Antifungal and Photocatalytic Potentials of Zinc Oxide Nanoparticles Synthesized Using Various Fruit Peel Aqueous Extracts

Banana ( Musa spp ), mango ( Mangifera indica ) and pineapple ( Ananas comosos ) peel aqueous extracts were employed to synthesize zinc oxide nanoparticles (ZnONPs), namely; ZnO-BPE, ZnO-MPE and ZnO-PPE, respectively. A reference sample, ZnO-ppt (without fruit peel extract) was also synthesized by simple precipitation. These were calcined at 500 ºC and characterized using x-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), UV-visible spectroscopy (UV-VIS), Brunauer-Emmett-Teller (BET), Thermogravimetric analysis (TGA/DTG), scanning electron microscopy-electron dispersive x-ray (SEM-EDX) and Transmission electron microscopy (TEM) techniques. The XRD of the samples revealed a hexagonal wurtzite crystalline structure typical of ZnONPs, with the Debye Scherrer’s crystallite sizes ranging from 21-38 nm. FTIR spectra of the samples showed Zn-O vibration bands at ~521 cm ^-1 while the UV-vis showed a narrow band gap in the range of 2.41-2.85 eV, and good UV light absorption in all the samples. The SEM images showed significant differences in the morphology of the samples, including spherical-hexagonal shape for the ZnO-ppt sample, and flower-like shaped particles for the ZnO-MPE. Antifungal assay showed that all the samples are active against Trichosporon sp and Aspergilus niger isolates. Highest zones of inhibitions were obtained for the ZnO-MPE against Trichosporon sp. , while the ZnO-PPE sample showed the lowest MIC of 62.5 µg/ml against Aspergilus niger . Photodegradation potential of the samples against 10 ppm methylene blue solution showed 73-91 % degradation under UV-light irradiation. The best performing photocatalyst, ZnO-MPE, sustained its degradation efficiency over three regeneration cycles.