Nucleation and Growth of Magnetron-Sputtered Ag Nanoparticles as Witnessed by Time-Resolved Small Angle X-Ray Scattering

Kinetic aspects of the synthesis of Ag nanoparticles (NPs) by magnetron sputtering are studied by in situ and time-resolved small angle X-ray scattering (SAXS). Part of the NPs are found to become confined within a capture zone at 1–10 mm from the surface of the target and circumscribed by the plasma ring. Three regimes of the NP growth are identified: 1) early growth at which the average NP diameter rapidly increases to 90 nm; 2) cycling instabilities at which the SAXS signal periodically fluctuates either due to expelling of large NPs from the capture zone or due to the axial rotation of the NP cloud; and 3) steady-state synthesis at which stable synthesis of the NPs is achieved. The NP confinement within the capture zone is driven by the balance of forces, the electrostatic force being dominant. On reaching the critical size, large NPs acquire an excessive charge and become expelled from the capture zone via the electrostatic interactions. As a result, significant NP deposits are formed on the inner walls of the aggregation chamber as well as in the central area of the target.     

PdO nanoparticles decorated TiO2 film with enhanced photocatalytic and self-cleaning properties

Magnetron sputtering and gas aggregation source (GAS) approaches were combined for the preparation of columnar TiO₂ structures decorated with PdO nanoparticles (NPs). The totally solvent-free synthesis approach provides good control of surface coverage, size, morphology, and stoichiometry of PdO NPs in comparison to wet chemical synthesis methods. X-ray photoelectron spectroscopy (XPS) analysis showed that the heat treatment led to the formation of a mixed oxide state PdO/PdO₂ on the TiO₂ layer. A steady equilibrium between PdO (oxidation by free and adsorbed ?OH) and PdO₂ (reduced by trapped photogenerated electrons) phases under UV irradiation seems to provide an efficient electron-hole pair separation. Such robust PdO–TiO₂ thin films have a strong potential for use as photocatalytic and self-cleaning windows or similar out-door technical surfaces.     

Sensing performance of CuO/Cu2O/ZnO:Fe heterostructure coated with thermally stable ultrathin hydrophobic PV3D3 polymer layer for battery application

Gas sensors are demanded in many different application fields. Especially the ever-growing field of batteries creates a great need for early hazard detection by gas sensors. Metal oxides are well known for gas sensing; however, moisture continues to be a major problem for the sensors, especially for the application in battery systems. This study reports on a new type of moisture protected gas sensor, which is capable to solve this problem. Sensitive nano-materials of CuO/Cu₂O/ZnO:Fe heterostructures are grown and subsequently coated with an ultrathin hydrophobic cyclosiloxane-polymer film via initiated chemical vapor deposition to protect the sensor from moisture. The monomer 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane is combined with the initiator perfluorobutanesulfonyl fluoride to obtain hydrophobic properties. Surface chemistry, film formation and preservation of functional groups are confirmed by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. It turns out that the hydrophobicity is retained even after annealing at 400 °C, which is ideal for gas sensing. Molecular distances in the polymer nanolayer are estimated by geometry optimization via MMFF94 followed by density functional theory. Compared with unprotected CuO/Cu₂O/ZnO:Fe, the coated CuO/Cu₂O/ZnO:Fe exhibit a much better sensing performance at a higher relative humidity, as well as tunability of the gas selectivity. This is highly beneficial for hazard detection in case of thermal runaway in batteries because the sensors can be used under high concentrations of relative humidity, which is ideal for Li–S battery applications.     

Synthesis of α-Methylene-γ-Lactones via Cr and Sn Complexes of β-Carbethoxy and β-Nitrile Allyl Bromides

The synthesis of some α-methylene-γ-lactones employing allylic Cr and Sn complexes is described.     

Synthesis of 3-Hydroxy-2-Methylene Carbonyl Compounds - Effect of Catalyst and Substrate on Reaction Rate

3-Hydroxyquinuclidine enhances the rate of formation of the title compounds whereas the acetylated derivative is a poor catalyst. A comparative study shows that methyl vinyl ketone is more reactive than methyl acrylate in the Baylis-Hillman reaction.     

Rate Enhancement Effects in the Dabco Catalysed Synthesis of Hydroxyalkenoate Esters

Marked acceleration of the catalytic coupling of aldehydes with methyl acrylate is achieved by varying either the aldehyde or the catalytic system. Rapid and efficient formation of heterocyclic derivatives with significant synthetic potential is described.     

[Ho5(H2O)16(OH)2As6W64O220]25−, ein großes neuartiges Polyoxoanion aus trivakanten Keggin‐Fragmenten

[Ho₅(H₂O)₁₆(OH)₂As₆W₆₄O₂₂₀]^25?, a Large Novel Polyoxoanion from Trivacant Keggin Fragments The novel polyoxotungstate Na₇K₁₈[Ho₅(H₂O)₁₆(OH)₂As₆W₆₄O₂₂₀] · 56 H₂O ( 1 ) was synthesized in aqueous solution and characterized by X‐ray structure analysis, elemental analysis and IR spectroscopy. The anion in 1 represents one of the largest polyoxoanions known yet and exhibits an unusual arrangement of six Keggin units. It consists of six trivacant lacunary α‐B‐(AsW₉O₃₃)^9? Keggin fragments which are connected by a bridging [Ho₅W₁₀(H₂O)₁₆(OH)₂O₂₂]²⁹⁺ unit. The five Ho^III atoms are coordinated by eight oxygen atoms, forming a square‐antiprism.     

Sandwichartige Polyoxowolframate mit Indium(III) als Heteroatom — Synthese und Charakterisierung der ersten Vertreter einer neuen Familie von Anionen

Sandwich‐like Polyoxotungstates with Indium(III) as a Heteroatom — Synthesis and Characterization of the First Examples of a New Type of Anions The syntheses of three novel polyoxometalates containing indium as heteroatom are presented. The compounds are characterized by X‐ray structure analysis and vibrational spectra Na_5nH_2n[(In(H₂O)₂)_{1, 5}(Na(H₂O)₂)_{0, 5}(In(H₂O)₂)₂(SbW₉O₃₃)₂]_n · 28n H₂O ( 1 ) crystallizes in the monoclinic crystal system (C2/c) with a = 19.370(4), b = 17.852(4), c = 30.015(6) Å and β = 97.38(3)°. Na₂K₂H₂[(In(H₂O)₃)₂(In(H₂O)₂)₂(AsW₉O₃₃)₂] · 37 H₂O ( 2 ) crystallizes in the monoclinic crystal system (space group C2/m) with a = 20.323(4), b = 15.269(3), c = 16.014(3) Å and β = 94.06(3)°. Na₁₀H₂[In₄(H₂O)₂(CoW₉O₃₄)₂] · 43 H₂O ( 3 ) shows lattice constants of a = 13.047(3), b = 17.735(4), c = 21.054(4) Å and β = 93.38(3)° in monoclinic crystal system (space group P2₁/n). The heteropolyanions in 1 and 2 are examples of the so called M₂X₂M₂₀‐type. They are built up of two β‐B‐[XW₉O₃₃] fragments, which are derived from defect structures of the Keggin anion. These subunits are connected by four MO₆‐groups (with M = In^III or Na for 1 and In^III for 2 ). The heteropolyanion in 3 belongs to the M₄X₂W₁₈‐type, which contains two α‐B‐[XW₉O₃₃]‐units connected via a belt of four InO₆‐polyhedra.