This study presents the first evidence for the photocatalytic performance of ZnO/CuxO hexagonal nanowires leading to sulfamethazine (SMT) degradation. The chemical composition of the nanowires was determined by X-ray fluorescence (XRF). The sample with the composition ZnO/Cux=1.25O led to faster SMT-degradation kinetics. The SMT-degradation kinetics were monitored by high performance liquid chromatography (HPLC). The morphology of the hexagonal nanowires was determined by scanning electron microscopy (SEM) and mapped by EDX. The redox reactions during SMT degradation were followed by X-ray photoelectron spectroscopy (XPS). The interfacial potential between the catalyst surface and SMT was followed in situ under solar and indoor visible light irradiation. SMT-degradation was mediated by reactive oxidative species (ROS). The interfacial charge transfer (IFCT) between ZnO and CuxO is shown to depend on the type of light used (solar or visible light). This later process was found to be iso-energetic due to the potential energy positions of ZnO and CuxO conduction bands (cb). The intervention of surface plasmon resonance (LSPR) species in the SMT degradation is discussed.