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.  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. 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).  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.  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

Ratiometric Fluorescent pH Sensing with Carbon Dots: Fluorescence Mapping across pH Levels for Potential Underwater Applications

Ocean acidification has become a major climate change concern requiring continuous observation. Additionally, in the industry, pH surveillance is of great importance. Consequently, there is a pressing demand to develop robust and inexpensive pH sensors. Ratiometric fluorescence pH sensing stands out as a promising concept. The application of carbon dots in fluorescent sensing presents a compelling avenue for the advancement of pH-sensing solutions. This potential is underpinned by the affordability of carbon dots, their straightforward manufacturing process, low toxicity, and minimal susceptibility to photobleaching. Thus, investigating novel carbon dots is essential to identify optimal pH-sensitive candidates. In this study, five carbon dots were synthesized through a simple solvothermal treatment, and their fluorescence was examined as a function of pH within the range of 5-9, across an excitation range of 200-550 nm and an emission range of 250-750 nm. The resulting optical features showed that all five carbon dots exhibited pH sensitivity in both the UV and visible regions. One type of carbon dot, synthesized from m-phenylenediamine, displayed ratiometric properties at four excitation wavelengths, with the best results observed when excited in the visible spectrum at 475 nm. Indeed, these carbon dots exhibited good linearity over pH values of 6-9 in aqueous Carmody buffer solution by calculating the ratio of the green emission band at 525 nm to the orange one at 630 nm (I525nm/I630nm), demonstrating highly suitable properties for ratiometric sensing

Case studies and evidence-based approaches to addressing urban soil lead contamination

Urban soils in many communities in the United States and internationally have been contaminated by lead (Pb) from past use of lead additives in gasoline, deterioration of exterior paint, emissions from Pb smelters and battery recycling and other industries. Exposure to Pb in soil and related dust is widespread in many inner city areas. Up to 20–40% of urban children in some neighborhoods have blood lead levels (BLLs) equal to or above 5 μg per decilitre, the reference level of health concern by the U.S. Centers for Disease Control. Given the widespread nature of Pb contamination in urban soils it has proven a challenge to reduce exposure. In order to prevent this exposure, an evidence-based approach is required to isolate or remediate the soils and prevent children and adult's ongoing exposure. To date, the majority of community soil Pb remediation efforts have been focused in mining towns or in discrete neighborhoods where Pb smelters have impacted communities. These efforts have usually entailed very expensive dig and dump soil Pb remediation techniques, funded by the point source polluters. Remediating widespread non-point source urban soil contamination using this approach is neither economical nor feasible from a practical standpoint. Despite the need to remediate/isolate urban soils in inner city areas, no deliberate, large scale, cost effective Pb remediation schemes have been implemented to isolate inner city soils impacted from sources other than mines and smelters. However, a city-wide natural experiment of flooding in New Orleans by Hurricane Katrina demonstrated that declines in soil Pb resulted in major BLL reductions. Also a growing body of literature of smaller scale pilot studies and programs does exist regarding low cost efforts to isolate Pb contaminated urban soils. This paper reviews the literature regarding the effectiveness of soil Pb remediation for reducing Pb exposure and BLL in children, and suggests best practices for addressing the epidemics of low-level Pb poisoning occurring in many inner city areas

Iron nanoparticles synthesized using green tea extracts for the fenton-like degradation of concentrated dye mixtures at elevated temperatures

Environmental harm caused by the release of textile dye contaminated wastewater from industry is an issue that requires immediate attention, particularly in developing countries. We herein demonstrate that green tea derived amorphous iron nanoparticles, in conjunction with Fenton like chemical processes, catabolise anthraquinone and azo dye mixtures that constitute a significant proportion of industrial dye waste. Iron nanoparticles, synthesized following a green tea mediated greener synthesis approach were able to degrade concentrated dye mixtures with over 90% decolourisation in only 20min with 0.53ppm nanoparticle concentration at a temperature of 70°C. Detailed experimental degradation efficiencies were significantly pH and temperature dependant favouring lower pH values at temperatures between 70 and 90°C, conditions which are commonly found in textile wastewaters. This research has shown the capacity for green tea synthesized nanoparticles to be used as a promoter for Fenton like dye degradation reactions. This rapid treatment approach may gain interest in the textile industries for dye waste remediation

Polyaromatic hydrocarbon exposure: An ecological impact ambiguity

Polyaromatic hydrocarbons (PAHs) represent a fraction of petroleum hydrocarbons and are currently one of the foremost sources of generating energy in today's contemporary society. However, evidence highlighted in this review show that PAH pollution, as a result of oilspills, hazardous PAH-contaminated working environments and technologies which do not efficiently utilise fuels, as well as naturalsources of emissions (e.g. forest fires) may have significant health implications for all taxa. The extent of damage to organisms from PAH exposure is dependent on numerous factors including degree and type of PAH exposure, nature of the environment contaminated (i.e. terrestrial or aquatic), the ability of an organism to relocate to pristine environments, type and sensitivity of organism to specific hydrocarbon fractions and ability of the organism to metabolise different PAH fractions. The review highlights the fact that studies on the potential damage of PAHs should be carried out using mixtures of hydrocarbons as opposed to individual hydrocarbon fractions due to the scarcity of individualfractions being a sole contaminant. Furthermore, potential damage of PAHcontaminated sites should be assessed using an entire ecological impact outlook of the affected area

Phytofabrication of Iron Nanoparticles for Hexavalent Chromium Remediation

Hexavalent chromium is a genotoxic and carcinogenic byproduct of a number of industrial processes, which is discharged into the environment in excessive and toxic concentrations worldwide. In this paper, the synthesis of green iron oxide nanoparticles using extracts of four novel plant species [Pittosporum undulatum, Melia azedarach, Schinus molle, and Syzygium paniculatum (var. australe)] using a "bottom-up approach" has been implemented for hexavalent chromium remediation. Nanoparticle characterizations show that different plant extracts lead to the formation of nanoparticles with different sizes, agglomeration tendencies, and shapes but similar amorphous nature and elemental makeup. Hexavalent chromium removal is linked with the particle size and monodispersity. Nanoparticles with sizes between 5 and 15 nm from M. azedarach and P. undulatum showed enhanced chromium removal capacities (84.1-96.2%, respectively) when compared to the agglomerated particles of S. molle and S. paniculatum with sizes between 30 and 100 nm (43.7-58.7%, respectively) in over 9 h. This study has shown that the reduction of iron salts with plant extracts is unlikely to generate vast quantities of stable zero valent iron nanoparticles but rather favor the formation of iron oxide nanoparticles. In addition, plant extracts with higher antioxidant concentrations may not produce nanoparticles with morphologies optimal for pollutant remediation

Iron nanoparticles for contaminated site remediation and environmental preservation

The current chapter is aimed at outlining the current research relating to generating iron nanoparticles for the use within contaminated site remediation. Synthesis, characterization, coatings to facilitate movement and factors affecting nanoparticle reactivity will be discussed. Furthermore, their current use, efficiency and potential toxicity to the environment will have a focus. This chapter provides a brief overview on the current status of iron nanoparticle mediated environmental remediation. Catabolism of a vast array of different anthropogenic pollutant classes are possible with iron nanoparticles including heavy metals, nitrogen, pesticides, dyes, chlorinated solvents, hydrocarbons and inorganic ions to name a few. This chapter is targeted towards beginners and established environmental science researchers alike who will have limited understanding in the field of nanoremiediation employing Iron nanoparticles

Detection of helminth ova genera using in-situ biosynthesis of gold nanoparticles

In this study, a presumptive colorimetric method was used to detect and differentiate the ova of two major soil transmitted helminths in wastewater, Ascaris and Trichuris. Gold nanoparticles were synthesised following the reduction of tetrachloroauric acid by the surface moiety of Ascaris suum, resulting in a colour change. In contrast there was no colour change with Trichuris suis indicating the absence of gold nanoparticle synthesis. Analysis of the ova using scanning electron microscopy (SEM) revealed that the synthesis of nanoparticles on the surface of ova was confirmed as gold nanoparticles (91 w/w %) by energy dispersive X-ray analysis (EDX). This study indicated that the surface moieties of helminth ova could be a potential target for ova detection and differentiation using the biosynthesis of nanoparticles by colorimetry methods. Three advantages: Simple colorimetry based method requiring no sophisticated devices. No trained personnel required. Cost-effective and can be a potential candidate for biosensors

Incorporation of quantum carbon dots into a PVP/ZnO hydrogel for use as an effective hexavalent chromium sensing platform

Hydrogels offer a unique medium for sensing applications as they can draw upon the benefits of both solid and liquid sensing platforms. Incorporation of functionalised fluorescent nanoparticles within the hydrogel matrix results in a three-dimensional nanocomposite capable of interacting with water-soluble analytes, facilitating quantitative sensing applications. Here, we report the solvothermal synthesis of a novel Polyvinylpyrrolidone assembled hydrogel stabilised with zinc oxide quantum dots which does not require additional organic crosslinkers. Functionalization of these hydrogel with novel, brightly photoluminescent 2-amino-2-methyl-1-propanol quantum carbon dots (quantum yield of 62.5%) results in a composite capable of specific interaction with hexavalent chromium. Quantitative fluorescence quenching measurements of the hydrogel composite in the presence of hexavalent chromium shows a limit of detection of 1.2 μM Cr6+ which is below maximum allowable concentrations for drinking water. The hydrogel composite is cheap to manufacture and can be injected into 96 well plates for high throughput analysis of environmental water samples. These results are encouraging for the development of hydrogels and polymetric films to be used as novel fluorescent sensing platforms for environmental diagnostic applications

The application of hydrocarbonoclastic bacteria for the bioremediation of weathered crude oil

Hydrocarbon waste, including crude oil residues in tank bottoms represents an ongoing and growing environmental problem throughout the world as they are particularly persistent within the environment and have the potential to induce a vast array of serious negative health effects for all biological entities. Bioremediation offers a sustainable treatment that reduces the levels of a pollutant present in a soil, for example to sub-toxic concentrations or brings them in line with compliance criteria for safe use or for disposal. In so doing, the risk following release to the environment is ameliorated. The aim of this study was to assess the potential of a hydrocarbonoclastic bacterial consortium, isolated from previously contaminated environments to both survive in contaminated environments and degrade weathered crude oil. Significant changes in the waste oil occurred through incubation with the microbial consortia including, emulsification, loss of viscosity and reduced hydrocarbon content, particularly in the high carbon chain (C20-C70 region). Profiling of the microbial community using denaturing gradient gel electrophoresis confirmed the influence of the addition of the microbial consortia on enhanced diversity of the microflora. Sequence identity of the individual strains present in the microbial consortia identified Pseudomonas sp. as well as several non-cultured garnma-proteobacteria. The result highlights the potential of hydrocarbonoclastic bacterial consortia for use in bioremediation