Self-assembled SnO2 micro- and nanosphere-based gas sensor thick films from an alkoxide-derived high purity aqueous colloid precursor

View at Publisher| Export | Download | Add to List| More... Nanoscale Volume 8, Issue 13, 7 April 2016, Pages 7056-7067 Self-assembled SnO2 micro- and nanosphere-based gas sensor thick films from an alkoxide-derived high purity aqueous colloid precursor (Article) Kelp, G.ab, Tätte, T.a , Pikker, S.a, Mändar, H.a, Rozhin, A.G.c, Rauwel, P.d, Vanetsev, A.S.ah, Gerst, A.a, Merisalu, M.a, Mäeorg, U.e, Natali, M.f, Persson, I.g, Kessler, V.G.g a Institute of Physics, University of Tartu, Ravila 14C, Tartu, Estonia b Department of Physics, University of Texas at Austin, Austin, TX, United States c Aston University, Aston Triangle, Birmingham, United Kingdom d Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, PO Box 1048 Blindern, Oslo, Norway e Institute of Chemistry, University of Tartu, Ravila 14A, Tartu, Estonia f ICIS, CNR, CorsoStatiUniti 4, Padova, Italy g Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences, P.O. Box 7015, Uppsala, Sweden h General Physics Institute RAS, 38 Vavilov str., Moscow, Russian Federation Hide additional affiliations View references (53) Abstract Tin oxide is considered to be one of the most promising semiconductor oxide materials for use as a gas sensor. However, a simple route for the controllable build-up of nanostructured, sufficiently pure and hierarchical SnO2 structures for gas sensor applications is still a challenge. In the current work, an aqueous SnO2 nanoparticulate precursor sol, which is free of organic contaminants and sorbed ions and is fully stable over time, was prepared in a highly reproducible manner from an alkoxide Sn(OR)4 just by mixing it with a large excess of pure neutral water. The precursor is formed as a separate liquid phase. The structure and purity of the precursor is revealed using XRD, SAXS, EXAFS, HRTEM imaging, FTIR, and XRF analysis. An unconventional approach for the estimation of the particle size based on the quantification of the Sn-Sn contacts in the structure was developed using EXAFS spectroscopy and verified using HRTEM. To construct sensors with a hierarchical 3D structure, we employed an unusual emulsification technique not involving any additives or surfactants, using simply the extraction of the liquid phase, water, with the help of dry butanol under ambient conditions. The originally generated crystalline but yet highly reactive nanoparticles form relatively uniform spheres through self-assembly and solidify instantly. The spheres floating in butanol were left to deposit on the surface of quartz plates bearing sputtered gold electrodes, producing ready-for-use gas sensors in the form of ca. 50 ?m thick sphere-based-films. The films were dried for 24 h and calcined at 300°C in air before use. The gas sensitivity of the structures was tested in the temperature range of 150-400°C. The materials showed a very quickly emerging and reversible (20-30 times) increase in electrical conductivity as a response to exposure to air containing 100 ppm of H2 or CO and short (10 s) recovery times when the gas flow was stopped.