Nanoparticles with photoinduced precipitation for the extraction of pollutants from water and soil

Nanotechnology may offer fast and effective solutions for environmental clean-up. Herein, amphiphilic diblock copolymers are used to develop a platform of photosensitive core-shell nanoparticles. Irradiation with ultraviolet light removes the protective layer responsible for colloidal stability; as a result, the nanoparticles are rapidly and irreversibly converted to macroscopic aggregates. The associated phase separation allows measuring the partitioning of small molecules between the aqueous phase and nanoparticles; data suggests that interactions are enhanced by decreasing the particle size. Adsorption onto nanoparticles can be exploited to efficiently remove hydrophobic pollutants from water and contaminated soil. Preliminary in vivo experiments suggest that treatment with photocleavable nanoparticles can significantly reduce the teratogenicity of bisphenol A, triclosan and 17α-ethinyl estradiol without generating obviously toxic byproducts. Small-scale pilot experiments on wastewater, thermal printing paper and contaminated soil demonstrate the applicability of the approach.


Supplementary Figure 2.
A. 60-nm nanoparticles with different content of cleavable diblock copolymer can be synthesized. After synthesis, all nanoparticles have the same overall PEG density (full triangles). Upon UV irradiation, the PEG density on the surface of the nanoparticles (empty triangles) is inversely proportional to the amount of cleavable diblock copolymer used in the preparation of the nanoparticles. B. Shedding of the PEG corona does not appear to significantly affect the size distribution of the nanoparticles, possibly because the negative surface charges (COO -) cause electrostatic repulsion. C. The shedding of the PEG corona increases the negative charge of the nanoparticles. D. Neutralization of the surface charge by cations (Ca 2+ or Na + ) or acidic pH (pH 1) triggers precipitation of the nanoparticles. Figure 3. After very short UV irradiation, the nanoparticles lose their protective PEG layer and precipitate in presence of calcium. The time needed to precipitate the nanoparticles is in agreement with the kinetics of copolymer cleavage obtained from GPC data. The adsorption of dyes onto nanoparticles is evidenced by phase separation. In order to avoid photobleaching of the dyes, the nanoparticles were irradiated prior to incubation with the dyes.

Supplementary
Supplementary Figure 5. A The partitioning into nanoparticles of chemicals with different physicochemical properties appears to increase with decreasing particle size. Values represent each replicate, n = 9-12. B. The increase in partitioning appears to correlate with an increase in surface-to-volume ratio. To facilitate comparison, partition coefficients for each chemicals were normalized to those obtained with 160-nm nanoparticles. Values represent mean ± standard deviation, n = 9-12.
Supplementary Figure 6. For all tested particle sizes, the adsorption onto nanoparticles appears to correlate with the hydrophobicity of the small molecules, suggesting that hydrophobic interactions are at least partly responsible for the interactions between the chemicals and the nanoparticles.

Supplementary Figure 7.
In the absence of nanoparticles (dark red), the photodegradation of most chemicals is reduced, suggesting that the photocleavable linker plays an active role in the reaction. Different degradation mechanisms might be involved since, for some chemicals (i.e., pentachlorophenol, triclosan and methoxychlor), photodegradation appears to be reduced in the presence of nanoparticles (light pink).

Supplementary Figure 8. A.
To show that the reduced teratogenicity observed after treatment with photo-responsive nanoparticles was due to extraction and photodegradation of BPA, control experiments were carried out in which an equivalent amount of BPA was irradiated with UV light (in gray), or irradiated with UV light in the presence of non-photo-responsive nanoparticles (in dark blue). In both groups, all fish died during the 2 nd day post exposure to BPA, while fish not exposed to BPA survived (> 90% survival) (n = 96, p < 0.001). B. Functionalization of PEG with the hydroxyethyl photolinker did not enhance the teratogenicity of the polymer either before or after UV irradiation (> 90% survival). Here, the concentrations of the functionalized polymers were 10 times higher than those of unmodified PEG (log rank, p = 0.788, n = 48). Figure 9. A. Amount of BPA extracted from thermal printing paper using acetonitrile. The total BPA content was calculated by adding the values of two consecutive extraction steps. B. The amount of BPA remaining in the thermal printing paper is inversely proportional to the amount extracted with water or nanoparticles.