Effect of Encapsulating Agents on Dispersion Status and Photochemical Reactivity of C 60 in the Aqueous Phase
School of Civil and Environmental Engineering, Georgia Institute of Technology, 200 Bobby Dodd Way, Atlanta, Georgia 30332-0373, USA. Environmental Science and Technology
(Impact Factor: 5.33).
04/2008; 42(5):1552-7. DOI: 10.1021/es702552a
This study demonstrates that the degree of C60 clustering in the aqueous phase is strongly dependent on the type and concentration of encapsulating agents, such as surfactant, polymer, and natural organic matter that interact with C60. The degree of C60 clustering was quantitatively analyzed using ultraviolet-visible spectral characteristics. The dispersion status played a critical role in determining the photochemical reactivity of C60, in particular, its ability to mediate energy transfer and to produce singlet oxygen in the presence of oxygen. Consistent with findings in the organic phase, C60 in the aqueous phase lost its intrinsic photochemical reactivity when they formed aggregates. Experiments performed using a laser flash photolysis suggested that the loss of reactivity resulted from a drastic decrease in lifetime of a key reaction intermediate, that is, triplet-state C60. This study suggests that the photochemical reactivity of C60 in the aqueous phase, which has been linked to oxidative damage in biological systems in earlier studies, is strongly dependent on the media environment surrounding C60.
Available from: Dengjun Wang
- "The cationic surfactant cetyltrimethylammonium bromide (CTAB) readily adsorbs onto negatively charged NPs through the attractive electrostatic interactions between cationic quaternary ammonium groups (CTA + ) on CTAB and negatively charged NPs    . Such attractive interactions facilitate formation of large NP aggregates that lead to decreased transport potential in granular media by increasing their rates of settling and likelihood for straining   . On the other hand, the adsorbed CTAB layer may enhance steric repulsion between CTAB-modified NPs that would increase their stability . "
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ABSTRACT: Little is known about the mobility of engineered nanoparticles (ENPs) in granular media at environmentally relevant concentrations of surfactants, which represents a critical knowledge gap in employing ENPs for in situ remediation of contaminated groundwater. In this study, transport and retention of alizarin red S (ARS)-labeled hydroxyapatite nanoparticle (nHAP) were investigated in water-saturated sand at environmentally relevant concentrations of surfactants: anionic sodium dodecyl benzene sulfonate (SDBS, 0-50 mg L-1) and cationic cetyltrimethylammonium bromide (CTAB, 0-5 mg L-1). Transport of ARS-nHAP increased with increasing SDBS concentration because of enhanced colloidal stability and reduced aggregate size arising from enhanced electrostatic, osmotic, and elastic-steric repulsions between ARS-nHAP and sand grains. In contrast, transport decreased significantly with increasing CTAB concentration due to reduced surface charge and enhanced aggregation of ARS-nHAP. Osmotic and elastic-steric repulsions played a minor role in enhancing ARS-nHAP colloidal stability in CTAB tests. Retention profiles of ARS-nHAP exhibited hyperexponential-shapes for all conditions tested and became more pronounced as CTAB concentration increased. The phenomenon was attributed to the aggregation and ripening of ARS-nHAP in the presence of surfactants, particularly CTAB. Overall, the present study suggests that surfactant type and concentration may be important considerations in employing nHAP for engineered in situ remediation of metal- and radionuclide-contaminated groundwater.
Available from: Divina A Navarro
- "C 60 , C 70 , etc.) have received considerable attention due to their unique characteristics, and numerous potential commercial and scientific applications . One of the most notable characteristics of fullerenes is its strong photochemical reactivity – a property largely attributable to their highly symmetric carbon ring structure  . Fullerenes can act as efficient electron acceptors (i.e. "
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ABSTRACT: Owing of their wide-range of commercial applications, fullerene (C60) nanoparticles, are likely to reach environments through the application of treated sludge (biosolids) from wastewater treatment plants to soils. We examined the release behaviour of C60 from contaminated biosolids added to soils with varying physicochemical characteristics. Incubation studies were carried out in the dark for up to 24 weeks, by adding biosolids spiked (1.5mg/kg) with three forms of C60 (suspended in water, in humic acid, and precipitated/particulate) to six contrasting soils. Leaching of different biosolids+soil systems showed that only small fractions of C60 (<5% of applied amount) were released, depending on incubation time and soil properties (particularly dissolved organic carbon content). Release of C60 from unamended soils was greater (at least twice as much) than from biosolids-amended soils. The form of C60 used to spike the biosolids had no significant effect on the release of C60 from the different systems. Contact time of C60 in these systems only slightly increased the apparent release up to 8 weeks, followed by a decrease to 24 weeks. Mass balance analysis at the completion of the experiment revealed that 20-60% of the initial C60 applied could not be accounted for in these systems; the reasons for this are discussed.
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ABSTRACT: An explanation is proposed for the electrorheological effect under fields based on the fact that the field distribution is controlled by the conduction properties (linear and nonlinear) of both the solid particles and the carrying liquid. A simplified analysis gives an expression for the attraction force between two very slightly conducting spheres in contact, immersed in a dielectric liquid, as a function of the imposed field and the ratio of conductivities. The predictions are confirmed by a large-scale experiment and qualitatively account for some observations on an electrorheological fluid
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