Stabilization of Ag–Au Bimetallic Nanocrystals in Aquatic Environments Mediated by Dissolved Organic Matter: A Mechanistic Perspective

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-active moieties present in dissolved organic matter initiates the nucleation of the NPs. Alloy formation and interdiffusion of Au and Ag atoms are further facilitated by a galvanic replacement reaction between AuCl₄^– and Ag. Charge-transfer from Au to Ag stabilizes the formed bimetallic NPs. A more pronounced agglomeration of the Ag–Au NPs is observed when HA is used compared to FA as the reducing agent. The bimetallic NPs are stable for greater than four months, which suggests the possible persistence and dispersion of these materials in aquatic environments. The mechanistic ideas have broad generalizability to reductive mineralization processes mediated by dissolved organic matter

Hybrid Nanocomposite Films Comprising Dispersed VO₂ Nanocrystals: A Scalable Aqueous-Phase Route to Thermochromic Fenestration

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 near-infrared transmittance as a function of temperature and can potentially be harnessed for this purpose. Here, we demonstrate that a nanocomposite thin film embedded with well dispersed sub-100-nm diameter VO₂ nanocrystals exhibits a combination of high visible light transmittance, effective near-infrared suppression, and onset of NIR modulation at wavelengths <800 nm. In our approach, hydrothermally grown VO₂ nanocrystals with <100 nm diameters are dispersed within a methacrylic acid/ethyl acrylate copolymer after either (i) grafting of silanes to constitute an amorphous SiO₂ shell or (ii) surface functionalization with perfluorinated silanes and the use of a perfluorooctanesulfonate surfactant. Homogeneous and high optical quality thin films are cast from aqueous dispersions of the pH-sensitive nanocomposites onto glass. An entirely aqueous-phase process for preparation of nanocrystals and their effective dispersion within polymeric nanocomposites allows for realization of scalable and viable plastic fenestration elements

Biomimetic Plastronic Surfaces for Handling of Viscous Oil

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 strongly ejected upon immersion in water with water contact angles in excess of 160°. The functionalized substrates demonstrate remarkable superoleophobic behavior toward viscous crude oil with contact angles reaching 156° and are furthermore stable to temperatures of 290 °C. The remarkable results evidenced here hold promise for deployment of these constructs in the handling of viscous oil in order to reduce losses associated with transportation from railroad cars, pipelines, and other oil-handling equipment

Modulating the Hysteresis of an Electronic Transition: Launching Alternative Transformation Pathways in the Metal–Insulator Transition of Vanadium(IV) Oxide

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 stabilization of nanoscopic M₂ domains at the interface of the monoclinic M₁ and tetragonal phases. In contrast, the reverse cooling transition is mediated by point defects, giving rise to a pronounced size dependence of the hysteresis. Mechanistic elucidation of the influence of dopant incorporation on hysteresis provides a means to rationally modulate the hysteretic width and kinetic asymmetry, suggesting a remarkable programmable means of altering hysteretic widths of an electronic phase transition