Structural evolution of SnO2 nanostructure from core–shell faceted pyramids to nanorods and its gas-sensing properties

Tin oxide (SnO2) nanorods were synthesized through an aqueous hexamethylenetetramine (HMTA) assisted synthesis route and their structural evolution from core–shell type faceted pyramidal assembly was investigated. Structural analysis revealed that the as-synthesized faceted SnO2 structures were made of randomly arranged nanocrystals with diameter of 2–5 nm. The shell thickness (0–80 nm) was dependent on the molar concentration of HMTA (1–10 mM) in aqueous solution. It was revealed that the self-assembly was possible only with tin (II) chloride solution as precursor and not with tin (IV) chloride solution. At longer synthesis hours, the pyramidal nanostructures were gradually disintegrated into single crystalline nanorods with diameter of about 5–10 nm and length of about 100–200 nm. The SnO2 nanorods showed high sensitivity towards acetone, but they were relatively less sensitive to methane, butane, sulfur dioxide, carbon monoxide and carbon dioxide. Possible mechanisms for the growth and sensing properties of the nanostructures were discussed.