Mechanism for the formation of tin oxide nanoparticles and nanowires inside the mesopores of SBA-15

The formation of polycrystalline tin oxide nanciparticles (NP) and nanowires was investigated using nanocasting approach included solid-liquid strategy for insertion of SnCl2 precursor and SBA-15 silica as a hard template. HR-TEM and XRD revealed that during the thermal treatment in air 5 nm tin oxide NP with well defined Cassiterite structure were formed inside the SBA-15 matrix mesopores at 250 degrees C. After air calcination at 700 degrees C the NP assembled inside the SBA-15 mesopores as polycrystalline nanorods with different orientation of atomic layers in jointed nanocrystals. It was found that the structure silanols of silica matrix play a vital role in creating the tin oxide NP at low temperature. The pure tin chloride heated in air at 250 degrees C did not react with oxygen to yield tin oxide. Tin oxide NP were also formed during the thermal treatment of the tin chloride loaded SBA-15 in helium atmosphere at 250 degrees C. Hence, it is well evident that silanols present in the silica matrix not only increase the wetting of tin chloride over the surface of SBA-15 favoring its penetration to the matrix pores, but also react with hydrated tin chloride according to the proposed scheme to give tin oxide inside the mesopores. It was confirmed by XRD, N-2-adsorption, TGA-DSC and FTIR spectra. This phenomenon was further corroborated by detecting the inhibition of SnO2 NP formation at 250 degrees C after inserting the tin precursor to SBA-15 with reduced silanols concentration partially grafted with tin chloride. (C) 2009 Elsevier Inc. All rights reserved.