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Radio frequency (RF) induction heating was compared to conventional thermal heating for the hydrogenation of oleic acid to stearic acid. The RF reaction demonstrated decreased coke accumulation and increased product selectivity at comparable temperatures over mesoporous Fe3O4 catalysts composed of 28-32 nm diameter nanoparticles. The Fe3O4 supports were decorated with Pd and Pt active sites and served as the local heat generators when subjected to an alternating magnetic field. For hydrogenation over Pd/Fe3O4, both heating methods gave similar liquid product selectivities, but thermogravimetric analysis-differential scanning calorimetry measurements showed no coke accumulation for the RF-heated catalyst versus 6.5 wt % for the conventionally heated catalyst. A different trend emerged when hydrogenation over Pt/Fe3O4 was performed. Compared to conventional heating, the RF increased the selectivity to stearic acid by an additional 15%. Based on these results, RF heating acting upon a magnetically susceptible nanoparticle catalyst would also be expected to positively impact systems with high coking rates, for example, nonoxidative dehydrogenations. [ABSTRACT FROM AUTHOR]

The presence of a temperature gradient between the magnetic nanoparticle (NP) surface and the bulk medium during induction heating has been observed across several fields. While no noticeable increase in bulk temperature is observed, biological (DNA denaturation, tumor apoptosis) and chemical (bond cleavage) evidence indicates high temperatures near/at the NP surface. Unfortunately, current methods for temperature probing rely on bulk temperature measurements (fiber-optic IR probes) or are limited by thermal stability and spatial resolution (organic molecules). To further the understanding of magnetic heating as a driving force in catalysis, as well as drug delivery/hyperthermia treatments, a more accurate description of the nanoparticle surface temperature is needed. This work uses inorganic luminescent probes in direct contact with the particle surface, entailing the deposition of YVO4:Eu3+ around a Fe3O4|SiO2 structure, to measure the local temperature. The luminescent response is calibrated in situ via a controlled temperature stage to extract the field-dependent heating. The luminescent probe results in a high spatial resolution (<5.5 nm) with temperatures up to 64 °C higher than standard fiber-optic probes. The direct contact between the photoluminescence (PL) probe and Fe3O4 allows for ballistic transport and improved temporal resolution, mimicking an adiabatic system (negligible long-range heat dissipation). Other advantages include avoiding measurements in liquid media, where the distance between the heat source and the probe cannot be controlled, adding to the uncertainty of the temperature measurement due to changes in colloidal anisotropy (which changes with the heating profile) of the magnetic cores and surface quenching of the luminescent signal. [ABSTRACT FROM AUTHOR]

Ni can be used as a catalyst for dry reforming of methane (DRM), replacing more expensive and less abundant noble metal catalysts (Pt, Pd, and Rh) with little sacrifice in activity. Ni catalysts deactivate quickly under realistic DRM conditions. Rare earth oxides such as CeO 2 , or as CeO 2 -ZrO 2 -Al 2 O 3 (CZA), are supports that improve both the activity and stability of Ni DRM systems due to their redox activity. However, redox-active supports can also enhance the undesired reverse water gas shift (RWGS) reaction, reducing the hydrogen selectivity. In this work, Ni on CZA was coated with an ultrathin Al 2 O 3 overlayer using atomic layer deposition (ALD) to study the effects of the overlayer on catalyst activity, stability, and H 2 /CO ratio. A low-conversion screening method revealed improved DRM activity and lower coking rate upon the addition of the Al 2 O 3 ALD overcoat, and improvements were subsequently confirmed in a high-conversion reactor at long times onstream. The overcoated samples gave an H 2 /CO ratio of ∼1 at high conversion, much greater than uncoated catalysts, and no evidence of deactivation. Characterization of used (but still active) catalysts using several techniques suggests that active Ni is in formal oxidation state >0, Ni-Ce-Al is most likely present as a mixed oxide at the surface, and a nominal thickness of 0.5 nm for the Al 2 O 3 overcoat is optimal., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Anion engineering has proven to be an effective strategy to tailor the physical and chemical properties of metal oxides by modifying their existing crystal structures. In this work, a low-temperature synthesis for rare earth (RE)-doped Y 2 O 2 SO 4 and Y 2 O 2 S was developed via annealing of Y(OH) 3 intermediates in the presence of elemental sulfur in a sealed tube, followed by a controlled reduction step. The crystal structure patterns (X-ray diffraction) and optical spectra (UV-IR) of Y 2 O 2 SO 4 , Y 2 O 2 S, and crystalline Y 2 O 3 were collected throughout the treatment steps to correlate the structural transformations (via thermogravimetric analysis) with the optical properties. Local and long-range crystallinities were characterized by using X-ray and optical spectroscopy approaches. Systematic shifts in the Eu 3+ excitation and emission peaks were observed as a function of SO 4 2- concentrations resulting from a crystal evolution from cubic (Y 2- concentrations resulting from a crystal evolution from cubic (Y 2 O 3 ) to trigonal (Y 2 O 2 S) and monoclinic (Y 2 O 2 SO 4 ), which can modify the local hybridization of sensitizer dopants (i.e., Ce 3+ ). Ultimately, Tb 3+ and Tb 3+ /Ce 3+ doping was employed in these hosts (Y 2 O 2 SO 4, Y 2 O 2 S, and Y 2 O 3 ) to understand energy transfer between sensitizer and activator ions, which showed significant enhancement for the monoclinic sulfate structure., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Culturing cancer cells in a three-dimensional (3D) environment better recapitulates in vivo conditions by mimicking cell-to-cell interactions and mass transfer limitations of metabolites, oxygen, and drugs. Recent drug studies have suggested that a high rate of preclinical and clinical failures results from mass transfer limitations associated with drug entry into solid tumors that 2D model systems cannot predict. Droplet microfluidic devices offer a promising alternative to grow 3D spheroids from a small number of cells to reduce intratumor heterogeneity, which is lacking in other approaches. Spheroids were generated by encapsulating cells in novel thiol-acrylate (TA) hydrogel scaffold droplets followed by on-chip isolation of single droplets in a 990- or 450-member trapping array. The TA hydrogel rapidly (∼35 min) polymerized on-chip to provide an initial scaffold to support spheroid development followed by a time-dependent degradation. Two trapping arrays were fabricated with 150 or 300 μm diameter traps to investigate the effect of droplet size and cell seeding density on spheroid formation and growth. Both trapping arrays were capable of ∼99% droplet trapping efficiency with ∼90% and 55% cellular encapsulation in trapping arrays containing 300 and 150 μm traps, respectively. The oil phase was replaced with media ∼1 h after droplet trapping to initiate long-term spheroid culturing. The growth and viability of MCF-7 3D spheroids were confirmed for 7 days under continuous media flow using a customized gravity-driven system to eliminate the need for syringe pumps. It was found that a minimum of 10 or more encapsulated cells are needed to generate a growing spheroid while fewer than 10 parent cells produced stagnant 3D spheroids. As a proof of concept, a drug susceptibility study was performed treating the spheroids with fulvestrant followed by interrogating the spheroids for proliferation in the presence of estrogen. Following fulvestrant exposure, the spheroids showed significantly less proliferation in the presence of estrogen, confirming drug efficacy.

Rare earth (RE) doped yttria sesquioxide has been widely used as host materials for upconversion (UC) phosphors due to their high refractive index, wide band gap, and high melting point. Meanwhile, while fluoride matrices with low phonon cutoff energies exhibit stronger UC emissions, RE-doped oxides exhibit better thermal stability and higher thermal sensitivity when applied as optical temperature sensors. In this work, Sc 3+ is substituted in RE-doped Y 2 O 3 lattices to generate smaller cation sites, enhancing the crystal field and modifying the allowed optical transitions. Er 3+ is used as a photoluminescent probe to study the effect of site position and symmetry on the UC performance. In comparison with the traditional hydrothermal method, Sc 3+ is successfully incorporated into the Y 2 O 3 lattice via the co-precipitation/molten salt method without segregating observed. The Judd-Ofelt analysis was applied to determine the local symmetry and efficiency changes. Sc was found to be able to improve the luminescence performances of Er in Y 2- x Sc x O 3 (YScO) hosts by adjusting the local symmetry level around the luminescent sites. The local symmetry level was reduced with less than 30 mol % of Sc doping concentration based on the changes in Ω 2 values. Meanwhile, the YScO oxide was found to significantly improve the luminescence intensity and red-to-green ratio at a lower Yb 3+ concentration (5 mol %) instead of a higher concentration (20 mol %) commonly used. This was attributed to an increased energy transfer between the closer Yb 3+ -Er 3+ pairs. Overall, this work allows the spatial occupancy of luminescence centers in the metal oxide host materials to optimize the UC luminescence performance and develop a high-efficiency oxide material for high-temperature applications such as optical thermometry., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The presence of surface/deep defects in 4d- and 5d-perovskite oxide (ABO 3 , B = Nb, Ta, Mo, etc.) nanoparticles (NPs), originating from multivalent B-site cations, contributes to suppressing their metallic properties. These defect states can be removed using a H 2 /Ar thermal treatment, enabling the recovery of their electronic properties (i.e., low electrical resistivity, high carrier concentration, etc.) as expected from their electronic structure. Therefore, to engineer the electronic properties of these metastable perovskites, an oxygen-controlled crystallization approach coupled with a subsequent H 2 /Ar treatment was utilized. A comprehensive study of the effect of the post-treatment time on the electronic properties of these perovskite NPs was performed using a combination of scattering, spectroscopic, and computational techniques. These measurements revealed that a metallic-like state is stabilized in these oxygen-reduced NPs due to the suppression of deep rather than surface defects. Ultimately, this synthetic approach can be employed to synthesize ABO 3 perovskite NPs with tunable electronic properties for application into electrochemical devices.

Rare-earth based A 2 B 2 O 7 compounds have been considered as potential host materials for nuclear waste due to their exceptional chemical, physical, capability of accommodating high concentration of actinides at both A- and B-sites, negligible leaching, tendency to form antisite defects, and radiation stabilities. In this work, La 2 Hf 2 O 7 (LHO) and Gd 2 Hf 2 O 7 (GHO) nanoparticles (NPs) were chosen as the RE-based hafnates to study the structural changes and the formation of different U molecular structures upon doping (or alloying) at high concentration (up to 30 mol %) using a combined coprecipitation and molten-salt synthesis. These compounds form similar crystal structures, i.e., ordered pyrochlore (LHO) and disordered fluorite (GHO), but are expected to show different phase transformations at high U doping concentration. X-ray diffraction (XRD) and Rietveld refinement results show that the LHO:U NPs have high structural stability, whereas the GHO:U NPs exhibit a highly disordered structure at high U concentration. Alternatively, the vibrational spectra show an increasingly random oxygen distribution with U doping, driving the LHO:U NPs to the disordered fluorite phase. X-ray spectroscopy indicates that U is stabilized as different U 6+ species in both LHO and GHO hosts, resulting in the formation of oxygen vacancies stemming from the U local coordination and different phase transformation. Interestingly, the disordered fluorite phase has been reported to have increased radiation tolerance, suggesting multiple benefits associated with the LHO host. These results demonstrate the importance of the structural and chemical effect of actinide dopants on similar host matrices which are important for the development of RE-based hafnates for nuclear waste hosts, sensors, thermal barrier coatings, and scintillator applications.

Owing to their chemical and mechanical stability, metal-oxides have emerged as potential alternatives for conventional pure-metal and organic molecule-based solid-state electronic devices. Traditionally, band engineering of these metal-oxides has been performed to improve the efficiency of solar cells and transistors. However, recent advancements in the field of oxide-based electronic devices demand reversible band structure engineering for applications in next-generation adaptive electronics and memory devices. Therefore, this work aims to reversibly engineer the surface band structure of doped metal-oxides using stable organic ligands with weak dipoles. Para -substituted benzoic acid (BZA) ligands with positive and negative dipole moments were adsorbed in situ on the surface of TiO 2 :Ni 2+ thin film to modify the interfacial dipole moment, and the valence band structure was probed using surface-sensitive ultraviolet photoelectron spectroscopy (UPS). UPS, paired with density functional theory (DFT) simulations, demonstrate the ability to selectively tune interfacial electronic/chemical landscapes with ligand-dependent dipole moment. The unique ability to reversibly tune the band bending at the organic-inorganic interface of doped metal-oxide semiconductors using molecular dipoles is expected to play a key role in the development of metal-oxide-based adaptive electronics that outperform the conventional polymer-based and Si-based devices.

Devices driven by above-equilibrium "hot" electrons are appealing for photocatalytic technologies, such as in situ H 2 O 2 synthesis, but currently suffer from low (<1%) overall quantum efficiencies. Gold nanostructures excited by visible light generate hot electrons that can inject into a neighboring semiconductor to drive electrochemical reactions. Here, we designed and studied a metal-insulator-metal (MIM) structure of Au nanoparticles on a ZnO/TiO 2 /Al film stack, deposited through room-temperature, lithography-free methods. Light absorption, electron injection efficiency, and photocatalytic yield in this device are superior in comparison to the same stack without Al. Our device absorbs >60% of light at the Au localized surface plasmon resonance (LSPR) peak near 530 nm-a 5-fold enhancement in Au absorption due to critical coupling to an Al film. Furthermore, we show through ultrafast pump-probe spectroscopy that the Al-coupled samples exhibit a nearly 5-fold improvement in hot-electron injection efficiency as compared to a non-Al device, with the hot-electron lifetimes extending to >2 ps in devices photoexcited with fluence of 0.1 mJ cm -2 . The use of an Al film also enhances the photocatalytic yield of H 2 O 2 more than 3-fold in a visible-light-driven reactor. Altogether, we show that the critical coupling of Al films to Au nanoparticles is a low-cost, lithography-free method for improving visible-light capture, extending hot-carrier lifetimes, and ultimately increasing the rate of in situ H 2 O 2 generation.

Y 2 Zr 2 O 7 (YZO) is widely used as a host material for luminescent centers because of its high stability and the ability to accommodate anion defects. In this work, the effects of Ce and Tb doping on the photoluminescence (PL) properties of YZO nanoparticles (NPs) are studied in detail to correlate the emission intensity with the dopant concentration. Herein, a two-step synthesis method of coprecipitation and molten salt was employed to prepare the YZO:Tb,Ce NPs. The single doped YZO:Tb (2 mol %) NPs shows a strong Tb 3+ emission. However, after codoping with Ce ions, the Tb 3+ emission is quenched instead of the expected sensitization. To identify the mechanism of quenching (oxidation state/local symmetry), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) were performed. The Ce 4+ ions were observed to drive further oxidation of Tb to a nonluminescent +4 oxidation state. Alternatively, Eu 3+ was employed to probe local symmetry changes upon Ce doping. The asymmetry ratio of the magnetic and electronic transitions indicates that the Ce dopant also pushes the system into a higher symmetry, resulting in two separate quenching mechanisms.

The macroscopic device performance of organic solar cells is governed by interface physics on a nanometer scale. A comb-like bilayer all-polymer morphology featuring a controlled enhancement in donor-acceptor interfacial area is employed as a model system to investigate the fundamental processes of exciton separation and polaron recombination in these devices. The different nanostructures are characterized locally by SEM/AFM, and the buried interdigitating interface of the final device architecture is statistically verified on a large area via advanced grazing incidence X-ray scattering techniques. The results show equally enhanced harvesting of photoexcitons in both donor and acceptor materials directly correlated to the total enhancement of interfacial area. Apart from this beneficial effect, the enhanced interface leads to significantly increased polaron recombination losses both around the open-circuit voltage and maximum power point, which is determined in complement with diode dark current characteristics, impedance spectroscopy, and transient photovoltage measurements. From these findings, it is inferred that a spatially optimized comb-like donor-acceptor nanonetwork alone is not the ideal morphology even though often postulated. Instead, the energetic landscape has to be considered. A perfect morphology for an excitonic solar cell must be spatially and energetically optimized with respect to the donor-acceptor interface.