Zinc oxide (ZnO) nanoparticles (NPs) were synthesized by a conventional method using Pithecellobium dulce peel extract. The phytochemicals present in the peel act as stabilizing agents. The ZnO NPs were characterized by UV–vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. The XRD pattern confirmed the formation of crystals, which exactly matched with JCPDS card no.36–1451. The nondestructive XRD pattern showed a hexagonal crystalline nature and scanning electron microscopy revealed a spherical shape. Further, the ZnO NPs exhibited excellent photodegradation efficiency with regard to the dye methyleneblue (MB), a major water pollutant released by the textile industry. A kinetic study of photodegradation of MB showed 63{\%} degradation and a rate constant of 0.00812 min−1. The antifungal activity of the ZnO NPs resulted in 37.81{\%} and 63.57{\%} inhibition of the growth of Aspergillus flavus and 40.21{\%} and 43.04{\%} of growth inhibition of Aspergillus niger at 500 and 1000 ppm of ZnO NPs, respectively.