A single-source precursor approach to solution processed indium arsenide thin films

This paper reports the synthesis of the novel single-source precursor, [{(MeInAstBu)3}2(Me2InAs(tBu)H)2] and the subsequent first report of aerosol-assisted chemical vapour deposition of InAs thin films. Owing to the use of the single-source precursor, highly crystalline and stoichiometric films were grown at a relatively low deposition temperature of 450 °C. Core level XPS depth profiling studies showed some partial oxidation of the film surface, however this was self-limiting and disappeared on etch profiles. Valence band XPS analysis matched well with the simulated density of state spectrum. Hall effect measurements performed on the films showed that the films were n-type with promising resistivity (3.6 × 10−3 Ω cm) and carrier mobility (410 cm2 V−1 s−1) values despite growth on amorphous glass substrates

Bismuth oxyhalides: synthesis, structure and photoelectrochemical activity

We report the synthesis and photoelectrochemical assessment of phase pure tetragonal matlockite structured BiOX (where X = Cl, Br, I) films. The materials were deposited using aerosol-assisted chemical vapour deposition. The measured optical bandgaps of the oxyhalides, supported by density functional theory calculations, showed a red shift with the increasing size of halide following the binding energy of the anion p-orbitals that form the valence band. Stability and photoelectrochemical studies carried out without a sacrificial electron donor showed the n-type BiOBr film to have the highest photocurrent reported for BiOBr in the literature to date (0.3 mA cm−2 at 1.23 V vs. RHE), indicating it is an excellent candidate for solar fuel production with a very low onset potential of 0.2 V vs. RHE. The high performance was attributed to the preferred growth of the film in the [011] direction, as shown by X-ray diffraction, leading to internal electric fields that minimize charge carrier recombination

Dopant stability in multifunctional doped TiO 2's under environmental UVA exposure

We present a UV irradiation study of three nanomaterials which have been investigated and published by peer review previously, specifically tantalum, tungsten and phosphorus doped TiO2. These nanomaterials have been previously synthesised, characterised and designed with specific applications in mind, from photo-catalysts to transparent conducting oxides (TCO's) for use in solar cells and touchscreens. We show in this work, using X-ray photoelectron spectroscopy (XPS) that under sustained levels of environmental UVA Irradiation (0.42 mW cm−2) Ta5+ and W6+ substitutional doped TiO2 exhibits little to no variation in dopant concentration and distribution as a function of irradiation time. Interestingly P5+ and P3− co-doped TiO2 experiences a pronounced and nuanced change in dopant distribution and concentration across the surface through to the bulk as a function of irradiation time. Combined with our previous work with nitrogen doped TiO2, whereby 28 days of environmental UVA irradiation causes interstitial dopant loss and the attrition of functional properties, these results demonstrate that much is still to be understood regarding dopant stability in metal oxides such as TiO2 under environmental conditions

The use of time resolved aerosol assisted chemical vapour deposition in mapping metal oxide thin film growth and fine tuning functional properties

Time resolved analysis of a thin film has allowed, for the first time, analysis of how thin film growth occurs and changes over time by aerosol assisted CVD. This method has also allowed tuning of the materials' functional properties. In this report a hydrophobic and highly photocatalytic TiO2/SnO2 system is studied, which exhibits surface segregation of SnO2 and thus the novel formation of a natural hetero-junction charge transfer system. The time resolved samples were investigated by a variety of methods. The films were characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Ultraviolet-visible absorption spectroscopy (UV-vis). Functional properties were investigated by photo-activity measurements and water contact angles before and after UV irradiation. The generation of representative samples at different times during the deposition sequence permitted changes in crystal structure, relative concentrations of atoms, and surface morphology to be linked intrinsically to changes in functional properties

Efficient and Eco-Friendly Perspectives for C-H Arylation of Benzothiazole Utilizing Pd Nanoparticle-Decorated Chitosan

In this contribution, an eco-friendly, sustainable, and efficient palladium nanoparticle-decorated chitosan (Pd@Chitosan) catalyst was synthesized by a simple impregnation method. The synthesized material was utilized as a heterogeneous catalyst for the C-H arylation of benzothiazole under ultrasonic irradiation. The Pd@Chitosan catalyst efficiently catalyzed the conversion of aryl iodides and bromides to 1-(4-(benzothiazol-2-yl)phenyl)ethan-1-one selectively. A single product of 83–93% yield was obtained in N,N-dimethylformamide solvent at 80 °C for 2.5h. This study reveals that Pd@Chitosan is an efficient catalyst, which catalyzes the C-H arylation with good reaction yields. The activity of the Pd@Chitosan is due to the presence of highly dispersed Pd(0) nanoparticles on the surface of the chitosan and Pd2+; a tentative mechanism was proposed based on the XPS results of the fresh catalyst and spent catalyst

Solvent-free selective epoxidation of cyclooctene using supported gold catalysts

none7siOxidation is one of the major pathways for the synthesis of chemical intermediates. The epoxidation of alkenes by the electrophilic addition of oxygen to a carbon-carbon double bond remains one of the most significant challenges in oxidation. Of key importance is the use of oxygen as the oxidant, but in many cases more reactive, and less green, sources of oxygen are used. We report the solvent-free epoxidation of cyclooctene with air using supported gold catalysts with small amounts of a hydroperoxide. We identify the appropriate reaction conditions to maximize the selectivity of the epoxide. In the absence of a hydroperoxide initiator, using air at atmospheric pressure, no reaction is observed. Choice of the peroxide initiator is crucial and in the absence of a catalyst or a support the reaction of the alkene can be observed with di-t-butyl peroxide and t-butyl hydroperoxide (TBHP) only when high concentrations are used at high temperatures ≥ 80°C, and TBHP was found to be the more selective to epoxide formation. In contrast, cumene hydroperoxide was highly reactive under all conditions evaluated. TBHP was selected for more detailed study. Use of graphite as a support was found to give the best combination of selectivity and conversion. In general the selectivity to the epoxide increased with reaction temperature from 60-80°C and was highest at 80°C. Other carbon supports, e.g. activated carbon, were found to be less effective. TiO2- and SiO2-supported Au catalysts were also selective for the epoxidation reaction and the general order of activity was: graphite > SiO2 > TiO2. The major by-product is the allylic alcohol and the reaction pathways to the epoxides and the allylic alcohol are discussed. Preparation of catalysts using a sol-immobilisation method significantly enhanced catalyst activity with retention of selectivity to the epoxide. © 2009 The Royal Society of Chemistry.mixedBawaked, Salem*; Dummer, Nicholas F.; Dimitratos, Nikolaos; Bethell, Donald; He, Qian; Kiely, Christopher J.; Hutchings, Graham J.Bawaked, Salem*; Dummer, Nicholas F.; Dimitratos, Nikolaos; Bethell, Donald; He, Qian; Kiely, Christopher J.; Hutchings, Graham J

Alumina-coated Ag nanocrystal monolayers as surfaceenhanced Raman spectroscopy platforms for the direct spectroscopic detection of water splitting reaction intermediates

A novel Ag-alumina hybrid surface-enhanced Raman spectroscopy (SERS) platform has been designed for the spectroscopic detection of surface reactions in the steady state. Single crystalline and faceted silver (Ag) nanoparticles with strong light scattering were prepared in large quantity, which enables their reproducible self-assembly into large scale monolayers of Raman sensor arrays by the Langmuir-Blodgett technique. The close packed sensor film contains high density of sub-nm gaps between sharp edges of Ag nanoparticles, which created large local electromagnetic fields that serve as "hot spots" for SERS enhancement. The SERS substrate was then coated with a thin layer of alumina by atomic layer deposition to prevent charge transfer between Ag and the reaction system. The photocatalytic water splitting reaction on a monolayer of anatase TiO2 nanoplates decorated with Pt co-catalyst nanoparticles was employed as a model reaction system. Reaction intermediates of water photo-oxidation were observed at the TiO2/solution interface under UV irradiation. The surface-enhanced Raman vibrations corresponding to peroxo, hydroperoxo and hydroxo surface intermediate species were observed on the TiO2 surface, suggesting that the photo-oxidation of water on these anatase TiO2 nanosheets may be initiated by a nucleophilic attack mechanism. [Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg