Green synthesis of cerium oxide nanoparticles from turmeric and kinds of honey: Characterisations, antioxidant and photocatalytic dye degradation activities

The environmentally compatible and cost-effective green synthesis of cerium oxide nanoparticles (CeO2-NPs) was performed starting from bioactive natural materials, i.e., blossom, pine, chestnut honey, and turmeric extracts. The sizes, surface charges, morphologies, band gap energies, antioxidant, and photocatalytic activities of the synthesised nanoparticles were examined comparatively. The x-ray diffraction (XRD) studies confirmed the crystallinity and purity of CeO2-NPs. Transmission electron microscope (TEM) images indicated that the CeO2-NPs synthesised have spherical shapes. Particle sizes of honey originated NPs changed as 1.23, 2.61, 3.02 nm for the blossom, chestnut, and pine honey, respectively. NPs obtained from turmeric extract had 6.08 nm particle size. The isoelectric points of CeO2-NPs were about 4 when the starting material was blossom and pine honey. For the chestnut honey and turmeric as starting material, the isoelectric points of NPs were about 6 and 9.5, respectively. The band gap energies changed between 2.80-3.21 eV. All green synthesised nanoparticles exhibited high antioxidant activities according to the DPPH method, changing between 32.4 and 64.5 μg ml-1 as IC50 values. Activity values increased in the order of blossom, pine, chestnut honey, and turmeric. All synthesised NPs reflected the literature antioxidant rankings of the starting natural materials. Thanks to the strong redox property of the CeO2-NPs, high degradation efficiencies (between 83.9 and 93.4%) were obtained for MB under UV light irradiation. The natural starting materials used created differences in the physical and activity properties of the NPs. Green synthesis of CeO2-NPs with new natural materials will expand their usage areas.