SnO_2 nanoparticles in the pores of non-structured SiO_2 and Si-MCM-41: Comparison of their properties in gas sensing

摘要

Nano-sized SnO_2 particles were stabilized in SiO_2 matrices directly during a sol-gel process using modified organic precursors as well as in the pores of Si-MCM-41 by chemical vapour deposition (cvd) or impregnation. The dimensions of the SnO_2 particles found in the sol-gel samples vary between 3 and 20 nm depending on the use of the acidic or basic synthesis route. In Si-MCM-41 the combination of adsorption isotherms, transmission electron microscopy and DR-UV/Vis reveals the formation of a carpet of SnO_2 clusters on the inner pore walls due to strong interactions of the tin oxide species with the silanol groups of the Si-MCM-41 matrix. The reversible detection of reducing and oxidizing gas atmospheres (CO, O_2) is possible with all the samples, however, differences in the sensitivity of the samples result from different sizes of the formed SnO_2 nanoparticles and their interaction with the matrices. Due to the smaller sizes of the embedded tin species Si-MCM-41 appears to be the most promising matrix for the hostage of gas sensing composites working at moderate temperatures.