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Surgical aortic valve replacement with a rapid deployment valve (RDV) is a relatively recent treatment option. The aim of this study was to compare the hemodynamic performance of balloon-expandable (BE)-RDVs and BE-transcatheter heart valves (THVs) in a high surgical risk and frail-elderly population.

Multifunctional composites that couple high-capacity adsorbents with catalytic nanoparticles (NPs) offer a promising route toward the degradation of organophosphorus pollutants or chemical warfare agents (CWAs). We couple mesoporous TiO2aerogels with plasmonic Cu nanoparticles (Cu/TiO2) and characterize the degradation of the organophosphorus CWA sarin under both dark and illuminated conditions. Cu/TiO2aerogels combine high dark degradation rates, which are facilitated by hydrolytically active sites at the Cu||TiO2interface, with photoenhanced degradation courtesy of semiconducting TiO2and the surface plasmon resonance (SPR) of the Cu nanoparticles. The TiO2aerogel provides a high surface area for sarin binding (155 m2g–1), while the addition of Cu NPs increases the abundance of hydrolytically active OH sites. Degradation is accelerated on TiO2and Cu/TiO2aerogels with O2. Under broadband illumination, which excites the TiO2bandgap and the Cu SPR, sarin degradation accelerates, and the products are more fully mineralized compared to those of the dark reaction. With O2and broadband illumination, oxidation products are observed on the Cu/TiO2aerogels as the hydrolysis products subsequently oxidize. In contrast, the photodegradation of sarin on TiO2is limited by its slow initial hydrolysis, which limits the subsequent photooxidation. Accelerated hydrolysis occurs on Cu/TiO2aerogels under visible illumination (>480 nm) that excites the Cu SPR but not the TiO2bandgap, confirming that the Cu SPR excitation contributes to the broadband-driven activity. The high hydrolytic activity of the Cu/TiO2aerogels combined with the photoactivity upon TiO2bandgap excitation and Cu SPR excitation is a potent combination of hydrolysis and oxidation that enables the substantial chemical degradation of organophorphorus compounds.

Carbon monoxide (CO) oxidation is not only an important industrial reaction but also a useful model system for investigations into reaction dynamics involving new catalyst designs. In this work, we use CO oxidation to probe the metal−support interactions between Cu nanoparticles and a TiO2aerogel support. We utilized a packed-bed reactor to demonstrate the activity of a Cu/TiO2aerogel catalyst for CO oxidation at temperatures above 463 K. In situinfrared spectroscopic methods revealed that the reaction proceeds primarily by a Cu-assisted Mars-van-Krevelen type mechanism. Results indicate that Ti4+sites are reduced by CO to generate Ti3+sites adjacent to oxygen vacancies. Lattice oxygen extraction appears to be accompanied by interfacial charge transfer from lower work function copper nanoparticles to the TiO2support, as evidenced by variable-temperature infrared spectroscopic studies of adsorbed CO. The charge transfer is evidenced by differences in the nature of CO bound to Ti4+sites within aerogels in the presence and absence of Cu. The Cu particles on the TiO2support lower the vibrational frequency for CO bound to Ti4+sites by 3 cm–1and increase the binding enthalpy by 7 kJ/mol. Infrared spectroscopic probes of oxidation state cycling during catalysis contribute toward the development of an overall CO oxidation reaction mechanism on the Cu/TiO2aerogel.

Protocols that express functional materials in a way that amplifies their surface-to-volume ratio offer a means to probe the structural ambiguity and surface-mediated reactivity of technologically important materials. We previously reported that three-dimensional (3D) ultraporous scaffolds, such as silica aerogels, silica fiber paper, and carbon nanofoam paper (CNF), provide a form factor that expresses energy-storing, catalytic ruthenium oxide (RuOx) as essentially all-surface—and a highly disordered one at that. To track the chemical state and solid-state structure of the 3D-expressed RuOxnanoskins as a function of thermal processing, we use X-ray near-edge structure (XANES), extended X-ray fine structure (EXAFS), and differential pair-distribution function (DPDF) analyses. We find that a Ru-centered ∼2.4 Å correlation present in the as-deposited oxide, also observed in PDF analysis of RuO2·nH2O but previously unassigned, fits the metastable corundum-like Ru2O3structure. This corundum-like feature diminishes in concentration with increasing treatment temperature (25–200 °C), commensurate with an increase in relative rutile RuO2content, electrical conductivity, and charge-storing capacitance of the oxide. Yet disorder persists beyond 8 Å, and a rutile nanocrystalline structure is not attained until >200 °C. The combination of synthetic amplification and total scattering analyses offers a viable approach to elucidate the structural ambiguity of practical, disordered nanomaterials.

Thin-film ruthenium dioxide (RuO2) is a promising alternative material as a conductive electrode in electronic applications because its rutile crystalline form is metallic and highly conductive. Herein, a solution-deposition multilayer technique is employed to fabricate ca. 70 ± 20 nm thick films (nanoskins), and terahertz spectroscopy is used to determine their photoconductive properties. Upon calcining at temperatures ranging from 373 to 773 K, nanoskins undergo a transformation from insulating (localized charge transport) behavior to metallic behavior. Terahertz time-domain spectroscopy (THz-TDS) indicates that nanoskins attain maximum static conductivity when calcined at 673 K (σ = 1030 ± 330 S·cm–1). Picosecond time-resolved terahertz spectroscopy using 400 and 800 nm excitation reveals a transition to metallic behavior when calcined at 523 K. For calcine temperatures less than 523 K, the conductivity increases following photoexcitation (ΔE< 0) while higher calcine temperatures yield films composed of crystalline, rutile RuO2and the conductivity decreases (ΔE> 0) following photoexcitation.

Using a solution-based, non−line-of sight synthesis, we electrolessly deposit ultrathin films of RuO2(“nanoskins”) on planar and 3D substrates and benchmark their activity and stability for oxygen-evolution reaction (OER) in acid electrolyte under device-relevant conditions. When an electrically contiguous ∼9 nm thick RuO2nanoskin is expressed on commercially available, insulating SiO2fiber paper, the RuO2@SiO2electrode exhibits high current density at low overpotential (10 mA cm–2@ η = 280 mV), courtesy of a catalyst amplified in 3D; however, the mass-normalized activity falls short of that achieved for films deposited on planar, metallic substrates (Ti foil). By wrapping the fibers with a <100 nm thick graphitic carbon layer prior to RuO2deposition (RuO2@C@SiO2), we retain the high mass activity of the RuO2(40–60 mA mg–1@ η = 330 mV) and preserve the desirable macroscale properties of the 3D scaffold: porous, lightweight, flexible, and inexpensive. The RuO2@C@SiO2anodes not only achieve the 10 mA cm–2figure of merit at a low overpotential (η = ∼270 mV), but more importantly they do so while (1) minimizing the mass of catalyst needed to achieve this metric, (2) incorporating the catalyst into a practical electrode design, and (3) improving the long-term stability of the catalyst. Our best-performing anodes achieve state-of-the-art or better performance on the basis of area and mass, and do so with a catalyst density 300–580× less than that of bulk RuO2. By limiting the oxidizing potential required to evolve O2at the electrode, even at 10 mA cm–2, we achieve stable activity for 100+ h.

The spectrum of two-dimensional (2D) and layered materials ‘beyond graphene’ offers a remarkable platform to study new phenomena in condensed matter physics. Among these materials, layered hexagonal boron nitride (hBN), with its wide bandgap energy (∼5.0–6.0 eV), has clearly established that 2D nitrides are key to advancing 2D devices. A gap, however, remains between the theoretical prediction of 2D nitrides ‘beyond hBN’ and experimental realization of such structures. Here we demonstrate the synthesis of 2D gallium nitride (GaN) via a migration-enhanced encapsulated growth (MEEG) technique utilizing epitaxial graphene. We theoretically predict and experimentally validate that the atomic structure of 2D GaN grown via MEEG is notably different from reported theory. Moreover, we establish that graphene plays a critical role in stabilizing the direct-bandgap (nearly 5.0 eV), 2D buckled structure. Our results provide a foundation for discovery and stabilization of 2D nitrides that are difficult to prepare via traditional synthesis.

We use intensity-modulated photovoltage spectroscopy (IMVS) and intensity-modulated photocurrent spectroscopy (IMPS) to characterize carrier dynamics in titania (TiO2) aerogels under photocatalytic conditions. By systematically increasing the weight fraction of the sol–gel precursor during TiO2sol–gel synthesis, we are able to impart drastic changes in carrier transport/trapping and improve the photocatalytic activity of TiO2aerogels for two mechanistically divergent photochemical reactions: reductive water splitting (H2generation) and oxidative degradation of dichloroacetate (DCA). The lifetimes of photogenerated electrons increase in going from lowest-to-highest precursor concentrations, as measured by IMVS, indicating increasing site density for electron trapsa trend that correlates with an 8× improvement for photocatalytic H2generation. Electron mobility in the aerogel films, as measured by IMPS, decreases with increasing trap density, further implicating the trapping sites as reactive sites. In contrast, photocatalytic DCA degradationdriven primarily by direct hole transfer to adsorbed DCAdepends only weakly on the electron dynamics in the film. Transient infrared spectroscopy shows no difference in carrier decay among the aerogel samples on picosecond time scales, indicating that changes in carrier dynamics within these networked nanomaterials are only observable at time scales measured by IMPV and IMPS. Correlating hole-mediated and electron-mediated photocatalytic activity with direct measurement of electron dynamics under photocatalytically relevant conditions and time scales comprises a powerful approach to determine how synthetic modifications to networked nanostructured photocatalysts affect the relevant physicochemical phenomena underlying their photocatalytic performance.

Nickel-based heterogeneous catalysts are economical alternatives to traditional Pt or Au-based materials, but their specific activity and stability fall short of these precious metals. Many questions remain regarding the active Ni phase for CO oxidation and how the supporting oxide affects its activity and stability under operating conditions. We demonstrate that CeO2aerogel-supported Ni(OH)2nanoparticles (NPs) show superior activity compared to Ni(OH)2NPs supported by commercial, nanometric CeO2powder or TiO2aerogels. Ex situ X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy reveal that intimate contact between Ni(OH)2NPs and the bonded nanoparticulate CeO2network prevents the conversion to NiO seen with larger aerogel-supported aggregates of Ni(OH)2NPs and unsupported Ni(OH)2NPs. The best stability and activity per mole of Ni is achieved at 2.5 wt % Ni(OH)2on the CeO2aerogel, which converts 95% of CO at 200 °C and maintains activity after 12 h of continuous reaction under dry or humid feedstreams. Computational analysis indicates that CO has far lower adsorption energy on Ni(OH)2compared to NiO, resulting in less poisoning of the active surface sites.