Size-selected agglomerates of SnO2 nanoparticles as gas sensors

Abstract

The effect of nanoparticle structure on gas sensing performance is investigated. Size-selected nanostructured SnO 2 agglomerate particles for gas sensors were made by scalable flame spray pyrolysis. These particles were polydisperse ͑up to 12 m in diameter͒ and consisted of primary particles of 10 nm in grain and crystal size as measured by transmission electron microscopy, x-ray diffraction, and Berner low pressure impactor ͑BLPI͒. The effect of agglomerate size on thermal stability and sensing of ethanol vapor ͑4 -100 ppm͒ and CO ͑4-50 ppm͒ was investigated by selecting nearly monodisperse fractions of these agglomerates by the BLPI. Sensor layers made with these size-fractionated agglomerates exhibited higher thermal stability and dramatically enhanced sensitivity for both analytes than layers made with polydisperse agglomerates. This is attributed to their aggregate ͑or hard agglomerate͒ structure exhibiting small sinter necks between their constituent primary particles of tin dioxide that had also a narrow size distribution as expected for particles generated in flames. Upon further sintering of these optimally sized, nanostructured agglomerates, grain and neck growth degraded their superior sensitivity, supporting the proposed mechanism of their enhanced sensitivity: optimal primary particle necking.

Flame spray pyrolysis synthesis and aerosol deposition of nanoparticle films

“…At higher magnification (Figure 2d), the primary particle diameter (d p ) was about 10 nm. These results are in good agreement with the x-ray diffraction (XRD) (d XRD % 10 nm), 7 count mode (d po ¼ 9.5 nm), and geometric mean (d pe ¼ 10.4 nm) diameters reported 21 for FSP-made SnO 2 powders for the same process conditions. The primary particle diameter did not increase further with increasing HAB as determined by TEM (Figure 2d, inset) analysis of SnO 2 powders filter-collected at 50 cm HAB.…”

“…6 Selection of aerosol size fraction allows deposition of nearly monodisperse nanoparticles possibly improving performances as shown by differential mobility analyzer (DMA) 9 and Berner low-pressure impactor (BLPI). 21 Furthermore, accurate control of the aerosol concentration and/or charging resulted in unprecedented miniaturization of nanoparticle films both in terms of thickness (1-100 nm) 11 and horizontal spreading (10-500 nm). 5 However, translating these results into industrial products requires scalable nanoparticle sources and tight control over the resulting aerosol properties (e.g., particle coalescence, 20,22 air entrainment 23 ), as well as sufficient understanding of the main mechanisms controlling the film growth dynamics (e.g.…”

“…27 However, accurate prediction and control of the properties of liquid-fed spray flame aerosols remains challenging. In addition, the high primary particle concentration, usually obtained during liquid-fed spray flame synthesis, leads to the rapid formation of large agglomerates 8,21 with reduced diffusivity and drastically different film properties than that expected for nonagglomerated particles. In addition, the high primary particle concentration, usually obtained during liquid-fed spray flame synthesis, leads to the rapid formation of large agglomerates 8,21 with reduced diffusivity and drastically different film properties than that expected for nonagglomerated particles.…”

Low-cost photo-responsive nanocarriers by one-step functionalization of flame-made titania agglomerates withl-Lysine

“…At pH 9, TiO 2 surfaces possess negative charge (ESI Fig. 41) and conrm the high crystallinity of the ame-made samples. As a result, here, the signicant increase in agglomerate size to 3000 nm for alkaline conjugation is attributed to the increased occulation rate arising from the neutral surface charging and the higher sticking likelihood of the aminefunctionalized TiO 2 surface.…”

Calorimetric Study of Heats of Mixing in SnxTi1−xO2Rutile Solid Solutions

“…T he SnO 2 , TiO 2 , and their mixtures and solid solutions have attracted considerable attention 1–7 . Because of changes in electrical conductivity upon gas adsorption, both compounds have been applied in detecting the leakage of flammable and toxic gases and are also used for monitoring low levels of such gases 8–12 . At high temperatures, SnO 2 has good sensing properties but poor selectivity, while TiO 2 sensors exhibit good stability but low sensitivity 13,14 .…”