The search for innovative technologies to treat wastewater against the removal of heavy metals, microorganisms and pollutant organic compounds in aquatic environments arises as a dynamic branch of nanoscience. The use of hetero-nanocatalysts based on inorganic semiconductor crystals decorated with metal nanoparticles has attracted considerable interest for this application due to their synergistic interactions, which can improve the degradation process. In this work, we report a new and simple room-temperature method for preparing hetero-nanocatalysts based on a star-shaped zinc oxide (ZnO) crystals decorated with gold nanoparticles (GNPs) for enhanced degradation of an azo dye. The presence of thiourea during the precipitation of ZnO in alkaline conditions allowed the control of morphological features (e.g. average size and shape) and the surface functionalization with thiocyanate ions (SCN-). GNPs were deposited onto the ZnO surface by a photoreduction method and their average diameters (between 6-10 nm) could be easily controlled by changing the ZnO/HAuCl4 ratio. Also, when GNPs are prepared without removing the unadsorbed Au3+ ions before the photodeposition, GNPs grows with different sizes and shapes. The morphology and optical properties of the as-obtained pure and hybrid nanostructures were characterized by XRD, SEM, TEM, FTIR, UV-vis-NIR and PL. For the degradation studies, methylene blue (MB) was chosen as the model dye because of its wide range of utilization in industry (e.g. textile industry). Thus, the degradation of aqueous MB solutions was investigated by solar photocatalysis (samples were exposed to sunlight from 11 a.m. to 4 p.m. during the autumn of 2016 (April-May) under an average radiant exposure of 2900 kJ m−2 at the time of experiments), UV-A photocatalysis (using a photochemical reaction apparatus equipped with two black light fluorescent lamps (25 W, λ range = 320-400 nm)) and sonocatalysis (performed in dark conditions using a ultrasonic bath operating with at a fixed frequency of 35 kHz and 100 W ultrasound power). The degradation efficiencies of bare ZnO and hybrid ZnO/Au were estimated by UV/visible measurement. In all the cases, hybrid ZnO/Au particles presented the higher degradation efficiencies due the plasmon improved generation of reactive oxygen species (ROSs). Also, among the 3 methods, the photocatalysis performed under sunlight irradiation presented the higher rates of the dye degradation, which is interesting as it uses a clean, cheap and renewable energy.