Antifungal and photocatalytic potentials of zinc oxide nanoparticles synthesized using various fruit peel aqueous extracts

Banana (Musa spp), mango (Mangifera indica) and pineapple (Ananas comosus) 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 °C 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 to 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 Aspergillus 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 Aspergillus 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 efficiency over three regeneration cycles.