RESUMEN
Partial cation exchange reactions provide a synthetic pathway for rationally constructing heterostructured nanoparticles that incorporate different materials at precise locations. Multiple sequential partial cation exchange reactions can produce libraries of exceptionally complex heterostructured nanoparticles, but the first partial exchange reaction is responsible for defining the intraparticle frameworks that persist throughout and help to direct subsequent exchanges. Here, we studied the partial cation exchange behavior of spherical nanoparticles of roxbyite copper sulfide, Cu1.8S, with substoichiometric amounts of Zn2+. We observed the formation of ZnS-Cu1.8S-ZnS sandwich spheres, which are already well known in this system, as well as ZnS-Cu1.8S Janus spheres and Cu1.8S-ZnS-Cu1.8S central band spheres, which have not been observed previously as significant subpopulations of samples. Aliquots taken during the formation of the heterostructured nanoparticles suggest that substoichiometric amounts of Zn2+ limit the number of sites per particle where exchange initiates and/or propagates, thereby helping to define intraparticle frameworks that are different from those observed using excess amounts of exchanging cations. We applied these insights from mixed-population samples to the higher-yield synthesis of ZnS-Cu1.8S Janus spheres, as well as the higher-order derivatives ZnS-(CdS-Cu1.8S), ZnS-(CdS-ZnS), and ZnS-(CdS-CoS), which have unique features relative to previously reported analogues. These results demonstrate how the diversity of intraparticle frameworks in spherical nanoparticles can be expanded to produce a broader range of downstream heterostructured products.
RESUMEN
We report predictive guidelines for the substoichiometric cation exchange of model two-component metal sulfide nanorods containing divalent cations of similar hardness. Unit cell volume changes, cation radii, solubility constants, and solid state interfaces influence selectivity during substoichiometric exchange of Cu+ when multiple products are possible.
RESUMEN
Gold nanoparticles are well-known to exhibit size-dependent properties that are responsible for their unique catalytic, optical, and electronic applications. However, electron-phonon coupling, which is important for photocatalysis and light harvesting, is one of the rare properties of gold that is size-independent above a threshold value, e.g., for nanospheres larger than approximately 5 nm in diameter. Here, we show that when interfaced to a comparably sized Pt nanoparticle, the electron-phonon coupling constant of the hybrid material depends on the diameter of the Au domain. This is important because the electron-phonon coupling constant describes the efficiency by which hot electrons are converted to local heat by the primary electron-phonon scattering thermalization channel. We begin by synthesizing a library of Au-Pt hybrid nanoparticle heterodimers by growing size-tunable Au nanoparticles on Pt nanoparticle seeds. By systematically varying reagent concentration and reaction time, the Au domain diameter of the Au-Pt hybrid nanoparticle heterodimers can be tuned between 4.4 and 16 nm while the size of the Pt domain remains constant. Calibration curves allow us to dial in precise Au domain sizes, and microscopic analysis of the Au-Pt heterodimers provides insights into how they grow and how their morphologies evolve. Femtosecond time-resolved transient absorption spectroscopy reveals that for Au-Pt heterodimers having Au domain diameters of 8.7 to 14 nm, the electron-phonon coupling constant decreases by more than 80%, which is not observed for comparably sized Au nanoparticles. Interfacing smaller Au domains with Pt nanoparticle surfaces causes an increase in the density of states near the Fermi level of Au, which results in accelerated thermalization times through an increased number of electron-phonon interactions. The combination of precision hybrid nanoparticle synthesis and size-dependent electron-phonon coupling may be important for designing composite metals for photocatalytic and light-harvesting applications and for engineering different functions into established materials.
RESUMEN
In utero exposure to the endocrine disrupting compound bisphenol A (BPA) is known to disrupt mammary gland development and increase tumor susceptibility in rodents. It is unclear whether different periods of in utero development might be more susceptible to BPA exposure. We exposed pregnant CD-1 mice to BPA at different times during gestation that correspond to specific milestones of in utero mammary gland development. The mammary glands of early-life and adult female mice, exposed in utero to BPA, were morphologically and molecularly (estrogen receptor-α and Ki67) evaluated for developmental abnormalities. We found that BPA treatment occurring before mammary bud invasion into the mesenchyme [embryonic day (E)12.5] incompletely resulted in the measured phenotypes of mammary gland defects. Exposing mice up to the point at which the epithelium extends into the precursor fat pad (E16.5) resulted in a nearly complete BPA phenotype and exposure during epithelial extension (E15.5 to E18.5) resulted in a partial phenotype. Furthermore, the relative differences in phenotypes between exposure windows highlight the substantial correlations between early-life molecular changes (estrogen receptor-α and Ki67) in the stroma and the epithelial elongation defects in mammary development. These data further implicate BPA action in the stroma as a critical mediator of epithelial phenotypes.