Aggregation and adsorption processes of carbonaceous nanoparticles in aqueous environments

Carbonaceous nanoparticles (NPs), which are intentionally manufactured or originate from incomplete combustion, reach aqueous environments continuously through direct input, surface runoff, wastewater treatment plants, and atmospheric deposition. Upon release into aqueous environments, carbonaceous NPs will likely undergo aggregation and adsorption processes depending on the local solution chemistries and ambient species. Understanding the physiochemical interactions governing these two fundamental processes of carbonaceous NPs is crucial for evaluating their fate, transport, and potential applications in aqueous environments. The first part of this work focused on the aggregation and adsorption behaviors of a new class of manufactured carbonaceous NPs, nanosized activated carbons (NACs), in an effort to evaluate the applicability of NACs as adsorbents to be injected into groundwater systems for remediation purpose. Investigation on aggregation kinetics of four types of NACs demonstrated that, under solution chemistries typical of freshwater environments, NACs should remain stable as dispersed NPs with diameter below 200 nm. Such strong colloidal stability of NACs may enable long distance travel of these NPs to reach target pollutants when injected into groundwater systems. Study on the adsorption processes of NACs for two model aromatic pollutants, 4-chlorophenol (4-CP) and aniline, showed rapid removal of contaminants from water. More importantly, the equilibrium adsorption indicated that the adsorption capacities of NACs were 10-100 times greater than other nanosized adsorbents. The combined strong colloidal stability and adsorption capacity of NACs suggested their potential application as superior adsorbents for groundwater remediation. The second part of this dissertation investigated the aggregation process of soot NPs in aqueous environments. These carbonaceous NPs are produced unintentionally from incomplete combustion, are ubiquitously distributed, and are of serious environmental concerns. Results showed that aggregation kinetics of soot NPs were strongly influenced by solution chemistries including electrolyte compositions and concentrations as well as pH. The presence of macromolecules such as humic acid and proteins significantly enhance the colloidal stability of soot NPs. The aggregation behavior of soot NPs could be predicted by the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory using the Hamaker constant determined in this study. Soot NPs should remain stable against aggregation in typical freshwater environments and neutral rain droplets, but are likely to aggregate under saline (e.g., estuaries and oceans) and/or acidic (e.g., acid rain droplets) conditions. Results from this work imply that NACs with strong colloidal stability and high adsorption capacities may enable benign NP design and applications, whereas the toxic soot NPs having such high colloidal stability they could endanger human and environment health. In summary, this dissertation has furthered our understanding of the aggregation and adsorption processes of carbonaceous NPs, which may facilitate the prediction of their fate and transport in aqueous environments.Ph.D.Includes bibliographical referencesby Chengyu Che