Selective adsorption onto agarose gels has become a powerful method to separate single-walled carbon nanotubes (SWCNTs). A better understanding of the nature of the interactive forces and specific sites responsible for adsorption should lead to significant improvements in the selectivity and yield of these separations. A combination of nonequilibrium and equilibrium studies are conducted to explore the potential role that van der Waals, ionic, hydrophobic, π-π, and ion-dipole interactions have on the selective adsorption between agarose and SWCNTs suspended with sodium dodecyl sulfate (SDS). The results demonstrate that any modification to the agarose gel surface and, consequently, the permanent dipole moments of agarose drastically reduces the retention of SWCNTs. Because these permanent dipoles are critical to retention and the fact that SDS-SWCNTs function as macro-ions, it is proposed that ion-dipole forces are the primary interaction responsible for adsorption. The selectivity of adsorption may be attributed to variations in polarizability between nanotube types, which create differences in both the structure and mobility of surfactant. These differences affect the enthalpy and entropy of adsorption, and both play an integral part in the selectivity of adsorption. The overall adsorption process shows a complex behavior that is not well represented by the Langmuir model; therefore, calorimetric data should be used to extract thermodynamic information.

NMR techniques have been widely used to infer molecular structure, including surfactant aggregation. A combination of optical spectroscopy, proton NMR spectroscopy, and pulsed field gradient NMR (PFG NMR) is used to study the adsorption number for sodium dodecyl sulfate (SDS) with single-wall carbon nanotubes (SWCNTs). Distinct transitions in the NMR chemical shift of SDS are observed in the presence of SWCNTs. These transitions demonstrate that micelle formation is delayed by SWCNTs due to the adsorption of SDS on the nanotube surface. Once the nanotube surface is saturated, the free SDS concentration increases until micelle formation is observed. Therefore, the adsorption number of SDS on SWCNTs can be determined by the changes to the apparent critical micelle concentration (CMC). PFG NMR found that SDS remains strongly bound onto the nanotube. Quantitative analysis of the diffusivity of SDS allowed calculation of the adsorption number of strongly bound SDS on SWCNTs. The adsorption numbers from these techniques give the same values within experimental error, indicating that a significant fraction of the SDS interacting with nanotubes remains strongly bound for as long as 0.5 s, which is the maximum diffusion time used in the PFG NMR measurements.

A major area of growth for "nano-enabled" consumer products have been surface coatings, including paints stains and sealants. Ceria (CeO) nanoparticles (NPs) are of interest as they have been used as additives in these these products to increase UV resistance. Currently, there is a lack of detailed information on the potential release, and speciation (i.e., ion vs. particle) of CeO NPs used in consumer-available surface coatings during intended use scenarios. In this study, both Micronized-Copper Azole pressure-treated lumber (MCA), and a commercially available composite decking were coated with CeO NPs dispersed in Milli-Q water or wood stain. Coated surfaces were divided into two groups. The first was placed outdoors to undergo environmental weathering, while the second was placed indoors to act as experimental controls. Both weathered surfaces and controls were sampled over a period of 6months via simulated dermal contact using methods developed by the Consumer Product Safety Commission (CPSC). The size and speciation of material released was determined through sequential filtration, total metals analysis, X-Ray Absorption Fine Structure Spectroscopy, and electron microscopy. The total ceria release from MCA coated surfaces was found to be dependent on dispersion matrix with aqueous applications releasing greater quantities of CeO than stain based applications, 66±12mg/m and 36±7mg/m, respectively. Additionally, a substantial quantity of CeO was reduced to Ce(III), present as Ce(III)-organic complexes, over the 6-month experimental period in aqueous based applications.

The electronic-type separation of single-wall carbon nanotubes (SWCNTs) by selective adsorption onto hydrogel surfaces has become a highly researched method. However, large variations in both SWCNT dispersion and separation protocols have been reported, making it difficult to elucidate whether changes to dispersion state or separation parameters are responsible for the observations reported in the literature. This study systematically evaluates the role that hydrogel type (dextran- or agarose-based) and SWCNT loading concentration have on separation quality, throughput, and reproducibility. For dextran-based gels, increased dextran concentration rather than cross-linker concentration improves retention and selectivity, suggesting that hydroxyl groups rather than linker molecules are the active adsorption sites. SWCNTs have much stronger interactions with agarose- than dextran-based gels. This stronger adsorption capacity combined with the improved retention of SWCNTs at higher agarose concentration suggests that the double helices formed by agarose are important to the adsorption of nanotubes. The quality and selectivity of the separations are heavily influenced by the initial concentration of SWCNTs; the purity of the metallic fraction falls rapidly as SWCNT concentration increases from 20 to 70 mg/L in Sephacryl 200 HR columns. The reproducibility of the separation is greatly affected by the amount of cross-linking in the gel, but restabilization of the hydrogel remains a critical concern for continued use. In general, the highest-throughput separations are obtained with dextran-based gels, while agarose-based gels produce higher purity fractions of metallic SWCNTs (>98%) and better reproducibility in consecutive separations.