Plant-mediated routes for synthesising metal oxide nanoparticles are gaining tremendous attention due to the benefits of the technique: simplicity, cost-effectiveness, and eco-friendliness. We compared the properties of zinc oxide nanoparticles (ZnONPs) made from aqueous leaf extracts of Chromolaena odorata and Manihot esculenta, both of which are abundant on the African continent. The phytochemical composition of the extracts was first assessed using gas chromatography-mass spectrometry (GC-MS) to determine the types of biomolecules involved in the reducing and capping processes that result in ZnONP formation. After that, UV-Vis spectrophotometry, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, X-ray diffractometry, and Fourier transform infrared spectroscopy (FTIR) were used to study ZnONP formation, morphological characteristics, elemental composition, shape and size properties, and phase composition. The ZnONPs made with Chromolaena odorata leaf extract had a better distribution of spherical and hexagonal forms, with an average particle size of 42.35 nm. The ZnONPs made with Manihot esculenta leaf as a reductant had a particle size of 14.71 nm on average and were more agglomerated with poor particle distribution. Phytosterols were shown to be the most important biomolecules in the reduction and capping reactions, according to GC-MS and FTIR analyses. In this study, we created a cost-effective technique for the synthesis of eco-friendly ZnONPs for diverse applications, particularly in Africa, using Chromolaena odorata and Manihot esculenta leaves.

Characterisation of ZnO nanoparticles prepared using aqueous leaf extracts of Chromolaena odorata (L.) and Manihot esculenta (Crantz)

**Materials**

The Chromolaena odorata and Manihot esculenta leaves utilised in this study were obtained from a bush near Bells University of Technology in Ota, Ogun State, Nigeria, and their identities were confirmed at the University of Lagos’ Botany Department. Sigma-Aldrich (Gillingham, UK) provided the reagents utilised, which included Zn(NO3)2.6H2O and absolute ethanol.

**Preparation of the aqueous leaf extracts**

Dust and particle contaminants were removed from the leaves of Chromolaena odorata and Manihot esculenta by washing them first with tap water and then with deionised water to prepare the extracts. They were then dried in the sun and ground into fine granules to speed up the extraction process. Each powdered sample (24 g) was combined separately with 250 mL deionised water, sealed, and heated in a water bath for 15 min. The combinations were then cooled to ambient temperature and filtered to yield the aqueous extracts, which were then stored at 5–10 °C in the refrigerator for later use.

**Synthesis of ZnONPs**

The Chromolaena odorata and Manihot esculenta aqueous leaf extracts (250 mL) were added in drops to a 0.1-M solution of Zn(NO3)2.6H2O (50 mL) in a conical flask under a continual stirring condition using a magnetic stirrer to make ZnONPs. The 12-h addition time resulted in the production of solid-liquid dispersion mixtures, which were centrifuged for 15 min at 3835 g force. The supernatants were then removed, and the residues were rinsed with deionised water to remove any remaining Zn(NO3)2.6H2O and organic compounds. For drying, the remnants were placed in a 70 °C oven for 2 h. After that, ZnONPs were obtained by calcination in a muffle furnace at 500 °C for 3 h. To improve the dispersion of the ZnONPs, they were sonicated in ethanol at 40 °C for 1 h in an ultrasonic cleaner. ZnONPs from Chromolaena odorata were designated ZnO_CNPs, while those from Manihot esculenta were designated ZnO_MNPs.

**Characterisation**

The phytochemicals in the Chromolaena odorata and Manihot esculenta aqueous leaf extracts were determined using a gas chromatograph–mass spectrometer (GC-MS; Shimadzu QP2010SE, Markham, Ontario, Canada). Before injection into the GC-MS, ethanol was added to the crude aqueous extracts to obtain an ethanolic solution of the extracts at a mixture ratio of 1:1. From the retention times, fragmentation patterns and peak areas, the various phytochemicals present in the extracts and their concentrations were determined. The formation of ZnONPs was validated using a UV-Vis absorption spectrophotometer to measure the wavelengths of absorption of the mixture obtained during the reaction between Zn(NO3)2.6H2O and the Chromolaena odorata and Manihot esculenta leaf extracts, which ranged from 300 nm to 800 nm (Uniscope SM 7504).

In a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyser (EDX) unit (JEOL JSM 7660F), the microstructure and elemental composition of the ZnONPs were assessed to evaluate particle distribution and support the presence of ZnO in the samples. An accelerating voltage of 15 kV was used to evaluate the material.

“The samples were analysed using a transmission electron microscope (TEM; JEM-ARM200F-G) running at a 200-kV accelerating voltage to determine the particle size and shape of the ZnONPs. The average particle size of each sample was then calculated using ImageJ software from the TEM micrographs.

To establish the type of phases present and analyse the crystalline nature of the ZnONPs, the diffraction patterns of the samples were obtained using an X-ray diffractometer (XRD; Rigaku D/Max-IIIC).

Fourier transform infrared (FTIR) spectroscopy (Nicolet iS10) with a wavenumber in the range of 350–4000 cm-1 was used to determine the type of bonds present in the ZnONPs to complement the results of the GC-MS, UV-Vis, and XRD.

Preparation of Aqueous leaf extracts, Synthesis of ZnONPs & Characterisation

Mark Wesson is a highly skilled healthcare program professional with the skills needed to create high-quality healthcare programs. He has experience leading the analysis and restructuring of programs to improve the quality of care for patients. He is also adept at cultivating innovation using the latest technologies to improve information management and communication. Throughout his career, he has found and applied new and more effective ways of ensuring high-quality patient care. 

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