Single‐source precursors are used to produce nanostructured BiVO4 photoanodes for water oxidation in a straightforward and scalable drop‐casting synthetic process. Polyoxometallate precursors, which contain both Bi and V, are produced in a one‐step reaction from commercially available starting materials. Simple annealing of the molecular precursor produces nanocrystalline BiVO4 films. The precursor can be designed to incorporate a third metal (Co, Ni, Cu, or Zn), enabling the direct formation of doped BiVO4 films. In particular, the Co‐ and Zn‐doped photoanodes show promise for photoelectrochemical water oxidation, with photocurrent densities >1 mA cm−2 at 1.23 V vs reversible hydrogen electrode (RHE). Using this simple synthetic process, a 300 cm2 Co‐BiVO4 photoanode is produced, which generates a photocurrent of up to 67 mA at 1.23 V vs RHE and demonstrates the scalability of this approach.
Reducible supports can affect the performance of metal catalysts by the formation of suboxide overlayers upon reduction, a process referred to as the strong metal–support interaction (SMSI). A combination of operando electron microscopy and vibrational spectroscopy revealed that thin TiO
x
overlayers formed on nickel/titanium dioxide catalysts during 400°C reduction were completely removed under carbon dioxide hydrogenation conditions. Conversely, after 600°C reduction, exposure to carbon dioxide hydrogenation reaction conditions led to only partial reexposure of nickel, forming interfacial sites in contact with TiO
x
and favoring carbon–carbon coupling by providing a carbon species reservoir. Our findings challenge the conventional understanding of SMSIs and call for more-detailed operando investigations of nanocatalysts at the single-particle level to revisit static models of structure-activity relationships.
Amines in heteroaromatic systems and pharmaceutical intermediates were functionalized through N-methylation with methanol using a palladium-loaded titanium dioxide (Pd/TiO2) photocatalyst. This method provides access to a series of tertiary N-methylamines bearing NO O-, and/or S-containing heteroaromatic functionalities from primary/secondary amines and methanol under mild reaction conditions. Facile syntheses of several pharmaceuticals containing N-methyl or ethyl groups, as well as related deuterated drugs, was achieved through the late-stage functionalization of amines.
Direct functionalization of amino groups in complex organic molecules is one of the most important key technologies in modern organic synthesis, especially in the synthesis of bio-active chemicals and pharmaceuticals. Whereas numerous chemical reactions of amines have been developed to date, a selective, practical method for functionalizing complex amines is still highly demanded. Here we report the first late-stage N-alkylation of pharmaceutically relevant amines with alcohols at ambient temperature. This reaction was achieved by devising a mixed heterogeneous photocatalyst in situ prepared from Cu/TiO2 and Au/TiO2. The mixed photocatalytic system enabled the rapid N-alkylation of pharmaceutically relevant molecules, the selective mono- and di-alkylation of primary amines, and the non-symmetrical dialkylation of primary amines to hetero-substituted tertiary amines.
The synthesis of
gold nanorods requires the presence of symmetry-breaking
and shape-directing additives, among which bromide ions and quaternary
ammonium surfactants have been reported as essential. As a result,
hexadecyltrimethylammonium bromide (CTAB) has been selected
as the most efficient surfactant to direct anisotropic growth. One
of the difficulties arising from this selection is the low solubility
of CTAB in water at room temperature, and therefore the seeded growth
of gold nanorods is usually performed at 25 °C or above, which
has restricted so far the analysis of kinetic effects derived from
lower temperatures. We report a systematic study of the synthesis
of gold nanorods from pentatwinned seeds using hexadecyltrimethylammonium
chloride (CTAC) as the principal surfactant and a low concentration
of bromide as shape-directing agent. Under these conditions, the synthesis
can be performed at temperatures as low as 8 °C, and the corresponding
kinetic effects can be studied, resulting in temperature-controlled
aspect ratio tunability.
Ytterbium-doped LiYF4 (Yb:YLF) is a commonly used material
for laser applications, as a photon upconversion medium, and for optical
refrigeration. As nanocrystals (NCs), the material is also of interest
for biological and physical applications. Unfortunately, as with most
phosphors, with the reduction in size comes a large reduction of the
photoluminescence quantum yield (PLQY), which is typically associated
with an increase in surface-related PL quenching. Here, we report
the synthesis of bipyramidal Yb:YLF NCs with a short axis of ∼60
nm. We systematically study and remove all sources of PL quenching
in these NCs. By chemically removing all traces of water from the
reaction mixture, we obtain NCs that exhibit a near-unity PLQY for
an Yb3+ concentration below 20%. At higher Yb3+ concentrations, efficient concentration quenching occurs. The surface
PL quenching is mitigated by growing an undoped YLF shell around the
NC core, resulting in near-unity PLQY values even for fully Yb3+-based LiYbF4 cores. This unambiguously shows
that the only remaining quenching sites in core-only Yb:YLF NCs reside
on the surface and that concentration quenching is due to energy transfer
to the surface. Monte Carlo simulations can reproduce the concentration
dependence of the PLQY. Surprisingly, Förster resonance energy
transfer does not give satisfactory agreement with the experimental
data, whereas nearest-neighbor energy transfer does. This work demonstrates
that Yb3+-based nanophosphors can be synthesized with a
quality close to that of bulk single crystals. The high Yb3+ concentration in the LiYbF4/LiYF4 core/shell
nanocrystals increases the weak Yb3+ absorption, making
these materials highly promising for fundamental studies and increasing
their effectiveness in bioapplications and optical refrigeration.
Electron tomography has become a cornerstone technique for the visualization of nanoparticle morphology in three dimensions. However, to obtain in‐depth information about a nanoparticle beyond surface faceting and morphology, different electron microscopy signals must be combined. The most notable examples of these combined signals include annular dark‐field scanning transmission electron microscopy (ADF‐STEM) with different collection angles and the combination of ADF‐STEM with energy‐dispersive X‐ray or electron energy loss spectroscopies. Here, the experimental and computational development of various multimode tomography techniques in connection to the fundamental materials science challenges that multimode tomography has been instrumental to overcoming are summarized. Although the techniques can be applied to a wide variety of compositions, the study is restricted to metal and metal oxide nanoparticles for the sake of simplicity. Current challenges and future directions of multimode tomography are additionally discussed.
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