Fungal-mediated synthesis of zinc oxide (ZnO) as mono-, bi- and tri-metallic nanoparticles for removal of malachite green

Abstract This study synthesized ZnO-based nanoparticles into mono- (ZnO), bi- (ZnO/Ag, ZnO/Fe), and tri-metallic (ZnO/Ag/Fe) forms, using extracts from Trichoderma asperellum to generate nanoparticles (NPs) for the removal of Malachite Green (MG) dye in aqueous solution. The NPs were characterized based on UV/Vis Spectroscopy, Field Emission Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy, Energy Dispersive X-Ray, Fourier Transform Infrared Spectroscopy, and Dynamic Light Scattering. Results revealed that fungal-mediated biosynthesis successfully produced typical ZnO-based NPs that were spherical-shaped with sizes from 13.89 to 31.28 nm. The biogenic nature of the NPs was validated by the detection of functional groups (N–H, –OH, –COOH, –CH) originating from fungal extracts. All ZnO-based NPs achieved more than 89% of removal efficiencies using only 2 mg of NPs, with multi-metallic forms considerably outperforming their mono-metallic ZnO counterparts. The adsorption by the NPs is likely via multi-layered chemisorption as evidenced by the Freundlich isotherm (R 2 = 0.9661–0.9937) and pseudo-second-order model (R 2 = 0.9899–0.9991). The maximum monolayer adsorption capacities of ZnO, ZnO/Ag, ZnO/Fe, and ZnO/Ag/Fe NPs were determined to be 142.86, 37.45, 42.55, and 33.22 mg/g, respectively. As such, adsorption of MG dye particles may have involved hydrogen bonding, π–π stacking, and electrostatic interactions. These findings underscore the potential of fungal-mediated ZnO-based NPs, especially tri-metallic forms, as promising adsorbents for removal of MG or other dyes, with possibilities as well for other hazardous pollutants.