Richard Landers

Superparamagnetic nanoparticle-supported palladium: a highly stable magnetically recoverable and reusable catalyst for hydrogenation reactions

Here we present a magnetically recoverable palladium catalyst prepared by immobilization of palladium over silica-coated magnetite nanoparticles. The catalyst reduced by molecular hydrogen contains palladium nanoparticles well distributed and stabilized in the magnetizable support surfaces and converts cyclohexene to cyclohexane under mild reaction conditions (75 °C and 6 atm) with TOF of 11 500 h−1. The catalyst was easily recovered with a permanent magnet in the reactor wall and reused for up to 20 recycles of 2500 TON each without any significant loss in catalytic activity, demonstrating an efficient recycling process for hydrogenation reactions.

The role of oxygen partial pressure and annealing temperature on the formation of W = O bonds in thin WO3 films

Thin films of tungsten oxide were deposited onto silicon substrates using reactive rf sputtering. The structure of the films is strongly dependent on the conditions of deposition and post-treatment. Important issues are the influences of oxygen pressure during deposition and of annealing temperature. We used x-ray photoelectron spectroscopy to investigate the in-depth composition of the films. The most surface sensitive O 1s core level spectra are made up of two structures, one generated by photoelectrons emitted from oxygen atoms in WO3 (O–W–O) and other at lower energy generated by the photoelectrons emitted from oxygen atoms located at the boundary of the grains (W = O). Using Raman spectroscopy, an increase of the W = O/O–W–O ratio was correlated to an increase in the oxygen partial pressure used during the deposition. A decrease of this ratio was observed while annealing temperature was increased, which was correlated to an increase in the size of the grains that form the films.

Microvoids in diamond‐like amorphous silicon carbide

The correlation between composition, microstructure, and optical properties of a‐Si1−xCx:H thin films with different stoichiometries was established. The alloys were deposited by radio frequency glow discharge under ‘‘starving’’ plasma conditions from mixtures of SiH4 and CH4. The samples were characterized by small angle x‐ray scattering, ultraviolet‐visible and infrared spectrometry, and Auger electron spectroscopy. The results showed the presence of microvoids with sizes between ≂3 A and ≂8 A. The relative microvoid volume fraction displayed a maximum for x around 55 at. % and decreased for higher values of x. High carbon content alloys (x≂70 at. %) not only have a lower relative microvoid volume fraction, but show optical gaps as high as 3.7 eV, high resistivity, and very low refractive index, indicating the presence of a diamond‐like C‐C structure. These remarkable results are attributed to the deposition under ‘‘starving’’ plasma conditions.

Effects of Oxygen Partial Pressure and Annealing Temperature on the Formation of Sputtered Tungsten Oxide Films

Thin films of tungsten oxide were deposited on silicon substrates using reactive radio frequency sputtering. The structure of the films strongly depends on the conditions of deposition and post-treatment. Important issues are the influences of oxygen pressure during deposition and annealing temperature on the morphology. Atomic force microscopy and scanning electron microscopy revealed that films were formed by grains. The sample deposited with an Ar:O 2 partial pressure ratio of 1:1 showed the highest roughness and the smallest grains when annealed at 350°C. X-ray photoelectron spectroscopy analysis revealed that the films were close to their stoichiometric formulation irrespective the oxygen partial pressure used during film deposition. The number of W=O bonds at the grain boundaries was found to he dependent on the oxygen partial pressure. Analysis by Raman spectroscopy suggested that the structure of the films was monoclinic. On the basis of these results an annealing temperature of 350°C was selected as post-treatment for the fabrication of WO 3 gas sensors. These sensors were highly sensitive, highly selective to ammonia vapors, and moderately responsive to humidity.

Catalyst Recovery and Recycling Facilitated by Magnetic Separation: Iridium and Other Metal Nanoparticles

The immobilization of metal nanoparticles in magnetic responsive solids allows the easy, fast, and clean separation of catalysts; however, the efficiency of this separation process depends on a strong metal–support interaction. This interaction can be enhanced by functionalizing the support surface with amino groups. Our catalyst support contains an inner core of magnetite that enables the magnetic separation from liquid systems and an external surface of silica suitable for further modification with organosilanes. We report herein that a magnetically recoverable amino‐functionalized support captured iridium species from liquid solutions and produced a highly active hydrogenation catalyst with negligible metal leaching. An analogous Ir0 catalyst prepared with use of a nonfunctionalized support shows a higher degree of metal leaching into the liquid products. The catalytic performance in the hydrogenation of alkenes is compared with that of Rh and Pt catalysts.

Lithium insertion and electrochromism in polycrystalline molybdenum oxide films

In this work, molybdenum oxide thin films were deposited by r.f. reactive sputtering of metallic molybdenum target in an Ar + O 2 atmosphere. Thin films with different compositions and crystal structures were obtained by varying the oxygen flow (o). All samples, with the exception of the MoO 2 film, showed an electrochromic behavior, due to the reversible Li + /e insertion or extraction process. The transmittance change (λ = 632.8 nm), for the best sample, was ∼ 70%. The film having the best optical behavior is mostly formed by the β-MoO 3 phase. The composition, optical and mechanical properties were determined and analyzed in as-grown and in Li intercalated films. The local order structure was analyzed by X-ray absorption spectroscopy measurements at the Mo L 2,3 -edges. The valence band was studied by Photoelectron Spectroscopy.

Photoacoustic detection of ferromagnetic resonance in films

We report on the detection of the ferromagnetic resonance of Ni and Fe films through the photoacoustic effect. The photoacoustic signal dependence on both the magnetic field and the chopping frequency is also discussed in light of existing theoretical models for the production of the photoacoustic signals.

UHV and electrochemical studies of the surface properties of Ru + Pt + Ti mixed oxide electrodes

The surface properties of Ru0.3Pt0.4Ti0.3Ox, prepared by thermal decomposition of the respective chlorides on Ti in the temperature range 400–600°C, have been studied by XPS, AES and cyclic voltammetry in 1 M HClO4 solutions. The material loss during potential cycling has been determined by ICEPS of the electrolyte solution. Results have shown that, in the fresh electrodes, Pt is in the oxidation state of ca. +2, with a trend to decrease upon potential cycling. At the same time, Pt segregates to the surface and the voltammetric curve increasingly resembles that of a polycrystalline Pt electrode. XPS has confirmed that the surface concentration of Pt increases with the number of potential cycles, at the expense of that of Ru which is found preferentially dissolved in solution. The fact that the accumulation of metallic species in solution stops after a few tens of potential cycles suggests that (mechanical) erosion probably plays a predominant role with freshly prepared surfaces. Increasing the temperature of calcination improves the electrode stability, which has also been observed to be sensitive to the negative limit of the potential window.

Simultaneous determination of epinephrine and dopamine by electrochemical reduction on the hybrid material SiO2/graphene oxide decorated with Ag nanoparticles

This paper describes the synthesis, characterization and applications of a new hybrid material composed of mesoporous silica (SiO2) modified with graphene oxide (GO), SiO2/GO, obtained by the sol-gel process using HF as the catalyst. The hybrid material, SiO2/GO, was decorated with silver nanoparticles (AgNPs) with a size of less than 20 nanometres, prepared directly on the surface of the material using N,N-dimethylformamide (DMF) as the reducing agent. The resulting material was designated as AgNP/SiO2/GO. The Ag/SiO2/GO material was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and high-resolution transmission electron microscopy (HR-TEM). A glassy carbon electrode modified with AgNP/SiO2/GO was used in the development of a sensitive electrochemical sensor for the simultaneous determination of epinephrine and dopamine employing electrocatalytic reduction using squarewave voltammetry. Well-defined and separate reduction peaks were observed in PBS buffer at pH 7. No significant interference was seen for primarily biological interferents such as uric acid and ascorbic acid in the detection of dopamine and epinephrine. Our study demonstrated that the resultant AgNP/SiO2/GO-modified electrode is highly sensitive for the simultaneous determination of dopamine and epinephrine, with the limits of detection being 0.26 and 0.27 μmol L(-1), respectively. The AgNP/SiO2/GO-modified electrode is highly selective and can be used to detect dopamine and epinephrine in a human urine sample.

Influence of the deposition method on the morphology and elemental composition of SnO2 films for gas sensing: atomic force and X-ray photoemission spectroscopy analysis

Abstract The performance of metal oxide gas sensors is affected by their surface states, elemental composition, electronic and morphologic structures. Films of tin oxide were deposited onto silicon substrates using reactive radio frequency sputtering and drop-coating. In order to understand how the deposition procedure affects the morphology of the films, a structural characterisation based on atomic force microscopy was performed. The differences in elemental composition were analysed by X-ray photoemission spectroscopy. For sensors deposited by sputtering, a granular morphology and the presence of stannic sub-oxide (SnO) was observed. Sensors deposited by drop coating had a granular morphology but no stannic sub-oxide was present. The sensitivity of the drop-coated sensors to ethanol was found to be up to five times higher than the one of sputtered sensors. This difference can be associated to the presence of the stannic sub-oxide, grain size and inter-granular coupling.