Abstract
A sustainable future requires the use of smart fertilisers to improve productivity in the agricultural sector. The surge in nanomaterial development has driven numerous industrial applications that require greener synthetic approaches. Therefore, the use of chemicals and/or plant extracts for synthesising iron oxide (α-Fe2O3), zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles as nanofertilisers for seed germination and crop growth was investigated. Synthesised nanoparticles were characterised using a suite of analytical techniques to evaluate their crystallinity, morphology, and chemical composition.
The first phase was the use of Artemisia afra, a widely distributed South African medicinal plant, as a natural source of bioactive compounds for potential use in nanoparticle synthesis. The extraction of phytochemicals from A. afra leaves using different solvents (methanol, ethanol, isopropanol, and water) and concentrations (20 – 100 %) was tested under hot-plate extraction at temperatures of 50 °C and 75 °C. Extracts were analysed using high-performance liquid chromatography (HPLC) for non-chromophores (organic acids and sugars), and their total phenolic and flavonoid content assays, as well as their antioxidant activity, were evaluated using Ultraviolet-visible (UV-vis) spectrophotometry. The findings from the first phase (extraction studies) revealed that phytochemical yield was highly dependent on solvent polarity and temperature. The 40 % ethanol extract at 75 °C exhibited the highest total phenolic (50.5 mg gallic acid equivalent/g) and antioxidant activity (28 mg ascorbic acid equivalent/g). These findings positioned this condition as optimal for subsequent nanoparticle synthesis.
The second phase focused on the green synthesis of α-Fe2O3, ZnO, and MgO nanoparticles using optimised A. afra extract as a modulator and stabilising agent in a liquid state route. Depending on the metal precursor, the resulting nanoparticles primarily exhibited spherical shapes, with sizes ranging between 20 and 40 nm. Notably, the synthesised α-Fe2O3, ZnO, and MgO nanoparticles displayed distinct morphologies and crystallinity depending on the metal precursor. Furthermore, both chemical- and plant-based mechanochemical (solid state) routes were investigated, utilising Na2CO3, NaOH, and A. afra plant powder as modulators, respectively. These methods were explored under both neat and liquid-assisted grinding (LAG) conditions. The investigation comparing chemical and plant-mediated solid state routes demonstrated successful nanoparticle formation through neat grinding and LAG reaction media. Interestingly, for α-Fe2O3 nanoparticles, diverse morphologies were observed; neat...