Nanoparticle synthesis using phytochemical precursors – instilling beneficial properties with green methodologies for pollution remediation

Nanotechnology has become an emerging platform for the treatment of organic and inorganic contaminants. Nanoparticles high surface area to volume ratio enhances their capacity for reactions and interactions with pollutants to proceed at an elevated rate compared to larger particles. Concerns pertaining to their toxicity and suitability for environmental release have prevented many studies from progressing to commercial products. However, considerable toxicology research has reinforced that nanoparticles synthesized with non-toxic ingredients can be biocompatible and be used for therapeutics. The research conducted during this PhD candidature was focused on developing nanomaterials with pollution remediation capacities from ingredients which are ubiquitous in the environment, derived from natural sources or show environmental biocompatibility. With this approach, nanoparticles with future commercial application for site remediation are possible.  <br><br>Due to irons large intrinsic presence within many soil types, its potential for environmental biocompatibility is heightened. Iron nanoparticles were created in this study by reducing iron salt precursors with aqueous plant extracts. Green tea extract, rich in antioxidants was initially used for this approach and resulted in iron oxide nanoparticles with the capacity to rapidly degrade concentrated dye mixtures (99.1 % of 500 ppm concentrated dye mixture) with the aid of hydrogen peroxide to facilitate a Fenton-like degradation mechanism. This process generated nanoparticles with a tendency to stick together, required acidic conditions and removal rates were increased at elevated temperatures. Due to the downfalls of requiring acidic conditions, hydrogen peroxide and the particles containing agglomerated chains of particles, the focus of further experimentation was directed to adsorption studies. <br><br>In the second research chapter, iron nanoparticles were generated using differing plant extracts to investigate the influence of diverse phytochemical mixtures on the morphology of iron nanoparticles. The generated nanoparticles were then assessed for their capacity to adsorb hexavalent chromium (Cr6+) from aqueous solutions. Nanoparticle morphology differed significantly between the different plant extract reducing agents. No significant links between reducing powers, antioxidant concentration, phenolic concentration, protein concentration, reducing sugar concentration and iron chelating capacity were indicative of specific nanoparticle morphologies. However, high antioxidant concentrations did not result in optimal morphologies (chains of agglomerated particles) and small, monodisperse nanoparticles were shown to possess the greatest Cr6+ adsorption capacities (up to 96.2 % of 50 ppm Cr6+ solution).  <br><br>Silicon dioxide is a routinely used adsorbent material for the removal of environmental contaminants as it has high adsorption capacity and is environmentally benign. Within chapter 4 Helianthus annuus extract was incorporated into a reaction vessel with an aminosilicon precursor and subjected to high temperatures (200°C) and pressures. The resulting silicon nanoparticles possessed increased surface area compared to controls. Their concentrated mixed dye removal was apparent after 5 mins and showed extraordinary removal capacities between 416.67 - 714.29 mg dye adsorption per g of adsorbent.  These positively charged silanol nanoparticles showed little bacterial toxicity and are therefore likely to be suitable for environmental applications.  <br><br>In summary, a sustainable, natural approach for instilling beneficial properties to iron and silicon nanoparticles using plant extracts has been developed. The capacity for these nanoparticles to remove pollutants from aqueous solutions is substantial and upon further refinement, may be suitable for environmental remediation applications.