Search

Elucidating the interactions between metal ions and dissolved organic matter and deciphering mechanisms for their mineralization in the aquatic environment are central to understanding the speciation, transport, and toxicity of nanoparticles (NPs). Herein, we examine the interactions between Ag+ and Au3+ ions in mixed solutions (χAg = 0.2, 0.5, and 0.8) in the presence of humic acids (HAs) under simulated sunlight; these conditions result in the formation of bimetallic Ag-Au NPs. A key distinction is that the obtained alloy NPs are compositionally and morphologically rather different from NPs obtained from thermally activated dark processes. Photoillumination triggers a distinctive plasmon-mediated process for HA-assisted reductive mineralization of ions to bimetallic alloy NPs which is not observed in its dark thermal reduction counterpart. The initial nucleation of bimetallic NPs is dominated by differences in the cohesive energies of Ag and Au crystal lattices, whereas the growth mechanisms are governed by the strongly preferred incorporation of Ag ions, which stems from their greater photoreactivity. The bimetallic NPs crystallize in shapes governed by the countervailing influence of minimizing free energy through the adoption of Wulff constructions and the energetic penalties associated with twin faults. As such, assessments of the stability and the potential toxic effects of bimetallic NPs arising from their possible existence in aquatic environments will depend sensitively on the origins of their formation.

Metastable materials that represent excursions from thermodynamic minima are characterized by distinctive structural motifs and electronic structure, which frequently underpins new function. The binary oxides of hafnium present a rich diversity of crystal structures and are of considerable technological importance given their high dielectric constants, refractory characteristics, radiation hardness, and anion conductivity; however, high-symmetry tetragonal and cubic polymorphs of HfO2 are accessible only at substantially elevated temperatures (1720 and 2600 °C, respectively). Here, we demonstrate that the core–shell arrangement of VO2 and amorphous HfO2 promotes outwards oxygen diffusion along an electropositivity gradient and yields an epitaxially matched V2O3/HfO2 interface that allows for the unprecedented stabilization of the metastable cubic polymorph of HfO2 under ambient conditions. Free-standing cubic HfO2, otherwise accessible only above 2600 °C, is stabilized by acid etching of the vanadium oxide core. In contrast, interdiffusion under oxidative conditions yields the negative thermal expansion material HfV2O7. Variable temperature powder X-ray diffraction demonstrate that the prepared HfV2O7 exhibits pronounced negative thermal expansion in the temperature range between 150 and 700 °C. The results demonstrate the potential of using epitaxial crystallographic relationships to facilitate preferential nucleation of otherwise inaccessible metastable compounds.

Fenestration elements that enable spectrally selective dynamic modulation of the near-infrared region of the electromagnetic spectrum are of great interest as a means of decreasing the energy consumption of buildings by adjusting solar heat gain in response to external temperature. The binary vanadium oxide VO2 exhibits a near-room-temperature insulator–metal electronic transition accompanied by a dramatic modulation of the near-infrared transmittance. The low-temperature insulating phase is infrared transparent but blocks infrared transmission upon metallization. There is considerable interest in harnessing the thermochromic modulation afforded by VO2 in nanocomposite thin films. However, to prepare a viable thermochromic film, the visible-light transmittance must be maintained as high as possible while maximizing thermochromic modulation in the near-infrared region of the electromagnetic spectrum, which necessitates the development of high-crystalline-quality VO2 nanocrystals of the optimal particle siz...

Materials exhibiting pronounced metal–insulator transitions such as VO2 have acquired great importance as potential computing vectors and electromagnetic cloaking elements given the large accompanying reversible modulation of properties such as electrical conductance and optical transmittance. As a first-order phase transition, considerable phase coexistence and hysteresis is typically observed between the heating insulator → metal and cooling metal → insulator transformations of VO2. Here, we illustrate that substitutional incorporation of tungsten greatly modifies the hysteresis of VO2, both increasing the hysteresis as well as introducing a distinctive kinetic asymmetry wherein the heating symmetry-raising transition is observed to happen much faster as compared to the cooling symmetry-lowering transition, which shows a pronounced rate dependence of the transition temperature. This observed kinetic asymmetry upon tungsten doping is attributed to the introduction of phase boundaries resulting from stabi...

Buildings consume an inordinate amount of energy, accounting for 30–40% of worldwide energy consumption. A major portion of solar radiation is transmitted directly to building interiors through windows, skylights, and glazed doors where the resulting solar heat gain necessitates increased use of air conditioning. Current technologies aimed at addressing this problem suffer from major drawbacks, including a reduction in the transmission of visible light, thereby resulting in increased use of artificial lighting. Since currently used coatings are temperature-invariant in terms of their solar heat gain modulation, they are unable to offset cold-weather heating costs that would otherwise have resulted from solar heat gain. There is considerable interest in the development of plastic fenestration elements that can dynamically modulate solar heat gain based on the external climate and are retrofittable onto existing structures. The metal–insulator transition of VO2 is accompanied by a pronounced modulation of n...

Unconventional deposits such as extra heavy oil and bitumen represent a steadily increasing proportion of extracted fuels. The rheological properties of viscous crude oil represents a formidable impediment to their extraction, transportation, and processing and have necessitated considerable retooling and changes to process design. In this work, we demonstrate that highly textured inorganic substrates generated by depositing ZnO nanotetrapods onto periodically ordered stainless steel mesh substrates exhibit viscous oil contact angles exceeding 150° as well as enable the facile gliding of viscous oil. Such functionality is derived as a result of multiscale texturation and porosity achieved within these substrates, which are characterized by trapping of plastronic air pockets at the solid/liquid interface. Further reduction of the surface energy has been achieved by constituting a helical highly ordered self-assembled monolayer of a perfluorinated phosphonic acid on the ZnO surfaces. Such structures are str...

Metastable materials that represent excursions from thermodynamic minima are characterized by distinctive structural motifs and electronic structure, which frequently underpins new function. The binary oxides of hafnium present a rich diversity of crystal structures and are of considerable technological importance given their high dielectric constants, refractory characteristics, radiation hardness, and anion conductivity; however, high-symmetry tetragonal and cubic polymorphs of HfO

The azinomycins are a family of potent anti-tumor agents with the ability to form interstrand crosslinks with DNA. This study reports on the unusual biosynthetic formation of the 5-methyl naphthoate moiety, which is essential for effective DNA association. While sequence analysis predicts that the polyketide synthase (AziB) catalyzes the formation of this naphthoate, 2-methylbenzoic acid, a truncated single-ring product, is formed instead. We demonstrate that the thioesterase (AziG) acts as a chain elongation and cyclization (CEC) domain and is required for the additional two rounds of chain extension to form the expected product.

We present a study of optical modulation by the effect of temperature-induced insulator-to-metal phase transition of vanadium dioxide ( V O 2 ) nanocrystals deposited in an antiresonance hollow-core fiber (AR-HCF). We fabricate such a V O 2 -coated fiber by embedding alkylsilane functionalized V O 2 nanocrystals into the air holes of an AR-HCF. With this fiber, we achieve an optical loss modulation of ∼ 60 % at a temperature above ∼ 53 ∘ C over an ultrabroad spectral range that encompasses the S + C + L band.

Increasing intercalation of Li-ions brings about distortive structural transformations in several canonical intercalation hosts. Such phase transformations require the energy dissipative creation and motion of dislocations at the interface between the parent lattice and the nucleated Li-rich phase. Phase inhomogeneities within particles and across electrodes give rise to pronounced stress gradients, which can result in capacity fading. How such transformations alter Li-ion diffusivities remains much less explored. In this article, we use layered V

Gold and silver nanoparticles can be stabilized endogenously within aquatic environments from dissolved ionic species as a result of mineralization induced by dissolved organic matter. However, the ability of fulvic and humic acids to stabilize bimetallic nanoparticles is entirely unexplored. Elucidating the formation of such particles is imperative given their potential ecological toxicity. Herein, we demonstrate the nucleation, growth, and stabilization of bimetallic Ag–Au nanocrystals from the interactions of Ag+ and Au3+ with Suwannee River fulvic and humic acids. The mechanisms underpinning the stabilization of Ag–Au alloy NPs at different pH (6.0–9.0) values are studied by UV–vis spectrophotometry, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). Complexation of free Ag+ and Au3+ ions with the Lewis basic groups (carbonyls, carboxyls, and thiols) of FA and HA, followed by electron-transfer from redox-acti...

Buildings consume an inordinate amount of energy, accounting for 30-40% of worldwide energy consumption. A major portion of solar radiation is transmitted directly to building interiors through windows, skylights, and glazed doors where the resulting solar heat gain necessitates increased use of air conditioning. Current technologies aimed at addressing this problem suffer from major drawbacks, including a reduction in the transmission of visible light, thereby resulting in increased use of artificial lighting. Since currently used coatings are temperature-invariant in terms of their solar heat gain modulation, they are unable to offset cold-weather heating costs that would otherwise have resulted from solar heat gain. There is considerable interest in the development of plastic fenestration elements that can dynamically modulate solar heat gain based on the external climate and are retrofittable onto existing structures. The metal-insulator transition of VO