An official website of the United States government.
To provide an understanding of fundamental nanoscale phenomena and processes
Non-Technical Summary: The environmental behavior and biological effects of nanoparticles are not well understood. This project examines the stability of a few types of nanometer-sized particles in aqueous solutions and investigates their behavior in model systems. <P> Approach: Stability, degradation, and fate of nanoparticles. Clemson will study the behavior of several types of nanoparticles in aqueous environments. Particle dissolution, agglomeration, and precipitation in aqueous solutions simulating natural waters will be measured as well as changes in particle characteristics (e.g., size and composition). For selected particle types, transport through soil columns and toxicity to an aquatic invertebrate specie will be performed. Nanoparticles of polystyrene, titanium dioxide (TiO2), iron oxide (hematite (alpha-Fe2O3), copper oxide (CuO), and zinc oxide (ZnO) will be synthesized using solution techniques from the literature (Qu et al., 2005, Lee and Liu 2002; Mulvaney et al., 1988; Viano et al., 2003; Bahnemann et al. 1987). The particles sizes and crystal structures will be characterized using various electron microscopy techniques (e.g., transmission electron microscopy (TEM), scanning (EM), field emission scanning (FESEM)) and x-ray diffraction (XRD). Electron microscopes with energy dispersive x-ray (EDX) and x-ray photoelectron spectroscopy (XPS) capabilities will be used to check elemental composition and valence. Particle surface area will be determined with BET isotherm methods (typically N2 adsorption) using a Micromeritics ASAP 2010. Suspensions of nanosize particles are amenable to characterization by optical spectroscopic methods such as UV-vis absorption due to the absence of significant light scattering in solution. Semiconductor particles (i.e., TiO2, Fe2O3, and ZnO) often show bandgap absorption in the near-UV range, and this absorption onset is characteristic of particle size. Therefore, UV-vis absorption spectra will be obtained as a function of time for particles suspended in water and in solutions simulating natural waters (containing variable pH, alkalinity, sodium, hardness, chloride, sulfate). Loss of absorption intensity or decrease in bandgap energy are expected to provide an indication of particle growth, coagulation, and precipitation; spectral changes matching dissolved species (e.g., loss of bandgap absorption) indicate particle dissolution. Such tests will be performed to determine the stability of nanoparticle suspensions over time periods of several days. Following stability tests, particle characteristics will be reexamined by electron microscopy. For cases in which particle suspensions are stable for several days, transport and toxicity tests will be performed. Transport tests using soil columns will be performed following procedures outlined by Schrick (2004). Toxicity (mortality) of nanoparticle suspensions to an aquatic invetebrate, Ceriodaphnia dubia (water flea), will be performed as an indication of bioavailability of toxic substances, particularly metals (Huggett 1999; Suedel 1996).