| Catalyst-loaded oxide semiconductor yolk-shell nanostructures |
| Ji-Wook YOON |
| Korea University |
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Yolk-shell nanostructures, hollow spheres containing movable cores and multiple thin shells, are attractive nanoarchitectures for various applications in catalysis, batteries, micro-reactors, drug delivery and gas sensors because of high surface-to-volume ratio, rapid mass transfer, and superior tolerance to volume change. In particular, uniform loading of catalyst on yolk-shell nanostructures can enhance the performance of micro-reactors and gas sensors. The template or partial etching of core materials has been used to prepare multiple shelled yolk-shell oxide semiconductors. However, synthetic route requires prolonged multi-step processes, which hampers the application of yolk-shell nanostructures. In this contribution, SnO2 yolk-shell nanostructures uniformly loaded with Pd or Ag catalysts were prepared by one-pot spray pyrolysis of precursor solution containing noble metal precursors, Sn-oxalate, sucrose and nitric acid and subsequent heat treatment. The catalyst-loaded SnO2 yolk-shell nanostructures were prepared by the following steps during one-pot spray pyrolysis reaction: (a) the formation of catalyst-carbon-Sn precursor composite spheres by polymerization and carbonization of sucrose, (b) the development of outermost catalyst-loaded SnO2 shells by the partial oxidation of carbon and decomposition of precursors near the surface, (c) and subsequent oxidation and decomposition of interior portion of precursors. The dense, yolk-shell, and catalyst-loaded yolk shell SnO2 spheres were prepared and their gas sensing characteristics were compared to investigate the effect of catalyst loading and yolk-shell morphology on the gas sensing characteristics
The Ag-loaded SnO2 yolk-shell spheres showed ultrahigh and reversible response (Ra/Rg - 1= 613.9, where Ra is the resistance in air and Rg is the resistance in gas) to 5 ppm H2S with negligible cross-responses (0.6−17.3) to other 8 interference gases at 350C [1]. In contrast, neither high response/selectivity to H2S nor reversible H2S sensing characteristic was observed both in pure SnO2 spheres with dense inner structures and yolk-shell morphology. The superior H2S sensing characteristics were attributed to the enhancement of H2S response via gas accessible yolk-shell morphology, selective and sensitive detection of H2S via the strong chemical interaction between Ag and H2S, and Ag-induced suppression of SO2-related poisoning of SnO2 surface.
The Pd-loaded SnO2 yolk-shell spheres showed high response to methyl benzenes (o-xylene and toluene) with low cross-responses to C2H5OH, HCHO, benzene, H2, CO, and CH4 at 350C and 375C [2]. In contrast, both dense and pure SnO2 yolk-shell spheres showed the highest response (Ra/Rg; Ra: resistance in air, Rg: resistance in gas) to C2H5OH at 350-450C. The selective and sensitive detection of methyl benzene in Pd-loaded SnO2 yolk-shell spheres are attributed to the synergetic combination between the effective in-diffusion of o-xylene and toluene through thin and semipermeable shells and their subsequent dissociation into smaller and active species by catalytic Pd particles on yolk or inner part of the shell. This clearly shows that the micro-reactors using catalyst-loaded yolk-shell nanostructures provide promising nanoarchitectures to design high performance gas sensors.
References:
[1] J.-W. Yoon, Y.J. Hong, Y.C. Kang, and J.H. Lee, RSC Advances 4 (2014) 16067.
[2] Y.J. Hong, J.-W. Yoon, Y.C. Kang, and J.H. Lee, Chem. Eur. J. 20 (2014) 2737.
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| Acknowledgements : |
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