Chapter 30 - Physicochemistry of Polyelectrolyte Coatings that Increase Stability, Mobility, and Contaminant Specificity of Reactive Nanoparticles Used for Groundwater Remediation

Abstract

Novel reactive nanomaterials offer the potential for efficient targeted delivery of remedial agents to subsurface contaminants such as chlorinated solvents and heavy metals. The primary challenge to their application is to overcome rapid aggregation and deposition of these nanomaterials in water-saturated porous media, and to improve the efficiency by increasing the specificity of the nanoparticles for specific subsurface contaminants. Coating particles with amphiphilic copolymers, commercially available polyelectrolytes (e.g., polystyrene sulfonate (PSS)), and biopolyniers (e.g., polyaspartate) affords electrosteric repulsions necessary to prevent, rapid aggregation and deposition of nanomaterials to aquifer media, and can significantly enhance mobility under typical groundwater geochemical conditions. The coating properties such as the adsorbed polyelectrolyte mass and the conformation of the adsorbed polyelectrolyte layer correlate with the observed increase in dispersion stability and mobility enhancement, implying the ability to select a transport distance based on the choice of surface modifier and site groundwater geochemistry. The amphiphilic nature of some coatings provides the particles specificity for the dense nonaqueous phase liquid (DNAPL)/water interface, whereas other coatings use ligands to specifically sequester heavy metals or hydrophobic nanoparticles to selectively adsorb very hydrophobic organic contaminants. Here we describe the state-of-the art in polymeric surface modification for reactive nanoparticles used for in situ groundwater remediation and explain the fundamental physicochemical processes by which polyelectrolyte surface modification and functionalization inhibit aggregation and deposition and increases mobility in the subsurface. We also describe the methods used for targeting specific subsurface contaminants. Remaining challenges and ongoing research and development opportunities are also discussed.