FATE AND TRACKING OF ENGINEERED NANOMATERIALS IN AQUEOUS ENVIRONMENTS

colloids;nanoparticles;carbon nanotubes;photodecarboxylation;silica;gold;total internal reflection microscopy;dark field microscopy;Chemistry

Bitter, Julie LynnFairbrother, D. Howard ;

Johns Hopkins University

关键词: colloids;    nanoparticles;    carbon nanotubes;    photodecarboxylation;    silica;    gold;    total internal reflection microscopy;    dark field microscopy;    Chemistry;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/37041/BITTER-DISSERTATION-2014.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Engineered nanomaterials are incorporated into over 1600 commercially available products on the market today, increasing the likelihood of nanoparticle release during a nano-containing product’s life cycle. To determine any potential risks associated with nanoparticle release, it is important to develop a detailed understanding of their behavior in different aquatic systems. Towards this goal, this thesis focuses on the use of various microscopic and spectroscopic techniques to study how the physical and chemical properties of different nanoparticles affect their behavior in bulk aquatic media and near environmental surfaces under a variety of conditions. Suspensions of oxidized multiwalled and single walled carbon nanotubes (O-MWCNTs/O-SWCNTs) were used to examine nanoparticles in bulk aquatic environments. The effect of ultraviolet (UV) radiation on their colloidal stability was investigated because UV light is used in drinking and waste water treatment to destroy harmful pathogens; however, its effect on engineered nanomaterials remains unclear. Results have shown that absorption of 254nm light causes colloidal O-MWCNTs to become unstable and aggregate from a loss of surface oxygen by a photodecarboxylation mechanism. There were observed removal and changes in functional group densities at the O-MWCNT surface. The same mechanism was exhibited by O-SWCNTs; however, whereas this transformation proceeds in the absence of any significant mass loss or changes to the O-MWCNT structure, O-SWCNTs were effectively mineralized by the UV radiation. To examine nanoparticles near environmental surfaces, video microscopy was used to track individual and ensemble averages of silica microspheres and micron-sized gold rods under various aquatic conditions above silicate surfaces. Using image analysis algorithms and theoretical calculations, accurate and quantitative measurements of weak (kT-scale) particle-surface interactions, diffusion behavior, and stability were obtained. Hydrodynamic interactions provided evidence that silica ;;gel-layers”, which decrease in thickness with increasing ionic strength, gave rise to anomalous colloidal stability of silica microspheres seen over a range of solution conditions. These interactions were also probed by examining the position dependent translational and rotational diffusion of gold rods through slit pores and model 2-dimensional porous media. Theoretical calculations were found to fit experimental rod trajectories well, exhibiting an ionic strength mediated particle-surface separation dependence of the translational diffusion.