Interaction of emerging contaminants at the colloidal and planar interfaces : influence on environmental fate and transport

Abstract

The increasing concerns regarding emerging contaminants in aquatic ecosystems provide a need to understand the role surface chemistry plays in the fate and transport of pollutants. The overarching aim of this thesis has been to investigate adsorption of selected emerging pollutants to colloids and elucidate how these surface interactions influence their fate and mobility in aquatic systems. Research presented here advances our understanding of pollutant-colloid interactions and provides a methodology for systematic fate and transport studies. In Chapter 1, the diverse and rich research revolving around emerging contaminants and the natural environment are demonstrated. Strides have been made in trying to understand pollutant fate and transport in an aqueous environment. Adsorption to natural and man-made surface appears to be dependent on pH, electrolyte/ionic strength, functional group, and competing molecules on the removal of ECs from the aqueous phase. Chapter 2 focuses on the theory behind instruments used for data collection throughout this thesis. It highlights a surface sensitive laser spectroscopy technique called second harmonic generation, dynamic light scattering, surface tensiometery, and gravimetric analysis using quartz crystal microbalance. Chapter 3 addresses questions relating to fundamental parameters of magnetic colloids with the potential to serve as a remediation tool for industrial cationic dye removal from water. The influence of aggregation on the effectiveness of colloids as a remediation tool is discussed. Chapter 4 presents research questions regarding fate and transport of pharmaceuticals. The binding affinity and adsorption mechanisms of pharmaceuticals onto colloidal NOM and model colloidal NOM is explored. Chapter 5 is dedicated to the development of an analytical tool to detect pollutants at low concentrations in aqueous solution. This final chapter also discusses future direction and potential research projects. Using a variety of spectroscopic tools, fundamental and practical insights have been gained throughout this thesis. Major results include, but not limited to, (1) determination of aggregation of particles in the presence of man-made pollutants and (2) characterization of binding mechanisms involved in the adsorption of pharmaceuticals to model natural colloids. The first major results show significant aggregation of magnetic particles (MP) occur in aqueous solution upon the adsorption of malachite green (MG). Treating aggregation as a linear function of dye concentration enabled the development of a modified Langmuir model to determine binding affinity. Using this model, binding affinity of MG onto MP has been determined to be – 39.8 (± 0.7) kJ/mol. The second major results demonstrate that amlodipine (AMP) and carbamazepine (CBZ) adsorb to colloidal natural organic matter (NOM) with binding affinities of –41.2 (± 0.7) and – 38.2 (± 0.7) kJ/mol, respectively. AMP and CBZ have also been found to adsorb to polymeric based magnetic particles functionalized with –COOH and –NH2 with binding affinities on the same order of magnitude as colloidal NOM. This study reveals adsorption to –COOH and –NH2 functionalized particles is not limited to electrostatic interactions. The research in this thesis also include development and application of analytical methods, such as a quartz crystal microbalance (QCM) to detect water pollutants in the nano- to micro-molar concentration range. Results indicate MG and AMP can be detected with QCM functionalized with a self-assembled monolayer (SAM) from aqueous solution at initial concentrations as low as 91 nM. Future QCM research will explore other environmentally relevant functionalized SAMs, as well as, NOM surfaces. Also, preliminary adsorption experiments involving emerging contaminants binding to hydrophobic surfaces will help to better understand hydrophobic binding interactions.