeneous advanced oxidation processes (ZnO nanoparticle / UV). The Synthesized ZnO nanoparticles (NPs) were characterized using Fourier transforms infrared (FTIR), transmission electron microscopy (TEM), Scanning electron microscope (SEM), X-ray diffraction (XRD), UV–Vis spectroscopy, and the photoluminescence (PL). The formation of ZnO NPs was confirmed by FTIR with a broad band at 420.50 cm−1. TEM analysis shows that the synthesized ZnO NPs particle size ranged between 19.1 and 33.1 nm. The ZnO NPs hexagonal phase was observed from XRD analysis. Photo-Fenton (FeSO4.7H2O/ UV/H2O2) showed high decolorization rate of RB5 reached 98% within the first 5 min. While ZnO NPs showed lower decolorization rate during the same period. The effects of FeSO4.7H2O initial dosage, RB5 initial concentrations, ZnO initial dosage and contact time were investigated as well.