Flame-coating of titania particles with silica

Silica/titania composite particles were prepared by co-oxidation of titanium-tetra-isopropoxide and hexamethyldisiloxane in a co-flow diffusion flame reactor. The influence of precursor composition on product powder characteristics was studied by x-ray diffraction, nitrogen adsorption, electron microscopy, elemental mapping, and energy-dispersive x-ray analysis. The flame temperature was measured by Fourier transform infrared spectroscopy. The evolution of composite particle morphology from ramified agglomerates to spot- or fully coated particles was investigated by thermophoretic sampling and transmission/scanning electron microscopy. At 40-60 wt% TiO2, particles with segregated regions of silica and titania were formed, while at 80 wt% TiO2 rough silica coatings were obtained. Rapid flame-quenching with a critical flow nozzle at 5 cm above the burner nearly halved the product particle size, changed its crystallinity from pure anatase to mostly rutile and resulted in smooth silica coatings on particles containing 80 wt% TiO

Sensing low concentrations of CO using flame-spray-made Pt/SnO2 nanoparticles

Tin dioxide nanoparticles of different sizes and platinum doping contents were synthesized in one step using the flame spray pyrolysis (FSP) technique. The particles were used to fabricate semiconducting gas sensors for low level CO detection, i.e. with a CO gas concentration as low as 5ppm in the absence and presence of water. Post treatment of the SnO2 nanoparticles was not needed enabling the investigation of the metal oxide particle size effect. Gas sensors based on tin dioxide with a primary particle size of 10nm showed signals one order of magnitude higher than the ones corresponding to the primary particle size of 330nm. In situ platinum functionalization of the SnO2 during FSP synthesis resulted in higher sensor responses for the 0.2wt% Pt-content than for the 2.0wt% Pt. The effect is mainly attributed to catalytic consumption of CO and to the associated reduced sensor response. Pure and functionalized tin dioxide nanoparticles have been characterized by Brunauer, Emmett and Teller (BET) surface area determination, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) while the platinum oxidation state and dispersion have been investigated by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). The sensors showed high stability (up to 20days) and are suitable for low level CO detection: <10ppm according to European and 50ppm according to US legislation, respectivel

Dispersed nanoelectrode devices

The enhanced performance and reduced scale that nanoparticles can bring to a device are frequently compromised by the poor electrical conductivity of nanoparticle structures or assemblies. Here, we demonstrate a unique nanoscale electrode assembly in which conduction is carried out by one set of nanoparticles, and other device functions by another set. Using a scalable process, nanoparticles with tailored conductivity are stochastically deposited above or below a functional nanoparticle film, and serve as extensions of the bulk electrodes, greatly reducing the total film resistance. We apply this approach to solid-state gas sensors and achieve controlled device resistance with an exceptionally high sensitivity to ethanol of 20 ppb. This approach can be extended to other classes of devices such as actuators, batteries, and fuel and solar cells

Tailored Nanostructures for Microgassensors by Flame Spray Pyrolysis

Integration of nanoparticle synthesis and deposition in micro-machining processes is a mandatory step toward development of nanodevices. Indeed, large scale production of tailored particles is achievable in aerosol reactors. Direct deposition from the aerosol leads to formation of nanostructured layers avoiding the cumbersome steps of wet-methods. Nevertheless, improvement of nanoparticle cohesion and adhesion by isothermal sintering results in deterioration of the device performance due to crystal and grain growth. Furthermore, sufficient stabilisation is not always possible at substrate compatible temperatures. Here, we describe the synthesis and deposition of SnO2, TiO2 and SnO2-SiO2 nanostructured layers that can be utilised for micro-machined gas sensors

Thermally Stable, Silica-Doped ε-WO3 for Sensing of Acetone in the Human Breath

Acetone in the human breath is a key marker for noninvasive diagnosis of diabetes. Here, sensing films of pure and SiO2-doped WO3 nanoparticles have been made, directly deposited and in situ annealed onto interdigitated electrodes by scalable flame aerosol technology. A unique innovation here is that these films consist of ε-WO3, a metastable phase that has a high selectivity to acetone. The effect of nontoxic Si doping on the ε-phase content and crystal and grain sizes was investigated and correlated to the acetone sensing performance of these films. The thermal stability of these materials was characterized as well, revealing a unique opportunity for reliable sensing of acetone and noninvasive diagnostics of diabetes. An optimal doping level with 10 mol % SiO2 resulted in highly sensitive and highly selective acetone sensors down to 20 ppb