Thermal valorisation extracts of selected agro-waste for human pathogen antibacterial NiO nanoparticles synthesis

Abstract Waste management stays a challenge in developing countries. This research reports on the valorisation of agro-waste for the synthesis of nickel oxide nanoparticles (NiO NPs), useful as antibacterial agents to assure the sustainable use of renewable waste resources for human health protection. Agro-waste extracts from Persea americana seed, Zea mays silk and Eucalyptus globulus leaves were used as chelating agents in combination with nickel nitrate to synthesis NiO NPs. Optical, physical and chemical characteristics of synthesised NiO NPs were analysed by Ultraviolet spectroscopy studies (UV–VIS analysis), X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM); Fourier Transform Infrared analysis (FTIR) and Energy Dispersive X-Ray Spectroscopy (EDS), respectively. Antibacterial activity of each synthesised NiO-NPs was determined by cell culture in nutrient agar using well diffusion method. The UV–VIS results showed the formation of NiO NPs at wavelength range 300 – 400 nm. The XRD patterns demonstrated the crystalline form of the NiO NPs with a lattice face-centered cubic with average size of 14, 18 and 19 nm for NiO NPs from Persea americana seed, Zea mays silk and Eucalyptus globulus leaves, respectively. SEM images revealed the spherical, pleomorphism and nanosheet surface shape of the synthesised NiO NPs. Chemical elements K, P, Mg, Na, C and O were detected by EDS analysis as forming part of the elemental composition of the NiO NPs synthesised. Chemical bending between O–H, C–H, C–C and C-N was observed using FTIR. Furthermore, antibacterial studies showed the efficacy of all the NiO NPs synthesised against pathogen microbial growth with the largest inhibition zone (IZ) of 26 mm for the NiO NPs from Eucalyptus globulus leaves being observed. Therefore, Eucalyptus globulus leaves are recommended to synthesise NiO NPs for antibacterial applications.