Browsing by Author "Fortner, John D."

Now showing 1 - 3 of 3
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    C60 in Water: Aggregation Characterization, Reactivity and Behavior
    (2007) Fortner, John D.
    Industrial scale production, coupled with unique material properties, underpin rising concerns of nano-scale materials inadvertently impacting the health and function of natural systems. Fullerenes, C60 in particular, have been proposed for a variety of applications and are soon expected to be produced in multi-ton quantities. Understanding how these materials behave in natural matrixes, specifically aqueous systems, is needed for accurate risk assessment and to manage waste disposal practices appropriately. Research presented here addresses outstanding questions and expands upon current knowledge regarding C60 nano-scale aggregation in water (nano-C60). Four areas of focus are: 1.) Aggregate formation, composition, and stability 2.) Reactivity with a dissolved reactant (ozone) 3.) Association with mineral surfaces and 4.) Interaction with selected biological systems. Results indicate that aggregates are crystalline in order and remain as underivatized C60 throughout the formation/stabilization process. The aggregate suspensions readily react with dissolved ozone resulting in a molecularly soluble, highly oxidized fullerene. Furthermore, nano-C60 associates with mineral surfaces as a function of surface charge and is observed to accumulate at the cell wall of a fungal culture. Taken together, results indicate that nano-scale, fullerene aggregates must be considered appropriately, as they deviate from predictions based on bulk and molecular property estimates.
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    Measuring the Grafting Density of Nanoparticles in Solution by Analytical Ultracentrifugation and Total Organic Carbon Analysis
    (American Chemical Society, 2012) Benoit, Denise N.; Zhu, Huiguang; Lilierose, Michael H.; Verm, Raymond A.; Ali, Naushaba; Morrison, Adam N.; Fortner, John D.; Avendano, Carolina; Colvin, Vicki L.
    Many of the solution phase properties of nanoparticles, such as their colloidal stability and hydrodynamic diameter, are governed by the number of stabilizing groups bound to the particle surface (i.e., grafting density). Here, we show how two techniques, analytical ultracentrifugation (AUC) and total organic carbon analysis (TOC), can be applied separately to the measurement of this parameter. AUC directly measures the density of nanoparticle–polymer conjugates while TOC provides the total carbon content of its aqueous dispersions. When these techniques are applied to model gold nanoparticles capped with thiolated poly(ethylene glycol), the measured grafting densities across a range of polymer chain lengths, polymer concentrations, and nanoparticle diameters agree to within 20%. Moreover, the measured grafting densities correlate well with the polymer content determined by thermogravimetric analysis of solid conjugate samples. Using these tools, we examine the particle core diameter, polymer chain length, and polymer solution concentration dependence of nanoparticle grafting densities in a gold nanoparticle–poly(ethylene glycol) conjugate system.
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    Ultra-high capacity, multifunctional nanoscale sorbents for PFOA and PFOS treatment
    (Springer Nature, 2023) Lee, Junseok; Kim, Changwoo; Liu, Chen; Wong, Michael S.; Cápiro, Natalie L.; Pennell, Kurt D.; Fortner, John D.
    Here, we describe surface functionalized, superparamagnetic iron oxide nanocrystals (IONCs) for ultra-high PFAS sorption and precise, low energy (magnetic) separation, considering perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). As a function of surface coating, sorption capacities described are considerably higher than previous studies using activated carbon, polymers, and unmodified metal/metal oxides, among others. In particular, positively charged polyethyleneimine (PEI) coated IONCs demonstrate extreme sorption capacities for both PFOA and PFOS due to electrostatic and hydrophobic interactions, along with high polymer grafting densities, while remaining stable in water, thus maintaining available surface area. Further, through a newly developed method using a quart crystal microbalance with dissipation (QCM-D), we present real-time, interfacial observations (e.g., sorption kinetics). Through this method, we explore underpinning mechanism(s) for differential PFAS (PFOA vs PFOS) sorption behavior(s), demonstrating that PFAS functional head group strongly influence molecular orientation on/at the sorbent interface. The effects of water chemistry, including pH, ionic composition of water, and natural organic matter on sorption behavior are also evaluated and along with material (treatment) demonstration via bench-scale column studies.