Tungsten trioxide nanorod arrays are deposited using aerosol assisted chemical vapor deposition. The electronic structure, defect chemistry, optical bandgap, and photocatalytic activity are found to vary progressively with nanorod length. Nanorods less than 1 µm in length show a widening of the optical bandgap (up to 3.1 eV), more disorder states within the bandgap, an absence of reduced tungsten cation states, and increased photocatalytic activity for destruction of a test organic pollutant (stearic acid) compared to nanorods of 2 µm length or greater which possessed bandgaps close to the bulk value for tungsten oxide (2.6–2.8 eV), the presence of reduced tungsten states (W4+), and lower photocatalytic activity. The results indicate that for maximum photocatalytic performance in organic pollutant degradation, tungsten oxide should be engineered such that the bandgap is widened relative to bulk WO3 to a value above 3 eV; although less photons are expected be absorbed, increases in the overpotential for oxidation reactions appear to more than offset this loss. It is also desirable to ensure the material remains defect free, or the defect concentration minimized, to minimize carrier recombination.

We report for the first time the successful synthesis of palladium (Pd) nanoparticle (NP)-decorated tungsten trioxide (WO3) nanoneedles (NNs) via a two-step aerosol-assisted chemical vapor deposition approach. Morphological, structural, and elemental composition analysis revealed that a Pd(acac)2 precursor was very suitable to decorate WO3 NNs with uniform and well-dispersed PdO NPs. Gas-sensing results revealed that decoration with PdO NPs led to an ultrasensitive and selective hydrogen (H2) gas sensor (sensor response peaks at 1670 at 500 ppm of H2) with low operating temperature (150 °C). The response of decorated NNs is 755 times higher than that of bare WO3 NNs. Additionally, at a temperature near that of the ambient temperature (50 °C), the response of this sensor toward the same concentration of H2 was 23, which is higher than that of some promising sensors reported in the literature. Finally, humidity measurements showed that PdO/WO3 sensors displayed low-cross-sensitivity toward water vapor, compared to bare WO3 sensors. The addition of PdO NPs helps to minimize the effect of ambient humidity on the sensor response.Keywords: aerosol-assisted CVD; gas sensor; nanoneedles; nanoparticles

BiFeO3 is an interesting multifunctional narrow band gap semiconductor that exhibits simultaneous multiferroic, photovoltaic, and photocatalytic behavior. Hence there is much interest in the growth of thin films of BiFeO3 via chemical vapor deposition (CVD); however, the number of suitable bismuth precursors is severely limited. A series of homoleptic bismuth(III) β-diketonate complexes were synthesized via simple room temperature ligand-exchange reactions from [Bi(N(SiMe3)2)3] and free diketonate ligands, which yielded the crystal structure of [Bi(acac)3] as a 1-D polymer. We attempted to use these complexes for low pressure CVD (LPCVD) growth of BiFeO3 films with [Fe(acac)3]; however, all bismuth complexes exhibited poor volatilities and decomposition characteristics, and as a result film growth was unsuccessful. Subsequently, the volatile alkoxide [Bi(OtBu)3], with [Fe(acac)3], was used to grow dense BiFeO3 films via low pressure CVD. The BiFeO3 films possessed multiferroic properties at room temperature and exhibited activity for visible light-driven water oxidation in the presence of a Ag+ electron scavenger, which improved significantly when modified with a cobalt surface cocatalyst. The increase in activity, probed by time-resolved photoluminescence spectroscopy, was attributed to improved charge carrier separation arising from the in-built internal electric field of BiFeO3 in addition to the presence of an efficient cobalt oxygen evolution catalyst.

A novel method for preparation of BiFeO3 films via a simple solution-based CVD method is reported using for the first time a single-source heterobimetallic precursor [CpFe(CO)2BiCl2]. BiFeO3 films display ferroelectric and ferromagnetic ordering at room temperature and possess direct band-gaps between 2.0 and 2.2 eV. Photocatalytic testing for water oxidation revealed high activities under UVA (365 nm) and simulated solar irradiation, superior to that exhibited by a commercial standard (Pilkington Activ® TiO2 film) resulting in an apparent quantum yield of ∼24%.

Bismuth(III) tert-butoxide [Bi(OtBu)3] was utilised as a single-source precursor to controllably deposit thin films of different phases of bismuth oxide (Bi2O3) on glass substrates via low-pressure chemical vapour deposition (LPCVD). Band gaps for the different phases have been measured (Eg = 2.3–3.0 eV) and the films displayed excellent photodegradation of water under near-UV irradiation.

Atmospheric pressure chemical vapour deposition of VCl4, WCl6 and water at 550 °C lead to the production of high quality tungsten doped vanadium dioxide thin films. Careful control of the gas phase precursors allowed for tungsten doping up to 8 at.%. The transition temperature of the thermochromic switch was tunable in the range 55 °C to − 23 °C. The films were analysed using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their optical properties were examined using variable-temperature transmission and reflectance spectroscopy. It was found that incorporation of tungsten into the films led to an improvement in the colour from yellow/brown to green/blue depending on the level of tungsten incorporation. The films were optimized for optical transmission, thermochromic switching temperature, magnitude of the switching behaviour and colour to produce films that are suitable for use as an energy saving environmental glass product.

A novel method for preparation of BiFeO3 films via a simple solution-based CVD method is reported using for the first time a single-source heterobimetallic precursor [CpFe(CO)2BiCl2]. BiFeO3 films display ferroelectric and ferromagnetic ordering at room temperature and possess direct band-gaps between 2.0 and 2.2 eV. Photocatalytic testing for water oxidation revealed high activities under UVA (365 nm) and simulated solar irradiation, superior to that exhibited by a commercial standard (Pilkington Activ® TiO2 film) resulting in an apparent quantum yield of ∼24%.

Bismuth(III) tert-butoxide [Bi(OtBu)3] was utilised as a single-source precursor to controllably deposit thin films of different phases of bismuth oxide (Bi2O3) on glass substrates via low-pressure chemical vapour deposition (LPCVD). Band gaps for the different phases have been measured (Eg = 2.3–3.0 eV) and the films displayed excellent photodegradation of water under near-UV irradiation.