Deposition of carboxymethylcellulose-coated zero-valent iron nanoparticles onto silica: roles of solution chemistry and organic molecules.

Zero-valent iron nanoparticles (nZVI) used in the remediation of contaminated subsurface environments are commonly stabilized using polymer coatings. A bottom-up synthesis approach was used to synthesize carboxymethylcellulose (CMC)-coated nZVI particles with increased colloidal stability. The influence of water chemistry and selected environmental molecules, namely, fulvic acids and rhamnolipids, on the aggregate size and surface charge of the bare and CMC-coated nZVI particles was systematically examined using dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), and laser Doppler velocimetry. A quartz crystal microbalance with energy dissipation monitoring (QCM-D) was used to quantify the deposition rates of bare and CMC-coated nZVI particles onto a silica surface over a broad range of solution ionic strengths and in the presence of naturally occurring molecules. Nanoscale ZVI particle deposition was found to increase with IS for many of the conditions investigated. CMC acted as a better colloidal stabilizer when covalently bound to nZVI particles than when physisorbed onto the nanoparticle surface after particle synthesis. The lowest nanoparticle deposition rates were observed for CMC-coated nZVI in the presence of the rhamnolipid biosurfactant.