We examined the physical and chemical characteristics of colloidal dispersions of fullerene materials (nC60) produced through several solvent exchange processes and through extended mixing in water only. The nC60 produced via the different methods were unique from each other with respect to size, morphology, charge, and hydrophobicity. The greatest dissimilarities were observed between the nC60 produced by extended mixing in water alone and the nC60 produced by solvent exchange processes. The role of the respective solvents in determining the characteristics of the various nC60 were attributed to differences in the solvent-C60 interactions and the presence of the solvent as a residual in the nC60 structure, indicating the significance of the solvent properties in determining the ultimate characteristics of the colloidal fullerene. Thus, fullerene C60 that may become mobilized through natural processes (agitation in water) may behave in dramatically different ways than those produced through more artificial means. These results highlight the difficulties in generalizing nC60 properties, particularly as they vary in potential toxicity considerations.

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The possibility of simultaneous particle aggregation and deposition in a porous medium was examined for the case of TiO(2) nanoparticles (NPs). While potential for particle aggregation is typically assumed to be negligible in porous media due to favored interactions with porous media surfaces (collectors), we show that nanoscale particle dimensions may favor aggregation kinetics, thus altering the transport and retention of these materials in saturated porous media. When surface chemistry favors nanoparticle-nanoparticle attachment (alpha(pp)) over nanoparticle-collector attachment (alpha(pc)), the rate of particle aggregation within pores may be comparable to that of deposition at ratios of collector to nanoparticle surface areas as high as 40. Aggregation of NPs in the porous media enhances NP deposition, however aggregates that are not removed will sample a smaller portion of the available pore network within the column due to size exclusion.

Buckminsterfullerene (C60) is a known photosensitizer that produces reactive oxygen species (ROS) in the presence of light; however, its properties in aqueous environments are still not well understood or modeled. In this study, production of both singlet oxygen and superoxide by UV photosensitization of colloidal aggregates of C60 in water was measured by two distinct methods: electron paramagnetic resonance (EPR) with a spin trapping compound, and spectrophotometric detection of the reduced form of the tetrazolium compound XTT. Both singlet oxygen and superoxide were generated by fullerol suspensions while neither was detected in the aqu/nC60 suspensions. A mechanistic framework for photosensitization that takes into account differences in C60 aggregate structure in water is proposed to explain these results. While theory developed for single molecules suggests that alterations to the C60 cage should reduce the quantum yield for the triplet state and associated ROS production, the failure to detect ROS production by aqu/nC60 is explained in part by a more dense aggregate structure compared with the hydroxylated C60.

The heteroaggregation of engineered nanoparticles (ENPs) with natural colloids (NCs), which are ubiquitous in natural surface waters, is a crucial process affecting the environmental transport and fate of ENPs. Attachment efficiencies for heteroaggregation, α hetero, are required as input parameters in environmental fate models to predict ENP concentrations and contribute to ENP risk assessment. Here, we present a novel method for determining α hetero values by using a combination of laser diffraction measurements and aggregation modeling based on the Smoluchowski equation. Titanium dioxide nanoparticles (TiO2 NPs, 15 nm) were used to demonstrate this new approach together with larger silicon dioxide particles (SiO2, 0.5 μm) representing NCs. Heteroaggregation experiments were performed at different environmentally relevant solution conditions. At pH 5 the TiO2 NPs and the SiO2 particles are of opposite charge, resulting in α hetero values close to 1. At pH 8, where all particles are negatively charged, α hetero was strongly affected by the solution conditions, with α hetero ranging from <0.001 at low ionic strength to 1 at conditions with high NaCl or CaCl2 concentrations. The presence of humic acid stabilized the system against heteroaggregation.

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A number of commercialized nanomaterials incorporate TiO(2) nanoparticles. Studying their structural stability in media mimicking the environment or the conditions of use is crucial in understanding their potential eco-toxicological effects. We focused here on a hydrophobic TiO(2) nanoparticle-based formulation used in cosmetics: T-Lite SF. It is composed of a TiO(2) core, coated with two successive protective layers of Al(OH)(3), and polydimethylsiloxane. Soon after contact with water (pH = 5, low ionic strength), the T-Lite SF becomes hydrophilic and form aggregates. During this aging, 90%wt of the total Si of the organic layer is desorbed, and the PDMS remaining at the surface is oxidized. The Al(OH)(3) layer is also affected but remains sorbed at the surface. This remaining Al-based layer still protects from the production of superoxide ions from the photoactive/phototoxic TiO(2) core in our experimental conditions.