Cu₂ZnSnS₄–PtM (M = Co, Ni) Nanoheterostructures for Photocatalytic Hydrogen Evolution

We report the synthesis and photocatalytic and magnetic characterization of colloidal nanoheterostructures formed by combining a Pt-based magnetic metal alloy (PtCo, PtNi) with Cu₂ZnSnS₄ (CZTS). While CZTS is one of the main candidate materials for solar energy conversion, the introduction of a Pt-based alloy on its surface strongly influences its chemical and electronic properties, ultimately determining its functionality. In this regard, up to a 15-fold increase of the photocatalytic hydrogen evolution activity was obtained with CZTS–PtCo when compared with CZTS. Furthermore, two times higher hydrogen evolution rates were obtained for CZTS–PtCo when compared with CZTS–Pt, in spite of the lower precious metal loading of the former. Besides, the magnetic properties of the PtCo nanoparticles attached to the CZTS nanocrystals were retained in the heterostructures, which could facilitate catalyst purification and recovery for its posterior recycling and/or reutilization

Umweltgerechtes Verkehrsverhalten beginnt in den Köpfen

The control of the phase distribution in multicomponent nanomaterials is critical to optimize their catalytic performance. In this direction, while impressive advances have been achieved in the past decade in the synthesis of multicomponent nanoparticles and nanocomposites, element rearrangement during catalyst activation has been frequently overseen. Here, we present a facile galvanic replacement-based procedure to synthesize Co@Cu nanoparticles with narrow size and composition distributions. We further characterize their phase arrangement before and after catalytic activation. When oxidized at 350 °C in air to remove organics, Co@Cu core–shell nanostructures oxidize to polycrystalline CuO-Co₃O₄ nanoparticles with randomly distributed CuO and Co₃O₄ crystallites. During a posterior reduction treatment in H₂ atmosphere, Cu precipitates in a metallic core and Co migrates to the nanoparticle surface to form Cu@Co core–shell nanostructures. The catalytic behavior of such Cu@Co nanoparticles supported on mesoporous silica was further analyzed toward CO₂ hydrogenation in real working conditions

Size and Aspect Ratio Control of Pd₂Sn Nanorods and Their Water Denitration Properties

Monodisperse Pd₂Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd₂Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd₂Sn nanorods to have improved catalytic performance. In view of these results, Pd₂Sn nanorods were also evaluated for water denitration

Solvothermal, Chloroalkoxide-based Synthesis of Monoclinic WO₃ Quantum Dots and Gas-Sensing Enhancement by Surface Oxygen Vacancies

We report for the first time the synthesis of monoclinic WO₃ quantum dots. A solvothermal processing at 250 °C in oleic acid of W chloroalkoxide solutions was employed. It was shown that the bulk monoclinic crystallographic phase is the stable one even for the nanosized regime (mean size 4 nm). The nanocrystals were characterized by X-ray diffraction, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV–vis, Fourier transform infrared and Raman spectroscopy. It was concluded that they were constituted by a core of monoclinic WO₃, surface covered by unstable W­(V) species, slowly oxidized upon standing in room conditions. The WO₃ nanocrystals could be easily processed to prepare gas-sensing devices, without any phase transition up to at least 500 °C. The devices displayed remarkable response to both oxidizing (nitrogen dioxide) and reducing (ethanol) gases in concentrations ranging from 1 to 5 ppm and from 100 to 500 ppm, at low operating temperatures of 100 and 200 °C, respectively. The analysis of the electrical data showed that the nanocrystals were characterized by reduced surfaces, which enhanced both nitrogen dioxide adsorption and oxygen ionosorption, the latter resulting in enhanced ethanol decomposition kinetics

Surface Modification of TiO₂ Nanocrystals by WO_<i>x</i> Coating or Wrapping: Solvothermal Synthesis and Enhanced Surface Chemistry

TiO₂ anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic acid, in the presence of W chloroalkoxide, with W/Ti nominal atomic concentration (<i>R</i>_w) ranging from 0.16 to 0.64. The as-prepared materials were heat-treated up to 500 °C for thermal stabilization and sensing device processing. For <i>R</i>_0.16, the as-prepared materials were constituted by an anatase core surface-modified by WO_<i>x</i> monolayers. This structure persisted up to 500 °C, without any WO₃ phase segregation. For <i>R</i>_w up to <i>R</i>_0.64, the anatase core was initially wrapped by an amorphous WO_<i>x</i> gel. Upon heat treatment, the WO_<i>x</i> phase underwent structural reorganization, remaining amorphous up to 400 °C and forming tiny WO₃ nanocrystals dispersed into the TiO₂ host after heating at 500 °C, when part of tungsten also migrated into the TiO₂ structure, resulting in structural and electrical modification of the anatase host. The ethanol sensing properties of the various materials were tested and compared with pure TiO₂ and WO₃ analogously prepared. They showed that even the simple surface modification of the TiO₂ host resulted in a 3 orders of magnitude response improvement with respect to pure TiO₂

Scalable Heating-Up Synthesis of Monodisperse Cu₂ZnSnS₄ Nanocrystals

Monodisperse Cu₂ZnSnS₄ (CZTS) nanocrystals (NCs), with quasi-spherical shape, were prepared by a facile, high-yield, scalable, and high-concentration heat-up procedure. The key parameters to minimize the NC size distribution were efficient mixing and heat transfer in the reaction mixture through intensive argon bubbling and improved control of the heating ramp stability. Optimized synthetic conditions allowed the production of several grams of highly monodisperse CZTS NCs per batch, with up to 5 wt % concentration in a crude solution and a yield above 90%

Die Operationstechnik der erweiterten endonasalen Kieferhöhlenoperation

We report the fine-tuning of the localized surface plasmon resonances (LSPRs) from ultraviolet to near-infrared by nanoengineering the metal nanoparticle morphologies from solid Ag nanocubes to hollow AuAg nanoboxes and AuAg nanoframes. Spatially resolved mapping of plasmon resonances by electron energy loss spectroscopy (EELS) revealed a homogeneous distribution of highly intense plasmon resonances around the hollow nanostructures and the interaction, that is, hybridization, of inner and outer plasmon fields for the nanoframe. Experimental findings are accurately correlated with the boundary element method (BEM) simulations demonstrating that the homogeneous distribution of the plasmon resonances is the key factor for their improved plasmonic properties. As a proof of concept for these enhanced plasmonic properties, we show the effective label free sensing of bovine serum albumin (BSA) of single-walled AuAg nanoboxes in comparison with solid Au nanoparticles, demonstrating their excellent performance for future biomedical applications

Mn₃O₄@CoMn₂O₄–Co_<i>x</i>O_<i>y</i> Nanoparticles: Partial Cation Exchange Synthesis and Electrocatalytic Properties toward the Oxygen Reduction and Evolution Reactions

Mn₃O₄@CoMn₂O₄ nanoparticles (NPs) were produced at low temperature and ambient atmosphere using a one-pot two-step synthesis protocol involving the cation exchange of Mn by Co in preformed Mn₃O₄ NPs. Selecting the proper cobalt precursor, the nucleation of Co_<i>x</i>O_<i>y</i> crystallites at the Mn₃O₄@CoMn₂O₄ surface could be simultaneously promoted to form Mn₃O₄@CoMn₂O₄–Co_<i>x</i>O_<i>y</i> NPs. Such heterostructured NPs were investigated for oxygen reduction and evolution reactions (ORR, OER) in alkaline solution. Mn₃O₄@CoMn₂O₄–Co_<i>x</i>O_<i>y</i> NPs with [Co]/[Mn] = 1 showed low overpotentials of 0.31 V at −3 mA·cm^–2 and a small Tafel slope of 52 mV·dec^–1 for ORR, and overpotentials of 0.31 V at 10 mA·cm^–2 and a Tafel slope of 81 mV·dec^–1 for OER, thus outperforming commercial Pt-, IrO₂-based and previously reported transition metal oxides. This cation-exchange-based synthesis protocol opens up a new approach to design novel heterostructured NPs as efficient nonprecious metal bifunctional oxygen catalysts